Embed Size (px)
Citation preview
SOME STUDIES ON DEVELOPMENT OF
DIFFERENT ALL-OPTICAL LOGIC,
ARITHMETIC AND ALGEBRAIC PROCESSORS
DEBAJYOTI SAMANTA
“Some Studies on Development of Different All-
Optical Logic, Arithmetic and Algebraic
Processors”
Thesis submitted to
The University of Burdwan
for the award
of the degree of
Doctor of Philosophy
in
Physics
by
Debajyoti Samanta
Department of Physics,
The University of Burdwan,
Golapbag, Bardhaman,
West Bengal -713104, India
2012
Dedicated
to my
Reverend Parents
The University of Burdwan Department of Physics
Golapbag, Burdwan,
West Bengal -713104, India
Phone: 91-342-2657800
Fax: 91-342-2530452
Website: www.buruniv.ac.in
Dr. Sourangshu Mukhopadhyay
Professor & Head, Department of Physics
___________________________________________________
To whom it may concern
This is to inform to all concerned that the thesis entitled, “Some Studies on
Development of Different All-Optical Logic, Arithmetic and Algebraic Processors,” is
a sincere and bonafide work done by Mr. Debajyoti Samanta towards the award of the
Ph.D. degree. This work was studied under my supervision. The thesis has covered
many new approaches and techniques in the field of „optical parallel computation‟.
No portion of it, except the reviews and background work, was included in any Ph.D.
level thesis or in any dissertation work.
I believe, the readers will certainly get many new interesting ideas from it.
Date: .…….………………………………
Place: Burdwan (Prof. Sourangshu Mukhopadhyay)
Head,
Department of Physics
~ i ~
Preface
The practical limitations of conventional electronic digital computers have led
to the invention of a new technology which uses optics in computation. All-optical
data processing has been the subject of most research interest during last few decades.
The area of optical computing provides a challenge to the researchers as it is a
multidisciplinary area and the field is expanding rapidly. During my post graduate
classes I had come to know about „optical computing‟. After knowing the advantages
of optical parallel computation I became interested in this new promising and
flourishing field of study. Gradually I had dreamt of doing something new in this
field. I would like to take this opportunity to thank all those persons who have been
directly or indirectly involved with the preparation of this thesis. I have also taken
help of some academic institution and research organizations. Without such assistance
it would not be possible to write this thesis.
With a deep sense of gratitude I express my sincerest respect, thanks and
regards to Prof. Sourangshu Mukhopadhyay, Professor, Department of Physics, The
University of Burdwan, who was my teacher in post graduate classes as well as my
supervisor, for providing me the opportunity to undergo this identified field of
research work described in this thesis. Language fails me how to express my
indebtedness to him for his inspiration, blessings, encouragement, invaluable advice
and continuous patient guidance throughout this research work.
I bow to my parents Mrs. Rekha Samanta and Dr. Dilip Samanta. I would not
be in a position to write this thesis without their blessing and support. My deepest
regards, gratefulness are due to them.
I sincerely acknowledge The University of Burdwan for providing me
„university research fellowship‟ for pursuing the work. I wish to extend my heartiest
thanks to all of my co-researchers especially Dr. Puspendu Kuila, Mr. Shyamal
Kumar Pal, Mr. Bikash Chakraborty, Mr. Ashish Pal, Mrs. Soma Dutta and Mrs.
Nandita Mitra for their cooperation, hospitality and help at every step of my work. I
also like to thank all the staffs of the Department of Physics, The University of
Burdwan and my colleagues of Rampurhat College.
~ ii ~
I acknowledge the help from the SPIE University of Calcutta students‟ chapter
for providing some study materials. I also like to thank Department of Science and
Technology, New Delhi for extending some financial assistance to present a paper in
an international conference held in Japan.
I also like to thank my grandparents Mrs. Lilarani Samanta and Mr.
Ramkrishna Samanta and other relatives and well wishers for their inspiration,
affection and goodwill extended to me during these years. I convey my sincere thanks
to my beloved brother Mr. Dhrubajyoti Samanta for his constant inspiration and also
providing some study materials to me. It would be incomplete if I do not acknowledge
my dear wife Aparna. I wish to express my heartfelt thanks to her for the cooperation,
support and sacrifice extended to me to complete this thesis.
In this thesis some approaches towards some developments on different
optical logic and data processing are described. The whole content is divided into
thirteen chapters. First two chapters are preliminary discussions. From „chapter-3‟
through „chapter-12‟ different proposed optical schemes are depicted. In „chapter-13‟
a general conclusion is given. Finally at the end a list of some important reference and
my publications are attached.
Date: .…….…………………………
Place: Department of Physics (Mr. Debajyoti Samanta)
The University of Burdwan,
Bardhaman.
~ iii ~
Contents
Page
1. Chapter – 1
Introduction to optical logic, arithmetic and algebraic processing
and objective of the proposed thesis.
-------------------------------------------------------------------------------------
1.1. Introduction
1.2. Advantages of optics over electronics in data processing,
computation and in communication
1.3. Optical or photonic computing and its need
1.4. Optical architecture in optical computation
1.5. Different encoding/ decoding processes
1.6. Optical switching systems
1.6.1. Micro-electro-mechanical systems (MEMS)
1.6.2. Optical add-drop multiplexer (OADM)
1.6.3. Liquid crystal (LC) switch
1.6.4. Semiconductor optical amplifier (SOA)
1.6.5. Interferometric switch
1.6.6. Terahertz optical asymmetric demultiplexer (TOAD)
1.6.7. Optical isotropic nonlinear material (NLM)
1.6.8. Quantum dot switching
1.6.9. Electro-optical absorption switching
1.7. Objective of the proposed work
1.8. Conclusion
1 - 27
---------
2
2
3
4
8
11
11
13
14
15
16
21
22
23
24
25
27
2. Chapter – 2
Background review of some important works related to optical
computing.
-------------------------------------------------------------------------------------
2.1. Introduction
2.2. Some approaches for optical computing
28 – 39
---------
29
29
~ iv ~
2.3. Conclusion
39
3. Chapter – 3
A proposal for developing an integrated all-optical logic and
arithmetic unit using the Kerr - nonlinearity.
-------------------------------------------------------------------------------------
3.1. Introduction
3.2. Use of nonlinear material for implementation of optical logic
system
3.2.1. Optical isotropic Kerr nonlinear material (NLM) used
as a switch
3.2.2. Optical NOT logic gate using NLM
3.2.3. Optical AND and Ex-OR logic gates using NLM
3.3. An integrated scheme of implementing optical logic and
arithmetic processor (OLAP) with NLM
3.4. Conclusion
40 - 55
---------
41
41
41
44
45
47
55
4. Chapter – 4
A method of developing a prefixed intensity level for any logic
input/ output signal bit.
-------------------------------------------------------------------------------------
4.1. Introduction
4.2. All-optical method for controlling the intensity of the light
signal: the circuit description
4.3. Description of operation of the system
4.4. Conclusion
56 - 61
---------
57
57
59
61
5. Chapter – 5
A new proposal of implementing the polarization encoded optical
logic families.
-------------------------------------------------------------------------------------
5.1. Introduction
5.2. Polarization based encoding and decoding technique
62 - 74
---------
63
63
~ v ~
5.3. Use of polarization based encoding/ decoding technique and
nonlinear switching technique to implement optical logic gates
5.3.1. Implementation of a 2-input AND logic gate
5.3.2. Implementation of a 2-input OR logic gate
5.3.3. Implementation of a 2-input universal NAND logic gate
5.3.4. Implementation of 2-input Ex-OR logic gate
5.4. Conclusion
64
64
67
70
71
74
6. Chapter – 6
An all-optical method of developing an S-R flip-flop for storing a
set of digital inputs.
-------------------------------------------------------------------------------------
6.1. Introduction
6.2. A scheme to get a specified intensity level for a polarization
encoded light beam
6.3. Method of maintaining a prefixed intensity level of a polarization
encoded light signal
6.4. Method of implementing an optical S-R flip-flop by polarization
encoded light signal
6.5. Conclusion
75 - 85
---------
76
77
79
82
85
7. Chapter – 7
All-optical method for developing Master-Slave J-K flip-flop with
polarization encoded light signal.
-------------------------------------------------------------------------------------
7.1. Introduction
7.2. Polarization encoded all-optical M-S J-K flip-flop
7.2.1. Polarization encoded 3-input NAND logic gate
7.2.2. Developing the Master-Slave J-K flip-flop
7.3. Conclusion
86 - 95
---------
87
87
88
93
95
~ vi ~
8. Chapter – 8
All-optical technique of conversion of polarization encoded data
bit to an intensity encoded data bit and vice versa.
-----------------------------------------------------------------------------------
8.1. Introduction
8.2. All-optical scheme for obtaining a polarization encoded data
bit from intensity encoded data bit
8.3. All-optical scheme to get an intensity encoded data bit from a
polarization encoded data bit
8.4. Optical system for conversion of an optical intensity encoded
data to polarization encoded data
8.5. Conclusion
96-103
---------
97
97
100
101
103
9. Chapter – 9
An all-optical approach for developing a single optical pulse
generator.
------------------------------------------------------------------------------------
9.1. Introduction
9.2. Use of electro-optic modulator for phase delay
9.3. An integrated scheme to generate a single sub-nanosecond pulse
9.4. Conclusion
104-109
---------
105
105
107
109
10
.
Chapter – 10
A new scheme of developing an all-optical astable multivibrator.
------------------------------------------------------------------------------------
10.1. Introduction
10.2. Phase modulation by electro-optic modulator
10.3. Scheme for development of an all-optical astable multivibrator
10.4. Conclusion
110-116
----------
111
111
113
116
11
.
Chapter – 11
An all-optical polarization encoded multiplexer using optical
nonlinear material based switches.
117-130
~ vii ~
------------------------------------------------------------------------------------
11.1. Introduction
11.2. Polarization encoded logic gate with the use of optical nonlinear
material based switch
11.2.1. Polarization encoded all-optical 3-input AND logic
gate
11.3. Polarization encoded optical multiplexer
11.3.1. Polarization encoded 4×1 optical multiplexer
11.3.2. Polarization encoded 8×1 optical multiplexer
11.4. Conclusion
----------
118
119
119
124
124
127
130
12
.
Chapter – 12
An all-optical polarization encoded parity generator and checker.
------------------------------------------------------------------------------------
12.1. Introduction
12.2. Method of implementing an all-optical parity generator and
checker for polarization encoded light signal
12.3. Conclusion
131-136
----------
132
133
136
13
.
Chapter – 13
General conclusion and future scope of works.
------------------------------------------------------------------------------------
13.1. Introduction
13.2. Overall conclusion on the thesis
13.3. Future scope of works
137-140
----------
138
138
139
14
.
References 141-168
15
.
Publications
~ 1 ~
CHAPTER - 1
___________________________________________________
Introduction to Optical Logic, Arithmetic and
Algebraic Processing and Objective of the Proposed
Thesis
Abstract
The rate of data transfer is increasing enormously day by day. As a result the
demand is also increasing for such systems which can keep real link with such rate of
increase in data traffic. In this context logic processing, data processing, image
processing with optics as information carrying signal have shown a high degree of
potentiality. It is well established that optics can go far beyond electronics. It is
mainly because of the inherent advantages in optical signal. The field of optical
computing had appeared as a part of a new, promising and vast filed of research
interest. A large number of papers to utilize optical signal in computing have been
reported to date. In this chapter a general introduction to optical computing is
represented. The advantages of using optics in computing along with some important
steps taken towards the implementation of an optical parallel computer are illustrated.
Again the chapter also accommodates the objective of my contributed works in the
thesis.
~ 2 ~
1.1. Introduction
With the advancement in technology computational techniques also have achieved a
new dimension. Improvement of electronics has increased the level of performance of
conventional computing machines. By miniaturizing the size of the electronic
components to sub-micron level the speed has increased. But this is limited by the
interconnection problem. Again electron has a speed limit (According to Einstein‟s
relativity principle electron cannot move faster than light). So scientists were looking
for an alternative. In the seventies of the last century there was a revolutionary change
in the area of data processing. Optics had expressed itself as a potential candidate for
data processing. Here photon is the information carrier instead of electron in
electronic systems. Due to some inherent advantages optics appeared to be lucrative
technique over conventional electronic systems. Scientists then started an effort to
replace the conventional electronic systems with the optical counter parts. This was a
beginning of a new era of optical computing. Since then the field of optical computing
has flourished in many directions. Researches in optical computing have opened new
possibilities in high speed computing, communication and parallel algorithm
designing. Lots of improvements are being reported by the researchers in every corner
of the world. Initially optical computing was in analog nature. Then digital optical
data processing has become a success. Now the role of the optics is known to entire
scientific community. Today researchers are working all over the world to fully utilize
the advantages of optical signal in computation as well as in communication [20, 141,
191, 148, 254, 301, 302]. Already lots of developments are reported to implement
different optical systems in various techniques.
In this chapter we describe the advantages of optics or photonics in computing
over electronics. Recent innovations in optical computing are also summarized. Lastly
a brief description of the proposed work is given.
1.2. Advantages of optics over electronics in data processing,
computation and in communication.
Some advantages of optics over electronics have made optics so popular. When
electronic transistor was invented a new dimension was achieved in data processing.
Scientists looked for a higher speed of data processing but a smaller size of the
device. The conventional electronic systems have a band width limit, called the „bottle
~ 3 ~
neck‟ problem, above which more speed cannot be achieved. Where as in electronic
system a maximum speed of operation is 1010
Hz, in case of optical system up to 1015
logic operations per second can be performed. As optical signal can travel at a very
high speed there will be no propagation delay among the different parts of an optical
system. Thus light does not have time response limitation of electronics. So a real
time operational speed can be expected from an all-optical device. Electronic devices
also generate heat which can damage the components. Photon does not interact with
an electric or magnetic field, as electron does. Therefore there will be no distortion
due to electric and magnetic field during optical data communication. Optical signals
do not interfere among them. Thus the problem due to cross-talk and short-circuit can
be removed. Different optical signals (of different frequency or colour) can easily
propagate simultaneously. So an all-optical system can perform multiple data
operations at a time. The inherent advantage of parallelism associated with optical
signal has made it so popular for high speed communication and data and logic
processing [166, 167]. As channel requirement is lower in optics the system volume
would be smaller. Optical system can avoid the inconvenience of using only binary
logic. Wavelength division multiplexing is also a remarkable advantage in parallel
processing of optical data and also in computation.
Optics can reduce the energy required for transmission [251]. In optical
connection there is no need to charge the optical lines to signal voltage. Thus the
optical system will be more efficient, compact in size, lighter in weight and more cost
effective. So in respect of speed, size, complexity optics is favored far advantages
than electronics.
1.3. Optical or photonic computing and its need.
Before invention of the electronic transistor data and logic processing was very hard.
The computers were very slow and large in size. Transistors made the electronic
computers faster and smaller in size [300]. After that digital data processing was
started. With the development of electronics the sizes of the devices were reduced
greatly. A speed of the order of GHz can be achieved by Very Large Scale Integration
(VLSI) Technology. Unfortunately for integration complexity and interconnection
delay more speed of computation cannot be realized with electronics. Among the
limitation of VLSI circuits are limited number of pin and low bandwidth for
~ 4 ~
interconnection. But the demand for speed of operation is increasing enormously day
by day.
Now using all-optical system can be a way to get rid of the problem. The new
technology of using optics in the field of computation and parallel processing is
generally called as optical or photonic computing. Optical signals and optical
integrated circuits have several advantages as described earlier. Apart from these the
advantages of using optics in computing are limited not only to communication of
data but also memory storage capacity, 2-D and 3-D holography, Fourier transform,
correlation, optical pattern recognition, image edge detection, neural networking,
artificial intelligence, multiplexing-demultiplexing, channel based and channel free
operation, fuzzy logic operation and many more can be achieved. It can be said that
photonic technology is dedicated to generate, control, detect and utilize photons for
the development of mankind and civilization. By replacing electrons and wires by
photons and optical fiber, scientists hope to generate a new generation of optical
computer.
1.4. Optical architecture in optical computation.
In optical systems photon is the carrier of data instead of electron in electronic
systems. The performance of the computing systems can be enhanced by increasing
clock rate of serial data processing or by using parallel data processing. Due to
inherent parallelism in optics parallel processing is much more desirable. However
digital optical systems were not demonstrated at the very beginning of optical era. The
journey started with optical analog data and image processing systems. Often
photographic transparencies were used for processing of data in the form of 2-
dimensional images [299]. Then spatial light modulators (SLMs) were developed to
replace photographic films. SLMs were used massively for optical computing [75].
Optical and optoelectronic processing deal with the performance of
computation, algebraic analysis, artificial intelligence. The area of optical parallel
data processing can be divided into four sub-areas like (i) technique: this part falls
within the area of physics, electronics and computer engineering; (ii) algorithm: is a
mathematical topic; (iii) architecture: the design of optical circuit involving computer
scientists; and (iv) application. So this is an interdisciplinary area of research interest.
Therefore it demands for its success the collaboration of researchers from different
~ 5 ~
disciplines such as engineering, computer architecture, material research, chemistry
and physics.
For any optical device to fabricate optical counter part of every system is
required. To develop an optical processor we need optical logic and arithmetic unit,
optical memory unit, optical buses, optical input/output ports, optical power sources,
optical encoders, decoders, optical detectors are required. Logic gates are the building
block of any digital system. So for developing an optical arithmetic or algebraic
processor optical logic gates are essential.
Optical system is to be developed for performing mathematical operations like
addition, subtraction, multiplication, division etc. For performing addition operation
half-adder and full-adder are required to be developed. For binary addition the rules
followed are 0+0=00, 0+1=01, 1+0=01 and 1+1=10. The addition is carried out bit
wise from the right hand side bit towards left. The carry bit is carried to the next adder
circuit.
Optical memory is also needed to support the high rate of data processing by
optical processors [135, 136, 211]. Using the inherent parallelism large number of
data bit can be stored (or received) simultaneously into (or from) an optical memory.
Two types of optical memory can be found like arrays of one bit store element and
mass storage like hologram. Flip-flop circuits are common digital memory. Electro-
magnetically induced transparency (EIT), fiber delay line (FDL), optical cavities can
also be used for optical memory. EIT is caused due to interference of coherences
excited in the atom by the electromagnetic fields [25]. As a result an initially opaque
medium may become transparent. Quantum states of photons are transferred to
collective excitations of the medium. Hence EIT medium can act as quantum memory
for photon [106, 165]. Holographic memory can provide a real time high recording
density as well as high data access rate [97-100, 103, 122-125, 134]. Holography is a
method in which the amplitude and phase of light wave is recorded in a photo-
sensitive medium by interference. For formation of hologram basically a coherent
light beam coming from a laser is divided into two beams („figure -1.1‟). One beam
illuminates an object from which we get „object beam‟. The other beam is reflected
from a plane mirror and serves as a „reference beam‟. These two beams interfere
between them in the space where they superpose. A photo sensitive medium is made
to record the interference pattern is called hologram.
~ 6 ~
With the development of optical device for high speed computation the
interconnection technology is also to be developed at the same time. Wavelength
division multiplexing (WDM) is a suitable tool for optical interconnect [43]. Optical
time division multiplexing (OTDM) and dense wavelength division multiplexing
(DWDM) are two mention worthy techniques in this context. In OTDM technique
optical data stream are constructed by time multiplexing a number of lower bit rate
optical streams [8]. Again very high bit rate optical signal is demultiplexed to many
lower bit rate optical signals at the receiver end of the system. In WDM different
optical signals of different wavelengths (like 1, 2 and 3 in „figure -1.2‟) can be
multiplexed on a single optical fiber. It is often also termed as frequency division
multiplexing. Multiplexer and demultiplexer can be implemented with diffraction
grating, fiber Bragg grating etc. Fiber nonlinearity limits the number of channels can
be multiplexed in WDM.
Mirror
Object 3-D
Hologram
Laser source
Fig. 1.1: Schematic diagram for recording of hologram.
~ 7 ~
In conventional WDM system only few channels are accommodated in single optical
fiber. If laser has very narrow line width then more channels can be multiplexed into a
single optical fiber. This leads to DWDM technique.
Scientists first thought of an optical computer observing the nonlinearity in
optical nonlinear material. They needed some optical device which would replace the
electronic transistor in electronic computer. In a junction transistor electric current
(flow of electron) is controlled by another current. Optical bistable devices and logic
have been developed later. In these devices one light beam (flow of photon) is
controlled by another light beam. Bistable devices can be very small in size but offer a
very high operational speed. Optical bistable devices or optical flip-flops can be used
in optical communications and computing for threshold function, demultiplexing,
optical memory etc. Optical logic gates should be able to function at very small power
and at room temperature. That means optical nonlinear materials with larger
nonlinearity term are required. To make the energy per logic operation lower the
volume of the device material is to be minimized. The materials should have short
response and relaxation time. Some semiconductors, organic and photorefractive
materials can serve the purpose. Multi-layered photorefractive polymeric devices, as
the phase conjugation reflectivity depends on the incident beam polarization, can be
used in optical logic devices [113]. Electrons or photons with energies above the
WDM
MUX
WDM
DEMUX
Optical fiber
amplifier
Fig. 1.2: Wavelength division multiplexing.
1
2
3
1
2
3
~ 8 ~
band-gap energy can affect the electronic and optical properties of semiconductors.
Thus many semiconductors can be used for implementation of electronic, optical or
opto-electronic devices [300]. Optical bistability can be observed in many
semiconductors like GaAs, CuCl, CdS, InSb, ZnS etc.
For implementation of logic devices with optical signal the devices should
satisfy some criterion [251]. The output of any logic devices should be such that it can
be used as the input of another device. That means the logic devices will be
cascadable [260]. The optical logic device should have fan-out of at least two i.e. the
output of first device will be capable to drive the inputs of at least two subsequent
logic devices. If the optical signal quality becomes worse the logic level should be
restored in the concerned stage. Apart from these an optical device should have
separate input and output beams, should have an operating point which can be easily
established and the logic level should be independent of transmission loss. Future
optical logic devices should operate consuming energy only of the order of
auttojoules. The optical devices are to be made efficient to this extend. As optics has
passive components zero energy logic is possible.
1.5. Different encoding/ decoding processes.
A conventional computing machine cannot understand the mathematical digits like 0
and 1 (for binary). Hence it is necessary to encode the mathematical data by different
optical symbols. For data communication from one unit to other part of a system and
for conducting various computing operations several symbolic coding and decoding
techniques can be adopted to use the parallelism of optical signal. In some reports the
use of tri-state or other multivalued logic has also been observed.
Different techniques for encoding and decoding of data may be used to
implement optical data processor. These methods can be like intensity, phase,
polarization or frequency based encoding [259].
In intensity based coding one can assume presence of a prefixed intensity of
light signal beam as „logic 1‟ (high) state and absence of any light signal as „logic 0‟
(low) state (in binary). Alternatively input array can be represented by a number of
pixels in intensity coded symbolic substitution. Here a transparent pixel can be
represented by „logic 1‟ and „logic 0‟ is denoted by an opaque pixel. There are several
research works which have used intensity based encoding/decoding process. This is a
~ 9 ~
convenient method of encoding/ decoding. But there may arise some situation where
the intensity of the light signal beam may fall due to absorption, scattering etc. This
may lead to bit error problem.
The spatial encoding technique has been used successfully for implementation
of various logic and arithmetic operations [163]. In this method the input is encoded
by the combination of presence and absence of light signal in a spatially represented
coded mask. For two input variables (A and B) each rectangular half of the input
variables is spatially encoded („figure-1.3‟). When „A‟ is „logic 0‟ it can be assumed
that the upper rectangular half is transparent and lower half is opaque. Again „A‟
assumes „logic 1‟ when upper half is opaque and lower half is transparent. Similarly
input „B‟ can be assumed as „logic 0‟ or „logic 1‟ when left and right half is
transparent respectively.
Instead of using this type of coding one can use polarization based coding
[119]. Besides these two techniques one can describe an optical signal as logic 0 (low)
of logic 1 (high) if the beam has a predefined phase relationship with respect to a
reference signal. Again in case of frequency based encoding technique one can
represent two light signal of two different frequencies as „logic 0‟ (low) and „logic 1‟
(high) state.
~ 10 ~
Inputs
Logic
state
0 1
A
B
Fig. 1.3: Spatial input coding for two variables.
~ 11 ~
1.6. Optical switching systems.
Optical switching systems are the most important elements for implementing all-
optical devices. Several types of switches are reported [284]. Some of the switches are
electro-optic where as some are all-optical. Electro-optics systems are limited by the
speed of the electronic part. Here optical signal is converted to electronic signal. After
switching operation the electronic signal is again converted to optical one. Due to
repeated conversion process the effective switching operation become slower. Also
the cost of the switching device is higher due to the presence of the electronic parts.
All-optical components have advantages over electro-optic components. The general
principle of all-optical switches are controlling of light signal with another light
signal. So conversion of optical to electronic and electronic to optical signal is not
required in this case. There are different types of optical switches.
1.6.1. Micro-electro-mechanical systems (MEMS)
Micro-electro-mechanical systems (MEMS) are small integrated systems consisting of
electrical and mechanical parts. Advantages like batch fabrication, small size,
integratability etc. have made this type of switches popular. MEMS have small
movable mirrors which can be moved by the application of external current. The
switching speed of this type of switch is low as it involves movement of the mirrors.
There are two types of MEMS optical switches like 2D and 3D switches. In 2D
switches mirrors are arranged in a crossbar configuration. Mirrors are placed at the
intersections of light paths between inputs and outputs („figure -1.4‟). Each mirror can
reflect the light beam („ON‟ position) or let the light beam to pass unaffected („OFF‟
position). In 3D switches mirrors can rotate about two axes and thus can redirect the
light beams to multiple angles in space.
~ 12 ~
Inputs
Outputs
» Mirror in ON position
» Mirror in OFF position
Fig. 1.4: Schematic diagram of a 2D MEMS optical switch.
Inputs
Outputs
~ 13 ~
1.6.2. Optical add-drop multiplexer (OADM)
Optical add-drop multiplexer (OADM) can add or drop an optical signal into or from
an information channel. It is used in wavelength division multiplexing systems. This
device consists of two circulators connected by a fiber. A fiber grating placed in the
fiber can reflect a signal of particular wavelength. Let there are „n‟ number of
wavelengths (1, 2, 3,…, i-1, i , i+1,…, n) at the input („figure -1.5‟). The fiber
grating reflects a particular wavelength (i). This wavelength reenters the „circulator -
1‟ and leaves the circulator at the drop port. The remaining wavelengths (1, 2, 3,…,
i-1, i+1,…, n) enter to the „circulator -2‟. A signal which is absent in the input of
„circulator -2‟ can be added here. So the dropped wavelength (i) is injected through
the „add‟ port to the „circulator -2‟. The signal is now added to the mainstream and
exit with all other wavelengths at the output.
Input
Circulator 1
Circulator 2
drop add
Output
Fiber
grating
i
1, 2 ... i,
..n
i
1, 2 ... i,
..n 1,.., i-1 ,
i+1, ..n
Fig. 1.5: Schematic diagram of an optical add-drop multiplexer.
~ 14 ~
1.6.3. Liquid crystal (LC) switch
Liquid crystal (LC) switches are another type of optical switch. These materials are of
much interest as they show sensitivity to applied electrical field, consume less power,
have long lifetime and are cheaper. The operation of this type of switch is controlled
by applying voltage to the liquid crystals. These switches depend on the wavelength
of the signal. The operation of a LC switch is shown „figure -1.6‟.
Input Output -1
Output -2
Birefringent
plate LC
V=0
Fig. 1.6: Schematic diagram of a liquid crystal switch
Polarization
beam splitter Birefringent
plate
Birefringent
plate
Input Output -1
Output -2
V= V0
~ 15 ~
A birefringent plate in the input determines the polarization state of the input as
desired. The LC cell can pass the light with the state of polarization unaltered when
no biasing voltage (V=0) is applied to the cell [29]. The light beam is now passed
thought the polarization beam splitter and thus the output is received in „output -1‟.
When voltage is applied to the LC it changes the polarization of the light beam
passing through it. For a specific voltage (V=V0) it rotates the polarization state by
π/2 (↨ is changed to ●). Now the polarization beam splitter reflects the light beam to
the „output -2‟. Thus the LC can act as a switch. There are different mechanisms for
utilizing liquid crystal switch such as based on total internal reflection, polymer
containing nematic LC droplets etc. [60, 61, 104, 144-146].
1.6.4. Semiconductor optical amplifier (SOA)
The semiconductor optical amplifier (SOA) is similar to a semiconductor laser. SOA
are compatible with monolithic integration and hence are of low cost. SOA can be
used for all-optical functional applications like in line optical amplifier, optical
switching, wavelength conversion, pulse generation and logic gate [66, 91, 108, 126,
155, 180, 182, 186, 200, 221, 265, 291, 304]. SOA can amplify a light signal by
stimulated emission. An external electric current provides the necessary energy for the
gain. In SOA electrons or carriers are injected into the active region („figure -1.7‟)
from an external source. Large optical bandwidth can be expected in SOA. SOAs are
of two types namely Fabry-Perot SOA (FP-SOA) and travelling-wave SOA (TW-
SOA). In FP-SOA the signal passes many times through the amplifier due to the
reflections from the end facets. In TW-SOA reflection is negligible and the signal
passes only one time. SOA gate arrays can be used for high-speed switching. Four
types of nonlinearities seen in SOA are cross gain modulation (XGM), cross phase
modulation (XPM), self phase modulation (SPM) and four wave mixing (FWM)
[130].
~ 16 ~
1.6.5. Interferometric switch
An interferometric switch has two 3-dB couplers. Input beam is split into two arms of
equal length at the first coupler. The second coupler combines the beams and finally
splits again. A phase difference is introduced between the two beams. This results in
interference between the two beams. Depending on the path difference there will be
constructive or destructive interference between the two beams. Light beam
propagations in Michelson, Mach-Zehnder and Sagnac interferometer are shown
schematically in „figure -1.8‟. Mach-Zehnder interferometer, ultrafast nonlinear
interferometer and nonlinear optical loop mirror are different types of interferometric
switches [206].
Input
Output
Input facet
Active region
and
waveguide
Output
facet
Current
Fig. 1.7: Schematic diagram of an SOA.
~ 17 ~
Fig. 1.8: (a) Michelson interferometer, (b) Mach-Zehnder interferometer
(c) Sagnac interferometer
(a)
Beam
splitter
Mirror
Input
Output
(b)
(c)
Output
Output
Input
Input
~ 18 ~
Mach-Zehnder interferometer (MZI) based switch is a very commonly used
interferometric optical switch [264]. It consists of a nonlinear medium, generally an
SOA. The SOA is placed in the arms of the interferometer („figure -1.9‟). An optical
control signal is used to change the carrier density in the SOA. This causes refractive
index change. Thus a phase difference is introduced. Depending upon the interference
(constructive or destructive) between the two beams the data signal is diverted to
„output -1‟ or „output -2‟.
Fig. 1.9: MZI based optical switch.
SOA -1
SOA -2 Coupler Coupler
Input Output -1
Output -2
Control
signal
~ 19 ~
Ultrafast nonlinear interferometer (UNI) is in general a single arm polarization
interferometer. UNI works depending on the phase difference between the two
polarization components of the data signal. The input signal is split into two
orthogonal polarization components with a time-delay between them („figure -1.10‟).
This can be done by a polarization split and delay (PSD) which consists of a
polarization beam splitter (PBS) and a polarization maintaining fiber (PMF) [69]. The
SOA introduces a phase difference between the two components. The phase
difference is controlled by a control signal. An identical PSD is placed at the exit of
the SOA. This removes the delay between the components and forces the components
to interfere at the PBS. In absence of control pulse the data signal goes to „output -1‟
and in the presence of control pulse the data signal is received at the „output -2‟. Thus
switching action is achieved.
Fig. 1.10: A schematic diagram for UNI gate.
Input
Output -1
Output -2
Control
signal
SOA PBS PBS
PMF PMF
~ 20 ~
A nonlinear optical loop mirror (NOLM) is basically a Sagnac interferometer
in optical fiber with a nonlinear medium inserted in the loop („figure -1.11‟). A
nonlinear fiber is used in the loop. Input signal is split into two components at the
input 3 dB coupler. One component propagates in the clockwise direction and the
other travels in the anti-clockwise direction. After recombining at the neck the signal
interferes constructively at the input side but interferes destructively at the output
side. Thus the signal appears to be reflected to the input. So when the phase difference
is zero the interferometer seems to be a mirror. Phase difference can be changed by a
control pulse inserted to the loop through a second coupler. When a phase difference
of π is introduced between the two components the data signal will be transmitted to
the output.
Input
Output
Control
signal
Fig. 1.11: Schematic diagram of a nonlinear optical loop mirror (NOLM).
~ 21 ~
1.6.6. Terahertz optical asymmetric demultiplexer (TOAD)
Again Terahertz Optical Asymmetric Demultiplexer (TOAD) can be used for high-
speed switching [304]. It can also demultiplex a high speed optical time division
multiplexing (OTDM) stream. In TOAD switching is achieved by placing a SOA
asymmetrically from the center of an optical fiber loop mirror („figure -1.12‟). Data
signal is injected to the loop through a 50:50 coupler. The clockwise and anti-
clockwise propagating data signals arrive asynchronously at the SOA. A control pulse
is injected via a second coupler and is timed such that it arrives after one data pulse
but just before the other data pulse. Due to the phase change when the two counter-
propagating data signals components interfere on their return to the input coupler,
data pulse is switched out.
50:50 coupler
SOA
Control pulse
Output Input
Fig. 1.12: TOAD as optical switch.
~ 22 ~
1.6.7. Optical isotropic nonlinear material (NLM)
Optical isotropic nonlinear materials can also play a great role in optical switching.
These materials show Kerr type of nonlinearity. The refractive index of this type of
material changes with the intensity of the optical signal passing through the material.
As a result if the input light beam has two different intensity levels (at different time)
then the output will be received from two different output channels corresponding to
the two different input levels. For example when the intensity of the input light beam
„AO1‟ is a prefixed intensity „I‟ then output is received at „Y2‟ („figure -1.13‟). Now
no light will be received at „Y1‟. Again when the input intensity changes to „2I‟, the
refractive index of the linear material (LM) remains unaltered but that of the NLM is
changed (increased in this case). So the light beam is now travels through the channel
„Y1‟ causing no light in the channel „Y2‟. So these materials can be used for all-optical
switching [229]. Optical switching using this type of isotropic nonlinear material is
discussed in „chapter -3‟ in detail.
Fig. 1.13: Optical isotropic nonlinear material used as a switch.
Y1
Y2
A
O1
O2 LM
NLM
O3
O4
~ 23 ~
For performing all-optical switching operations pulsed Nd:YAG laser sources
are massively used in many schemes. But high electrical power is required for
production of Nd:YAG laser. Tunable diode lasers can also produce the required laser
pulse for optical switching. Therefore such nonlinear materials are required which
have larger nonlinearity so that it can provide significantly high nonlinear effect even
if a laser beam of low intensity travels through it. The all-optical switching with
nonlinear material utilizing Kerr effect the nonlinear absorption is also to be low
[184]. For chalcogenide glasses the third order susceptibility (χ3) is noticed 1000
times higher than the silica glass. Q-switching technique may be adopted to produce
high peak power pulse beam from continuous wave laser.
1.6.8. Quantum dot switching
Quantum Dots (QDs) can also be used for optical switching [87, 226, 257, 285]. QDs
show nonlinearity due their delta function intensity states. Sharp excitonic peak
having larger peak absorption than bulk or quantum wells can be seen in QDs.
Different states of QD are shown in „figure -1.14‟) Generally QD-SOA based Mach
Zehnder interferometer is used to utilize quantum dots based optical switching. The
QD-SOA is placed in the arms of the MZI. Quantum dots are excited by external
pump beam. This leads to a variation in the phase difference. This results in the
switching of the MZI.
~ 24 ~
1.6.9. Electro-optical absorption switching
Electro-optical absorption can also be use for optical switching. This type of
switching is based on shift of the absorption band edge of a semiconductor. It can be
achieved by Quantum Confined Stark Effect (QCSE). Quantum well shows electro-
optic effects due to birefringence and Kerr effects from QCSE near the excitonic
absorption edge [227]. Extension of wave function outside of the quantum well makes
the absorption band gap narrower. A reversed bias is applied to a p-n junction. A
pulse is absorbed in the junction area resulting in generation of carriers. The carriers
diffuse and cancel increase in the absorption area for the next pulse. So the next pulse
is not absorbed but transmitted.
Wetting layer
Injected current
Quantum dots
Input light Output light
Ground state
Excited quantum
dot states
Stimulated
emission to
valance band
Spontaneous
carrier escape
Spontaneous
recombination
Fig. 1.14: Schematic diagram of quantum dot states [257].
~ 25 ~
1.7. Objective of the proposed work.
The importance of using optics in computing is already established. Optics has been
being used in computation as well as communication since the last few decades.
Several approaches have been seen to increase the performance of computing
systems. Many optical logic, arithmetic and algebraic processors have been reported
but the search for new technology remains. Here we have attempted to make some
contribution to the wide field of optical computing. The broad target of our present
work is to develop different all-optical logic, arithmetic and algebraic processor in
some advantageous method.
Light is considered as a transverse electromagnetic wave consisting of
vibrating electric and magnetic field vectors at right angles to each other and also at
right angles to the direction of propagation of light. When the electric vector of a light
is confined to a definite direction then the light is called „plane polarized light‟
(„figure -1.15‟). The plane in which the electric vector and the propagation vector are
confined is known as „plane of vibration‟ and the plane perpendicular to the plane of
vibration is called „plane of polarization‟. Light signal can be represented in terms of
the state of polarization of the light beam. Advantage of this technique is that the state
of polarization of the optical signal is not generally changed of its own. During long
distance transmission of data signal the intensity of the light signal may decrease due
to various reasons. In case of intensity based coding the receiving system cannot
recognize the optical signal whose intensity is changed from the predefined value.
Therefore it becomes difficult for an optical system, operating on intensity based
coding, to work properly. In polarization based encoding this problem can be avoided.
Here one may consider a light signal polarized in the plane of paper as „logic 1‟ (high)
state and a light signal polarized perpendicular to the plane of paper as „logic 0‟ (low)
state. The powers in the two polarization states are equal. Optical isotropic nonlinear
material based switches are used in many cases for developing the optical system.
High speed all-optical logic gates are essential elements to fabricate high-speed
optical networks for performing optical signal processing functions. It is seen that
there is a scope to develop the all-optical logic gates in a different technique using
polarization based encoding and as well as the switching capacity of the optical
isotropic nonlinear material. As the polarization based coding method have some own
advantages therefore using this technique it is helpful to design an optical logic
~ 26 ~
system. Again in the polarization encoded data the average byte power is always same
whatever the number of „1‟s‟ and „0‟s‟ in the byte, but in intensity encoded data it is
not seen.
The objective of the proposed work is to develop a method of implementing (i) an
integrated logic and arithmetic unit in an alternative approach, (ii) polarization
encoded optical logic gates, (iii) an optical system for maintaining a prefixed intensity
of light signal, (iv) a photonic astable multivibrator, (v) polarization encoded optical
S-R flip-flop and M-S J-K flip-flop, (vi) optical polarization encoded adder,
subtractor etc., (vii) optical polarization encoded multiplexer, demultiplexer etc.
In „chapter -1‟ an introduction to optical logic, arithmetic and algebraic data
computing is given. We have discussed advantages of optical computing, architecture
of optical systems, how optical switches can be developed in various methods and
some approaches for an all-optical computer. In „chapter -2‟ we shall have a short tour
in the avenues of some important works to reach the goal of superfast computing
Direction of propagation
Unpolarised light
Plane polarized light with
vibration in the plane of
paper
Plane polarized light with
vibration perpendicular
to the plane of paper
Fig. 1.15: Polarized light signal
~ 27 ~
using optics. An all-optical, arithmetic and algebraic processor is proposed in „chapter
-3‟. It can perform any logical, arithmetic or algebraic operations. In „chapter -4‟ a
method of developing a prefixed light intensity for a logic signal bit is described.
Further in „chapter -5‟ the all-optical logic gates using polarization based encoding are
illustrated. Polarization encoded new optical S-R flip-flop and an M-S J-K flip-flop
are presented in „chapter -6‟ and „chapter -7‟ respectively. Sometimes it may require
achieving a polarization encoded data bit from an intensity encoded data bit or vice
versa. Such techniques are described in „chapter -8‟. A method of generating a single
optical pulse using electo-optic modulator is presented in „chapter-9‟. An astable
vibrator is discussed in „chapter-10‟. In „chapter -11‟ an all-optical technique for
developing optical multiplexer using polarization encoded logic gates is depicted. In
„chapter -12‟ we have discussed a method to implement an optical parity generator
and checker. Finally in „chapter -13‟ an overall conclusion is given and future scope
of work is discussed. At the end of this chapter a list of references is given. Lastly the
list of my publication and presentations are given.
1.8. Conclusion
In near future all-optical signal processing will be necessary to meet the increasing
demand for higher speed and larger capacity based optical communication networks.
Though a general purpose all-optical computer is very difficult to be practical, but the
technology is changing. The optical nonlinear materials and semiconductor optical
amplifier are playing important role to perform optical nonlinear operations. Many
approaches have been proposed to achieve all-optical logic functions based on the
nonlinear effects in semiconductor material, in optical fibers or in waveguides. With
new innovations with polarization encoding and optical nonlinear material it will be
helpful to arrive at the new world of higher speed of operation. Promising
nanotechnology like nanoresonators, nanometallics, plasmonics, quantum dots etc.
can give a light of hope towards the realization of an optical computer.
~ 28 ~
CHAPTER - 2
___________________________________________________
Background Review of Some Important Works
Related to Optical Computing
Abstract
Information all over the world is expanding every day. Simultaneously the rate
data transfer is also increasing day by day. Therefore it is necessary to develop such
computing system which can provide such tremendous speed of operation. Shifting to
the optical domain from the conventional electric one is the only way for such
upgradation. Already many approaches have been seen to achieve the goal of high
speed computation with optical signal. In this chapter a short review of such
development has been made.
~ 29 ~
2.1. Introduction
Optical device has become an interesting tool because of its many advantages in
different applications. It can solve many problems associated with conventional
electronic computing hardware. The limitation on the speed of the conventional
electronic technology can be overcome by the use of the photonic technology. All-
optical parallel computation is the key feature of optical network as well as part of
optical computer. All-optical systems have much higher speed of operation compared
to the electro-optic systems. Scientists and researchers in different corners of the
world are leaving no stone unturned to make the dream of an optical computer a
reality. In recent years numbers of optical logic gates, optical switches, optical
interconnections and optical memory have been developed. All-optical parallel
computing and data processing basically depends on the material nonlinearity. That is
why researchers are testing possibilities of using different materials for all-optical
logic. The twenty first century is expected to become the age of photonic materials
and optical technology. Different techniques have their advantages over other and
some limitations too. The operational speed as well as the power required for
operation is the main attention of the researchers. For any optical computation
systems optical memory elements are also significant for proper functioning of the
system. In optical computing signal synchronization is important. Many approaches
have also been seen where an unconventional method is explored for optical
computation.
2.2. Some approaches for optical computing.
Optics has successfully established itself as a promising technique for data computing.
Electronic computers generally perform some number of serial operations. On the
other hand all-optical parallel computation is possible with the inherent parallelism of
optical signal. Data can be communicated in parallel by incorporation of optics for
organizing an optical computer. So a higher rate of information processing can be
achieved for decision making and computing. Different approaches have already been
seen to reach the goal. Now it is established that optics can be successfully used for
implementing arithmetic, algebraic and data processing operations as well as in
communications.
~ 30 ~
The earliest computer could do only some prefixed operations. A stored
programmed computer was an improvement over earlier program-controlled machines
like electronic numerical integrator and computer (ENIAC). A von Neumann machine
has four parts like (i) processing unit, (ii) memory unit, (iii) control unit and (iv) I/O
unit. As the instruction and data streams share the same bus this limits the operational
speed of the computer.
In a computer architecture depending upon the number of simultaneous
instructions (or control) and data streams available, the system can be classified into
four classes like single instruction single data stream (SISD), single instruction
multiple data stream (SIMD), multiple instruction single data stream (MISD) and
multiple instruction multiple data stream (MIMD) [2]. SISD processing is like Von
Neumann architecture. SIMD can be divided into array processor, pipelined processor
and associative processor.
For implementation of optical computing machine the four units have to be
replaced by optical systems. To develop an optical computer an optical data processor
is needed. Optical numeric processor and optical nonnumeric processors are being
developed. Optical logic, arithmetic unit, correlator are numeric processors. On the
other hand nonnumeric processors perform optical text processing and optical
knowledge based processing [41]. For processing of data optical switching device is
an important element. Lot of proposals, analysis and new findings has been reported
in the last few decades to use optical signal in computations. The journey was started
with the discovery of LASER in around 1960. Solid state ruby laser and He-Ne gas
laser were reported at that time. Consequently semiconductor laser, dye laser etc.
were demonstrated followed by a revolutionary change in the area of data processing.
Researchers realized that classical optics could be utilized for the digital optical
computer [4]. It was supposed that if optical nonlinearity would not be significantly
high, then optical logic devices with satisfactory speed, size, and energy consumption
would not be implemented. Symbolic substitution was an important technique for
image processing. It was used to develop an elementary computer. Now laser diodes,
as a source of coherent light, are being produced in large scale. Optical CD is now
very common in computers.
Different approaches are seen to develop different logic, arithmetic and data
processors. Lots of logic and data processors have been implemented using different
techniques so far [14, 23, 31, 53, 70, 72, 76, 139, 147, 149, 172, 174-176, 187, 188,
~ 31 ~
193, 217, 235, 255]. Heinz et al. have reported an optical method for matrix
multiplication [1]. A real-time optical parallel processor for binary addition with a
carry is proposed by Mukhopadhyay et al. [6]. In some proposals the use of tristate
logic is found [13, 17]. The concept of modified signed-digit (MSD) number system
has been introduced in this context [7, 30]. The problem of „carry‟ and „borrow‟ based
operations in conventional adder, subtractor can be avoided by using MSD. Beside
this a negative number can be handled easily in MSD. Negative numbers are the
logical complement of the positive number.
Though some uncertainties about the future of optical computer have arisen
[3], optical computing remains a promising field of research [176]. The field of
optical computing is progressing rapidly. As a result of numerous developments
integrated optical logic has become practical and interesting. Two passive logic gates
(XOR and COINC) have been demonstrated [109, 156]. These consume no power in
principle.
Different encoding and decoding techniques are used in different reports for
fabrication of optical system. Alam et al. have designed an efficient combinational
logic circuit using polarization encoded optical shadow-casting [18]. Polarization
based encoding is used in some cases [19, 170, 171]. Zaghloul et al have reported
unforced polarization-based optical implementation of Binary logic [171]. A
technique for complete all-optical processing polarization based binary logic gates is
reported by them [170]. They have introduced the orthoparallel optical logic
architecture to design and implement different binary logic gates like AND, OR
NAND etc. An OR gate, introduced by them, is shown in the „figure - 2.1‟. They have
represented the „logic 1‟ and „logic 0‟ by linearly polarized waves at +45ᵒ and - 45
ᵒ
respectively. There are two branches logic zero branch (LZB) and logic one branch
(LOB). Only one beam is active at a time.
~ 32 ~
Different optical switches have been seen to be used for implementation of
optical systems. All-optical data processing and computing operation technique
basically depends on nonlinearity of material constituting the device. Optical isotropic
nonlinear material based switching is used in many cases. Pahari et al have proposed
an all-optical method for the addition of binary data by nonlinear materials [79].
For development of information processing architectures, the role of various
analog and digital data comparison is very important [225]. An all-optical comparison
scheme between two multi-bit data with optical nonlinear material has been proposed.
With proper laser source and optical nonlinear material an operational speed of 1-10
Tb/s can be expected. Pahari et al. have developed a new method of all-optical data
comparison scheme with nonlinear material using 1‟s compliment method [166].
Caulfield et al. have proposed generalized optical logic elements (GOLEs) and
directed logic [190]. It is a device that can do any of the 16 Boolean logic operations
on signals in an optical beam with very fast switching among functions. A Mach-
Zehnder interferometer with two mutually coherent inputs can perform lossless
computing.
0/ 180 P
P M
BS
LOB
LZB
Fig. 2.1: Schematic diagram for an optical OR gate [170].
~ 33 ~
All-optical switching has been demonstrated using in a laterally coupled
GaAs-AlGaAs microring resonators [44]. Nonlinear polarization switch can be used
for developing all-optical logic [114].
Optical tree architecture (shown in „figure - 2.2‟) can be found in many
applications [86, 223, 247]. It uses the switching capacity of optical nonlinear
material. The switch is managed in such a way that in the absence of controlling
optical signal „P‟ the light signal in the branch „A‟ (which comes from a constant laser
source (CLS)) goes to the lower branch „C‟. When there is a control optical signal „P‟
then the signal beam in the branch „A‟ is refracted to the upper channel „B‟. Similarly
the control signal „Q‟ in the branches „B‟ and „C‟ determines whether the light signal
in the concerned branch will travel to the respective lower branches or switch over to
the upper branches. Different output states for different control signal are depicted in
the „table - 2.1‟.
A
B
C
D
E
F
G
P Q
CLS
Fig. 2.2: Optical tree architecture.
~ 34 ~
Table - 2.1: Output states of tree architecture.
Control inputs Outputs
P Q D E F G
0 0 0 0 0 1
0 1 0 0 1 0
1 0 0 1 0 0
1 1 1 0 0 0
Semiconductor optical amplifier (SOA) based switches play an important role
in many cases [50, 59, 71, 73, 118, 189, 217, 232]. It is very similar to a laser. All-
optical logic gates based on the nonlinear effects in semiconductor optical amplifiers
(SOAs), like cross-gain modulation (XGM), cross-phase modulation (XPM), four-
wave mixing (FWM) and cross-polarization modulation are promising due to SOA‟s
high gain in the optical power, strong change of the refractive index and potential for
photonic integration. M. Kalyvas has reported a 40 Gb/s all-optical write/store
memory using a single semiconductor optical amplifier-based logic gate [35].
With the use of an integrated SOA based Mach Zehnder interferometer with a
differential modulation scheme an all-optical XOR has been demonstrated [112].
XOR logic gate can also be implemented by four-wave mixing in SOA [117, 120].
Mach-Zehnder interferometers with the help of SOAs can provide very high-
speed all-optical switching [28, 33, 52, 78, 121, 280]. XOR logic gate can also be
constructed based on Sagnac interferometric structure where SOA serves as the
nonlinear medium [47, 48, 157]. All-optical logic gates based on nonlinear optical
loop mirrors can also be found [162]. SOA in nonlinear optical loop mirrors or sagnac
interferometer is also used for data format conversion and other operations [49, 164].
An all-optical 40 Gbit/s NOR logic gate has been presented using SOA and an
optical bandpass filter [177]. All-optical AND and NAND logic gates based on
semiconductor microresonators have been constructed [68]. Multiple ring based logic
devices are advantageous for cascading in photonic circuit because more ports are
~ 35 ~
available. Photonic logic NOR gate has been also constructed based on symmetric
GaAs-AlGaAs microring resonators [84]. The switching energy of the gate is reported
as 20 pJ/pulse. It can be integrated to a large scale photonic circuit. As microring
resonators are ultracompact, they can be useful for developing optical logic gates [67,
261, 270].
The polarization shift keying modulation format is used in many schemes.
Based on an asymmetric nonlinear directional coupler all-optical logic gates have
been developed by Fraga et al [173]. All-optical logic OR gate using SOA and
delayed interferometer is implemented by Wang et al [175]. Mondal et al have
developed a method of conducting an all-optical NAND logic operation controlled
from a long distance [187].
Zhang et al have implemented optical switches and logic gates based on self-
collimated beams in two-dimensional photonic crystals [195]. The operating principle
is based on the interference of reflected and transmitted self-collimated beam. The
device is applicable for photonic integrated circuits. Liu et al have designed
theoretically the all-optical logic gates based on two-dimensional low-refractive index
nonlinear photonic crystal slabs [267]. They have demonstrated ultracompact all-
optical AND, NAND, OR, and NOR gates with two-dimensional nonlinear photonic
crystal slabs. They have showed that all-optical logic gates with low pump-power in
the order of tens of MW/cm2 can be achieved.
All-optical Boolean logic gates can also be realized using azo-dye doped
polymer film [158]. Bovino et al. have implemented an optical polarization based
logic function (XOR or XNOR) with nonlinear gallium nitride nanoslab [238]. They
have presented the scheme based on non phase-matched noncollinear second
harmonic generation from Gallium nitride. The polarization of the noncollinear
generated beam is a function of the polarization of both pump beams.
Periodically poled lithium niobate (PPLN) have been used in many reports
[45, 193, 216, 234, 245, 262, 282]. Single PPLN based simultaneous half-adder, half
–subtracter and OR logic gate are proposed by Wang et al. Bogoni et al have
developed 640 Gbit/s photonic logic gates. They have used pump depletion in a
periodically poled lithium niobate waveguide. Again Wang et al. have developed an
ultrafast all-optical three-input Boolean XOR operation for differential phase-shift
keying signals using periodically poled lithium niobate [216].
~ 36 ~
Fok et al. have experimentally developed an all-optical XOR gate with optical
feedback using highly Ge-doped nonlinear fiber and a terahertz optical asymmetric
demultiplexer [268]. The XOR gate is achieved based on cross-polarization rotation in
nonlinear fiber, while the optical feedback employs a terahertz optical asymmetric
demultiplexer (TOAD). The TOAD simultaneously cleans up the XOR output and
converts the wavelength of the feedback signal to allow proper feedback operation.
Optical soliton can also be used for logic operation and data processing [138, 143,
230].
Half adder and half subtractor are essential in data computing. The „sum‟ or
„difference‟ can be achieved by XOR logic operation between the two input variables
(„figure – 2.3‟). While the „carry‟ bit is generated by AND operation between the two
variables, the „borrow‟ bit is received by the AND logic operation of one variable
with the complement of other variable. An ultrahigh-speed all-optical half adder based
on four-wave mixing in semiconductor optical amplifier is reported by Li et al. [172].
Yang et al have developed a function-lock strategy in OR/NOR optical logic
gates based on cross-polarization modulation effect in semiconductor optical
A
B Sum
Carry
A
B Difference
Borrow
(i) (ii)
Fig. 2.3: (i) A half adder and (ii) A half subtractor
~ 37 ~
amplifier [196]. Leyder et al. have designed a polarization controlled optical gates by
interference of coherent polariton beams in microcavities [197]. Because of the
interference between coherent polaritons, this process is observed in the case of
polaritons generated from two collinearly polarized coherent pump beams. On the
contrary, if the beams are cross polarized, the scattering is suppressed. Emary et al.
report an optically controlled logic gates for two spin qubits in vertically coupled
quantum dots [198]. RayChaudhuri et al. have suggested molecular level all-optical
logic with chlorophyll absorption spectrum and polarization sensitivity [205].
Molecular devices can be used for photonic information processing and storage due to
their small size and light weight. The photochromic protein bacteriorhodopsin is
important in this context. Optical switching operation can be performed with
bacteriorhodopsin („figure - 2.4‟) [96, 116, 140, 159, 293]. The probe beam is focused
by the lens onto the sample. The pump and probe beams overlap on the sample.
Changing the intensity of the beams switching properties are studied.
Probe beam
Pump beam
Lense
Lense Filter
Filter
Filter
Sample Detector
Fig. 2.4: Schematic diagram of the experimental set up for optical switching
with bacteriorhodopsin film sample.
~ 38 ~
Chattopadhyay et al. have proposed an all-optical conversion scheme for
representing a binary to quaternary and vice versa [236]. Clark et al. have reported an
all-optical fiber polarization based quantum logic gate [237]. Ma et al. report a high
speed all optical logic gates based on quantum dot semiconductor optical amplifiers
[257].
Half adder/subtractor arithmetic operation can also be found by using dark-
bright soliton conversion control within an all-optical circuit consists of microring and
nanoring devices [279]. Here „logic 0‟ and „logic 1‟ are represented by dark and
bright soliton respectively. An all-optical half adder based on cross structures in two-
dimensional photonic crystals is implemented by Liu et al. [215].
With the use of optical nonlinear material based switching and spatial input
encoding binary addition and subtraction operation can be performed [163].
Polarization coding technique and nonlinear total reflectional optical switches are also
used for optical half adder and full adder operations [253].
Gayen et al. have proposed an all-optical adder/ subtractor based on terahertz
optical asymmetric demultiplexer [239]. They have exploited the advantages of
terahertz optical asymmetric demultiplexer based optical switch to design an
integrated all-optical circuit which can perform binary addition and subtraction.
All-optical half adder has been demonstrated with interferometric SOA gates
[111]. This all-optical device generates simultaneously four Boolean operations at 10
Gb/s.
All-optical flip-flop, designed as bistable elements, can serve as temporary
memory elements and help in realizing optical networks. Flip-flops have been
proposed in different ways by many researchers [150]. Flip-flop memory based on
two coupled nonlinear polarization switches is reported [65]. The principle of
polarization dependent semiconductor optical amplifier gain is applied to a nonlinear
polarization switch.
Designing of all-optical flip-flop is also reported using directionally coupled
bistable laser diode [110]. The nonlinear effects of the saturable absorber and the
directional coupler are utilized to demonstrate the flip-flop. Multimode interference
bistable laser diodes are also used to establish flip-flop operation [107, 160].
Optical bistability in a SOA or distributed feedback SOA can be employed to
achieve all-optical flip-flop operation [115].
~ 39 ~
Again flip-flop is designed depending upon coherent nonlinear feedback
[181]. The nonlinearity is due to interference of two coherent optical fields. The lasers
remains above the lasing threshold always and thus carrier density changes are lower.
This makes the transient times reduced.
All-optical flip-flop has been designed based on single distributed feedback
laser diode [208-210]. A bistability is achieved due to the spatial hole burning effect
by injecting continuous wave light in the laser diode. Switching time below 75 ps and
repetition rates of 2 GHz are reported by using pulses with energies below 200 fJ.
Using of multivalued logic in optical computing can increase the logic density.
In trinary system memory elements also have much importance for better
performance [228]. A trinary flip-flop is different from a binary flip-flop. While a
binary flip-flop has two stable states, a trinary flip-flop has three states.
New conducting polymers are being used to develop transistor like switches
[40, 41]. These switches are smaller and faster than the silicon transistors. We can
dream for an optical transistor which can operate with a single photon [224]. Now all-
optical transistor can be expected in reality [161, 250, 252]. As the rate of data
transmission is increasing sharply demand for optical technology is also
strengthening. Optics is now being used in long distance telecommunication as well
as in shorter distance interconnection [251].
There are also many more all-optical processors already developed by
different workers.
2.3. Conclusion
Since the birth of the optical computing technique it has become much matured today.
Yet it seems to be in competition with the electronic computing. With the invention of
new optical and optoelectronic technologies the goal of superfast computing with
optics can be achieved. The field of quantum computing, based on quantum nature of
photon, is also flourishing. Linear optical logic devices can be utilized to develop an
optical quantum computer. All-optical digital data processing seems to be the
technology for the new generation computing systems in the optical domain. Again
optical computing technique is believed to be highly useful in quantum cryptography.
~ 40 ~
CHAPTER - 3
___________________________________________________
A Proposal for Developing an Integrated All-Optical Logic
and Arithmetic Unit Using the Kerr - Nonlinearity
Abstract
The advantages of using optical signal in logic, data and arithmetic processing
are now well known to the optical community over the globe. Some optical isotropic
nonlinear materials can play an important and essential role in developing such logic
and arithmetic processors. This type of nonlinear materials can be successfully used
also as an optical switch. Different all-optical logic gates using this type of switching
are already reported several times. Here in this chapter a new method to develop an
integrated, compact and dedicated all-optical system is described. This system can
perform many logic and arithmetic operations in parallel as required for the purpose
of processing of optical data.
Publications related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “All optical method of implementing
integrated logic and arithmetic processor (ILAP) using nonlinear material,”
XXXIII OSI Symposium on Optics and Optoelectronics, Department of
Electronics & Communication Engineering, Tezpur University, Napaam,
Assam-784028, India, 18th
-20th
December, 2007. Full paper was published in
the proceedings „Contemporary Optics and Optoelectronics‟, Tata McGraw-
Hill Publishing Company Limited, page 118-120.
2. J. N. Roy, A. K. Maity, D. Samanta, S. Mukhopadhyay, “Tree-net architecture
for integrated all-optical arithmetic operations and data comparison scheme
with optical nonlinear material,” Optical Switching and Networking (Elsevier),
4, 231-237 (2007).
~ 41 ~
3.1. Introduction
Since the middle of seventies there started an effort to implement data processors with
optical signal instead of so-called electronic signal. This is because of tremendous
inherent processing advantages with optics as information carrying signal. Optical
signal has a strong role in parallelism. Very high speed operation (for above the THz
limit) can be achieved if optics is suitably used. Even a femto-second pulse can be
used as an optical data bit if required. In last three decades lots of proposals already
came forward where logic operations, arithmetic operations, algebraic operations, data
processing, computation and image processing are done by either optical signal alone
(i.e. all-optical) or by opto-electronic mechanism. To implement the above all-optical
system we have seen the massive use of optical nonlinear material based optical
switches, photo-refractive and electro-optical material based optical switches etc.
Nonlinear material based switches have also several applications. Working principle
of this type of switches depends on the intensity level of the light signal existing at the
time of passing the information carrying signal through the nonlinear material. Most
all-optical logic and arithmetic operations can successfully be implemented by some
isotropic nonlinear materials [79, 127-129]. Here a new approach is proposed to
accommodate several all-optical systems in a single, compact and integrated
architecture for performing different logic and arithmetic operations. To develop it the
inherent all-optical switching capacity of optical isotropic nonlinear material is used
as far as practicable.
3.2. Use of nonlinear material for implementation of optical logic
system.
3.2.1. Optical isotropic Kerr nonlinear material (NLM) used as a switch
There are some isotropic nonlinear materials (NLMs) which can show also Kerr type
of nonlinearity. This type of materials can exhibit the character of self-focusing [303].
For this type material the 2nd
order nonlinear term, in the expression of polarization
( ), has a significant value and cannot be no longer neglected. Considering up to the
2nd
order nonlinear term and neglecting the higher order terms the expression for
dielectric polarization becomes
… (3.1)
For isotropic materials
~ 42 ~
… (3.2)
Hence the above equation becomes
… (3.3)
where . Now the displacement vector can be expressed as
… (3.4)
Hence the refractive index of the isotropic nonlinear material becomes
as [
So, … (3.5)
Here is the constant linear refractive index term,
is the nonlinear correction term and is the intensity of the
light signal passing through the NLM.
In „equation - 3.5‟ it is seen that if the intensity „I‟ increases the refractive
index of the nonlinear material also increases linearly. This character of the NLM can
be used to implement an all-optical switch shown in „figure - 3.1‟. Let us consider a
light beam AO1 of intensity „I‟ is made incident from air to an ordinary glass made
linear material (LM) interface at the point „O1‟ of a LM-NLM block. After refraction
the beam propagates through the linear material and then it is incident at the boundary
of linear and non-linear material (at the point „O2‟). The beam is now refracted
through the NLM and leaves the NLM at the point „O4‟. So this beam is received in
the channel „Y2‟. If the intensity of the light beam incident at „O2‟ (originally it falls at
„O1‟) changes from „I‟ to „2I‟ value, then the refractive index of the NLM increases
according to „equation - 3.5‟. As a result the light beam now leaves the NLM from the
point „O3‟ and it is then received through the channel „Y1‟ instead of the channel „Y2‟.
Thus the NLM can be used as an optical switch, where the change of the outcoming
channel of the light signal from the NLMs depends on its intensity level.
Fused Silica glass, carbon di sulphide (CS2) and many other dielectric
materials can be used as a non-linear device. For fused silica, n0 =1.458,
Wmn /107.2 2202
and for CS2, n0 =1.63 and Wmn /10514 2202
[309]. For an
~ 43 ~
example the deviation of the light signal passing through CS2 for different intensity
level of the light beam can be calculated very easily. For an ordinary CW laser of
100mW power and 50µm2 beam cross-section the intensity becomes 29 /102 mW .
Now if the above continuous wave (CW) beam is changed to a pulsed beam of pulse
duration 10-9
s the pulse power reaches a value of 218 /102 mW . This pulsating beam
can be obtained by the use of a suitable Q-switching or mode locking mechanism.
Considering the average intensity of the pulse 218 /102 mWI the value of „n‟
becomes 11.91 for CS2. Now considering the angle of incidence of the pulsed light at
LM and NLM interface as 45° one can find the value of the angle of refraction in the
NLM (θ2) as 529.4 . The above value of θ2 can be easily obtained from Snell‟s law.
Now if the intensity of the light passing through it is made doubled then „n‟ reaches
the value of 22.19 and the value of θ2 goes to 429.2 . So the change of the angle of
refraction (2) is 2.1, for the doubling of intensity.
Fig. 3.1: Optical nonlinear material used as a switch.
Y1
Y2
A
O1
O2 LM
NLM
O3
O4
45
∆θ2
~ 44 ~
For 1cm thickness of the NLM the separation between the two exit points
(„O3‟ and „O4‟) of the NLM (i.e. the lateral separation between the two channels „Y1‟
and „Y2‟) becomes 0.3mm for that value of 1.22 . This is a very large separation
in case of a micro-device. Therefore this type of NLM can be made useful for
implementing all-optical logic devices as a suitable channel can be selected by using a
proper laser intensity of a pulse having the order of nanosecond duration. The logical
systems are to be operated certainly in digital/ pulsating mode of the signal otherwise
the high amount of power is required to exploit the nonlinear switching character.
There are some nonlinear materials which can show very fast response time even in
sub-picoseconds range. Already several proposals of all-optical logic systems using
this type of switching have been reported.
There are also some nonlinear materials for which the refractive index is
expressed by the following equation
… (3.6)
For this type of material the effect will be reverse of the aforesaid nonlinear material
i.e. for increase in the intensity of the light beam passing through the NLM the
refractive index decreases.
The nonlinear material referred here in this thesis is only the first type of
nonlinear material. Different all-optical logic gates can be successfully implemented
by such type of optical isotropic nonlinear material. The logic states can be encoded
by the intensity level variation of the light signal. Here the presence of a light signal
of some predetermined intensity „I‟ is considered as „logic 1‟ (high state) and the
absence of light (zero intensity) is considered as „logic 0‟ (low state).
3.2.2. Optical NOT logic gate using NLM
An optical NOT logic gate using nonlinear material is shown in „figure - 3.2‟. Here
„A‟ is the input and „CLS‟ is a constant laser source. The operation of the scheme is
similar to the operation of the scheme shown in „figure - 3.1‟. Here the input channel
„A‟ and the constant light source (CLS) are combined together and the combination is
incident at the point „O1‟ on the linear material (LM). Then it is incident at the point
„O2‟ on the interface of the linear and nonlinear materials and finally it is refracted
through the NLM.
~ 45 ~
Now if A=0 then the intensity of the combined beam incident at the point „O1‟
(and also at „O2‟) is „I‟ only. So this light beam is refracted through the NLM along
the continuous line shown in the figure and leaves the NLM at the point „O4‟.
Therefore at the output „Y‟ a light beam of intensity „I‟ (which is because of the
intensity of the CLS) is received. Again if the input A=1 then the intensity of the
combined light beam incident at the point „O1‟ becomes „2I‟ and as a result of this the
light beam the refractive index of the NLM increases. So the light beam is now
refracted through the NLM along the dotted line shown in the „figure - 3.2‟ and leaves
the NLM at the point „O3‟. Therefore no light (logic 0) is received at the output „Y‟.
Thus the NOT logic operation is performed.
3.2.3. Optical AND and Ex-OR logic gates using NLM
Using the similar method other optical logic gates can also be implemented. How an
all-optical 2-input AND logic gate and an Ex-OR logic gate can be realized is shown
in the „figure - 3.3‟. „A‟ and „B‟ are the two input channels. These two light beams are
combined and made incident at the point „O1‟. After passing though the LM the light
Fig. 3.2: An all-optical NOT logic gate using
nonlinear material.
Y=
A O1
O2 LM
NLM
O3
O4
CLS
~ 46 ~
beam is incident at the point „O2‟ on the interface of LM and NLM. Then the light
beam is refracted through the NLM and leaves the medium at the point „O3‟ or at the
point „O4‟ according to the intensity of the combined light beam.
When A=B=0 i.e. no light is given to the inputs „A‟ and „B‟ then the intensity
of the combined light beam is zero. Therefore no light is obtained at the output
channels „Y1‟ and „Y2‟. So for the input condition A=B=0 the output Y1=0, Y2=0.
When A=0 and B=1 or A=1 and B=0 the intensity of the combined light beam
incident at the point „O1‟ is „I‟ only. This light beam passes through the LM and is
incident at the point „O2‟ on the LM and NLM boundary surface. Now this light beam
propagates through the NLM along the continuous line shown in the figure and leaves
the NLM at the point „O4‟. This light beam is received in the channel „Y2‟. Therefore
no light is found in the channel „Y1‟. Hence for the 2nd
and 3rd
input conditions the
output yields the result Y1=0 and Y2=1.
Fig. 3.3: All-optical AND and Ex-OR logic gates using
nonlinear material.
Y2=
A O1
O2 LM
NLM
O3
O4
B
Y1=A.B
~ 47 ~
For the last input condition A=B=1 i.e. both the input gets light of the prefixed
intensity „I‟. So the intensity of the combined light beam becomes „2I‟. The refractive
index of the LM does not change with intensity. So the combined light beam travels
through the LM in the same path as earlier and finally is incident at the point „O2‟ on
the LM and NLM interface. Now as the refractive index of the NLM increases with
the intensity of the light beam the combined light beam is refracted through the NLM
along the dotted line shown in the „figure - 3.3‟. Finally this beam leaves the NLM at
the point „O3‟ and is traced at the channel „Y1‟. This results no light in the channel
„Y2‟. So for this input condition the outputs become Y1=1 and Y2=0.
Thus it is seen that only when both the two inputs „A‟ and „B‟ get light (high
state) then only output Y1=1 (high state) and for the other input conditions Y1=0. So
output „Y1‟ gives the output of AND logic gate. On the other hand when only one of
the inputs gets light (high state) then only the output Y2=1 (high state) and for the
input conditions A=B=0 and A=B=1 the output channel „Y2‟ gets no light (low state).
Therefore the output channel „Y2‟ gives the result of Ex-OR logic operation between
the two inputs „A‟ and „B‟.
3.3. An integrated scheme of implementing optical logic and
arithmetic processor (OLAP) with NLM.
Here an all-optical integrated scheme is proposed. The system can perform different
logic operations as well as some arithmetic operations. Using this scheme optical
logic expressions in Sum of Product (SOP) form can be implemented. This scheme
can also be parallelly used as an arithmetic processor. The scheme is shown in the
„figure - 3.4‟. Here „A‟, „B‟, „C‟ are three input variables. From these inputs the „ A ‟,
„ B ‟ and „ C ‟ signals are generated using NOT logic gates. There are eight other
optical blocks in the „figure - 3.4‟. The blocks (1-8) are made of optical linear and
nonlinear materials.
The internal architecture of each block is shown in „figure -3.5‟. Here „x‟
represents the serial number of the blocks (x=1, 2,…., 8). „A‟, „B‟, „C‟, „ A ‟, „ B ‟ and
„ C ‟ are the respective input data channels of each block. There are also seven control
inputs like xA, xB, xC, x A , x B , x C and Px. If the control channel „Px‟ is made high
(logic 1) by giving light in the input terminal the corresponding block will be
~ 48 ~
activated otherwise the corresponding block will not work. When „Px‟ is high then the
output of the block will be the product of two or more terms among A, B, C, A , B
and C . Which terms appear in the output depend on the status of the corresponding
control input channel. The terms A, B, C, A , B or C will appear in the output only
if the corresponding control terminal xA, xB, xC, x A , x B , x C respectively are high
(logic 1). For example if the SOP term is A BC then to get the respective result of the
product we require 1 A , 1B, 1 C and P1 control terminals as „1‟ (high state) and
remaining control terminals as low for the block-1 in „figure -3.4‟. On the other hand
if the control input „Px‟ is at low (logic 0) state then the corresponding block will not
function and output of the block will be low.
In „figure - 3.5‟ it is seen that Px is one of the inputs of the last AND gate.
Now for „block-1‟ (x=1) if P1=1 then only the block is activated and output „Y1‟ gives
the desired result. Now the function of each block is described. Let us consider the
„block-1‟. The control input „1A‟ and the „data A‟ are combined by an AND logic
gate and parallelly „1A‟ control terminal and a constant light source (CLS) of
intensity „I‟ are also combined together by an NOT logic gate. „G‟ and „H‟ give the
output of the AND logic gate and the NOT logic gate respectively. If light is applied
(logic 1) to the control input „1A‟ then the data „A‟ can be recovered in the channel
„G‟. Now the channel „H‟ remains at the „logic 0‟ state (i.e. no light is obtained in the
channel „H‟). Again if the control input „1A‟ gets no light signal (logic 0) then the
output „G‟ remains at „logic 0‟ state (i.e. no light is available in the channel) and the
output „H‟ goes to „logic 1‟ state. The other control input channels in the block also
function in the same manner. The channels „G‟ and „H‟ are combined together (by OR
operation) to get the channel „J‟. Similarly, the same type of channels can be formed
by combining the every AND and NOT logic output channels for other control inputs
in the same block. Thus the channels „K‟, „L‟, „M‟, „N‟ and „O‟ are obtained. These
channels and the control channel „P1‟ (here P1=1) are connected to the inputs of the
final AND logic gate of the block producing the output „Y1‟. In such way other
outputs (Y2, Y3…., Y8) from other blocks of „figure -3.4‟ can be obtained.
The outputs of the blocks are added (by OR operation) as shown in „figure -
3.4‟ by suitable beam combining system to get the final output „Y‟. There are also two
more control inputs „Q1‟ and „Q2‟ in „figure - 3.4‟. In some specific application of the
scheme „Q1‟ and „Q2‟ are made high (logic 1) and then the output is to be taken at the
~ 49 ~
channels „S/D‟ and „C0/B0‟ (shown as dotted lines) respectively instead of getting the
output at „Y‟.
A logical processor can be implemented using this integrated scheme. For this
purpose the instructions which are to be followed are Q1=Q2=0. The control channel
Px (where x=1, 2,.., 8 for respective blocks) is to be made high (logic 1). The number
of blocks which are to be activated is the number of minterms present in the given
expression which is to be executed. For the first term in the expression, the block-1 is
activated by making P1=1. Then the control inputs (among 1A, 1B, 1C, 1 A , 1 B , 1 C
) corresponding to the variables (among A, B, C, A , B , C ) in the term are made to
be high. Similarly other blocks are also activated if required. Data are given in the
input channels „A‟, „B‟, „C‟. Now at the final output „Y‟ (in „fig. - 3.4‟) the required
result of digital operation can be achieved. Thus the system can be used to implement
the logical expression given in SOP form, under three-variable scheme.
The same integrated scheme can also be used as a half adder for adding two
data bits „A‟ and „B‟. The truth table of half adder is given in „table - 3.1‟. To use the
scheme as a half adder the instructions which are to be followed are (i) Q1=Q2=1, (ii)
P1= P2= P5=1, (iii) 1 A =1B=1, (iv) 2A=2 B =1, and (v) 5A=5B=1. As the controlled
inputs „Q1‟ and „Q2‟ are made high (logic 1) so no light signal can now be retrieved at
the terminal „Y‟. Rather the output is to be taken from the terminals „S/D‟ and
„C0/B0‟. For this operation only block -1, block-2 and block-5 are activated by making
the control inputs „P1‟, „P2‟ and „P5‟ high. After executing the above instructions the
scheme becomes ready for the half adder operation. Now if the data (augend and
addend) is applied at the input channels „A‟ and „B‟ the sum(S) is obtained at the
output channel „S/D‟ and the carry (C0) at the channel „C0/B0‟.
To use the scheme as a full adder (i.e. for adding the data „A‟, „B‟, and „C‟ )
the required instructions which are to be followed are (i) Q1=Q2=1, (ii) P1= P2= P3=
P4= P5= P6= P7=1, (iii) 1 A =1 B =1C=1, (iv) 2 A =2B=2 C =1, (v) 3A=3 B =3 C =1,
(vi) 4A=4B=4C=1, (vii) 5A=5B=1, (viii) 6B=6C=1, (ix) 7C=7A=1. The truth table of
the full adder is given in „table - 3.2‟. Now the data is to given in the input channels
„A‟, „B‟, „C‟ and then the sum (S) is obtained at the output channel „S/D‟ and the
carry (C0) is received at the output channel „C0/B0‟ (shown in „fig.- 3.4‟). The truth
table is exactly supported.
~ 50 ~
Again the integrated scheme („fig. - 3.4‟) can be used as a half subtractor also.
For this purpose the instructions which is to be followed are i) Q1=Q2=1, ii) P1= P2=
P5=1, iii) 1 A =1B=1, iv) 2A=2 B =1, v) 5 A =5B=1. Now if we give the data (minued
and subtrahend) at the input channels A and B we get the difference bit (D) at the
output channel „S/D‟ and the borrow bit (B0) at the channel „C0/B0‟. The truth table is
given in „table - 3.3‟.
Similarly a full subtractor can also be implemented using the same integrated
scheme. To do this the necessary instructions which to be followed are i) Q1=Q2=1, ii)
P1= P2= P3= P4= P5= P6= P7=1, iii) 1 A =1 B =1C=1, iv)2 A =2B=2 C =1, v) 3A=3 B =3
C =1, vi) 4A=4B=4C=1, vii) 5 A =5B=1, viii) 6 A =6C=1, ix) 7B=7C=1. The truth
table for the full adder is given in „table - 3.4‟. Now one requires to put the data at the
input channels A, B, C. Then the difference bit (D) can be taken from the output
channel „S/D‟ and the borrow bit (B0) from the channel „C0/B0‟. Here also the truth
table given in „table - 3.4‟ is supported.
~ 51 ~
A B C
Data input
CLS
Block - 1
Block - 2
Block - 3
Block - 4
Block - 5
Block - 6
Block - 7
Block - 8
A B
C
CLS CLS
NOT NLM
LM
Q1
Q2
S/D
C0/Bo
Y
Fig. 3.4: An integrated all optical logic and arithmetic processor using
nonlinear material.
LM
N
L
M
~ 52 ~
A CLS
B
C
G H
J
AND NOT AND NOT AND
AND AND AND
NOT
NOT NOT NOT
CLS CLS
xA xB xC
CLS CLS CLS
AND
Y1
Px
K L
M N O
LM
NLM
LM
NLM
x
x
x
Fig. 3.5: The internal architecture of each of the block (1-8) in fig.-3.4.
(x=1, 2, …, 8; beam splitters and beam combiners are not shown in the fig.)
~ 53 ~
Table – 3.1: Truth table for a half adder.
Table – 3.2: Truth table for a full adder
A B C C0 S
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
0 0
0 1
0 1
1 0
0 1
1 0
1 0
1 1
A B C0 S
0 0
0 1
1 0
1 1
0 0
0 1
0 1
1 0
~ 54 ~
Table – 3.3: Truth table for a half subtractor
A B B0 D
0 0
0 1
1 0
1 1
0 0
1 1
0 1
0 0
Table-3.4: Truth table for a full subtractor.
A B C B0 D
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
0 0
1 1
1 1
1 0
0 1
0 0
0 0
1 1
~ 55 ~
3.4. Conclusion
The above integrated system is all-optical in nature. The whole unit uses the strong
parallelism of optics as far as possible. Not changing the internal architecture of the
system, but only applying optical signal in proper terminals, and in proper control-
channels of the blocks used in the scheme one can receive any desired logic and
arithmetic operation as and when necessary. For example if we like to get a full
addition between three optical bits we should first apply the optical signal carrying the
instructions for performing the addition of bits, then optical signals for data-bit values.
Similarly with the same system we can get the result of full subtraction and that of
any logical expression.
The architecture shown above can also be minimized .It could be minimized
more if a single block is used in replacement of multiple blocks. As the whole
scheme is all-optical one therefore the real-time speed of operation can be expected
from here. The system can be implemented properly if a suitable laser source and
nonlinear material are available. Semiconductor optical amplifier and the necessary
diode laser can be mentioned in this regard.
There is a drawback of the logic gates with the intensity level dependent
encoding of the data signal. However this problem is resolved later. The scheme may
be successfully used for different logic and arithmetic operations.
~ 56 ~
CHAPTER - 4
___________________________________________________
A Method of Developing a Prefixed Intensity Level for any
Logic Input/ Output Signal Bit
Abstract
Optical isotropic nonlinear materials can be used as successful optical switch
to implement a logic or arithmetic processor. Optical systems can be developed very
easily using this type of optical switch. These switches act on changing the intensity
level of an optical signal. The primary requirement for proper functioning of such
nonlinear material based logic devices is a fixed intensity level of the optical signal
against a specific logic state. In this chapter a technique for obtaining fixed intensity
level of optical signal against a specific logic state is illustrated for the purpose of
optical data processing.
Publications related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “All-optical method for maintaining a fixed
intensity level of a light signal in optical computation” Optics
Communications, 281(19), 4851-4853(2008).
~ 57 ~
4.1. Introduction
Optical signals are seen to be used widely since the last few decades to implement
data and image processing operations [26, 27, 34, 36, 37, 39, 42, 54-58, 62, 64, 77,
81, 82, 89, 93-95, 101, 102, 105, 131, 137, 151, 152, 178, 199]. This is due to the
tremendous inherent advantages of optical signal in comparison to the conventional
electronic signal. Naturally when optical signal is used for communication of data,
one feels the necessity for encoding and decoding of the data bits. This can be done
with various optical/ opto-electronic techniques. For example the variation of levels
of intensity, polarization or phase of a light signal can be used for encoding or
decoding of data bit. In intensity based encoding technique generally the absence of
any light signal is treated as „logic 0‟ (low) state and the presence of a predetermined
intensity of light signal is considered as „logic 1‟ (high) state. To implement optical
data processors using the intensity based encoding technique, optical nonlinear
materials and photo-refractive materials have been widely used in many proposals
[83, 90, 142, 274, 287, 305]. Several papers are also published where tri-state and
quaternary state logic operations are seen to be implemented with optical data. In
those systems where nonlinear material based switches are used, the intensity of the
optical signal is very important for proper functioning of the switches. This is because
the refractive index of the isotropic Kerr type of nonlinear material varies with the
intensity of the optical signal passing through it. This mechanism is utilized to
develop optical switch. Now if there is a loss due to the absorption during propagation
of the light signal or any other reasons, the intensity of the data signal may change.
This can cause problems in the switching operation of the nonlinear material based
switch and consequently the cascaded system may lead to a malfunction. Therefore
the intensity of the optical signal against a specific bit is to be kept constant with a
predetermined value for getting a desired operation. Here in this chapter a new
concept is reported for maintaining a fixed intensity level of the light signal against
specific logic state in case of all-optical data processing.
4.2. All-optical method for controlling the intensity of the light signal:
the circuit description.
The proposed scheme is shown in „figure - 4.1‟. The scheme is developed using the
switching capacity of the optical isotropic nonlinear material. The refractive index of
~ 58 ~
this type of nonlinear material depends on the intensity of the light signal passing
through the material. The scheme is designed in such a way that the output of the
scheme will give a fixed intensity value „I‟ of light signal when there is a light signal
at the input and there will be no light at the output when there will be no light signal
at the input. Four constant intensity laser sources (CLS) are used in the scheme. The
intensity of the light emitted from a constant laser sources CLS-1, CLS-2, CLS-3 and
CLS-4 are „I/2‟, „I/4‟, „I‟ and „I/4‟ respectively where „I‟ is a prefixed value of
intensity of the laser light. The respective intensities of the constant laser sources are
to be ensured constant for achieving the specific intensities for specific bits.
Let it is assumed that an optical data signal, after travelling through a long
distance, arrive at the input of the aforesaid („fig.-4.1‟) system. As the beam moves
through a long distance it may undergo losses, thereby a decrease in the intensity may
occur.
Now the given light signal is fed to the input channel „A‟. Let it is considered
first that the intensity of this light beam is „I1‟. This light beam is splitted into two
beams at the point „B‟ by a 50:50 beam splitter. So the intensity of each of the two
beams becomes „ 21I ‟. The first component is incident on a nonlinear material
(NLM) at the point „C‟. Only if the intensity of this component equals „I/2‟ then it
goes to the channel „D‟. Otherwise the beam is refracted through other direction and
does not propagate through the channel „D‟. This is because the refractive index of the
material changes with the intensity of the light beam passing through it. The other
component of the input light is added to the light from CLS-3 at the point „H‟.
The light signal coming from channel „D‟ is combined with the light signal
coming from CLS-1 at the point „E‟. This combined beam is now incident at the point
„O1‟ at the boundary of linear material (LM) and nonlinear material (NLM) of a LM-
NLM block. Therefore the beam (of intensity „I‟) is refracted through the channel „F‟
and received at the output „Y‟. If the light from channel „D‟ is absent, then the light
only from the CLS-1 is refracted through the channel „G‟ which results in absence of
light in the channel „F‟.
On the other hand the combined light beam at the point „H‟ is made incident at
the point „O3‟ at a LM and NLM boundary. When there is no light at the input „A‟
then the beam is refracted through the channel „J‟; otherwise it does not go through
the channel „J‟. This beam (of intensity „I‟) from the channel „J‟ is now combined
~ 59 ~
with the light coming from CLS-4 and is made incident at the point „O4‟ on a LM and
NLM boundary. The refracted beam goes to the channel „K‟ only when there is no
light in the channel „J‟. The light beam (of intensity „I/4‟) coming from the channel
„K‟ is now combined with the light from CLS-2 and the light (of intensity „I/2‟) from
the channel „G‟ at the point „L‟. Only if all of these three light beams are present then
the combined beam, after incidence at the point „O2‟ at a LM and NLM boundary is
refracted through the channel „R‟. The channels „R‟ and „F‟ are combined at the point
„S‟ and the final output is obtained at the point „Y‟.
4.3. Description of operation of the system.
The functioning of the scheme is described as follows. The whole operation is
discussed in three different cases, i) when I1 = I, ii) when II 1 , and iii) when I1= 0.
i) When the input light intensity ‘I1’ is equal to ‘I’
First let us consider that a light beam of intensity I1 (=I) falls on the input „A‟.
This beam is splitted into two sub-beams (each of intensity „I/2‟) at the point „B‟.
Here we assume that there is no loss of light in the system as the volume of the whole
system is small enough. Now as depicted earlier, the first component at the point „C‟
goes to the channel „D‟ as its intensity is „I/2‟. As a result the combined beam at the
point „E‟ is of intensity „I‟ and is refracted through the channel „F‟. On the other hand,
due to presence of the second component at the point „H‟, no light is obtained in the
channel „J‟. This will, in turn, result in a light beam of intensity „I/4‟ at the channel
„K‟. Now at the point „L‟ only two beams, one from CLS-2 and other from channel
„K‟, prevail while no light comes from the channel „G‟. So the combined incident
light beam at the point „O2‟ will not be refracted through the channel „R‟. Therefore at
the point „S‟ only the light from the channel „F‟ prevails. This offers a light signal of
intensity „I‟ at the output „Y‟.
ii) When the input light intensity ‘I1’ not equals ‘I’
In the second case, if the intensity of the input light beam at the point „A‟ is
II 1 , then no light will be received at the channel „D‟. Therefore the light from
CLS-1 will be refracted through the channel „G‟ while no light will be obtained at the
channel „F‟. On the other hand, similar to the previous case, a light of intensity „I/4‟
~ 60 ~
will be received in the channel „K‟. Now in this case, as all of the three beams are
present at the point „L‟, the combined beam of intensity „I‟ will go to the channel „R‟.
So, at the point „S‟ only the light from the channel „R‟ exists. This beam now
produces a light of intensity „I‟ at the output „Y‟.
Thus it is seen that, the light of intensity „I‟ is obtained at the output „Y‟ for
any value of intensity of the input beam at the point „A‟.
iii) When the input channel accepts no light
Now if there is no light at the input „A‟, no light will be received in the
channel „D‟. This will result in, similar to the second case, no light in the channel „F‟.
On the other hand, at the point „H‟ no light comes from the point „B‟. So the beam
incident at „O3‟ (due to CLS-3 only) now goes to the channel „J‟. This will result in no
light in the channel „K‟. Therefore, at the point „L‟ only two light beams one from the
channel „G‟ and the other from CLS-2 prevail. As a result the combined beam,
A B
C
H
Fig. 4.1: Scheme to obtain a fixed intensity for a signal bit.
CLS-3
(I) J
CLS-4
(I/4)
D E
CLS-1
(I/2)
CLS-2
(I/4)
F
G
K
L
S
R
Y
NLM
O1
O2
O3
O4
~ 61 ~
incident at „O2‟, will not be refracted through the channel „R‟. So at the point „S‟,
light from neither the channel „F‟ nor the channel „R‟ prevails. This leads to no light
at the final output „Y‟, when no light is given at the input „A‟.
The proposed system can not only be useful for developing all-optical logic
circuits, it can be used in multiplexing and de-multiplexing of optical data too. There
already exists some scheme of optical multiplexer, demultiplexers, data converters
etc. in the area of optical computing and parallel processing. If this scheme or a
modified version of this scheme is used in such multiplexers, demultiplexers, data
converters etc., the proper intensity values against each bits or digits of the
multiplexed or demultiplexed data can be ensured and this will help transmission with
less noise, i.e. with high signal to noise (S/N) ratio and with very low probability
error.
In a brief it can be said that the proposed system can ensure no light if no light
signal comes at the input of the proposed scheme and at the same time it ensures also
a fixed intensity „I‟ of light beam whatever the input light intensity becomes. That
means it offers the „I‟ intensity of light at the output if the input light intensity is equal
to, greater or less than „I‟ except zero intensity.
4.4. Conclusion
The above scheme is all-optical one. So anyone can certainly expect a real time speed
of operation of the scheme. The system must be operated with high pulse power
digital signals to exploit the material nonlinearity for optical switching. As the scheme
ensures the specific intensity value of data „bit 1‟ or of „bit 0‟, it may be highly useful
in any nonlinear material based digital optical processing system. In case of digital
optical communication one can use this scheme successfully both at the input and at
the output ends and specially also at the repeater stations. This will help also for
readjusting the intensity values of bits to avoid the problem of intensity falling when
optical bits travel a long distance. Using the scheme the signal to noise ratio can be
improved at a high level and the bit error rate can be reduced. The scheme may be
extended to specify the intensity value of digits of tristate, quaternary state or even
decimal states of logic system.
~ 62 ~
CHAPTER - 5
___________________________________________________
A New Proposal of Implementing the Polarization Encoded
Optical Logic Families
Abstract
Optics has already been established as a meaningful signal in logic, algebraic
and data processing. Several all-optical data processors are reported in last few
decades. Different techniques and methods are utilized to develop the data processors.
A new concept of implementing all-optical logic gates is proposed in this chapter
where the logic states of bits are represented by different states of polarization of an
optical signal. As the state of polarization of the light signal is very much suitable and
advantageous for encoding and detecting the input as well as output bits of data of a
digital signal so the scheme can certainly extend some wide applications both in all-
optical parallel computation and information processing.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “A new scheme of implementing all-optical
logic systems exploiting material nonlinearity and polarization based encoding
technique,” Optoelectronics Letters (Springer), 4(3), 172-176 (2008).
~ 63 ~
5.1. Introduction
Optical signal has a strong role in parallelism. Very high speed operation can be
achieved if the inherent advantages of optics are properly exploited. That is why, a
strong effort to implement data processors with optics as information carrying signal
instead of electronic signal is being tried in almost every corner of the world. In the
last few decades lots of proposals have already come forward where logic, arithmetic,
algebraic operations, data processing, computation and image processing are done by
either optical signal alone or by opto-electronic mechanism [9, 46, 74, 85, 88, 92,
131-133, 153, 169]. To implement the Boolean logic operations using nonlinear
material as switching element, the variation of intensity level of the used light signal
is generally considered to indicate the logic states. So, to represent any logic state,
there, it is highly required to fix a specific intensity level of the light signal in favour
of each bit. Still there lies a problem. In long distance communication of optical signal
the intensity of the signal may change due to various reasons. Then the logic
processor which operates on the basis of the intensity level of the signal fails to work
properly in the detecting side. This difficulty may be avoided if the principle of
polarization based encoding/decoding technique is adopted. Use of optical
polarization state for implementing logic family is already proposed by Lohmann et al
[4, 5]. In this chapter polarization based encoding / decoding technique of bits and the
switching activity of some 2nd
order nonlinear materials are jointly used to implement
some important and dedicated Boolean logic gates, like AND, OR, NAND, and EX-
OR gates.
5.2. Polarization based encoding and decoding technique.
In this technique of encoding and decoding the logic states are defined on the basis of
the state of polarization of the optical data signal. Here one orthogonally polarized
light beam (say, polarized along perpendicular to the plane of paper (•)) is assumed as
„logic 0‟ (low) state and the other orthogonally polarized light beam (say, polarized in
the plane of paper (↨)) is represented as the state of „logic 1‟ (high).
A half-wave plate or a λ/2 plate is usually made of thin sheets of split mica or
of quartz crystal cut parallel to its optic axis, which introduces a phase difference of
„π‟ between two orthogonal polarized components, if a suitable wavelength of the
light is used. Thus when a light polarized perpendicular to the plane of paper, passes
~ 64 ~
through a half-wave plate, it becomes polarized in the plane of paper and vice-versa at
the outlet. So a half-wave plate can act as an all-optical NOT gate.
As the NLM is isotropic one and the light beam passing through it is not
splitted into ordinary and extra-ordinary components, so the NLM will not change the
state of polarization of the light beam during its propagation though NLM, what a
half-wave plate does. Here it is also assumed that the light beams at the inputs are of
„I‟ intensity each, whatever their polarizations become i.e. polarized perpendicular to
the plane of paper (•) or polarized in the plane of paper (↨). The inputs can be taken
from a coherent source.
5.3. Use of polarization based encoding/decoding technique and
nonlinear switching technique to implement optical logic gates.
Here AND, OR, NAND and Ex-OR logic gates are proposed by the proper use of the
techniques of polarization encoding /decoding and that of the non-linear switching.
These gates extend the fundamental logic operations, which can be very useful for all-
optical computation or data processing.
5.3.1. Implementation of a 2-input AND logic gate
The truth table for 2-input AND gate is given in „table - 5.1‟ and the respective
schematic diagram is depicted in „figure - 5.1‟. „A‟ and „B‟ are two inputs and Y is
the output. A dot (•) on a line in the figure signifies that there is a connection (may be
by a beam combiner or splitter) between the beam lines. The polarizer „P1‟ and „P2‟
can pass the light polarized perpendicular to the plane of paper (•) and polarizers „P3‟
and „P4‟ can pass the light polarized in the plane of paper (↨). Each of the inputs „A‟
and „B‟ are splitted into two beams of equal intensity („I/2‟) by a 50:50 beam splitter.
Between the two parts driven from the input „A‟ the first one is passed through the
polarizer „P1‟ and second through „P4‟. First beam now is combined with a component
of the input „B‟, and the combined beam is passed through „P2‟. On the other hand the
other portion of the input beam „B‟, after passing through „P3‟ is combined with the
beam coming from „P4‟ at the point „J‟. This combined light beam is now made
incident on the linear and non-linear material (LM-NLM) boundary. If this light beam
is of intensity „I/2‟ or „I‟, it is then refracted along the channels „S‟ or „R‟
~ 65 ~
respectively. This is because of the dependence of the refractive index of the NLM on
the intensity of the light signal passing through it.
On the other hand the output from the polarizer „P2‟ is also made incident on a
similar LM-NLM block. If the intensity of this light beam is „I/2‟ (or „I‟) then the
beam is received in the channel „E‟ (or „F‟) after refraction through the NLM. The
light from the channel „E‟ is combined with the light from the constant laser source
(CLS) emitting light of intensity „I/2‟ and polarized perpendicular to the plane of
paper (•). Now the combined beam is made incident on boundary of another LM-
NLM block. If the intensity of this combined light beam is „I/2‟ (or „I‟) then the beam
is received in the channel „H‟ (or „G‟). The channels „G‟ and „F‟ are combined
together at the point „Q1‟. The light beam from „Q1‟ and the channel „R‟ are now
combined at the point „Q2‟. This combined beam produces the final output of AND
gate at „Y‟. The beam splitters and mirrors are not shown in the figure for clarity.
Table-5.1: Truth table for the 2-input AND logic gate
The operation of the scheme is now described in brief.
(i) When A=B=0, both inputs „A‟ and „B‟ gets light having „•‟ polarization
(logic 0). As the polarizers „P1‟ and „P2‟ pass only light having „•‟ polarization, one
gets at the output of polarizer „P2‟ a light beam of „•‟ polarization. The intensity of the
light beam is „I‟ because of the contribution of the two parts (each of intensity „I/2‟)
from the two input beams. So the light beam is refracted through the channel „F‟. As
Inputs Output
A B Y= BA.
0 (•)
0 (•)
1 (↨)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
0 (•)
0 (•)
0 (•)
1 (↨)
~ 66 ~
the channel „E‟ gets no light only the light from the CLS (intensity „I/2‟) is incident
on the LM-NLM boundary. Therefore the beam is refracted to the channel „H‟. As a
result no light is obtained in the channel „G‟. Thus at the point „Q1‟ only light from
channel „F‟ is received. On the other hand P3 and P4 block the light from the inputs.
Therefore light can be received neither in the channel „R‟ nor in the channel „S‟. So at
the point „Q2‟ only light (•) from the point „Q1‟ is available. As a result at the final
output „Y‟ the light beam polarized perpendicular to the plane of paper (•) is
observed.
(ii) For the second input condition A=0, B=1, as „P1‟ and „P2‟ can only pass
the light of „•‟ polarization, so the output of „P2‟ can have light of „•‟ polarization (of
intensity „I/2‟). Now the light beam is refracted through the channel „E‟ while no light
is obtained in the channel „F‟. So a light beam of „•‟ polarization (and intensity I) is
received in the channel „G‟ as well as at the point „Q1‟. On the other hand a part of the
light from input „B‟ (having „↨‟ polarization) passes through P3. But P4 don‟t pass any
Fig. 5.1: Polarization encoded 2-input AND logic gate.
A
B
P1
P4
P3
P2
Y
R
S LM NLM
Q1 Q2
CLS
(, I/2)
LM
NL
M
E
F
G
H J
~ 67 ~
light in this case. So the light beam (of intensity I/2) is refracted through the channel
„S‟. And no light is available in the channel „R‟. Therefore at the point „Q2‟ only the
light beam from „Q1‟ prevails. As a result at the output „Y‟ only the light of (•)
polarization is observed.
(iii) For the third input condition A=1, B=0, the light beam from „A‟ cannot
pass through „P1‟ but pass through „P4‟. Again light from „B‟ cannot pass through „P3‟
but it passes through „P2‟. So similar to the second condition, in this case no light is
obtained in the channels „F‟ and „R‟. At the point Q2 the light beam from „G‟ only is
present. Therefore one gets at the output „Y‟ a light of „•‟ polarization (logic 0).
(iv) The last input condition is A=B=1. Here „P1‟, „P2‟ block the light beams.
So at Q1 no light is received. Polarizer „P3‟ and „P4‟ pass the light of „↨‟ polarization.
As this combined beam at the point „J‟ is of intensity „I‟ it is refracted therefore to the
„R‟ channel. This leads the output „Y‟ to get a light of polarization „↨‟ (logic 1). Thus
the truth table of AND logic gate is satisfied for the operation of the AND logic
system given in „fig.-5.1‟.
5.3.2. Implementation of a 2-input OR logic gate
The truth table for a 2-input OR logic gate is given in „table - 5.2‟ and the schematic
diagram for the OR operation is given in „figure - 5.2‟. In „table - 5.2‟ it is seen that
the output light beam is a „•‟ polarized one when both the input is „•‟ polarized and the
output is „↨‟ polarized for all other cases. In „fig.-5.2‟ it is depicted that the scheme of
OR gate has a little bit difference to that for the AND gate. Here the difference is that
the polarizers „P1‟ and „P2‟ pass only the „↨‟ polarized light beam and polarizers „P3‟
and „P4‟ can pass only light having „•‟ polarization. The operation is similar to that of
the scheme in „fig.-5.1‟.
Now the operation of the scheme of „fig.-5.2‟ is described.
(i) When the inputs A=B=0, polarizers „P1‟and „P2‟ don‟t pass any light („•‟)
coming from inputs. So no light signal is traced in the channels „E‟, „F‟ and „G‟. Light
beam from the CLS is refracted to the channel „H‟. On the other hand „P3‟ and „P4‟
pass the light signals obtained from the inputs. So the intensity of the combined beam
at the point „J‟ is „I‟. When this beam is passed through the NLM it is refracted to the
channel „R‟. This beam results a light signal of intensity „I‟ at the final output „Y‟ and
it is polarized perpendicular to the plane of paper (•) (logic 0).
~ 68 ~
Table-5.2: Truth table for the two-input OR logic gate
Inputs Output
A B Y=A+B
0 (•)
0 (•)
1 (↨)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
1 (↨)
1 (↨)
Fig. 5.2: Polarization encoded 2-input OR logic gate.
A
B
P1
P4
P3
P2
Y
R
S LM NLM
Q1 Q2
CLS
(„↨‟, I/2)
LM
NL
M
E
F
G
H J
~ 69 ~
(ii) When A=0, B=1, input light beam „A‟ (•) cannot pass through „P1‟ but
passes through the polarizer „P4‟. Again the input beam „B‟ („↨‟) passes through „P2‟
but fails to cross „P3‟. Therefore the light beam at the point „J‟ is of intensity „I/2‟. It
goes to the channel „S‟ after refraction through the NLM. This results no light signal
in the channel „R‟. On the other hand the output beam from the polarizer „P2‟ is of
intensity „I/2‟ and polarized in the plane of paper („↨‟). It is now refracted to the
channel „E‟. This beam is combined with the light (of intensity „I/2‟ and polarized in
the plane of paper) from the constant light source (CLS). This combined beam is now
refracted to the channel „G‟. No light is detected in the channel „F‟ and „H‟. So at the
point „Q2‟ only the light beam from the channel „G‟ is available. This beam yields „↨‟
polarized light at the output „Y‟. Thus the output light beam „Y‟ is (of intensity „I‟
and) polarized in the plane of paper („↨‟) (logic 1).
(iii) For the third input condition, A=1, B=0, input light beam „A‟ („↨‟) can
pass through „P1‟ and „P2‟ but cannot passes through the polarizer „P4‟. Again the
input beam „B‟ („•‟) passes through „P3‟ but fails to cross „P2‟. So in this case a light
beam (of intensity „I‟ and) polarized in the plane of paper („↨‟) (logic 1) is obtained at
the final output „Y‟. This output comes for the light transmitted through „E‟ and
combined with CLS. This ultimately goes to „Q1‟ passing through „G‟ where as no
light comes from „R‟ for joining at „Q2‟.
(iv) For the input condition A=B=1, no input light beam can pass through the
polarizers „P3‟ and „P4‟. So one cannot receive any light in the channel „R‟ and „S‟.
On the other hand the output of the polarizer „P2‟ is of intensity „I‟ and polarized in
the plane of paper („↨‟), due to the contribution of the two components from the inputs
„A‟ and „B‟. This beam is now refracted to the channel „F‟ and no signal is produced
at the channel „E‟. So a light beam from the CLS to refract along the channel „H‟
contributing no light in the channel „G‟. Therefore at the output „Y‟, due to the beam
from the channel „F‟, one gets a light signal (of intensity „I‟) polarized in the plane of
paper (logic 1). Thus the truth table for the OR logic operation as given in „table –
5.2‟ is supported.
~ 70 ~
5.3.3. Implementation of a 2-input universal NAND logic gate
The truth table for the NAND gate is shown in „table-5.3‟ and the scheme is shown
„figure - 5.3‟. In the truth table one can see that the output „Y‟ gets light of „↨‟
polarization (logic 1) when any one or both the two inputs A and B gets light of „•‟
polarization (low, logic 0) and the output gets light of „•‟ polarization only when both
the inputs gets light of „↨‟ polarization (high state or logic 1). To implement a NAND
logic gate the output of an AND gate (of „fig.-5.1‟) is sent through a half-wave plate.
The half-wave plate introduces a „π‟ phase differences between the components of the
light at the output „Y‟. This plate changes the light signal of „•‟ polarization (logic 0)
to a light signal of „↨‟ polarization (logic 1) and vice-versa. Thus for the first three
input conditions, while the output of a AND gate was described by „•‟ polarized light,
then the output for the NAND gate here produces a „↨‟ polarized light (logic 1 or high
state) at the output. Similarly for the last input condition A=B=1, light having „•‟
polarization (logic 0 or low state) is obtained at the output „Y‟ („fig.-5.3‟). This
scheme supports the truth table of a NAND gate satisfactorily.
Table-5.3: Truth table for the two-input NAND logic gate
Inputs Output
A B Y= BA.
0 (•)
0 (•)
1 (↨)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
1 (↨)
1 (↨)
1 (↨)
0 (•)
~ 71 ~
5.3.4. Implementation of 2-input Ex-OR logic gate
Proceeding in the same way an Ex-OR logic gate can also be developed. In the „table
- 5.4‟ the truth table for a two-input Ex-OR gate is shown and the proposed scheme is
shown in „figure- 5.4‟. The polarizers „P1‟ and „P2‟ allow only the „↨‟ polarized light
to pass through them and the polarizers „P3‟ and „P4‟ only pass the „•‟ polarized light
beam. The operation of the scheme is described as follows.
(i) For the first input condition A=B=0, polarizers „P1‟ and „P2‟ block the input
light beam and „P3‟ and „P4‟ pass the respective light beams. So no light is obtained at
„Q1‟. Now each of the two light beams coming through polarizers „P3‟ and „P4‟ are „•‟
polarized and of intensity „I/2‟. So at the point „O2‟ they combine to give a light beam
of intensity „I‟. The combined beam is now refracted through the NLM along the
channel „T‟. Thus at the point „Q2‟ the light of „•‟ polarization (and intensity „I‟) is
received. Therefore the output „Y‟ gets the light signal of „•‟ polarization (logic 0).
Fig. 5.3: Polarization encoded 2-input NAND logic
gate.
A
B
P1
P4
P3
P2
Y
R
S LM NLM
Q1 Q2
CLS
(, I/2)
LM
NL
M
E
F
G
H J
Half-wave
plate
~ 72 ~
(ii) For the second input condition A=0, B=1; polarizers „P1‟ and „P4‟ block
the light and polarizers „P2‟ and „P3‟ allow the light signal to pass. It results at O1 the
light of „↨‟ polarization (of intensity „I/2‟). As a result this beam is refracted through
the NLM along „S‟ channel. Thus at „R‟ no light is seen. At Q1 a light of „↨‟
polarization is obtained because of the presence of light both at the channels „S‟ and
CLS. On the other hand at O2 we get light of „•‟ polarization. As intensity of this
beam is „I/2‟, it is refracted along the channel U giving no light at Q2. Therefore the
output Y gives only a light of „↨‟ polarization.
(iii) For the third input condition, A=1, B=0, the polarizers P1 and P4 pass the
light and P2 and P3 block the light signal. This case is nearly similar to that of the
second condition. At O1 we get light of „↨‟ polarization. Because of the presence of
light both at the channels „S‟ and CLS, this combined light signal is refracted through
channel „V‟ to „Q1‟. On the other hand, at O2 we get a light of „•‟ polarization which
goes to the channel „U‟. Therefore at the output Y the light of „↨‟ polarization is
obtained.
(iv) For the last condition A=B=1, P1 and P2 pass the light signal and P3 and P4
block the light signal. Therefore at O2 and so in the channel T no light is obtained but
the point O1 gets light of „↨‟ polarization having intensity „I‟ (for the combination of
two beams). So the beam is refracted to the channel R giving no light at S. The light
beam after traveling through the half-wave plate becomes „•‟ polarized. Therefore
ultimately at the output Y we get light having „•‟ polarization for the application of „↨‟
polarization light at the inputs. Thus the truth table of Ex-OR operation is satisfied
and the scheme acts as an Ex-OR logic gate.
~ 73 ~
Table-5.4: Truth table for the two-input Ex-OR logic gate
Inputs Output
A B Y= BA
0 (•)
0 (•)
1 (↨)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
0 (•)
1 (↨)
1 (↨)
0 (•)
Fig. 5.4: Polarization encoded optical 2-input Ex-OR logic
gate.
A
B
P1
P4
P3
P2
Y R
S
LM NLM
Q1
Q2
Half-wave
plate
O2
O1
LM
NL
M
T
U
CLS
(↕, I/2)
V
~ 74 ~
5.4. Conclusion
As the basic and fundamental logic gates are implemented by the above mechanism,
therefore the any other all-optical logic operations can also be implemented
successfully with the same methodology. The all-optical switching speed with Kerr
type of nonlinear materials is very fast. On the other hand the polarization of light is a
property of the light signal which normally does not change during communication
unless we do it. Again the powers in the two polarization states are equal. The above
schemes use therefore the advantages of both the nonlinear optical material based
systems and polarization encoded system. If the inputs are drawn from a suitable laser
source and the other optical components are suitably used the schemes can be
implemented to execute any desired logical result. These schemes can be directly used
in developing optical arithmetic and algebraic units. Again combinational and
sequential logic systems can be developed using the schemes discussed in this
chapter.
~ 75 ~
CHAPTER - 6
___________________________________________________
An All-Optical Method of Developing an S-R Flip-Flop for
Storing a Set of Digital Inputs
Abstract
Optical storage device is an essential part to implement an all-optical
computing system. S-R flip-flop is a primary circuit of different digital storage device.
Here in this chapter an all-optical method for developing a polarization encoded S-R
flip-flop is proposed. For this purpose a special optical scheme is also used. This
scheme can be used to maintain a prefixed intensity level against the polarization
encoded optical bits. For developing the all-optical S-R flip-flop the switching
character of optical isotropic nonlinear material and the special optical scheme are
jointly utilized.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “A method of maintaining the intensity level
of a polarization encoded light signal,” Vidyasagar University Journal of
Physical Sciences, 11, 87-91(2007).
2. D. Samanta, S. Mukhopadhyay, “Implementation of an optical S-R flip-flop
with polarization encoded light signal”, Optoelectronics Letters (Springer),
5(1), 57-60 (2009).
~ 76 ~
6.1. Introduction
Many logic gates and data processors are already reported where different optical
methods of encoding and decoding are used [5, 51, 128, 219, 233, 240, 244, 258, 266,
305]. Among all the encoding techniques intensity based encoding is used most
extensively. Here Boolean states (1, 0) are represented by different intensity levels of
the light signal. To implement the optical logic units and logic based systems based
on intensity based encoding mechanism, optical nonlinear materials and photo-
refractive materials can be used successfully. Electro-optic materials, Mach-Zehnder
interferometer, semiconductor optical amplifier can also be used for this purpose.
There lies also many works which use polarization or frequency of a light signal for
encoding or decoding purpose of bits. Polarization encoding technique is found
advantageous than intensity encoding as the state of polarization of a light signal
cannot change of its own unless it is compelled to do so. Therefore during the
propagation of light signal through a long distance the information can remain intact
in case of polarization encoding. Since the last few decades lots of contributions using
polarization encoding is reported [18, 19, 22, 75, 119, 201, 306].
In „chapter - 5‟ different all-optical logic gates based on polarization encoding
technique are discussed. Again a method to maintain a fixed intensity level of light
signal against a logical bit required for a digital optical processor of nonlinear
material based switches has been described in „chapter-4‟. This is very important for a
system which works depending on the intensity of light signal. As the optical
nonlinear material (NLM), used for switching, is isotropic one and the light beam
passing through it is not splitted into ordinary and extra-ordinary components, so the
NLM will not ordinarily change the state polarization of the light beam during the
propagation though it, what the half-wave plate does.
Based on the two systems an optical S-R flip-flop with polarization encoded
light signal is described here. In this scheme also it is assumed that the light beam
polarized along perpendicular to the plane of paper (•) represents „logic 0‟ state and
light beam polarized in the plane of paper (↨) represents the state of „logic 1‟, i.e. „1‟
and „0‟ are encoded with two orthogonal polarized light beams. So a half-wave plate
can act as an NOT gate. Flip-flops are basically bistable multivibrators. They can
provide a strong role in implementation of optical computer. Flip-flop can be used to
store optical data. At first a scheme to get a desired value of intensity for a
~ 77 ~
polarization encoded light bit is described. Then using the scheme the method of
implementing polarization encoded the optical S-R flip-flop is discussed.
6.2. A scheme to get a specified intensity level for a polarization
encoded light beam.
The scheme is shown in „figure - 6.1‟. It can be used to increase or to maintain the
same intensity level of a polarization encoded light signal. The operation of the
scheme is now described. Let a light beam of intensity „I‟ is given. The light beam
may be polarized either in the plane of the paper (↨) or perpendicular to the plane of
paper (•). The signal beam is coming in the channel „A‟. Now our first goal is to raise
the intensity of this given signal to a specific value of intensity „2I‟.
The light beam is splitted into two beams at the point „B‟ by a 50:50 beam
splitter. These two beams are now made incident on two polarizers „P1‟ and „P2‟. „P1‟
can pass only light beam polarized in the plane of paper („↨‟) and only the light beam
polarized perpendicular to the plane of paper („•‟) can pass through „P2‟. As the
intensity of the light beam from channel „A‟ is „I‟ so each of the two beams coming
from „B‟ is assumed to have an intensity level „I/2‟. „CLS-1‟ and „CLS-2‟ are two
constant laser sources which emit light beam of predetermined intensity. „CLS-1‟
emits light beam polarized in the plane of paper („↨‟) and the light beam from „CLS-
2‟ is polarized perpendicular to the plane of paper (•).
Now, in the first case, if the light beam coming from „A‟ is polarized in the
plane of paper (↨) then the polarizer „P1‟ allows the light beam to pass through it and
„P2‟ blocks the light beam. Therefore light of intensity „I/2‟ arrives at the point „C‟.
This beam is now combined with the light beam of intensity „3I/2‟ (polarized as „↨‟)
coming from a constant laser source (CLS-1) as shown in the figure. This combined
light beam is incident at the point „O1‟ at the linear material (LM) and nonlinear
material (NLM) boundary. As the intensity of the incident beam is „2I‟ it is refracted
to the channel „E‟ having the less angle of refraction then that of „F‟ channel
[dedicated for transmission of light beam of intensity „3I/2‟]. On the other hand no
light passes through „P2‟ in this case. So at the point „D‟, only the light from „CLS-2‟
prevails. The light beam from the „CLS-2‟ has intensity level „3I/2‟ [and is polarized
perpendicular to the plane of paper (•)]. Therefore the light beam, after incidence at
the point „O2‟ at the second LM and NLM boundary, is refracted to the channel „H‟.
~ 78 ~
Naturally no light is obtained at the channel „G‟. Thus at the point „S‟ only the light
beam from the channel „E‟ is received. This light beam will yield light of intensity
„2I‟ with „↨‟ polarization at the output „Y‟.
In the second case, the light coming from „A‟ is assumed to have intensity „I‟
and polarized perpendicular to the plane of paper (•). Similar to the first case, this
light beam is splitted into two beams with each of intensity level „I/2‟ at the point „B‟.
The first component cannot pass through the polarizer „P1‟ (as it can pass only „↨‟
polarized beam). So the light beam incident at „O1‟ is of intensity „3I/2‟ (due to „CLS-
1‟ only) and refracted through the NLM to the channel „F‟. Thus it contributes no
light signal at the point „S‟. On the other hand the second component of the light
beam from the point „B‟ passes through the polarizer „P2‟ and reaches at the point „D‟.
This beam is now combined with the light beam (of intensity „3I/2‟ and „•‟ polarized)
Fig. 6.1: A scheme for maintaining the intensity level of a
polarized light.
A B
P1
P2
Y E
O1
LM NLM
C
D
S
G
H
F
O2
CLS-1
CLS-2
LM NLM
~ 79 ~
coming from the „CLS-2‟. Thus the combined light beam incident at the point „O2‟
has the intensity level „2I‟ and refracted through the NLM to the channel „G‟. This
beam only arrives at the point „S‟ now. Thus the output „Y‟ gives a light beam of
intensity „2I‟ with „•‟ polarization.
Thus the scheme can provide a desired level of intensity of the input light
beam. When there is no light signal in the input channel „A‟ then no signal is
available at the output „Y‟.
6.3. Method of maintaining a prefixed intensity level of a polarization
encoded light signal.
In the previous scheme one can keep the intensity level of the given signal at the same
level as that of the input signal or can increase the intensity level. But the scheme
cannot be used to decrease the intensity level of the optical signal to a specified value.
In the „section - 4.2‟ and in „section - 4.3‟ a scheme to obtain a prefixed
intensity of light signal has already been illustrated. The scheme provides a prefixed
intensity of light signal at its outlet irrespective of the intensity of the input signal.
When there is no light in the input of the system then no light is obtained at the outlet
of the scheme. This scheme is shown in „fig.-4.1‟ and also in „figure - 6.2‟. This
scheme can also be extended to maintain a prefixed intensity level for a polarization
encoded light signal. The extended scheme is shown in „figure - 6.3‟. The internal
architecture of the „block-1‟ and „block-2‟ shown in „fig.-6.3‟ are similar to the
scheme depicted in „fig.-4.1‟. These blocks represent the aforesaid scheme. Only
difference between the two blocks is that the constant light sources (CLS) used in
„block-1‟ give light signal polarized perpendicular to the plane of paper (•) whereas
the CLS used in block-2 give light signal polarized in the plane of paper (↨).
Now the given optical signal is coming from the channel „A‟. As before this
light signal may be either polarized perpendicular to the plane of paper (•) or
polarized in the plane of paper (↨). The output „Y‟ of the scheme shown in „fig.-6.3‟
should be of a prefixed intensity „I‟ irrespective of the intensity of the given input
beam but should have same polarization state as the input signal.
~ 80 ~
A B
C
H
Fig. 6.2: Scheme to obtain a fixed intensity for a signal bit.
CLS-3
(I) J
CLS-4
(I/4)
D
E CLS-1
(I/2)
CLS-2
(I/4)
F
G
K
L
S
R
Y
NLM
O1
O2
O3
O4
Block-1
Block-2
Fig. 6.3: Scheme to maintain the intensity level of a
polarization encoded light signal.
A B C
Y
P1
P2
~ 81 ~
Let a light signal (of any intensity) polarized perpendicular to the plane of
paper (•) is given to the input „A‟. Now this beam is splitted by beam splitter at the
point „B‟ into two beams. The polarizer „P1‟ can only pass light signal polarized
perpendicular to the plane of paper (•) whereas the polarizer „P2‟ can pass only the
light signal polarized in the plane of paper (↨). So the component of the input beam
from the point „B‟ cannot pass through „P2‟. The other component passes through „P1‟
and enters the „block-1‟. „Block-1‟ provides, at its output, a light signal of a prefixed
intensity „I‟ and polarized perpendicular to the plane of paper (•). As no light enters to
the „block-2‟ therefore this block does not produce any light signal at the outlet of it.
The operation of these blocks is similar to the scheme of „section-4.3‟. So at the point
„C‟ only light from „block-1‟ comes. Thus when input „A‟ is a light polarized
perpendicular to the plane of paper (•) the output „Y‟ assumes to get a light signal
having same polarization state having a prefixed intensity „I‟.
Similarly when a light beam polarized in the plane of paper (↨) is given to the
input „A‟ the beam cannot pass through „P1‟. It passes through „P2‟ and enters into
„block-2‟. Now the „block-1‟ gives no light at the outlet of it. But „block-2‟ produces
a light signal of intensity „I‟ and polarized in the plane of paper (↨) at the point „C‟
and also at the output „Y‟.
Thus the scheme shown in „fig.-6.3‟ gives, at the output „Y‟, a light signal
having a prefixed intensity „I‟ and having the same polarization state as that of the
input light beam. When there is no light in the input „A‟ then no light comes out at the
output „Y‟.
Thus using the above scheme the intensity of a polarized encoded light beam
can be maintained or raised at a desired level. The strength of the CLS guides whether
the signal intensity level would be kept same or increased. So the intensity as well as
the polarization of a light signal both can be maintained simultaneously by the proper
application of the proposed method. This scheme will be very useful in logic
processors where a prefixed intensity level of a signal with proper polarization is
required for digital operation. This scheme can support the strengthening of the
intensity level of a signal whatever its state of polarization is („↨‟ or „•‟), i.e. keeping
the state of input polarization conserved.
~ 82 ~
6.4. Method of implementing an optical S-R flip-flop by polarization
encoded light signal.
Here a scheme for optical S-R flip-flop by polarization encoded light signal is
described. To implement this scheme optical isotropic nonlinear material and half-
wave plate can be used jointly. The proposed scheme is shown in the „figure - 6.4‟.
„S‟ and „R‟ are the two inputs whereas „Q‟ is the output of the S-R flip-flop and „ Q ‟
is the inverted output. „P1‟, „P2‟, „P3‟ and „P4‟ are the four half-wave plates. „Block-3‟
and „block-4‟ includes the same scheme as described in „fig.-6.3‟. The scheme works
as follows.
(i) At first if no light is given to the inputs „S‟ and „R‟, no light will be
received at the outputs „Q‟ and „ Q ‟.
(ii) When a light beam polarized along perpendicular to the plane of paper (•)
(assumed as logic state 0) is given to the input „S‟ and another light beam polarized in
the plane of paper (↨) (logic state 1) is applied to the input „R‟ the scheme will
function as follows. The input light beam at „S‟ after passing through the half-wave
plate „P1‟ will be polarized in the plane of paper (↨) at the point „A‟. This light beam
after passing through the half-wave plate „P2‟ will be again polarized along
perpendicular to the plane of paper (•). Therefore the output „Q‟ will receive the light
polarized along perpendicular to the plane of paper (•). Similarly the light beam from
the input „R‟ (polarized in the plane of paper (↨)) after passing through two half-wave
plates „P3‟ and „P4‟ will result a light beam polarized in the plane of paper (↨) at „ Q ‟.
Thus for the input condition S=0 and R=1 the outputs become Q=0 and Q =1.
Now if the inputs are withdrawn (that means no light signal is given to the
inputs) at that instant the intensities of the light beam entering the „block-3‟ and
„block-4‟ will tend to be reduced. Now the blocks will maintain the intensity level of
the signal as described in the scheme shown in „fig.6.3‟. So the output of the „block-3‟
will be a light beam of a prefixed intensity „I‟ (and polarized along perpendicular to
the plane of paper (•)) whereas the „block-4‟ will produce at the output of it a light
beam of a prefixed intensity „I‟ (and polarized in the plane of paper (↨)). Now at the
point „B‟ only the light beam from the outlet of „block-4‟ comes. No light comes from
the point „A‟ as there is no light signal in the input „S‟. Thus the intensity of the light
beam incident at the point „O1‟ on a linear material (LM) –nonlinear material (NLM)
~ 83 ~
boundary is only „I‟. Therefore the light beam is refracted through the channel „D‟.
This light beam after passing through the half-wave plate „P2‟ produces a light beam
polarized perpendicular to the plane of paper (•) at the output „Q‟.
Similarly the light beam (of intensity „I‟ and polarized as (•)) emerges from „block-3‟
and incident at the point „O2‟ in another NL-NLM boundary surface. After refraction
this beam propagates through the channel „K‟ (as there is no light from „R‟) as
intensity of it is „I‟ only. This beam passes through the half-wave plate „P4‟. It results
a light beam polarized in the plane of paper (↨) at the output „ Q ‟. Therefore even
when the inputs are withdrawn the output continues to maintain at the last achieved
states Q=0 and Q =1.
Q
Q
Half wave
plate P4
Half wave
plate P2
S
R
Half wave
plate P1
Half wave
plate P3
Fig. 6.4: Schematic diagram of a polarization encoded
S-R flip-flop.
B
A
C D
E F
G
H J K
L M
O1
O2
Block-3
Block-4
~ 84 ~
(iii) If now the input states are interchanged that means a light beam polarized
in the plane of paper ((↨), logic 1) is given to the input „S‟ and a light beam polarized
perpendicular to the plane of paper ((•) or logic 0) is applied to the input „R‟ the
outputs will be altered accordingly. The light beam which is applied to „S‟ will result
in a light beam polarized perpendicular to the plane of paper (•) at the point „A‟. So,
now at the point „B‟ two light beams; one from point „A‟ and another from the „block-
4‟ are combined together. Therefore the intensity of the beam incident at the point
„O1‟ increases and the beam is now refracted through the channel „C‟, whereas no
light is obtained through the channel „D‟. So only the light beam (•) from the point
„A‟ arrives at the point „E‟. This beam after passing through „P2‟ produces a light
signal (↨) at the point „F‟ and at the final output „Q‟. A similar process occurs for the
input „R‟. The input light beam (•), from the input „R‟, produces a light beam (↨) at
the point „G‟. A portion of this beam and the light beam coming from „block-3‟ are
combined at the point „H‟. Due to this joint beam refractive index of the NLM
increases and the combined light beam, which is incident at the point „O2‟, is refracted
through the channel „J‟. This results the absence of any light signal in the channel „K‟.
Thus the only light beam from the point „G‟ arrives at the point „L‟. This beam, after
passing through „P4‟, again produces a light beam (•) at the point „M‟ and at the
output „ Q ‟. Thus for the input condition S=1 and R=0 the output becomes Q=1 and
Q =0.
Similar to the condition described earlier if now the input light beams are
withdrawn, no light will be obtained at point „A‟ and „G‟. The intensity of the light
beams at the points „F‟ and „M‟ tend to be reduced at that moment when the inputs are
just withdrawn. Immediately the „block-3‟ and „block-4‟ maintain the intensity levels
of their inputs beams. The output of „block-3‟ gives now a light beam polarized in the
plane of paper (↨) and of intensity „I‟ and the „block-4‟ produces a light beam (•) of
intensity „I‟. Then the light coming from „block-4‟ is incident at the point „O1‟ and
refracted through the channel „D‟. This beam after passing through „P2‟ results in a
light beam (↨) (of intensity „I‟) at the point „F‟ and passes it to the output „Q‟.
Similarly the beam coming from „block-3‟ is incident at „O2‟ and refracted through
the channel „K‟. This beam now produces a light beam (•) at „M‟ and sends it to „ Q ‟.
Thus the output takes Q=1 and Q =0 even after the withdrawal of the signal input S=1
and R=0 that is the flip-flop maintains the last state here also.
~ 85 ~
Table - 6.1: Truth table of the polarization encoded S-R flip-flop
Input Output
S R Q Q
● (0) ↨ (1) ● (0) ↨ (1)
↨ (1) ● (0) ↨ (1) ● (0)
● (0) ● (0) Forbidden Forbidden
↨ (1) ↨ (1) Forbidden Forbidden
No light No light Last state Last state
(iv) Thus the scheme follows the function of a polarization encoded all-optical
S-R flip-flop and its truth table given in „table - 6.1‟. The input condition, when both
the input receives same logic state S=R=1 and S=R=0, are forbidden.
6.5. Conclusion
The above scheme of S-R flip-flop is an all-optical one. So real time speed of
operation can be achieved from the scheme. Again the system accommodates the
polarization encoding techniques which has many advantageous sides over intensity
encoding. Here each logic state caries same amount of light power (intensity) whether
the logic state indicates „0‟ or „1‟. Therefore at the time of transmission of
polarization encoded data the average power of a „byte‟ remains constant and it does
not change on the number of „zeroes‟ and „ones‟ in it. This polarization encoded flip-
flop can act as a real time memory cell also. So the storage of optical data bits can be
easily achieved by this unit. The mechanism can be extended to develop some other
improved version of polarization encoded optical flip-flops. It is important to say that
the nonlinear materials in the flip-flop can be replaced by semiconductor optical
amplifier (SOA), if necessary. This replacement can implement the flip-flop at a very
low power.
~ 86 ~
CHAPTER - 7
___________________________________________________
All-Optical Method for Developing Master-Slave J-K Flip-
Flop with Polarization Encoded Light Signal
Abstract
Memory elements are the essential part of a digital optical system. These
elements can store binary information. Flip-flops can also be treated as storage device
of one bit of binary information. Depending on the working procedure flip-flops are
of different types. Here in this chapter a method to develop an all-optical polarization
encoded Master-Slave J-K flip-flop is discussed. To implement the flip-flop
polarization based encoding technique with optical signal is used. Also the switching
capacity of isotropic nonlinear material is utilized for the scheme.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “All optical M-S J-K flip-flop using
polarization encoded light signal,” International Conference on Optics &
Photonics (ICOP-2009), XXXIV Symposium of the Optical Society of India,
Central Scientific Instruments Organisation (CSIO), Sector -30 C, Chandigarh,
India, October 30 – November 1, 2009.
~ 87 ~
7.1. Introduction
Invention of electronic digital computer has made the computing process very much
easier. But increasing demand for higher and higher speed of computation has
compelled researchers to switch to optical domain. Optical signal has been being
used since long ago for data processing and communication [168, 185, 192, 202, 218,
256, 263, 269, 281, 283, 292]. To achieve real time speed of operation scientific
community are trying to develop all-optical logic and data processing system. Due to
many inherent advantages, optics is found to be more suitable in data processing as
well as in communication.
To achieve an optical computer development of an optical memory is
essential. In a sequential circuit flip-flops are used as memory cells. Flip-flops can
store a binary data until an input signal is applied to change the binary state. The basic
flip-flop is an S-R flip-flop. In „chapter -6‟ a method to implement an S-R flip-flop is
described. There are also other types of flip-flops like J-K flip-flop, D flip-flop and T
flip-flop etc. The differences among various flip-flops are in the number of inputs of
the flip-flops and in the way how the input signal affects the output. Here in this
chapter a process for developing a polarization encoded optical M-S J-K flip-flop is
illustrated. Master-Slave J-K flip-flop is constructed by adding an R-S flip-flop to a J-
K flip-flop. The J-K flip-flop circuit acts as „master‟ and the other performs as „slave‟.
The J-K flip-flop is a modification over the S-R flip-flop described in the previous
chapter. In J-K flip-flop the input „J‟ is used to „set‟ the flip-flop (similar to the input
„S‟ in S-R flip-flop) and input „K‟ is used instead of „reset‟.
Encoding and decoding of optical signal by its variation of the state of
polarization is one convenient method. Here the light signal polarized along the
perpendicular to the plane of paper (•) is considered as „logic 0‟ (low) state whereas
the light signal polarized in the plane of paper (↨) is treated as the „logic 1‟ (high)
state. In „chapter-5‟ different polarization encoded all-optical logic gates are depicted.
Here a polarization encoded optical M-S J-K flip-flop is developed using the
polarization encoded logic gates.
7.2. Polarization encoded all-optical M-S J-K flip-flop.
In „section-5.3.3‟ a 2-input polarization encoded optical NAND gate is described.
This logic gates have been implemented using proper use of the switching capacity of
~ 88 ~
the optical isotropic nonlinear material. For developing the Master-Slave (M-S) J-K
flip-flop here a 3-input NAND logic gate is described first. As the earlier concept this
NAND gate also uses polarization based encoding of data signal. Finally the above
logic gates are used to develop an M-S J-K flip-flop.
7.2.1. Polarization encoded 3-input NAND logic gate
The scheme for 3-input NAND logic gate is shown in „figure - 7.1‟ and the truth table
is shown in „table - 7.1‟. The scheme for 2-input NAND logic gate is extended to
develop a 3-input NAND gate. „A‟, „B‟ and „C‟ are the three inputs and „Y‟ is the
output. Inputs can be either a light signal perpendicular to the plane of paper (•) (logic
0) or a light beam polarized in the plane of paper (↨) (logic 1) where each with a
prefixed intensity „I‟. The polarizer „P1‟, „P2‟, „P3‟ and „P5‟ can pass the light signal
polarized perpendicular to the plane of paper (•). Again polarizers „P4‟, „P6‟ and „P7‟
can pass the light polarized in the plane of paper (↨). Each of the inputs „A‟, „B‟ and
„C‟ are splitted into two beams of equal intensity („I/2‟) by using 50:50 beam splitters.
Between the two components from the input „A‟ the first one is passed through the
polarizer „P1‟ and second through „P7‟. Similarly the two components from input „B‟
are passed through polarizer „P2‟ and „P5‟ respectively. One component from the input
„C‟ is passed through „P4‟ and the other component is combined with the beam
coming from the polarizer „P2‟.
This combined been is now passed through the polarizer „P3‟ and then is
incident on a linear material (LM) –nonlinear material (NLM) boundary. When the
intensity of the incident beam is „I/2‟ or „I‟ then the beam is refracted through the
channel „F‟ or „E‟ respectively. At the point „Q5‟ the beam „E‟ is divided into two
equal parts. One part goes to the channel „L‟. The signal channels „F‟, „L‟ and the
beam from „P1‟ are combined together at the point „Q1‟. This combined beam is now
made incident at a LM-NLM boundary. When the intensity of this beam is „I‟ or „I/2‟
then the beam is refracted through the channel „H‟ or „G‟ respectively. The channel
„G‟ is then combined with the light beam coming from a constant laser source (CLS).
The CLS emits a light beam polarized perpendicular to the plane of paper (•) and of
intensity „I/2‟. This combined beam is now incident on another LM-NLM boundary.
This beam refracted to the channel „K‟ when its intensity is „I‟ and travels through
~ 89 ~
channel „J‟ when its intensity is „I/2‟. Channel „H‟ and „K‟ are combined at the point
„Q2‟.
On the other hand the output channels of the polarizer „P4‟ and „P5‟ are
combined at the point „Q3‟. This combined light beam is now made incident on
another boundary of linear and nonlinear material. When the intensity of this
combined beam is „I/2‟ or „I‟ it is refracted to the channel „S‟ or „R‟ respectively. If
the light signal in the channel „S‟ is polarized in the plane of paper (↨) then only it can
pass through the polarizer „P6‟ and reaches the point „Q4‟. At this point it is combined
with the channel coming from the polarizer „P7‟. If the intensity of this combined
beam becomes „I‟ only then it is refracted to the channel „T‟, otherwise it goes to the
channel „U‟ when its intensity remains „I/2‟.
A
B
P1
Y
Half-
wave
plate
C
CLS
(●, I/2)
P2
Fig. 7.1: A 3-input polarization encoded optical NAND logic gate.
P3
P4
P5 P6
P7
E
F
G
H
J
K
R
S T
U
Q1
Q2
Q6 Q3
Q4
Q5
L
LM
NL
M
LM
NL
M
LM
NL
M
~ 90 ~
The light from the channel „T‟ and from the point „Q2‟ are combined at the
point „Q6‟. Finally this beam passes through a half-wave plate and yields the final
output „Y‟.
Now the function of the scheme is described as follows. (i) When A=B=C=0
no light is obtained at „Q4‟ as well as in the channel „T‟. Intensity of the light beam at
the output of „P3‟ is „I‟. So it goes to channel „E‟ resulting no light in the channel „F‟.
Now the beam „E‟ is splitted by a beam splitter and a portion (of intensity I/2) is taken
in the channel „L‟. Finally at the point „Q1‟ the intensity of light beam is „I‟ because of
the two beams coming from „L‟ and „P1‟. So the combined beam is refracted through
„H‟. No light is obtained in the channel „G‟ and „K‟. The light from the CLS is
refracted to „J‟. So at the point „Q6‟ only light from the channel „H‟ is obtained. It is
now passed through the half-wave plate. Therefore at the output „Y‟ a light beam of
„↨‟ polarization (and of intensity I) is obtained.
Table 7.1: Truth table of polarization encoded 3-input NAND gate
Inputs Output
A B C
0 (•) 0 (•) 0 (•)
0 (•) 0 (•) 1 (↨)
0 (•) 1 (↨) 0 (•)
0 (•) 1 (↨) 1 (↨)
1 (↨) 0 (•) 0 (•)
1 (↨) 0 (•) 1 (↨)
1 (↨) 1 (↨) 0 (•)
1 (↨) 1 (↨) 1 (↨)
1 (↨)
1 (↨)
1 (↨)
1 (↨)
1 (↨)
1 (↨)
1 (↨)
0 (•)
(ii) When A=0, B=0 and C=1, then light from „A‟ passes through „P1‟ and
cannot pass through „P7‟. The intensity of the light beam at the output of „P3‟ is „I/2‟.
~ 91 ~
So it propagates through the channel „F‟. No light is obtained in „E‟. Similar to the
previous case intensity of the light beam at „Q1‟ is „I‟. So „•‟ polarized light (of
intensity I) is received at „Q2‟. On the other hand the desired light passes through „P4‟
and „P5‟. These beams are combined at „Q3‟. As these two beams are coherent the
intensity of the combined beam becomes „I‟. So it is refracted to „R‟. As a result no
light is obtained in „S‟ and also in „T‟. Therefore at „Q6‟ only light from „H‟ is
present. This results a light beam of „↨‟ polarization (and of I intensity) at the output
„Y‟.
(iii) When A=0, B=1 and C=0, similar to the previous case light from input
„A‟ passes through „P1‟ and cannot pass through „P7‟. Light from input „B‟ cannot
pass through either „P2‟ or „P5‟. The intensity of the light beam at the output of „P3‟ is
„I/2‟ as before. As a result this beam is refracted to the channel „F‟. Similar to the
previous case a light beam polarized along perpendicular to the plane of paper („•‟) is
received in the channel „H‟. On the other hand no light signal can reach the point „Q3‟.
So no light signal is received at the channel „T‟. Thus only the light signal from the
channel „H‟ is available at the point „Q6‟. This beam now passes through the half-
wave plate. Therefore at the output „Y‟ light of „↨‟ polarization (logic 1) is received
for the input condition A=0, B=1 and C=0.
(iv) When A=0, B=1 and C=1, only light from „A‟ is present at the point „Q1‟.
Intensity of this beam is „I/2‟. So this beam is refracted through „G‟ which results no
light in the channel „H‟. Now the light from the channel „G‟ is combined with the
light coming from CLS (emitting light of intensity I/2 and „•‟ polarized). This
generates a light beam (of intensity I) in the channel „K‟. On the other hand at the
point „Q3‟ only the light signal from the input „C‟ is available. So this beam (of
intensity I/2) is refracted through the nonlinear material to the channel „S‟. This
crosses „P6‟ and arrives at the point „Q4‟. As no light comes through „P7‟ the light
beam from „S‟ is now refracted to the channel „U‟. So no light is obtained in the
channel „T‟. Thus at the point „Q6‟ only the light signal from the channel „K‟ prevails.
Therefore in this case also the output „Y‟ gets logic 1 state (a light beam of „↨‟ is
received at Y).
(v) For the input condition A=1, B=0 and C=0, light from „A‟ passes through
„P7‟. This light beam (of intensity I/2) is now refracted to „U‟, as because the light
beam from „B‟ passes through „P5‟ but cannot pass through „P6‟. Again light signal
from input „C‟ cannot pass through „P4‟. Therefore no light is obtained in „T‟.
~ 92 ~
Because of the joint effect of two beams coming from inputs „B‟ and „C‟ the intensity
at the output of „P3‟ is „I‟. This beam goes to „E‟. So at the point „Q1‟ only light (of
intensity I/2) from „L‟ is available. Similar to the fourth case a light beam polarized
along perpendicular to the plane of paper („•‟) (and of „I‟ intensity) is obtained in the
channel „K‟. This beam after passing through the half-wave plate generates a light
beam polarized in the plane of paper („↨‟). Therefore for this input condition the
output „Y‟ also receives logic 1 state.
(vi) When A=1, B=0 and C=1 then, only light from input „B‟ is received at
the point „Q1‟. As the intensity of this beam is „I/2‟ it is refracted through the
nonlinear material to the channel „G‟. So, as depicted before, in the channel „K‟ a
light beam of „•‟ polarization (and of intensity I) is obtained. No light is received in
the channel „H‟. On the other hand „P7‟, „P5‟ and „P4‟ pass the corresponding light
beams. So at „Q3‟ the combined light intensity becomes „I‟. Therefore it is refracted
through the channel „R‟. As a result at „Q4‟ only light (of intensity „I/2‟) from „P7‟ is
available. This light beam is refracted to „U‟. So no light can be traced in „T‟. Thus in
this case also at the output „Y‟ a light beam polarized in the plane of paper („↨‟) (and
of intensity „I‟) is received (logic 1).
(vii) When the inputs are A=1, B=1 and C=0 then, at the point „Q4‟ only light
signal (of intensity „I/2‟) from the output of „P7‟ is available. This beam, after
refraction through the isotropic nonlinear material, goes to the channel „U‟. So no
light is received in the channel „T‟. On the other hand at „Q1‟ the light intensity is I/2
because of the only light coming from input „C‟ (that is from „F‟). So as before, at the
point „Q6‟ only light from „K‟ is present. Thus output „Y‟ gets a light beam polarized
in the plane of paper („↨‟) (and of intensity I). Therefore for the input condition A=1,
B=1 and C=0 the output becomes Y=1.
(viii) For the last input condition A=1, B=1 and C=1, light beam from input
„A‟ passes through „P7‟ but cannot pass through „P1‟. Input beam from „B‟ can pass
neither through „P2‟ nor through „P5‟. Again light signal from input „C‟ can pass
through „P4‟ but unable to pass through „P3‟. Thus no light beam can arrive at the
point „Q1‟. So at the point „Q2‟ no light signal is present. On the other hand at „Q3‟
only light (of intensity I/2) from „P4‟ is available. So this beam is refracted to the
channel „S‟ and passes through „P6‟. This beam is now combined with the light signal
coming through „P7‟. Therefore at „Q4‟ the intensity of the combined light beam
becomes „I‟. So this beam of „↨‟ polarization is now refracted through the nonlinear
~ 93 ~
material to the channel „T‟. As a result now only the light from „T‟ is present at the
point „Q6‟. This beam is now passed through the half-wave plate. So finally at the
output „Y‟ one gets a light beam of intensity „I‟ and polarized along perpendicular to
the plane of paper („•‟) (logic 0). So for this input condition one gets Y=0 when
A=B=C=1. Thus the scheme serves as a 3-input polarization encoded NAND logic
gate.
7.2.2. Developing the Master-Slave J-K flip-flop
Now the NOT and NAND logic gates discussed before can be used properly to
implement the M-S J-K flip-flop. The scheme is shown in „figure - 7.2‟ and the
function (truth) table is shown in „table - 7.2‟.
3-input
NAND
1
3-input
NAND
4
3-input
NAND
2
3-input
NAND
3
2-input
NAND
5
2-input
NAND
8
2-input
NAND
6
2-input
NAND
7
NOT
Fig.7.2: Logic diagram of a polarization encoded optical M-S J-K
flip-flop.
J
K
CLK
CLR
PR
Qn
nQ
A
B
C
D
E
F
Master Slave
~ 94 ~
Table 7.2: Function table of M-S J-K flip-flop
Inputs Output
J K Qn nQ
0 (•) 0 (•)
0 (•) 1 (↨)
1 (↨) 0 (•)
1 (↨) 1 (↨)
Last state
0 (•) 1 (↨)
1 (↨) 0 (•)
Toggle
An M-S J-K flip-flop is constructed by adding a inverted clocked S-R flip-flop
at the output of another ordinary J-K flip-flop. „J‟ and „K‟ are the inputs of the M-S J-
K flip-flop and „Qn‟ and nQ are the outputs. CLK is the clock signal. The NAND
gates shown in the blocks are same as the scheme shown in „fig.-7.1‟ and „fig.-5.3‟.
The first part of the optical circuit (consisting of four 3-input NAND gates) acts as the
„master‟ part. And the last part serves as the „slave‟. A half-wave plate functions as a
NOT gate. The slave is provided an inverted clock. Thus when clock signal to the
master part is high then it is low for the slave part and vice versa. Both of the „master‟
and „slave‟ flip-flops work only when the clock provided to them is high („↨‟). Thus
when CLK=1 the „master‟ part is active and when CLK=0 then the „slave‟ part is
active. Preset (PR) and clear (CLR) terminals are used for setting the initial values of
„Qn‟ and nQ .
If one makes the inputs J=0 and K=1, when the CLK becomes „1‟ then the
output of the master flip-flop „C‟ gets „logic 0‟ (and output „D‟ goes to „logic 1‟)
state. At the moment the slave flip-flop is disabled as the clock for this part is low.
When CLK becomes „0‟ (low) then the master part is inactive and the „slave‟ is
active. Now the output of the master part is transmitted to the output of the slave part.
So the output „Qn‟ gets the logic state „0‟ and nQ (the inverted output) is „1‟ for J=0,
K=1. These outputs are feeded back to the input „J‟ and „K‟. But until CLK becomes
high, the master part is isolated from the taking of „J‟ and „K‟ inputs.
Now the data inputs are made J=K=0 when Qn=0 and . Then as before
when CLK=1 the output of the master part becomes C=0 and D=1. When CLK=0 this
~ 95 ~
information is carried to the output of the slave. So the final output becomes Qn=0 and
nQ becomes „1‟. Therefore the flip-flop maintains the last state for the input condition
J=K=0. When Qn=1 and , the outputs remain same if J=K=0. This condition
tells that the flip-flop acts also as memory cell, as it maintains the last state of values
at the outputs when the inputs are made „0‟.
Similarly for the other input conditions the flip flop works according to the
function table. Now if the inputs are given as J=1 and K=0, „master‟ flip-flop does not
respond to the input till the clock becomes high. When CLK=1, the information at the
input „J‟ and „K‟ are transmitted to the output of the „master‟ part. This has no effect
on the „slave‟ part until CLK becomes „0‟. When CLK=0 slave is active and the
output of the „master‟ is transferred to the output of the „slave‟. Thus the outputs
become Qn=1 and , for J=1 and K=0.
Now if the inputs are made as J=K=1, on arrival of the next clock CLK=1, the
previous outputs states are transferred to the „master‟ part. Thus output of the „master‟
changes. When clock becomes CLK=0, this information is transferred to the „slave‟.
So outputs of the slave change to its inverted values. After the application of the next
clock the outputs will be again changed from Qn=1/0 and to Qn+1=0/1 and
. Thus for the input condition J=K=1, the output will toggle after
application of every clock signal. Thus the scheme acts as an M-S J-K flip-flop.
7.3. Conclusion
The method for implementing the M-S J-K flip-flop is all-optical one. Again due to
polarization encoding technique both the logic bit gets same amount of optical power.
The beam splitters and mirrors used in the schemes are not shown in the figures to
avoid complexity. A dot („•‟) on any line in the figures implies that there is a
connection between the optical channels. All the inputs are to be either a light beam
polarized perpendicular to the plane of paper („•‟) for „logic 0‟ state or a light beam
polarized in the plane of paper („↨‟) for „logic 1‟ state. As the input signals serve both
as the power supply and data inputs for the flip-flop, so the flip-flop stores the data bit
till there are light signal at the inputs. If the input signals are withdrawn then the flip-
flop fails to work.
~ 96 ~
CHAPTER - 8
___________________________________________________
All-Optical Technique of Conversion of Polarization
Encoded Data Bit to an Intensity Encoded Data Bit and Vice
Versa
Abstract
Among different techniques for encoding and decoding of data bit, intensity
based encoding and polarization based encoding techniques are two important
methods. So both the two methods have wide applications. Depending on the
encoding methods the digital optical systems are named different. Their operation
techniques are also different. Now if the situation demands that the output data signal
of an optical data processor which works on intensity coding, is to be processed by an
optical polarization encoded data processor then the later system cannot function
properly. The reverse is also true. Here in this chapter two optical systems are
described which transforms intensity encoded data bit to a polarization encoded data
bit and vice-versa.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “An all-optical method for obtaining
polarization encoded data bit from intensity encoded data bit and vice versa,”
7th
International Conference on Optics-photonics Design & Fabrication
(ODF’10 Yokohama), held at Pacifico Yokohama, Yokohama, Japan, April
19-21, 2010.
~ 97 ~
8.1. Introduction
The use of optical signal in logic and data processing is not new in the present day‟s
technological context. Since the seventies of the last century lots of proposals have
been reported using the light beam as the signal carrier instead of electronic signal
[10, 154, 246, 286, 288, 290]. Different techniques have been incorporated for
encoding and decoding of optical data signal. Among these various methods intensity
based and polarization based coding mechanisms are two important techniques. In the
intensity based coding technique one may assume the presence of a prefixed intensity
(I) of light signal as the „logic 1‟ (high) state and absence of light signal as „logic 0‟
(low) state. On the other hand in the polarization based encoding technique one may
assume a light beam polarized perpendicular to the plane of paper (•) as the „logic 0‟
(low) state and its orthogonal light beam polarized in the plane of paper (↨) as „logic
1‟ (high) state. So there are many optical devices in which intensity based coding is
used. At the same time there are also some devices which works on polarization based
coding technique. Often it is necessary to cascade two types of devices. Then if the
output of the intensity encoded data processor is applied into the input of a
polarization encoded data processor then the later device cannot give proper result.
The reverse condition is also true. In such situations the output data bit from the
intensity encoded device is to be first converted to a polarization encoded data bit and
then is to be applied to the input of the polarization encoded device. Similarly when
the output of a polarization encoded data processor goes to the input of an intensity
encoded data processor, it needs the conversion of the polarization encoded data bit to
the corresponding intensity encoded data bit. Here in this chapter a scheme is
described to obtain polarization encoded optical data bit from intensity encoded
optical data bit. Similarly another method is illustrated to get an intensity encoded
data bit from a polarization encoded data bit. To implement the schemes the switching
capacity of isotropic nonlinear material [38, 127, 305] is utilized. The properties of
this type of nonlinear materials are already described in „section-3.2.1‟.
8.2. All-optical scheme for obtaining a polarization encoded data bit
from intensity encoded data bit.
The scheme is shown in „figure - 8.1‟. „A‟ is the data input. The input signal is
intensity encoded. So it can be done either by a light signal of a prefixed intensity „I‟
~ 98 ~
(for logic 1) or absence of the light signal (for logic 0). The input signal beam is now
combined with the light coming from a constant laser source (CLS-1) at the point „B‟.
CLS-1 emits light of a prefixed intensity „I‟ and polarized perpendicular to the plane
of paper (•). This combined light beam is now made incident on a linear material
(LM) and nonlinear material (NLM) block. Only when there is no light in the input
„A‟ then this beam is refracted through the NLM such that it is received in the channel
„C‟. Otherwise the intensity of the combined beam is greater than the prefixed
intensity level „I‟ and is not refracted to the channel „C‟. Again the light signal from
the channel „C‟ is combined at the point „E‟ with the light coming from another CLS
(CLS-2). CLS-2 also emits light of prefixed intensity „I‟ and polarized perpendicular
to the plane of paper (•). This combined beam (from „E‟) is again made incident on a
LM-NLM boundary. When the intensity of combined light beam is „I‟ and „2I‟ then it
is refracted to the channel „F‟ and „G‟ respectively. The light beam from the channel
„F‟ is passed through a half wave plate. On the other hand the signal from the channel
„G‟ is splitted by 50:50 beam splitter and one part goes to the channel „H‟. Now this
light beam is combined with the signal from the half-wave plate at the point „J‟. This
combined light signal gives the final output at „Y‟.
Now the operation of the scheme is depicted. When the input „A‟ gets no light
(for „logic 0‟) then at the point „B‟ only the light from „CLS-1‟ prevails. This beam is
made incident on a LM-NLM boundary. As the intensity of the beam is „I‟ so it is
refracted through the NLM to the channel „C‟. Now at the point „E‟ this beam is
combined with the light beam (of intensity „I‟ and „•‟ polarized) coming from „CLS-
2‟. So the intensity of the combined beam is now „2I‟. Therefore when this combined
beam is made incident on the other LM-NLM block it is refracted through the NLM
to the channel „G‟. On the other hand no light is obtained in the channel „F‟. The light
beam from „G‟ is splitted by the 50:50 beam splitter. So the intensity of the signal in
the channel „H‟ is „I‟. This beam produces the output at „Y‟. So as a result at the
output „Y‟ a light beam, polarized perpendicular to the plane of paper (•) (and of a
prefixed intensity „I‟), is received (logic 0). Thus from the intensity encoded „logic 0‟
data bit applied in the input channel „A‟ one gets a polarization encoded „logic 0‟ data
bit at the output „Y‟.
~ 99 ~
When the input „A‟ gets a light of prefixed intensity „I‟ (for „logic 1‟) then the
intensity of the combined beam at the point „B‟ becomes „2I‟. So when this beam is
passed through the NLM this is refracted to the channel „D‟. As a result no light
signal is propagated into the channel „C‟. So at the point „E‟ only the light („•‟
polarized) from the „CLS-2‟ is available. Intensity of this beam is „I‟. As a result
when this beam is passed through the NLM it is refracted to the channel „F‟. Now
there is no signal in the channel „G‟. The beam from the channel „F‟ is now passed
through a half wave plate. Due to birefringence property the half wave plate
introduces a phase change of „π‟. After passing through the half wave plate the light
beam becomes polarized in the plane of paper (↨). This gives the output „Y‟. Thus for
a data bit of „logic 1‟ (intensity encoded) in the input, one gets a polarization encoded
„logic 1‟ signal bit at the output.
A
0/ I
CLS -1
(, I)
B
CLS -2
(, I)
C
D
E G
F Half-wave
plate
Y
/ ↨
Fig. 8.1: Scheme to obtain polarization encoded optical data bit
from intensity encoded data bit.
LM
NL
M
LM
NL
M
H
J
~ 100 ~
Fig.8.2: Scheme to obtain intensity encoded optical data
bit from polarization encoded data bit.
P1
CLS (I)
A
Y / ↨
0/ I
B
C
D
LM
NL
M
8.3. All-optical scheme to get an intensity encoded data bit from a
polarization encoded data bit.
The scheme for obtaining an intensity encoded data bit from a polarization encoded
data bit is shown in „figure - 8.2‟. Here „A‟ is the input which receives either a light
beam polarized perpendicular to the plane of paper ((•), logic 0) or a light beam
polarized in the plane of paper ((↨), logic 1). The input beam is passed through a
polarizer „P1‟. The polarizer is oriented in such a way that it can pass only the light
beam perpendicular to the plane of paper (•). The light beam which is passed by „P1‟
is now combined at the point „B‟ with the light beam (of a prefixed intensity „I‟)
coming from a constant laser source (CLS). Now the combined light beam is made
incident on the boundary surface of linear (LM) and nonlinear material (NLM). When
the intensity of the combined beam is „I‟ only (that means when no light passes
through „P1‟) then the beam is refracted towards the channel „C‟. Light beam from
channel „C‟ provides the output „Y‟.
When the input „A‟ gets a light beam polarized perpendicular to the plane of
paper (•) (logic 0) then this input light beam is passed through „P1‟. Now the light
~ 101 ~
beam is combined with the light from CLS. So the intensity of this combined beam is
greater than a prefixed intensity „I‟. As a result the beam is not refracted to the
channel „C‟. Therefore no light is obtained in the output „Y‟, which signifies intensity
encoded „logic 0‟ state.
On the other hand when the input „A‟ receives a light beam polarized in the
plane of paper (↨) (logic 1) then this light beam is not passed through the polarizer
„P1‟. So at the point „B‟ only the light beam of intensity „I‟ from CLS is obtained.
That is why the beam is now refracted through the NLM to the channel „C‟. Therefore
at the output „Y‟ a light beam of intensity „I‟ is received (logic 1). Thus one can get an
intensity encoded data bit from a polarization encoded data bit.
8.4. Optical system for conversion of an optical intensity encoded
data to polarization encoded data.
The optical scheme depicted in „fig.–8.1‟ can be extended for conversion of an optical
intensity encoded (n-bit) data to polarization encoded data (as shown in „figure –
8.3‟). „A1‟, „A2‟, …. , „An-1‟ and „An‟ are the data inputs. The input signals are
intensity encoded. So these can be done either by a light signal of a prefixed intensity
„I‟ (for logic 1) or absence of the light signal (for logic 0). „Y1‟, „Y2‟, …, „Yn-1‟ and
„Yn‟ are the corresponding data outputs. The operation of the scheme is similar to that
depicted in „section – 8.2‟. Every input signal beam is combined with the light coming
from a constant laser source (CLS). These CLSs emit light of a prefixed intensity „I‟
and polarized perpendicular to the plane of paper (•). The combined light beams are
now made incident at different points on a linear material (LM) and nonlinear
material (NLM) block. The outputs are polarization encoded. The output becomes low
(•) or high (↨) according the status of the corresponding input.
~ 102 ~
A1 0/ I
CLS
(, I)
B
CLS
(, I)
C
D
E G
F Half-wave
plate
Y1
/ ↨
Fig. 8.3: Scheme to obtain polarization encoded optical data
from intensity encoded data.
LM
NL
M
LM
NL
M
H
J
A2 0/ I
An-1 0/ I
An 0/ I
CLS
(, I)
CLS
(, I)
CLS
(, I)
CLS
(, I)
CLS
(, I)
CLS
(, I)
Y2
/ ↨
Yn-1
/ ↨
Yn
/ ↨
.
.
.
.
.
.
~ 103 ~
8.5. Conclusion
The above method is all optical one. So real time operational speed can be achieved
from the scheme. The mirrors and the entire beam splitters used in these schemes are
not shown in the figures to avoid complexity in representation. This scheme may be
useful where one optical system running with intensity encoding mechanism is
connected to a polarization encoded optical system, and vice versa.
~ 104 ~
CHAPTER - 9
___________________________________________________
An All-Optical Approach for Developing a Single Optical
Pulse Generator
Abstract
It is established that optics has lots of advantages over an electronic signal as
information carrier. Optics has strong use in data processing. Lot of all-optical data
processors has been proposed in last few decades. Again it is well-known that in
many practical cases an optical pulse is very much useful to trigger an optical data
processing circuit. In this chapter a method of generating a sub-nanosecond optical
pulse is described for the use as triggering pulse. Electro-optic modulator and
nonlinear material have been exploited here to generate the pulse.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “A method of generating single optical pulse
in nanosecond range with the joint uses of electro-optic modulator and
nonlinear material” Optik - International Journal for Light and Electron
Optics, 121, 1129-1132 (2010).
~ 105 ~
9.1. Introduction
Optics is found as a strong and potential candidate in information and data processing.
Several all-optical data processors are already been proposed in last few decades [11,
15, 179, 194, 207, 222, 241, 272, 273, 275-277]. For implementation of such data
processors, different techniques are used. Some of these used intensity based coding
technique whereas polarization based coding of the optical signal is used in some
systems. Optical nonlinear material is used in many systems for switching purpose.
For such systems the intensity of the optical signal is kept in a prefixed value for
proper operation [307]. To implement an all-optical processor, the massive use of
isotropic optical nonlinear material and photo-refractive material based optical
switches are seen in many communications. Here the presence of a prefixed intensity
of light („I‟) represents the „logic 1‟ (high) state and the absence of light represents the
„logic 0‟ (low) state. There are also many other materials which are used in many
communications using different techniques. In electronic and photonic data
processing systems the role of single pulse is very much essential. This single pulse is
generally required for triggering an electronic, opto-electronic or all-optical photonic
circuit. For organizing a time controlled data processing operation in spatial domain
one requires the single pulse very much to generate the starting signal. In this
situation the power of a single pulse is so high, that it can activate easily a circuit with
a power far above its threshold requirement. The on time duration of the pulse can be
made lower to enhance the pulse power higher. This upliftment of pulse power can
also be done by Q-switching or mode-locking mechanism of laser radiation. A
method of developing an all-optical circuit for generating a high powered optical
pulse is described in this chapter. To generate such a pulse the character of optical
modulation of nonlinear material and also that of electro-optic material are exploited.
9.2. Use of electro-optic modulator for phase delay.
The electro-optic effect has a wide application in many optical and opto-electronic
devices for modulation (amplitude, phase, and frequency) of light. In this effect an
externally applied electric field alters the refractive indices of the crystal or alters the
birefringence property of the crystal. Lithium niobate (LiNbO3) and lithium tantalate
(LiTaO3) are two very commonly used important electro-optic materials. These are
trigonal crystal of point group 3m. Lithium niobate is a negative uniaxial crystal (no>
~ 106 ~
d
Light
x y
z
Fig. 9.1: Biasing of an electro-optic modulator.
Vz
l
ne) whereas lithium tantalate is a positive uniaxial crystal. When an external electric
field Ez is applied along the optic axis (chosen as the z-axis) of the lithium niobate or
lithium tantalate crystal, the refractive indices for a light wave polarized along the
crystallographic x, y and z directions are given by
1.9.....2
1
2
1
2
1
333
133
133
zeez
zooy
zoox
Ernnn
Ernnn
Ernnn
where r13 and r33 are the electro-optic coefficients of the respective material [308].
When the external electric field is applied, the crystal becomes biaxial. So if it is
assumed that the light beam is propagating along the y-direction and that of the
incident light is linearly polarized at 45 to the z-direction in the x-z plane, then it can
be considered to have two components of light, one along x and other along z axes.
Therefore a phase difference will be introduced between the z and x components of
the light at the outlet of the crystal. The function of an electro-optic material based
system is shown in „figure - 9.1‟.
~ 107 ~
9.3. An integrated scheme to generate a single sub-nanosecond pulse.
A scheme for an optical single pulse generation is depicted here. The scheme (shown
in „figure- 9.2‟) is developed with the use of electro-optic material and nonlinear
material. To implement such scheme a constant light source (CLS) of some prefixed
intensity „2I0‟ is used. Coherent light beam coming from the CLS is passed
successively through a polarizer P3, „electro-optic modulator (EOM)-1‟ and then
through another polarizer P4. The pass axes of the two polarizers P3 and P4 are
mutually perpendicular to each other and oriented at an angle 45° to the x-axis on the
„x-z‟ plane. When a voltage equal to Vπ is applied to the crystal (electro-optic
modulator-1) it rotates the polarization of the light signal passing through it by 90°.
As a result only when a voltage equal to „Vπ‟ is applied to the electro-optic modulator,
the light from the CLS can reach the point „R‟. This beam is now splitted into two
rays (each of intensity „I0‟) by a beam splitter at the point „R‟. These two rays are
incident on the two different LiNbO3 crystals through the two polarizers P1 and P2.
The pass axes of the polarizers „P1‟ and „P2‟ are „z‟ and „x‟ axes respectively. Let the
intensity of each of these two beams incident on the „EOM- 2‟ and „EOM- 3‟ is „I‟
( 45cos 2
0II ). Here it is considered that the light beam propagates along y-
direction and the external electric field is applied along z-direction. Due to the applied
electric field these two components along x and z-axes which are in phase at the plane
of incidence will suffer a phase difference at the outlet of the crystals. So the phase
difference between the two beams after emerging from the crystals at the points A1
and A2 is different than that between the two beams entering the crystals. The light
beam emerged at A2, after passing through a „λ/2 plate‟ (which rotates the plane of
polarization of the incident beam by π/2), is combined with the light beam coming
from A1 at the point „S‟. The combined light beam is made incident at the boundary
surface of linear and nonlinear material (i.e. at „O‟). This produces the Ex-OR logic
output at „Y‟ between the two beams coming from A1 and A2.
~ 108 ~
If the voltage „Vπ‟ is not applied to the „electro-optic modulator-1‟, then no light is
received at the output „Y‟ i.e. the output Y is at „logic 0‟ (low) state. Now the two
predetermined voltages V1 and V2 are applied across the two crystals (electro-optic
modulator-2 and electro-optic modulator-3 respectively) along their optic axes (z-
axis) and a voltage Vπ across the „electro-optic modulator-1‟. Then the light beam
from the CLS arrives at the point „R‟. The beam is polarized along the pass axis (that
is along a direction 45° to the x-axis) of the polarizer P4. The light beam is now
splitted into two components as depicted earlier. As the refractive indices are different
for two light beams vibrating along x and z directions, the times required to travel the
length „l‟ of the crystals are different for the two beams. Thus one of the two beams
reaches the point „S‟ before another. So a light beam is received at the output „Y‟ for
the ray which comes first at „S‟ due to its higher velocity, i.e. the output is at „logic 1‟
(high) state. After a very small interval of time t , the other component of the light
beam reaches at the point „S‟. So the light beam incident at the point „O‟ is now
V1
V2
z
P1
P2 x
CLS A1
A2
π/2 rotator
S
T
Y
x y
z
Fig. 9.2: Scheme for generation of a single optical pulse.
Electro-optic
modulator-3
Electro-optic
modulator-2
o Vπ
P3 P4
Electro-optic
modulator-1
R
~ 109 ~
refracted through the channel „T‟ as its intensity is nearly double because of the joint
effect of the two beams. Therefore no light is obtained through the output channel „Y‟
after the arrival of the second (slower) beam at „S‟. This makes the output „Y‟ low
(logic 0) level when both the beam comes at „S‟. Thus a single light pulse of width
t can be found at the output „Y‟ when the voltage „Vπ‟ is applied to the „electro-
optic modulator-1‟. This time ∆t can be calculated as
2.9...)](2
1)[(
)(
2333
1133 VrnVrn
dnn
c
l
nnc
lt
eoeo
zx
where „c‟ is the speed of light in vacuum and „d‟ is the width of the crystals along z-
axis.
Here it is seen that the time ∆t depends on the voltages V1 and V2. If one keeps
any one of V1 and V2 (let V1) fixed and vary the other (let it is V2), or varies both the
V1 and V2 then one can change ∆t as desired. For LiNbO3, no=2.297, ne=2.208,
r13=8.6, r33=30.8. If someone assumes l =1 cm, d=1 cm and V1=76.1 V and V2=23.9 V
then st 91075.12 .
9.4. Conclusion
The above scheme may extend many important applications in the area of data
processing. This method may be applied to the cases, where only a single pulse is
required for triggering or starting the operation of a circuit or system. As and when a
voltage Vπ is applied to the „electro-optic modulator-1‟ a single optical pulse is
obtained through the output channel „Y‟. In the above scheme we may get the
dimension of the pulse as required, and it can be done very easily by changing only
the input level voltages applied to the „EOM-2‟ or „EOM-3‟. The pulse duration can
be made narrower according to the requirement. In the above scheme all the
conventional losses have been ignored. The time lag suffered by the light beam during
passing through the λ/2 plate is not also considered. This time lag is adjusted by the
path difference in the two wings of the system. The scheme can be implemented
successfully by the joint application of electro-optic modulator and non-linear
material with a suitable laser.
~ 110 ~
CHAPTER - 10
___________________________________________________
A New Scheme of Developing an All-Optical Astable
Multivibrator
Abstract
In any computation the need of an oscillator is very much essential. The
astable multivibrator is often used for oscillatory signal generation. In this chapter a
method to develop an all-optical astable multivibrator is illustrated. The scheme
generates oscillation with the joint use of electro-optic modulator and optical
nonlinear material.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “A photonic astable multivibrator with the
joint accommodation of LiNbO3 based modulator and isotropic nonlinear
material,” Short term course cum workshop on Physics and Technology of All
Optical Communication Components and Devices, Department of Physics and
Meteorology, IIT, Kharagpur, October 11-16, 2007.
~ 111 ~
10.1. Introduction
Due to several advantages optical systems have become popular over the electronic
systems. Different optical logic, arithmetic and algebraic processors using different
techniques are already proposed during last few decades [12, 16, 183, 203, 204, 213,
214, 220, 243, 248]. Due to inherent parallelism very high speed operation can be
achieved with the optical system. The systems are either all-optical or electro-optic.
Optical nonlinear material and electro-optic material can be used in this context [32,
63, 80, 278]. In the previous chapter the electo-optic effect was utilized to get a single
optical pulse. In electronics and as well as in optical data-processing system the role
of astable multivibrator is very much important. Here a new concept to implement an
optical astable multivibrator is described. The scheme is constructed using electro-
optic material and optical nonlinear material. Optical isotropic nonlinear materials can
be successfully used for switching operation. This is already described in the „section-
3.2‟. These nonlinear materials can also be used for implementing different logic
operations.
A half-wave plate or a λ/2 plate is usually made of thin sheets of split mica or
of quartz crystal cut parallel to its optic axis. This plate introduces a phase difference
of π between the two components of the light beam for a certain wavelength of the
light. Thus the half-wave plate alters the direction of vibration of plane-polarized light
by an angle 2θ, where θ is the angle between the incident vibrations and the principal
section. Therefore when a light, linearly polarized perpendicular to the plane of paper,
passes through a half-wave plate, it becomes polarized in the plane of paper and vice-
versa at the outlet.
10.2. Phase modulation by electro-optic modulator.
The electro-optic effect has been described in „section-9.2‟.In this effect an externally
applied electric field alters the refractive indices of the crystal or alters the
birefringence property of the crystal for the wave passing through it [308]. When an
external electric field is applied, the crystal becomes biaxial. So if we assume that the
light beam is propagating along the y-direction and that of the incident light is linearly
polarized at 45 to the z-direction in the x-z plane, then it can be considered to have
two components along x and z axes. Therefore a phase difference will be introduced
~ 112 ~
d
Light
x y
z
Fig. 10.1: Biasing of an electro-optic modulator.
Vz
L
between the z and x components of the light at the output of the crystal. The biasing
of an electro-optics modulator is shown in „figure - 10.1‟.
The phase difference between the two components at a distance L from the
input plane will be
Where V=Ezd is the applied voltage. Therefore a phase modulated light beam will be
obtained at the output of the crystal. The half-wave voltage (the voltage required to
introduce a phase difference of „π‟ between the two components) of this modulator is
lower than that of KDP crystal and it depends on the ratio (d/L). If the field of the
input light beam is expressed as then the wave emerging from the
crystal will be given by
~ 113 ~
Where (2π/0) = k0 = (/c). Now if an alternating potential V=V0 sinmt is applied
across the electro-optic modulator then the above equation becomes
Here
is the phase modulation index. Thus a sinusoidal applied
electric field results a sinusoidal phase variation at the output. If we use the following
identities,
then we have,
From the above equation we can see that at the output of electro-optic modulator we
can recover several optical frequencies like , ±m, ±2m etc.
10.3. Scheme for development of an all-optical astable multivibrator.
To implement the scheme for an astable multivibrator the electro-optic material and
nonlinear material are jointly used. The scheme is shown in „figure- 10.2‟. A constant
light source (CLS) of a prefixed intensity „2I‟ is used. Now at the point „C‟ the
coherent light beam coming from the CLS is combined with the light beam coming
from the channel „T‟, which is a second output channel. Now the combined beam is
made incident at the LM and NLM boundary at the point „O1‟. This beam is now
refracted to the channel „D‟ if its intensity is „2I‟ or to the channel „E‟ if its intensity is
„4I‟. The light beam taken from „D‟ is now splitted into two rays of intensity „I‟ each.
These two rays are passed through two polarizers P1 and P2 and then incident on two
different LiNbO3 crystals. The pass axes of the polarizers „P1‟ and „P2‟ are z and x
axes (mutually perpendicular) respectively. Here it is assumed that the beam is
propagated to the „y‟ direction through the electro-optic modulator and the external
electric field is applied along the „z‟ direction by applying two proper voltages V1 and
V2 respectively. The two light beams whose vibrations are along „z‟ and „x‟
~ 114 ~
directions, are in phase, when they are incident at the electro-optic modulator input.
When the field is given the electro-optic materials become biaxial. So the two light
beams suffer a phase difference at the outlet of the crystals. Thus the phase difference
between the two beams after emerging from the crystals at the points „A1‟ and „A2‟ is
different from that between the two beams while entering the crystals. The light beam
emerged at A2, after passing through the half-wave plate (which changes the „x‟
polarized light to „z‟ polarized light beam) is combined at the point „S‟ with the light
beam coming from „A1‟. The combined light beam is now made incident at the
boundary surface of another LM and NLM (at „O2‟) block. This produces at the
output „Y‟ an Ex-OR logic output between its two incoming beams from „A1‟ and
„A2‟. When both the beams from „A1‟ and „A2‟ are present, the refracted beam
through the NLM goes to the channel „T‟ causing no light at „Y‟. The light beam from
„T‟ is passed through a medium of high refractive index and suffers multiple
reflections there by two parallel mirrors. Therefore a delay (let t2) is introduced to the
beam. Finally the beam is combined with the light beam coming from the CLS at the
point „C‟.
Now the operation of the astable vibrator is described. When the CLS is made
off, no light is received at the output „Y‟ and also at „T‟. Therefore the output is at
„logic 0‟ (low) state. Now the two predetermined voltages V1 and V2 are applied
across the two crystals. Then the CLS is switched on. As at the beginning no light is
coming from „T‟, thus the intensity of the light beam incident at „O1‟ is only „2I‟. As a
result, it is refracted to the channel „D‟. This beam is splitted into two rays as depicted
earlier. As the electro-optic materials offer different refractive indices for the two
light beams polarized along „z‟ and „x‟ directions, the time required to travel the
length „L‟ of the crystals is different for the two beams. Thus one of the two beams
reaches at the point „S‟ earlier than another. This causes a light at the output „Y‟ for a
very small time. Thus the output „Y‟ goes to „logic 1‟ (high) state for the faster
moving ray. In this condition the channel „T‟ gets no light for that time. After a time
∆t, the other component of the light beam also arrives at the point „S‟. Now the light
beam (of intensity „2I‟) is incident at O2 and therefore it is refracted through the
channel „T‟. So the output Y goes to „logic 0‟ state after the time ∆t. The light beam
coming from „T‟ arrives at „C‟ after a delay time t2. Then the light incident at „O1‟ is
refracted to the channel „E‟ (due to increase of the intensity of the light beam at „C‟)
causing no light at „D‟. This will ultimately result no light at „Y‟ and „T‟ both.
~ 115 ~
Therefore no light will go from „T‟ to the point „C ‟in this time. This will reduce the
intensity of the light beam incident at „O1‟ to „2I‟ (due to CLS only). So the light
beam is now again refracted through „D‟. This makes the output Y high (logic 1)
again similar to the situation when the CLS was made on at the beginning.
V1
V2
O2
z
P1
P2 x
CLS
A1
A2
π/2
rotator
S
T
Y
x
y
z Electro-optic
modulator
Electro-optic
modulator O1
LM NLM
LM NLM
Medium of high
refractive index
Fully reflective
mirror
Fig. 10.2: Scheme for an all-optical astable multivibraor.
D
E C
~ 116 ~
The above process is cumulative in nature. Thus an optical rectangular pulse
train is obtained at the output „Y‟. The on-time of the wave is ∆t and off time is 2t2.
The time ∆t can be calculated as
)](2
1)[(
)(
133
3
213
3 VrnVrnd
nnc
L
nnc
Lt
eoeo
zx
……(10.1)
Here „c‟ is the speed of light in vacuum and „d‟ is the width of the crystals along z-
axis.
The above equation shows that the time ∆t depends on the voltages V1 and V2.
So if any one of V1 and V2 is kept fixed and the other is varied, or both is changed
then ∆t can be changed as desired. For LiNbO3, no=2.297, ne=2.208, r13=8.6, r33=30.8.
If we assume L =9.5 mm, d=0.25 mm and V1= V2=40 V then we get st 41076.5
. Again if we fix V1=10 V and V2=30 V then st 95.11 . The off time can also be
varied if needed.
10.4. Conclusion
In the above scheme all the conventional losses are ignored. The time lag suffered by
the light beam during passing through half-wave plate is not also considered and it is
adjusted in the path and the two wings. The scheme exploits the joint advantages of
electro-optic modulator and nonlinear material. If suitable material and Laser beams
are available the scheme can be implemented successfully and the system can be used
nicely for pulse generation in different all-optical devices. The pulse duration can also
be controlled. It is also important to mention that the pulsating nature of optical output
can be received at „T‟ and „E‟ channels also. This method can provide pulsating
output in Mega-Watt range.
~ 117 ~
CHAPTER - 11
___________________________________________________
An All-Optical Polarization Encoded Multiplexer Using
Optical Nonlinear Material Based Switches
Abstract
Optics has been used since last few decades in data and logic processing. The
inherent parallelism and many other advantages have made optics a strong candidate
as information carrying signal in computing. Till now lot of research proposals are
reported which use optical signal for implementation of several optical logic devices.
Again encoding and decoding of data bits on the basis of different states of
polarization of optical signal is a highly advantageous and a popular method over
intensity based encoding. In this chapter a new technique to realize a polarization
encoded optical multiplexer is illustrated. This multiplexer is based on different
polarization encoded optical logic devices which are already described earlier. Optical
isotropic nonlinear material based switches take the key role for implementing this
multiplexer.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “Method of developing a polarization
encoded optical multiplexer,” International Conference on Radiation Physics
and its Applications (ICRPA 2010), organized by Department of Physics, The
University of Burdwan; held at Science Centre, Golapbag, Bardhaman,
January 16 & 17, 2010.
~ 118 ~
11.1. Introduction
The concept of computation with optics instead of electronics as information carrying
signal is not new. The inherent parallelism and many other advantages of optical
signal can be exploited to achieve the goal of building the architecture of an optical
superfast computer and data processor.
Logic gates are the building blocks of any data processing circuit. To develop
an optical computing system optical logic gates are primarily essential. Already many
optical encoding and decoding techniques have been proposed [271, 306, 310]. In this
context, optical isotropic nonlinear materials, optical bistable materials, SLMs,
semiconductor optical amplifiers etc. are successfully used for the required switching
actions. All optical logic systems like AND, OR, NOT, NAND, Ex-OR etc. are
developed following Boolean methodology. Several approaches are seen also where
tri-state and quaternary state logic operations are physically implemented with optical
data. Many non-Boolean logic systems with wider advantages have been developed
with optics.
Optical arithmetic and algebraic processors can also be very easily developed
once the all optical logic gates are implemented. Since the last few decades many
optical arithmetic, algebraic, image and data processors have been developed and
reported. Some of them followed the techniques of conventional arithmetic operations
in Boolean mechanism, whereas some alternative approaches are developed to
implement arithmetic and algebraic operations, i.e. optical symbolic substitution
technique, space variant technique and residue technique etc. which extend many new
advantages in data processing. In all those drives optics successfully replaced
electronics as signal carrier to do the arithmetic and algebraic operations.
In any communication and computation mechanism multiplexer and
demultiplexer are the essential part for proper channel selection. Hence optical
computer needs an optical parallel multiplexer and demultiplexer. In this chapter an
all-optical method for developing a polarization encoded multiplexer is described.
~ 119 ~
11.2. Polarization encoded logic gate with the use of optical nonlinear
material based switch.
The technique for using an optical isotropic nonlinear material as a switch is already
described in the previous chapters. Among different techniques for encoding and
decoding of optical signal, polarization based encoding and decoding is an important
and popular one. Encoding and decoding of light signal based on polarization of light
signal may be a very convenient technique. Here if the light signal polarized along
perpendicular to the plane of paper (•) is considered as „logic 0‟ state then the light
beam polarized in the plane of paper (↨) is treated as the state of „logic 1‟. Different
all-optical polarization encoded logic gates are also implemented with the help of
optical nonlinear material based switching. In the „section- 5.3.1‟ and „section- 5.3.2‟
a polarization encoded 2-input AND logic gate and a polarization encoded 2-input OR
logic gate respectively have been depicted. Here a polarization encoded 3-input AND
logic gate is illustrated.
11.2.1. Polarization encoded all-optical 3-input AND logic gate
The schematic diagram for the polarization encoded 3-input AND logic gate is shown
in „figure - 11.1‟ and the truth table is shown in „table - 11.1‟. „A‟, „B‟ and „C‟ are the
three inputs and „Y‟ is the output. Inputs can be either a light signal polarized along
the perpendicular to the plane of paper (•) (logic 0) or a light beam polarized in the
plane of paper (↨) (logic 1) but each of a prefixed intensity „I‟. The polarizer „P1‟, „P2‟,
„P3‟ and „P5‟ can pass the light signal polarized perpendicular to the plane of paper (•).
Again the polarizers „P4‟, „P6‟ and „P7‟ can pass the light signal polarized in the plane
of paper (↨). Each of the inputs „A‟, „B‟ and „C‟ are splitted into two beams of equal
intensity („I/2‟) by three beam splitters. Between the two components from the input
„A‟ the first one is passed through the polarizer „P1‟ and second through „P7‟.
Similarly the two component channels from input „B‟ are passed through polarizer
„P2‟ and „P5‟. One component from the input „C‟ is passed through „P4‟ and the other
component is combined with the channel coming from the polarizer „P2‟.
This combined channel is now passed through the polarizer „P3‟ and then is
incident on a linear material (LM) –nonlinear material (NLM) boundary. When the
intensity of the incident beam is „I/2‟ or „I‟ then the beam is refracted through the
channel „F‟ or „E‟ respectively. At the point „Q5‟ the beam „E‟ is divided into two
~ 120 ~
equal parts. One part goes to the channel „L‟. The signal channels „F‟, „L‟ and the
beam from „P1‟ are combined at the point „Q1‟. This combined beam is now made
incident at a LM-NLM boundary. When the intensity of this beam is „I‟ or „I/2‟ then
the beam is refracted through the channel „H‟ or „G‟ respectively. The channel „G‟ is
then combined with the light beam coming from a constant laser source (CLS). The
CLS emits a light beam polarized perpendicular to the plane of paper (•) and of
intensity „I/2‟. This combined beam is now incident on another LM-NLM boundary.
This beam is refracted to the channel „K‟ only when its intensity is „I‟ and travels
through channel „J‟ when its intensity is „I/2‟. Channel „H‟ and „K‟ are combined at
the point „Q2‟.
A
B
P1
Y C
CLS
(●, I/2)
P2
Fig. 11.1: A polarization encoded optical 3-input AND logic gate.
P3
P4
P5 P6
P7
E
F
G
H
J
K
R
S T
U
Q1
Q2
Q6 Q3
Q4
Q5
L
LM
NL
M
LM
NL
M
LM
NL
M
~ 121 ~
On the other hand the output channels of the polarizer „P4‟ and „P5‟ are
combined at the point „Q3‟. This combined light channel is now made incident on
another boundary of linear and nonlinear material. When the intensity of this
combined beam is „I/2‟ or „I‟ it is refracted to the channel „S‟ or „R‟ respectively. If
the light signal in the channel „S‟ is polarized in the plane of paper (↨) then only it can
pass through the polarizer „P6‟ and reaches the point „Q4‟. At this point it is combined
with the channel coming from the polarizer „P7‟. If the intensity of this combined
beam becomes „I‟ only then it is refracted through the NLM to the channel „T‟,
otherwise it goes to the channel „U‟ when its intensity remains „I/2‟.
The light from the channel „T‟ and the point „Q2‟ are combined at the point
„Q6‟. This combined beam yields the final output „Y‟.
Now the function of the scheme is described as follows. (i) When A=B=C=0,
no light signal is obtained at the point „Q4‟ as well as in the channel „T‟. On the other
hand the intensity of the light beam at the output of the polarizer „P3‟ is „I‟ because of
the two components from inputs „B‟ and „C‟. So this beam goes to channel „E‟ after
refraction through the NLM. It results no light in the channel „F‟. Now the beam „E‟ is
splitted by a 50:50 beam splitter and a portion (of intensity I/2) is taken in the channel
„L‟. Finally at the point „Q1‟ the intensity of light beam is „I‟ because of the two
beams coming from „L‟ and „P1‟. So the combined beam is refracted to the channel
„H‟. No light is obtained in the channel „G‟ and „K‟. The light from the CLS is
refracted to „J‟. So at the point „Q6‟ only light from the channel „H‟ is obtained.
Therefore at the output „Y‟ a light beam polarized along the perpendicular to the plane
of paper (•) (and of intensity „I‟) is obtained.
(ii) When A=0, B=0 and C=1, then light from „A‟ passes through „P1‟ and
cannot pass through „P7‟. The intensity of the light beam at the output of „P3‟ is „I/2‟.
So it propagates through the channel „F‟. No light is obtained in the channel „E‟.
Similar to the previous case intensity of the light beam at „Q1‟ is „I‟. So „•‟ polarized
light (of intensity I) is received at „Q2‟. On the other hand the input light beams from
„C‟ and „B‟ pass through „P4‟ and „P5‟ respectively. These beams are combined at the
point „Q3‟. As these two beams are coherent the intensity of the combined beam
becomes „I‟. So it is refracted to the channel „R‟. As a result no light is obtained in „S‟
and also in „T‟. Therefore at „Q6‟ only light from „H‟ is present. This results a light
beam polarized along the perpendicular to the plane of paper (•) (and of „I‟ intensity)
at the output „Y‟.
~ 122 ~
Table 11.1: Truth table of a 3-input AND logic gate
Inputs Output
A B C Y=ABC
0() 0() 0()
0() 0() 1(↕)
0() 1(↕) 0()
0() 1(↕) 1(↕)
1(↕) 0() 0()
1(↕) 0() 1(↕)
1(↕) 1(↕) 0()
1(↕) 1(↕) 1(↕)
0()
0()
0()
0()
0()
0()
0()
1(↕)
(iii) When A=0, B=1 and C=0, similar to the previous case light from input
„A‟ passes through „P1‟ and cannot pass through „P7‟. Light from input „B‟ cannot
pass through either „P2‟ or „P5‟. Input signal from „C‟ cannot pass through polarizer
„P4‟ but passes through „P3‟. The intensity of the light beam at the output of „P3‟ is
„I/2‟ as before. As a result this beam is refracted to the channel „F‟. Similar to the
previous case a light beam polarized along perpendicular to the plane of paper („•‟) is
received in the channel „H‟. On the other hand no light signal can reach the point „Q3‟.
So no light signal is received at the channel „T‟. Thus only the light signal from the
channel „H‟ is available at the point „Q6‟. Therefore at the output „Y‟ light beam
polarized along the perpendicular to the plane of paper (•) (logic 0) is received for the
input condition A=0, B=1 and C=0.
(iv) When A=0, B=1 and C=1, only light from „A‟ is present at the point „Q1‟.
Intensity of this beam is „I/2‟. So this beam is refracted through the NLM to the
channel „G‟. This results no light in the channel „H‟. Now the light from the channel
„G‟ is combined with the light coming from CLS (emitting light of intensity I/2 and
„•‟ polarized). This generates a light beam (of intensity I) in the channel „K‟. On the
other hand at the point „Q3‟ only the light signal from the input „C‟ is available. So
this beam (of intensity I/2) is refracted through the nonlinear material to the channel
~ 123 ~
„S‟. This beam crosses through the polarizer „P6‟ and arrives at the point „Q4‟. As no
light comes through „P7‟ the light beam from „S‟ is now refracted to the channel „U‟.
So no light is obtained in the channel „T‟. Thus at the point „Q6‟ only the light signal
from the channel „K‟ prevails. Therefore in this case also the output „Y‟ assumes
„logic 0‟ state (a light beam polarized along the perpendicular to the plane of paper
(•)).
(v) For the input condition A=1, B=0 and C=0, light from „A‟ passes through
„P7‟. Again light signal from input „C‟ cannot pass through „P4‟. The light beam from
the input „B‟ passes through polarizer „P5‟ and goes to the channel „S‟. Now it cannot
pass through „P6‟. So the at the point „Q4‟ only signal from „P7‟ is present. This light
beam (of intensity I/2) is now refracted to „U‟. Therefore no light is obtained in „T‟.
On the other hand due to the joint effect of two beams coming from inputs „B‟ and
„C‟ the intensity at the output of „P3‟ is „I‟. This beam, after refraction through the
NLM, goes to the channel „E‟. So at the point „Q1‟ only light (of intensity I/2) from
„L‟ is available. Similar to the fourth case a light beam polarized along perpendicular
to the plane of paper („•‟) (and of „I‟ intensity) is obtained in the channel „K‟. This
beam produces the output „Y‟.
(vi) When A=1, B=0 and C=1 then, only light from input „B‟ is received at
the point „Q1‟. As the intensity of this beam is „I/2‟ it is refracted through the
nonlinear material to the channel „G‟. So, as depicted before, in the channel „K‟ a
light beam of „•‟ polarization (and of intensity I) is obtained. No light is received in
the channel „H‟. On the other hand polarizers „P7‟, „P5‟ and „P4‟ pass the
corresponding light beams. So at the point „Q3‟ the combined light intensity becomes
„I‟. Therefore it is refracted through the channel „R‟. As a result at „Q4‟ only light (of
intensity „I/2‟) from „P7‟ is available. This light beam is refracted to „U‟. So no light
signal can be traced in „T‟. Thus in this case also at the output „Y‟ a light beam
polarized along the perpendicular to the plane of paper (•) (and of intensity „I‟) is
received (logic 0).
(vii) When the inputs are A=1, B=1 and C=0 then, at the point „Q4‟ only light
signal (of intensity „I/2‟) from the output of „P7‟ is available. This beam, after
refraction through the isotropic nonlinear material, goes to the channel „U‟. So no
light is received in the channel „T‟. On the other hand at „Q1‟ the light intensity is I/2
because of the only light coming from input „C‟ (that is from „F‟). So as before, at the
point „Q6‟ only light from „K‟ is present. Thus output „Y‟ gets a light beam polarized
~ 124 ~
along the perpendicular to the plane of paper (•) (and of intensity I). Therefore for the
input condition A=1, B=1 and C=0 the output Y=0.
(viii) For the last input condition A=1, B=1 and C=1, light beam from input
„A‟ passes through „P7‟ but cannot pass through „P1‟. Input beam from „B‟ can pass
neither through „P2‟ nor „P5‟. Again light signal from input „C‟ can pass through „P4‟
but unable to pass through „P3‟. Thus no light beam can arrive at the point „Q1‟. So at
the point „Q2‟ no light signal is present. On the other hand at „Q3‟ only light (of
intensity I/2) from „P4‟ is available. So this beam is refracted to the channel „S‟ and
passes through „P6‟. This beam is now combined with the light signal coming through
„P7‟. Therefore at „Q4‟ the intensity of the combined light beam becomes „I‟. So this
beam of „↨‟ polarization is now refracted through the nonlinear material to the
channel „T‟. As a result now only the light from „T‟ is present at the point „Q6‟. So
finally at the output „Y‟ one gets a light beam of intensity „I‟ and polarized in the
plane of paper (↨) (logic 1). Thus the scheme serves as a polarization encoded 3-input
AND logic gate.
11.3. Polarization encoded optical multiplexer.
The all-optical polarization encoded logic gates can be now utilized to implement a
polarization encoded optical multiplexer. A half-wave plate can act as a polarization
encoded NOT as described earlier.
11.3.1. Polarization encoded 4×1 optical multiplexer
A schematic diagram of an optical multiplexer is shown in the „figure - 11.2(a)‟ along
with the block diagram of a 4×1 optical polarization encoded multiplexer in the
„figure - 11.2(b)‟. Here „A‟ and „B‟ are the control signal inputs. „X1‟, „X2‟, „X3‟ and
„X4‟ are the data signal inputs. All input signals are polarization encoded. So the
signal can be either polarized along the perpendicular to the plane of paper (•) or
polarized in the plane (↨) of paper. The data signal inputs go to four different
polarization encoded optical 3-input AND logic gates. The internal structure of these
AND gates are similar to that shown in the „fig.-11.1‟. The control input signal „A‟ is
connected directly to the inputs of „AND gate-3‟ and „AND gate-4‟ and is inverted
before connecting to the inputs of „AND gate-1‟ and „AND gate-2‟. Similarly the
control input signal „B‟ is connected directly to the inputs of „AND gate-2‟ and „AND
~ 125 ~
gate-4‟ and is inverted before connecting to the inputs of „AND gate -1‟ and „AND
gate-3‟. The outputs of the „AND gate-1‟ and „AND gate-2‟ go to the inputs of the
„OR gate-1‟. The outputs of the „AND gates 3‟ and „AND logic gate- 4‟ are connected
to the inputs of the „OR logic gate-2‟. The outputs of these two OR gates are
connected to the inputs of a 3rd
2-input OR logic gate. The output of this OR gate
gives the final output at the terminal „Y‟ of the multiplexer.
Optical 2-
input OR -1
Optical 3-
input AND
gate -1
Optical 3-
input AND
gate -2
Optical 3-
input AND
gate -3
Optical 3-
input AND
gate -4
Optical 2-
input OR -2
Optical 2-
input OR -3
A
B
A B
X1
X2
X3
X4
Y
Fig. 11.2(a): Scheme for polarization encoded optical 4×1 multiplexer.
N
OT
A B
N
OT
N
OT
Q1
Q2
Q3
Q4
Q5
Q6
~ 126 ~
(i) When A=B=0, = =1. The output of the „AND gate-1‟ („Q1‟) gives the
data signal „X1‟. But for the other three AND gates, as any one or both the two control
input is „0‟, each output becomes „0‟. Now for the „OR gate-1‟ one input („Q1‟) is „X1‟
and other is logic 0 („0‟). This causes the output of „Q1‟ to be „X1‟. In case of the „OR
gate-2‟ both the two inputs are at low state („0‟). As a result the output of this gate is
„logic 0‟. So in the channel „Q5‟ the data „X1‟ is available whereas in the channel „Q6‟
„0‟ is received. Therefore in the output „Y‟ the data „X1‟ is retrieved.
(ii) When A=0 and B=1, both the two control inputs for the „AND gate-2‟ are
high („1‟). So output of this AND gate „Q2‟ gives the data signal „X2‟. In this case the
other three AND gates give the low („logic 0‟) outputs. So the output of the „OR logic
gate -1‟ becomes data signal „X2‟. In this case also the output of the „OR logic gate- 2‟
will be „logic 0‟ signal. Thus the output of the „OR logic gate- 3‟ will produce data
signal „X2‟ at the output „Y‟.
(iii) When A=1 and B=0, only for the „AND gate-3‟ both the two control
inputs are high. As a result for this AND gate the output „Q3‟ gives the data signal
4×1
MUX
X1
X2
X3
X4
A B
Y
Fig. 11.2(b): Block diagram of a polarization
encoded 4×1 optical multiplexer.
~ 127 ~
„X3‟. On the other hand the outputs of the three other AND gates become low („logic
0‟) as before. Now the output of the „OR gate-1‟ becomes „logic 0‟ (light signal
polarized along the perpendicular to the plane of paper). On the other hand the output
of the „OR gate- 2‟ is now the data bit „X3‟. Therefore in the output channel „Y‟ one
can get the data „X3‟.
(iv) When A=B=1, only for the „AND gate-4‟ both the two control input is
high (logic 1). So the output of the gate „Q4‟ gives the data signal „X4‟. On the other
hand the outputs of the other three AND gates are low („logic 0‟ state). Similar to the
previous case now in the output „Y‟ the data „X4‟ is retrieved.
Thus the scheme can function as an optical 4×1 multiplexer.
11.3.2. Polarization encoded 8×1 optical multiplexer
A polarization encoded optical 8×1 multiplexer can be implemented using the 4×1
multiplexer described earlier. The scheme for the 8×1 multiplexer is shown in the
„figure - 11.3‟. The two blocks, indicated as „MUX-1‟ and „MUX-2‟, include two 4×1
multiplexers. The internal architectures of these two blocks are same as described in
„fig.-11.2(a)‟. The outputs of „MUX-1‟ and „MUX-2‟ are „Y1‟ and „Y2‟ respectively.
For an 8×1 multiplexer there are three control inputs „A‟, „B‟ and „C‟. „B‟ and
„C‟ control inputs are directly connected to the control inputs of the two 4×1
multiplexers. One can get the inverted signal „ ‟ by passing the control input signal
„A‟ through a half-wave plate (served as a NOT logic gate). AND logic operations is
performed between each of the first four data input signals „X1‟, „X2‟, „X3‟ and „X4‟
and the inverted control input signal „ ‟ by four 2-input AND logic gates. The four
outputs from these four AND gates are connected to the four data inputs of the MUX-
1. Similarly AND logic operation is executed between each of the data signals „X5‟,
„X6‟, „X7‟ and „X8‟ and the control signal „A‟ by four other polarization encoded
optical 2-input AND logic gates. The outputs from these four AND gates are
connected to the four data inputs of MUX-2. Now the outputs „Y1‟ and „Y2‟ are
connected to the inputs of a polarization encoded 2-input OR logic gate. The output of
this gate gives the final output „Y‟ of the 8×1 multiplexer. An 8×1 multiplexer has 8
control input states (000, 001, 010, 011, 100, 101, 110 and 111). For the first four
control input conditions of a 8×1 multiplexer (when A=0 (or =1)) the data inputs
„X1‟, „X2‟, „X3‟ and „X4‟ are available at the outputs of the respective AND gates and
~ 128 ~
can reach the data inputs of the MUX-1. So MUX-1 now gives result at the output
„Y1‟ according to the control inputs „B‟ and „C‟. At this time the remaining four data
input signals „X5‟ through „X8‟ cannot reach to the outputs of the respective AND
gates as one of two inputs for each AND gate is low (logic 0 state). So all of the data
inputs for MUX-2 are low (logic 0). Therefore for the first four control input
conditions the output of MUX-2 becomes low (logic 0). Similarly for last four control
input conditions (100 through 111 when A=1) all of the data inputs for MUX-1 are
low (logic 0) and the data inputs „X5‟ to „X8‟ can reach successfully the data inputs of
„MUX-2‟.
MUX -1
MUX -2
Optical 2-
input AND
Y1
Y2
B C
Optical 2-
input AND
Optical 2-
input AND
Optical 2-
input AND
Optical 2-
input AND
Optical 2-
input AND
Optical 2-
input AND
Optical 2-
input AND
X1
X2
X3
X4
X5
X6
X7
X8
A
N
OT
Optical 2-
input OR Y
Fig. 11.3: Scheme for a polarization encoded optical 8×1 multiplexer.
~ 129 ~
(i) When A=0, B=0, C=0, the data inputs signals „X1‟, „X2‟, „X3‟ „X4‟ can
reach the data inputs of MUX-1. Now MUX-1 acts similar to the scheme described in
the „section- 11.3.1‟. So for B=C=0 the output „Y1‟ produces the data signal „X1‟. On
the other hand all the data inputs for MUX-2 are low (logic 0). Hence the output „Y2‟
of this 4×1 multiplexer is a light signal polarized along the perpendicular to the plane
of paper (•) (logic 0). Therefore at the output „Y‟ of the 8×1 multiplexer one can
retrieve the data signal „X1‟ for the first control input condition A=B=C=0.
(ii) When A=0, B=0, C=1, the data inputs signals „X1‟, „X2‟, „X3‟ „X4‟ can
reach to the data inputs of MUX-1 as before. For the condition B=0, C=1 the output
„Y1‟ gives the data signal „X2‟. In this case also the output „Y2‟ is low. So the output
„Y‟ retrieves only the data „X2‟.
(iii) When A=0, B=1, C=0 the data inputs signals „X1‟, „X2‟, „X3‟ „X4‟ can
reach the data inputs of MUX-1. As the control inputs of MUX-1 are B=1 and C=0 so
output „Y1‟ carries the data signal „X3‟. On the other hand „Y2‟ is low as before.
Therefore logic OR operation between „Y1‟ and „Y2‟ gives the data signal „X3‟ at the
output „Y‟.
(iv) When A=0, B=1, C=1 the data inputs signals „X1‟, „X2‟, „X3‟ „X4‟ can
reach the data inputs of MUX-1. Here for the condition B=1, C=1 the output „Y1‟
gives the data signal „X4‟. The output „Y2‟ is also low in this condition. So the final
output „Y‟ retrieves the data signal „X4‟.
(v) When A=1, B=0, C=0, the first four data inputs signals „X1‟, „X2‟, „X3‟
„X4‟ cannot reach to the data inputs of MUX-1. Whereas the last four data input
signals „X5‟, „X6‟, „X7‟ and „X8‟ can reach the data inputs of MUX-2. So in this case
the output „Y1‟ of MUX-1 is low (logic 0). But now for the condition B=C=0 the
MUX-2 carries the data signal „X5‟ at the output „Y2‟. Therefore at the output „Y‟ one
can receive the data signal „X5‟.
(vi) When A=1, B=0, C=1, similar to the condition (v) as all of the inputs of
the „MUX- 1‟ are at logic low state, the output „Y1‟ becomes low (logic 0). For the
control inputs B=0 and C=1 for the „MUX- 2‟ the output „Y2‟ produces the data signal
„X6‟. Now at the output „Y‟ also the data „X6‟ is available.
(vii) When A=1, B=1, C=0, the last four data input signals „X5‟, „X6‟, „X7‟ and
„X8‟ can reach to the data inputs of MUX-2. The output „Y1‟ is low as before and
output „Y2‟ gives the data signal „X7‟ for the condition B=1 and C=0. Thus at the
output „Y‟ one can get the data signal „X7‟.
~ 130 ~
(viii) When A=1, B=1, C=1, all the data inputs of MUX-1 are low. So „Y1‟ is
also low (logic 0). On the other hand last four data signals „X5‟, „X6‟, „X7‟ and „X8‟
can reach the data inputs of MUX-2. Thus for B=C=1 „MUX-2‟ yields the data signal
„X8‟ at the output „Y2‟. Therefore one can retrieve the data signal „X8‟ at the output
„Y‟ for the control input condition A=B=C=1.
Thus the scheme serves as an optical polarization encoded 8×1 multiplexer.
11.4. Conclusion
The operation of the scheme is all-optical. So a real time operational speed can be
achieved from the system. Using the scheme optical demultiplexer can also be
implemented. One can very easily develop a higher input multiplexer and
demultiplexer expanding this proposed scheme just accommodating some additional
4×1 multiplexers and AND logic gates. The whole system can operate smoothly if
nonlinear material with higher „n2‟ is used as an optical switch. A single nonlinear
material block can be used to accommodate all the logic gates required for a
multiplexer. So an optical embedded system can be developed for developing an
integrated scheme of multiplexer.
~ 131 ~
CHAPTER - 12
___________________________________________________
An All-Optical Polarization Encoded Parity Generator and
Checker
Abstract
Polarization based encoding of data signal is an important method for
implementation of optical logic and data processor. Again to avoid any unwanted
error in data signal sometimes it becomes essential to check the data signal, especially
during transmission of data through large distance. Checking of the parity of the data
signal during transmission and reception is one way to ensure errorless transmission
of data. A method to implement an all-optical parity generator and checker, using
polarization encoded light signal, is proposed and described in this chapter. The
scheme uses the switching capacity of isotropic nonlinear material, where the 1st order
nonlinearity is absent but the 2nd
order nonlinearity is present. This scheme can be
used to check whether any error is occurred during transmission of optical data signal.
As parity checking is an essential component in any communication system and it
ensures the correctness of the sending data at the receiving point, so the all- optical
system can exhibit a strong application in optical communication as well as in
computation.
Publication related to this chapter -
1. D. Samanta, S. Mukhopadhyay, “All-optical method of developing parity
generator and checker with polarization encoded light signal,” XXXV Optical
Society of India Symposium and International Conference on Contemporary
Trends in Optics and Optoelectronics, jointly organized by Indian Institute of
Space Science and Technology and Optical Society of India, held at ATF
Campus, Veli, Thiruvananthapuram, Kerala, India, January 17-19, 2011.
2. D. Samanta, S. Mukhopadhyay, “All-optical method of developing parity
generator and checker with polarization encoded light signal,” accepted for
publication in Journal of Optics.
~ 132 ~
12.1. Introduction
As photon is a charge-less particle and therefore it does not create cross-talk problem
like electrons and supports its inherent parallelism during information processing and
computing. Because of these advantages of optical signal over electronic signal
scientists have been trying to implement optical systems replacing the conventional
electronic systems. Already several methods have been reported for implementing
optical logic, arithmetic and algebraic systems [21, 24, 212, 231, 242, 249, 289, 294-
296]. Again during transmission of light signal through a long distance if an optical
data is changed due to some noise or error then the logic processor which uses this
signal cannot respond properly. A parity bit is used to detect the errors during
transmission of binary information. It is an extra bit included with the binary
information to make the number of „1‟s‟ either odd or even [297, 298]. The parity of
the information as a bit is also transmitted with the data. At the receiving end the
parity is again checked. If the parity is same as that of the transmitted signal at the
transmitting end then it may be concluded that there is no error during transmission.
The circuit which generates the parity in the transmitting end is called „parity
generator‟ and the circuit that checks the parity at the receiving end is called „parity
checker‟ [129]. An all-optical method to implement a parity generator and parity
checker with polarization encoded light signal is depicted in this chapter.
To implement the scheme optical isotropic nonlinear material and polarization
based encoding are used. As the polarization of the optical signal is not generally
changed during propagation at a long distance being non-guided , and also when it is
guided through a polarization maintaining optical fiber ,so the encoding and decoding
of light signal based on its polarization property can be a very convenient technique.
Polarization encoding has been used in many works. Here the light signal polarized
along the perpendicular to the plane of paper (•) is considered as „logic 0‟ state and
the light beam polarized in the plane of paper (↨) is treated as the state of „logic 1‟. A
simple half wave plate can act as a polarization encoded NOT logic gate. This plate
introduces a phase difference of π if the wavelength of the light signal remains
constant. Thus when a light signal polarized perpendicular to the plane of paper (•)
(logic 0), passes through the half-wave plate, it becomes polarized in the plane of the
paper (↨) (logic 1) and vice-versa. A polarization encoded 2-input Ex-OR logic gate
was discussed in the „section- 5.3.4‟.
~ 133 ~
12.2. Method of implementing an all-optical parity generator and
checker for polarization encoded light signal.
The block diagram of the all-optical polarization encoded parity generator is shown in
„figure - 12.1(a)‟ and the detail internal structure of the block is shown in „figure -
12.1(b)‟. The block diagram for the parity checker is shown in the „figure - 12.2‟. In
these figures the Ex-OR and NOT logic gates, which are shown by some blocks,
represent the polarization encoded all-optical logic gates. The circuit incorporated at
the transmitting end („fig.-12.1(a)‟) is called parity generator and the similar circuit
(„fig.-12.2‟) used at the receiving end is called parity checker.
A, B, C, D are the four bits of an optical binary data which is to be transmitted. In
the input „P1‟ one can give either „1‟ („↨‟; a light signal polarized in the plane of
paper) or „0‟ („•‟; a light signal polarized along the perpendicular to the plane of
paper) data signal by a modulator „M‟. Ex-OR operation is performed between the
data „A‟ & „B‟ and between the data „C‟ & „D‟. The outputs from these two Ex-OR
operations are applied to the inputs of another all-optical polarization encoded Ex-OR
gate. The output of this gate is passed through a half-wave plate which acts as a NOT
logic gate. The output of this optical NOT gate and the signal from the input „P1‟ are
again made to go to the input of another polarization encoded Ex-OR gate. One gets
the output at „P2‟ depending on „P1‟ and the parity of the data. The bit „P2‟ is also
transmitted along with the data bits. At the receiving end the system shown in „fig.-
12.2‟ is incorporated. Here the signal bit „P2‟ is applied to the input „P3‟. Viewing the
resulting output at „P4‟ one can know if the data is transmitted correctly or any error
has been occurred.
If for P1=0 one get P2=1 then one can conclude that the data has even parity. The
same conclusion can be drawn if for P1=1 one receives P2=0. If someone gets the
result P2= P1 then the data has an odd parity. Let for example the data has even parity
and at the transmitting end one sets P1=0. As a result one gets P2=1 in the parity
generator circuit at the transmitting end. So, one can conclude that the data has even
parity. Now the data along with the parity bit „P2‟ is transmitted. At the receiving end,
for the parity checker circuit the data „P2‟ is treated as „P3‟. Thus P3=1. Therefore one
should get P4=0 for the even parity of the data signal. If one gets this result then it can
be decided that no error has been occurred during transmission. Because, the
transmitted data has even parity as it has been confirmed by the parity generator
~ 134 ~
Optical Ex-
OR gate- 1
Optical Ex-
OR gate- 2
Optical Ex-
OR gate- 3
Optical
NOT gate
Optical Ex-
OR gate- 4
A B C D
P1
P2
Fig. 12.1(a): All-optical polarization encoded
parity generator used at the transmitting end.
M
circuit. If one does not get this result it is decided that an error has been occurred
during transmission of the data.
~ 135 ~
A
B
R
S
LM NLM
Q1
Q2
Half-wave
plate
O2
O1
LM NLM
T
U
CLS
(↕)
C
D
P1
P2
Half-wave
plate
Fig. 12.1(b): Scheme for all-optical polarization encoded parity
generator.
~ 136 ~
Optical Ex-
OR gate- 1 Optical Ex-
OR gate- 2
Optical Ex-
OR gate- 3
Optical
NOT gate
Optical Ex-
OR gate- 4
A B C D P3
P4
Fig. 12.2: All-optical parity checker at the
receiving end.
12.3. Conclusion
Polarization encoded data communication is being popular more and more in all
optical communication, as the encoding technique bears some basic advantages . The
scheme offers an all-optical technique by which one can check a polarization encoded
optical data as well as it can generate a polarization encoded optical data which is
useful in optical communication. As the scheme uses polarization encoding technique,
same power can be considered for both „logic 1‟ and „logic 0‟ states. Therefore the
average power of a byte remains same whatever be the number of „0‟s and „1‟s. The
beam splitters and mirrors are not shown in the figure for simplicity. One can use a
different point on the surface of a single LM-NLM block instead of using multiple
LM-NLM blocks for increased number of switches as shown in the „figure- 12.1(b)‟.
Hence this scheme may extend a wide application in optical communication.
~ 137 ~
CHAPTER - 13
___________________________________________________
General Conclusion and Future Scope of Works
Abstract
Optics has been being used in logic and data processing since last few
decades. The field of optical computing is still flourishing. Although lots of research
proposals are already reported, still there are many more scopes to do for completely
utilizing the advantages of optics. In this chapter an overall conclusion on the whole
thesis is given and scopes of future works are discussed.
~ 138 ~
13.1. Introduction
The use of optical signal in logic and data processing was started few decades ago.
Since then optics has established itself as a potential candidate in optical computing
and optical communications. The study of optical computing spreads over a
multidisciplinary area in both science and engineering. Scientists and researchers all
over the world from different fields are continuously working to deploy optics in
computing. As a result of their effort a rapid growth has been noticed in the
implementation of different optical systems. This is because of highly expanding field
of applications. This has been made possible by introducing different techniques,
optical material etc. Optical components are very much useful in digital optical
computer. In optical parallel computation optical switches play an important role. In
this regard optical nonlinear material based switch is used in many systems. Optical
logic gates are the basic building block of any optical digital logic circuit. In the
previous chapters few approaches for the optical logic, arithmetic and data processing
are discussed. As these schemes can provide very fast speed of operation and can be
fabricated in a small volume, so it can be expected that these will be very much
helpful in superfast processing.
13.2. Overall conclusion on the thesis
With the ever increasing demand for higher speed of computing operation the search
for such efficient optical systems continues. Optical logic processors are the key
elements of such optical systems. In this thesis, I have tried to describe some optical
techniques for developing a few optical logic, arithmetic, algebraic and data
processors. Conclusions related to specific schemes are given in the respective
chapters. The all-optical schemes may offer real time speed of operation. As
polarization based encoding and decoding technique has some advantages, it has been
used in many of these optical processors. The two polarization based logic states have
equal energy. The figures, which describe different optical scheme, are schematic
only. These may have to be slightly shifted for practical situation. In some of the
schematic diagram for implementing the optical processors, the beam splitters and
mirrors are not shown for simplicity. In the background review section only some of
the sensible proposals for implementation of optical processors are mentioned. There
are no doubt many other related important works which are not referred in thesis due
~ 139 ~
to page limitation. A logic and arithmetic processor described in „chapter-3‟ can be
used to perform different operations only changing the control signal i.e. without
changing the system configuration. The volume of the optical systems can also be
smaller than they look in the diagrams, if different points on a single optical linear-
nonlinear material block can be used for multiple switching operations. This is
possible as optical signal beams do not interact with each other. For the
implementation of the schemes utilizing the Kerr effect in optical isotropic nonlinear
material, proper laser sources are required. In some cases the conventional loss was
not considered. The intensity maintaining scheme proposed in „chapter-4‟ can be
useful for cascading of optical devices working on intensity based encoding
technique. The polarization encoded 2-input optical logic gates described in „chapter-
5‟ can be extended for higher input logic gates. These polarization based logic gates
can be cascaded. Proposed flip-flops (in „chapter-6‟ and „chapter-7‟) are all-optical
and hence are very fast. The scheme in „chapter-8‟ can be useful for cascading
intensity encoded optical system with a polarization encoded optical system. I believe
that the schemes depicted in „chapter-9‟ through „chapter-12‟ will also find a wide
application.
13.3. Future scope of works
Since the seventies of the last century already lots of research works are reported
using optical signal for computing of data. Some all-optical approaches for
implementing different optical systems are depicted in this thesis. In the present thesis
we have just reached our initial target and a large amount of work beyond this is left
for our future study.
In „chapter-3‟ an integrated scheme for optical logic and arithmetic processor
(OLAP) is described. Similarly an integrated optical scheme can be developed which
will be able to perform any logic, arithmetic or algebraic operation as directed through
the control signal. This optical system may function depending on polarization based
encoding technique. The scheme for obtaining a prefixed intensity of light, illustrated
in „chapter-4‟, can be extended to specify the different intensity levels of a multi-
valued logic system. In multi-valued logic system the increase of logic density can
provide extra information through each connection. Different polarization encoded
optical logic gates have been developed. Now with the help of these optical logic
~ 140 ~
gates optical register, counter, demultiplexer etc. may be developed. A compact
optical polarization encoded scheme for performing various logic, arithmetic and
algebraic operations may be developed. Polarization encoded optical astable,
monostable multivibrator may also be constructed. Optical isotropic nonlinear
material has a key role in developing optical switch. In addition new materials are
being investigated to use their nonlinearity for switching action. Semiconductor
optical amplifier can also be used for optical computational purpose. We can also
show the results of the different schemes by simulation process. Again there is a vast
scope left for preparing proper nonlinear materials with organic materials which can
serve the above logic purposes due to their high material nonlinearity. Therefore I
think there is a lot of scope for my future works.
~ 141 ~
References
1. R. A. Heinz, J. O. Artman, S. H. Lee, “Matrix multiplication by optical
methods,” Applied Optics, 9(9), 2161-2168 (1970).
2. M. J. Flynn, “Some computer organizations and their effectiveness,” IEEE
Transaction on Computers, C-21(9), 948-960 (1972).
3. R. W. Keyes, “Optical logic in the light of computer technology,” Optica Acta:
International Journal of Optics, 32(5), 525-535 (1985).
4. A. W. Lohmann, “What classical optics can do for the digital optical computer,”
Applied Optics, 25(10), 1543-1549 (1986).
5. A. W. Lohmann, “Polarization and optical logic,” Applied Optics, 25(10), 1594-
1597(1986).
6. S. Mukhopadhyay, A. Basuray, A. K. Datta, “A real-time optical parallel
processor for binary addition with a carry,” Optics Communications, 66(4), 186-
190 (1988).
7. S. Mukhopadhyay, A. Basuray, A. K. Datta, “New coding scheme for addition
and subtraction using the modified signed-digit number representation in optical
computation,” Applied Optics, 27(8), 1375-1376 (1988).
8. R. S. Tucker, G. Eisenstein, S. K. Korotky, “Optical time-division multiplexing
for very high bit-rate transmission,” Journal of Lightwave Technology, 6(11),
1737-1749 (1988).
9. H. Zhai, R. Jaspert, S. Schilier, D. Jaeger, “2-D array of optoelectronic logic
XNOR gates for bipolar binary optical processing,” Japanese Journal of
Applied Physics, Part-2, 29, L1553-L1556 (1990).
10. V. S. Williams, Z. Z. Ho, N. Peyghambarian, W. M. Gibbons, R. P. Grasso, M.
K. O‟Brien, P. J. Shannon, S. T. Sun, “Picosecond all-optical logic gate in a
nonlinear organic etalon,” Applied Physics Letters, 57(23), 2399-2401 (1990).
~ 142 ~
11. R. G. A. Craig, G. S. Buller, F. A. P. Tooley, S. D. Smith, A.C. Walker, B. S.
Wherrett, “All-optical programmable logic gate,” Applied Optics, 29(14), 2148-
2152 (1990).
12. S. Mukhopadhyay, A. Basuray, A. K. Datta, “New technique of arithmetic
operation using the positional residue system,” Applied Optics, 29(20), 2981-
2983 (1990).
13. A. K. Ghosh, A. Basuray, “Trinary optical logic processors using shadow
casting with polarized light,” Optics Communications, 79(1-2), 11-14 (1990).
14. C. C. Yang, “All-optical ultrafast logic gates that use asymmetric nonlinear
directional coupler,” Optics Letters, 16(21), 1641-1643 (1991).
15. L. S. Tamil, A. K. Jordan, “An inverse-scattering model for an all-optical logic
gate,” Journal of Applied Physics, 70(3), 1882-1884 (1991).
16. J. M. Jeong, M. E. Marhic, “All-optical logic gates based on cross-phase
modulation in a nonlinear fiber interferometer,” Optics Communications, 85(5-
6), 430-436 (1991).
17. A. Basuray, S. Mukhopadhyay, H. K. Ghosh, A. K. Datta, “A tristate optical
logic system,” Optics Communications, 85(2-3), 167-170 (1991).
18. M. S. Alam, M. A. Karim, “Efficient combinational logic circuit design using
polarization encoded optical shadow-casting,” Optics Communications, 93(3-4),
245-252 (1992).
19. J. U. Ahmed, A. A. S. Awwal, “Polarization encoded optical shadow-casting
arithmetic-logic-unit design: separate and simultaneous output generation,”
Applied Optics, 31(26), 5622-5631 (1992).
20. T. Main, R. J. Feuerstein, H. F. Jordan, V. P. Heuring, J. Feehrer, C. E. Love,
“Implementation of a general-purpose stored-program digital optical computer,”
Applied Optics, 33(8), 1619-1628 (1994).
21. B. Lu, Y. C. Lu, J. Cheng, M. J. Hafich, J. Klem, J. C. Zolper, “High speed,
cascaded optical logic operations using programmable optical logic gate arrays,”
IEEE Photonics Technology Letters, 8(1), 166-168 (1996).
~ 143 ~
22. B. Wang, F. Yu, X. Liu, P. Gu, J. Tang, “Optical modified signed-digit addition
module based on Boolean polarization-encoded logic algebra,” Optical
Engineering, 35(10), 2989-2994 (1996).
23. L. A. Wang, S. H. Chang, Y. F. Lin, “Novel implementation method to realize
all-optical logic gates,” Optical Engineering, 37(3), 1011-1018 (1998).
24. H. Y. Lee, H. F. Yau, N. J. Cheng, “Incoherent optical XOR logic gate and
image subtractor with series self-pumped phase conjugators,” Optical
Engineering, 37(7), 2156-2161 (1998).
25. J. P. Marangos, “Topical review electromagnetically induced transparency,”
Journal of Modern Optics, 45(3), 471-503 (1998).
26. H. C. Neitzert, “A Wannier- Stark waveguide electroabsorption modulator as a
low- power switch and its application as NAND, NOR or Ex-OR all-optical
logic gates,” Journal of Optics A: Pure and Applied Optics, 3(3), 218-221
(2001).
27. P. O. Hedekvist, A. Bhardwaj, K. Vahala, H. Anderson, “Advanced all-optical
logic gates on a spectral bus,” Applied Optics, 40(11), 1761-1766 (2001).
28. M. T. Hill, H. de Waardt, G. D. Khoe, H. J. S. Dorren, “Fast optical flip-flop by
use of Mach-Zehnder interferometers,” Microwave and Optical Technology
Letters, 31(6), 411-415 (2001).
29. J. C. Chiao, “Liquid-crystal optical switches,” OSA Topical Meeting, Photonics
in Switching, Monterey, California, 11-15 June, 2001. A. Sawchuk ed, 59,
Optical Society of America Trends in optics and photonics series, JWB2.
30. R. S. Fyath, A. A. W. Alsaffar, M. S. Alam, “Optical two-step modified signed-
digit addition based on binary logic gates,” Optics Communications, 208(4-6),
263-273 (2002).
31. C. P. Singh, S. Roy, “All-optical switching in bacteriorhodopsin based on M
state dynamics and its application to photonic logic gates,” Optics
Communications, 218(1-3), 55-66 (2003).
32. S. Pereira, P. Chak, J. E. Sipe, “All-optical AND gate by use of a Kerr nonlinear
microresonator structure,” Optics Letters, 28(6), 444-446 (2003).
~ 144 ~
33. M. Zhang, Y. Zhao, L. Wang, J. Wang, P. Ye, “Desing and analysis of all-
optical XOR gate using SOA-based Mach-Zehnder interferometer,” Optics
Communications, 223(4-6), 301-308 (2003).
34. J. Barbe, J. Campos, J. Nicolas, C. C. Iemmi, “Multichannel optical correlator
for texture classification,” Optical Engineering, 42(7), 2062-2067 (2003).
35. M. Kalyvas, “40 Gb/s all-optical write/store memory using a single
semiconductor optical amplifier-based logic gate,” Optical Engineering, 42(11),
3073-3074 (2003).
36. D. Dragoman, M. Dragoman, “Biased micromechanical cantilever arrays as
optical image memory,” Applied Optics, 42(8), 1515-1519 (2003).
37. P. Boffi, D. Piccinin, M. C. Ubaldi, M. Martinelli, “All-optical pattern
recognition for digital real-time information processing,” Applied Optics,
42(23), 4670-4680 (2003).
38. K. Roychowdhury, S. Mukhopadhyay, “A new method of binary addition
scheme with massive use of non-linear material based system,” Chinese Optics
Letters, 1(4), 241-242 (2003).
39. G. J. Liu, J. Liu, B. M. Liang, Q. Li, G. L. Jin, “Nonlinear optical switching
matrix,” Optics Letters, 28(15), 1347-1349 (2003).
40. D. Goswami, “Optical computing: optical components and storage systems,”
Resonance, June issue, 56-71 (2003).
41. D. Goswami, “Optical computing: Research trends,” Resonance, July issue, 8-
21 (2003).
42. D. J. Blumenthal, J. E. Bowers, L. Rau, C. Hsu-Feng, S. Rangarajan, W. Wei,
K. N. Poulsen, “Optical signal processing for optical packet switching
networks,” IEEE Communications Magazine, 41(2), 23-29 (2003).
43. F. Zhao, Y. Zhang, J. Zou, Z. Shi, B. Bihari, X. Deng, J. Qiao, Z. Shi, R. T.
Chen, “Wavelength division multiplexer/demultiplexers for optical
interconnects in massively parallel processing,” Optical Engineering, 42(1),
273-280 (2003).
44. T. A. Ibrahim, W. Cao, Y. Kim, J. Li, J. Goldhar, P. T. Ho, C. H. Lee, “All-
optical switching in a laterally coupled microring resonator by carrier injection,”
IEEE Photonics Technology Letters, 15(1), 36-38 (2003).
45. T. Ohara, H. Takara, I. Shake, K. Mori, S. Kawanishi, S. Mino, T. Yamada, M.
Ishii, T. Kitoh, T. Kitagawa, K. R. Parameswaran, M. M. Fejer, “160 Gb/s
~ 145 ~
optical time division multiplexing with PPLN hybrid integrated planar
lightwave circuit,” IEEE Photonics Technology Letters, 15(2), 302-304 (2003).
46. H. Pishro-Nik, N. Rahnavard, J. Ha, F. Fekri, A. Adibi, “Low-density parity-
check codes for volume holographic memory systems,” Applied Optics, 42(5),
861-870 (2003).
47. T. Houbavlis, K. E. Zoiros, “Ultrafast pattern-operated all-optical Boolean XOR
with semiconductor optical amplifer- assisted Sagnac switch,” Optical
Engineering, 42(12), 3415-3416 (2003).
48. T. Houbavlis, K. E. Zoiros, “Ultrafast all-optical exclusive OR operation with
semiconductor optical amplifier-assisted fiber Sagnac switch,” Optical
Engineering, 42(9), 2481-2482 (2003).
49. T. Houbavlis, K. E. Zoiros, “10 GHz all-optical recirculating shift register with
semiconductor optical amplifier (SOA) assisted Sagnac switch and SOA
feedback,” Optical Engineering, 42(9), 2483-2484 (2003).
50. J. M. Kang, Y. S. Jeon, S. K. Han, S. Lee, “Performance variation of
preamplifier integrated cross-phase modulation wavelength converter by internal
reflectivity of semiconductor optical amplifiers,” Optical Engineering, 42(6),
1836-1842 (2003).
51. U. K. Sapaev, I. A. Kulagin, T. Usmanov, “Theory of second harmonic
generation for limited laser beams in nonlinear crystals,” Journal of Optics B:
Quantum and Semiclassical Optics, 5(4), 355-356 (2003).
52. M. Zhang, Y. Zhao, L. Wang, J. Wang, P. Ye, “Design and analysis of all-
optical XOR gate using SOA-based Mach Zehnder interferometer,” Optics
Communications, 223(4-6), 301-308 (2003).
53. H. Soto, J. D. Topomondzo, D. Erasme, M. Castro, “All-optical NOR gates with
two and three input logic signals based on cross-polarization modulation in a
semiconductor optical amplifier,” Optics Communications, 218(4-6), 243-247
(2003).
54. N. K. Nishchal, J. Joseph, K. Singh, “Fully phase encryption using fractional
Fourier transform,” Optical Engineering, 42(6), 1583-1588 (2003).
55. N. K. Nishchal, G. Unnikrishnan, J. Joseph, K. Singh, “Optical encryption using
a localized fractional Fourier transform,” Optical Engineering, 42(12), 3566-
3571 (2003).
~ 146 ~
56. N. K. Nishchal, J. Joseph, K. Singh, “Optical phase encryption by phase contrast
using electrically addressed spatial light modulator,” Optics Communications,
217(1-6), 117-122 (2003).
57. A. Sinha, K. Singh, “A technique for image encryption using digital signature,”
Optics Communications, 218(4-6), 229-234 (2003).
58. D. Ganotra, J. Joseph, K. Singh, “Second and first order phase-locked loops in
fringe profilometry and application of neural networks for phase-to-depth
conversion,” Optics Communications, 217(1-6), 85-96 (2003).
59. J. H. Kim, Y. T. Byun, Y. M. Jhon, S. Lee, D. H. Woo, S. H. Kim, “All-optical
half adder using semiconductor optical amplifier based devices,” Optics
Communications, 218(4-6), 345-349 (2003).
60. C. Vazquez, J. M. S. Pena, A. L. Aranda, “Broadband 1×2 polymer optical fiber
switches using nematic liquid crystals,” Optics Communications, 224(1-3), 57-
62 (2003).
61. H. Ono, M. Ito, “Characteristics of all-optical switching properties in a guest-
host liquid crystal Fabry-Perot device,” Optics Communications, 223(4-6), 399-
409 (2003).
62. A. A. Awwal, K. M. Iftekharuddin, M. A. Karim, R. D. Juday, “Optical pattern
recognition algorithms, architecture and applications: introduction to the future
issue,” Applied Optics, 42(23), 4647-4648 (2003).
63. L. R. Dalton, “Rational design of organic electro-optic materials,” Journal of
Physics: Condensed Matter, 15(20), R897-934 (2003).
64. J. B. Fasquel, M. M. Bruynooghe, “New hybrid opto-electronic method for fast
and unsupervised object detection,” Optical Engineering, 42(11), 3352-
3364(2003).
65. H. J. S. Dorren, D. Lenstra, L. Yong, M. T. Hill, G.D. Khoe, “Nonlinear
polarization rotation in semiconductor optical amplifiers: theory and application
to all-optical flip-flop memories,” IEEE Journal of Quantum Electronics, 39(1),
141-148 (2003).
66. M. L. Nielsen, B. Lavigne, B. Dagens, “Polarity-preserving SOA-based
wavelength conversion at 40 Gbit/s using bandpass filtering,” Electronics
Letters, 39(18), 1334-1335 (2003).
67. R. Grover, T. A. Ibrahim, T. N. Ding, Y. Leng, L. C. Kuo, S. Kanakaraju, K.
Amarnath, L. C. Calhoun, P. T. Ho, “Laterally coupled InP-based single-mode
~ 147 ~
microracetrack notch filter,” IEEE Photonics Technology Letters, 15(8), 1082-
1084 (2003).
68. T. A. Ibrahim, R. Grover, L. C. Kuo, S. Kanakaraju, L. C. Calhoun, P. T. Ho,
“All-optical AND/NAND logic gates using semiconductor microresonators,”
IEEE Photonics Technology Letters, 15(10), 1422-1424 (2003).
69. C. Bintjas, K. Vlachos, N. Pleros, H. Avramopoulos, “Ultrafast nonlinear
interferometer (UNI) based digital optical circuits and their use in packet
switching,” Journal of Lightwave Technology, 21(11), 2629-2637 (2003).
70. C. P. Singh, S. Roy, “Dynamics of all-optical switching in C60 and its
application to optical logic gates,” Optical Engineering, 43(2), 426-431 (2004).
71. A. D. McAulay, “Novel all-optical flip-flop using semiconductor optical
amplifiers in innovative frequency-shifting inverse-threshold pairs,” Optical
Engineering, 43(5), 1115-1120(2004).
72. M. Naruse, H. Mitsu, M. Furuki, I. Iwasa, Y. Sato, S. Tatsuura, M. Tian, F.
Kubota, “Terabit all-optical logic based on ultrafast two-dimensional
transmission gating,” Optics Letters, 29(6), 608-610 (2004).
73. H. Dong, Q. Wang, G. Zhu, J. Jaques, A. B. Piccirilli, N. K. Dutta,
“Demonstration of all-optical logic OR gate using semiconductor optical
amplifier-delayed interferometer,” Optics Communications, 242(4-6), 479-485
(2004).
74. X. Zhang, Y. Wang, J. Sun, D. Liu, D. Huang, “All-optical AND gate at 10
Gbit/s based on cascaded single-port-couple SOAs,” Optics Express, 12(3), 361-
366 (2004).
75. C. J. Cheng, M. L. Chen, “Polarization encoding for optical encryption using
twisted nematic liquid crystal spatial light modulators,” Optics Communications,
237(1-3), 45-52 (2004).
76. H. Soto, E. Alvarez, C. A. Diaz, J. Topomondzo, D. Erasme, L. Schares, L.
Occhi, G. Guekos, M. Castro, “Design of an all-optical NOT, XOR gate based
on cross-polarization modulation in a semiconductor optical amplifier,” Optics
Communications, 237(1-3), 121-131 (2004).
77. S. Roychowdhury, V. K. Jaiswal, R. P. Singh, “Implementing controlled NOT
gate with optical vortex,” Optics Communications, 236(4-6), 419-424 (2004).
~ 148 ~
78. T. Houbavlis, K. E. Zoiros, G. Kanellos, C. Tsekrekos, “Preformance analysis of
ultrafast all-optical Boolean XOR gate using semiconductor optical amplifier-
based Mach-Zehnder Interferometer,” Optics Communications, 232(1-6), 179-
199 (2004).
79. N. Pahari, D. N. Das, S. Mukhopadhyay, “All-optical method for the addition of
binary data by nonlinear materials,” Applied Optics, 43(33), 6147-6150 (2004).
80. G. M. Poladian, “Spatial light modulators based on structures containing
photoelectrets and electrooptic materials: key devices for optical computing,”
Journal of Optical Technology, 71(7), 478-486 (2004).
81. F. G. Haibach, M. L. Myrick, “Precision in multivariate optical computing,”
Applies Optics, 43(10), 2130-2140 (2004).
82. P. K. Kwan, Y. Y. Lu, “Computing optical bistability in one-dimensional
nonlinear structures,” Optics Communications, 238(1-3), 169-175 (2004).
83. K. Roychowdhury, S. Mukhopadhyay, “An all-optical binary comparator using
nonlinear material,” Journal of Optics, 33(2), 81-85 (2004).
84. T. A. Ibrahim, K. Amarnath, L. C. Kuo, R. Grover, V. Van, P. T. Ho, “Photonic
logic NOR gate based on two symmetric microring resonators,” Optics Letters,
29(23), 2779-2781 (2004).
85. V. R. Almeida, C. A. Barrios, R. R. Panepucci, M. Lipson, M. A. Foster, D. G.
Ouzounov, A. L. Gaeta, “All-optical switching on a silicon chip,” Optics
Letters, 29(24), 2867-2869 (2004).
86. K. Roychowdhury, S. Mukhopadhyay, “Binary optical arithmetic operation
scheme with tree architecture by proper accommodation of optical nonlinear
material,” Optical Engineering, 43(1), 132-136 (2004).
87. R. Prasanth, J. E. M. Haverkort, A. Deepthy, E. W. Bogaart, J. J. G. M. van der
Tol, E. A. Patent, G. Zhao, Q. Gong, P. J. van Veldhoven, R. Nötzel, J. H.
Wolter, “All-optical switching due to state filling in quantum dots,” Applied
Physics Letters, 84(20), 4059-4061 (2004).
88. H. J. S. Dorren, Y. Xuelin, A. K. Mishra, L. Zhonggui, J. Heongkyu, H. de
Waardt, G. D. Khoe, T. Simoyama, H. Ishikawa, H. Kawashima, T. Hasama,
“All-optical logic based on ultrafast gain and index dynamics in a
semiconductor optical amplifier,” IEEE Journal of Selected Topics in Quantum
Electronics, 10(5), 1079-1092 (2004).
~ 149 ~
89. C. M. Greiner, D. Iazikov, T. W. Mossberg, “Wavelength division multiplexing
based on apodized planar holographic Bragg reflectors,” Applied Optics, 43(23),
4575-4583 (2004).
90. A. K. Das, S. Mukhopadhyay, “General approach of spatial input encoding for
multiplexing and demultiplexing,” Optical Engineering, 43(1), 126-131 (2004).
91. I. Armstrong, I. Andonovic, A. Kelly, “Semiconductor optical amplifiers:
performance and applications in optical packet switching,” Journal of Optical
Networking, 3(12), 882-897 (2004).
92. L. Rau, S. Rangarajan, W. Wang, H. F. Chou, H. Poulsen, J. Bowers, D.
Blumenthal, “High-speed optical time-division multiplexed/ WDM networks
and their network elements based on regenerative all-optical ultrafast
wavelength converters,” Journal of Optical Networking, 3(2), 100-118 (2004).
93. G. Dyankov, H. Y. Chen, S. Chao, S. Chi, “Optimization of second harmonic
generation in nonlinear film structure,” Optics Communications, 236(1-3), 203-
208 (2004).
94. J. J. Ju, J. Kim, J. Y. Do, M. S. Kim, S. K. Park, S. Park, M. H. Lee, “Second
harmonic generation in periodically poled nonlinear polymer waveguides,”
Optics Letters, 29(1), 89-91 (2004).
95. O. Wada, “Femtosecond all-optical devices for ultrafast communication and
signal processing,” New Journal of Physics, 6(1), 183 (2004).
96. S. Roy, P. Sharma, A. K. Dharmadhikari, D. Mathur, “All-optical switching
with bacteriorhodopsin,” Optics Communications, 237(4-6), 251-256 (2004).
97. N. K. Nishchal, J. Joseph, K. Singh, “Fully phase encryption using digital
holography,” Optical Engineering, 43(12), 2959-2966 (2004).
98. N. K. Nishchal, J. Joseph, K. Singh, “Fully phase-based encryption using
fractional order Fourier domain random phase encoding: error analysis,” Optical
Engineering, 43(10), 2266-2273 (2004).
99. N. K. Nishchal, J. Joseph, K. Singh, “Fully phase-encrypted memory using
cascaded extended fractional Fourier transform,” Optics and Lasers in
Engineering, 42(2), 141-151 (2004).
100. N. K. Nishchal, J. Joseph, K. Singh, “Securing information using fractional
Fourier transform in digital holography,” Optics Communications, 235(4-6),
253-259 (2004).
~ 150 ~
101. D. Ganotra, J. Joseph, K. Singh, “Object reconstruction in multilayer neural
network based profilometry using grating structure comprising two regions with
different spatial periods,” Optics and Lasers in Engineering, 42(2), 179-192
(2004).
102. D. Ganotra, J. Joseph, K. Singh, “Modified geometry of ring-wedge detector for
sampling Fourier transform of fingerprints for classification using neural
networks,” Optics and Lasers in Engineering, 42(2), 167-177 (2004).
103. R. John, J. Joseph, K. Singh, “Phase-image based content-addressable
holographic data storage,” Optics Communications, 232(1-6), 99-106 (2004).
104. Y. Q. Lu, F. Du, S. T. Wu, “Polarization switch using thick holographic
polymer-dispersed liquid crystal grating,” Journal of Applied Physics, 95(3),
810-815 (2004).
105. M. Chen, S. Zhang, M. A. Karim, “Modification of standard image compression
methods for correlation based pattern recognition,” Optical Engineering, 43(8),
1723-1730 (2004).
106. R. G. Beausoleil, W. J. Munro, D. A. Rodrigues, T. P. Spiller, “Applications of
electromagnetically induced transparency to quantum information processing,”
Journal of Modern Optics, 51(16-18), 2441-2448 (2004).
107. M. Takenaka, Y. Nakano, “First realization of all-optical flip-flop based on
bistable laser diode with active multimode interference cavity,” Optical Fiber
Communication Conference (OFC), Los Angeles, WL4, 22 February, 2004.
108. J. Leuthold, D. M. Marom, S. Cabot, J. J. Jaques, R. Ryf, C. R. Giles, “All-
optical wavelength conversion using a pulse reformatting optical filter,” Journal
of Lightwave Technology, 22(1), 186-192 (2004).
109. H. J. Caulfield, J. Westphal, “The logic of optics and the optics of logic,”
Information Sciences, 162(1), 21-33 (2004).
110. M. Takenaka, Y. Nakano, “Realization of all-optical flip-flop using directionally
coupled bistable laser diode,” IEEE Photonics Technology Letters, 16(1), 45-47
(2004).
111. D. Tsiokos, E. Kehayas, K. Vyrsokinos, T. Houbavlis, L. Stampoulidis, G. T.
Kanellos, N. Pleros, G. Guekos, H. Avramopoulos, “10 Gb/s all-optical half-
adder with interferometric SOA gates,” IEEE Photonics Technology Letters,
16(1), 284-286 (2004).
~ 151 ~
112. L. Wang, M. Zhang, Y. Zhao, P. Ye, “Performance analysis of the all-optical
XOR gate using SOA-MZI with a differential modulation scheme,” Microwave
and Optical Technology Letters, 40(2), 173-177 (2004).
113. S. Tanaka, N. Nagayama, M. Yokoyama, “Control of reflectivity by beam
polarization state in self-pumped phase conjugation mirror using photorefractive
polymer,” Molecular Crystals and Liquid Crystals, 424(1), 233-239 (2004).
114. N. Calabretta, Y. Liu, F. M. Huijskens, M. T. Hill, H. de Waardt, G. D. Khoe,
H. J. S. Dorren, “Optical signal processing based on self-induced polarization
rotation in a semiconductor optical amplifier,” Journal of Lightwave
Technology, 22(2), 372-381 (2004).
115. Y. I. Kim, J. H. Kim, S. Lee, D. H. Woo, S. H. Kim, T. H. Yoon, “Broad-band
all-optical flip-flop based on optical bistability in an integrated SOA/ DFB-
SOA,” IEEE Photonics Technology Letters, 16(2), 398-400 (2004).
116. Y. Huang, S. T. Wu, Y. Zhao, “All-optical switching characteristics in
bacteriorhodopsin and its applications in integrated optics,” Optics Express,
12(5), 895-906 (2004).
117. K. Chan, C. K. Chan, L. K. Chen, F. Tong, “Demonstration of 20 Gb/s all-
optical XOR gate by four-wave mixing in semiconductor optical amplifier with
RZ-DPSK modulated inputs,” IEEE Photonics Technology Letters, 16(3), 897-
899 (2004).
118. M. Kalyvas, K. Yiannopoulos, T. Houbavlis, H. Avramopoulos, “Control signal
generation from flag pulses to drive all-optical gates,” IEEE Photonics
Technology Letters, 16(4), 1122-1124 (2004).
119. H. Y. Tu, C. J. Cheng, M. L. Chen, “Optical image encryption based on
polarization encoding by liquid crystal spatial light modulators,” Journal of
Optics A: Pure and Applied Optics, 6(6), 524-528 (2004).
120. I. Kang, C. Dorrer, J. Leuthold, “All-optical XOR operation of 40 Gbit/s phase-
shift-keyed data using four-wave mixing in semiconductor optical amplifier,”
Electronics Letters, 40(8), 496-498 (2004).
121. S. Randel, A. M. de Melo, K. Petermann, V. Marembert, C. Schubert, “Novel
scheme for ultrafast all-optical XOR operation,” Journal of Lightwave
Technology, 22(12), 2808-2815 (2004).
~ 152 ~
122. R. John, J. Joseph, K. Singh, “A new balanced modulation code for a phase-
image- based holographic data storage system,” Journal of Optics A: Pure and
Applied Optics, 7(8), 391-395 (2005).
123. R. John, J. Joseph, K. Sing, “An input-data page modulation scheme for content-
addressable holographic digital data storage,” Optics Communications, 249(4-
6), 387-395 (2005).
124. R. John, J. Joseph, K. Singh, “Phase-image based content-addressable
holographic data storage with security,” Journal of Optics A: Pure and Applied
Optics, 7(3), 123-128 (2005).
125. R. John, J. Joseph, K. Singh, “Holographic digital data storage using phase
modulated pixels,” Optics and Lasers in Engineering, 43(2), 183-194 (2005).
126. C. Zhao, X. Zhang, H. Liu, D. Liu, D. Huang, “Tunable all-optical NOR gate at
10 Gb/s based on SOA fiber ring laser,” Optics Express, 13(8), 2793-2798
(2005).
127. A. K. Das, S. Mukhopadhyay, “An all-optical matrix multiplication scheme with
non-linear material based switching system,” Chinese Optics Letters, 3(3), 172-
175 (2005).
128. K. Roy Chowdhury, P. P. Das, S. Mukhopadhyay, “All-optical time domain
multiplexing-demultiplexing scheme with nonlinear material,” Optical
Engineering, 44(3), 035201 (2005).
129. K. Roy Chowdhury, D. De, S. Mukhopadhyay, “Parity checking and generating
circuit with nonlinear material in all-optical domain,” Chinese Physics Letters,
22(6), 1433-1435 (2005).
130. T. P. Hessler, P. E. Selbmann, J. L. Pleumeekers, M. A. Dupertuis, B. Deveaud,
R. Schreieck, J. Y. Emery, B. Dagens, “Propagation effects on the ultrafast
cross-gain modulation in semiconductor optical amplifiers,” Optics
Communications, 248(1-3), 267-280 (2005).
131. M. Guignard, V. Nazabal, J. Troles, F. Smektala, H. Zeghlache, Y.
Quiquempois, A. Kudlinski, G. Martinelli, “Second-harmonic generation of
thermally poled chalcogenide glass,” Optics Express, 13(3), 789-795 (2005).
132. M. Airola, Y. Liu, S. Blair, “Second-harmonic generation from an array of sub-
wavelength metal apertures,” Journal of Optics A: Pure and Applied Optics,
7(2), S118-S123 (2005).
~ 153 ~
133. Y. Zhou, J. Wu, K. Xu, J. Lin, “A simple novel all-optical XOR logic gate
implementation,” Proceedings of the SPIE, 5624, 82-90 (2005).
134. H. Funakoshi, A. Okamoto, K. Sato, “Long-term reading experiment on a
photorefractive holographic memory with the hologram sustainment technique
by optical feedback,” Journal of Modern Optics, 52(11), 1511-1527 (2005).
135. A. Takita, H. Yamamoto, Y. Hayasaki, N. Nishida, H. Misawa, “Three-
dimensional optical memory using a human fingernail,” Optics Express, 13(12),
4560-4567 (2005).
136. J. Lim, M. Lee, E. Kim, “Three dimensional optical memory using
photoluminescence change in Sm-doped sodium borate glass,” Applied Physics
Letters, 86(19), 191105 (2005).
137. R. S. Fyath, S. A. Ali, M. S. Alam, “Four operand parallel optical computing
using shadow-casting technique,” Optics & Laser Technology, 37(3), 251-257
(2005).
138. M. Kato, K. Fujiura, T. Kurihara, “Asynchronous, all-optical signal processing
based on the self-frequency shift of a gigahertz Raman soliton,” Applied Optics,
44(8), 1442-1447 (2005).
139. N. Iizuka, K. Kaneko, N. Suzuki, “Sub-picosecond all-optical gate utilizing GaN
intersubband transition,” Optics Express, 13(10), 3835-3840 (2005).
140. G. Chen, C. Zhang, X. Shang, Z. Guo, X. Wang, J. Tian, Q. W. Song, “Real-
time intensity dependent all-optical switch of reverse image converter from
wavelength to wavelength based on bacteriorhodopsin film,” Optics
Communications, 249(4-6), 563-568 (2005).
141. A. Sinha, S. Mukhopadhyay, “Effect of higher order nonlinearity in frequency
variation of self-phase modulation in optical fiber communication,” Chinese
Optics Letters, 2(9), 500-502 (2005).
142. S. Dhar, S. Mukhopadhyay, “All-optical implementation of ASCII by use of
nonlinear material for optical encoding of necessary symbols”, Optical
Engineering, 44(6), 065201 (2005).
143. A. Sinha, H. Bhowmik, P. Kuila, S. Mukhopadhyay, “New method of
controlling the power of a Gaussian optical pulse through an electro-optic
modulator and a nonlinear waveguide for generation of solitons,” Optical
Engineering, 44(6), 065003 (2005).
~ 154 ~
144. Y. J. Liu, X. W. Sun, J. H. Liu, H. T. Dai, K. S. Xu, “A polarization insensitive
2×2 optical switch fabricated by liquid crystal-polymer composite,” Applied
Physics Letters, 86(4), 041115 (2005).
145. R. A. Ramsey, S. C. Sharma, “Switchable holographic gratings formed in
polymer-dispersed liquid-crystal cells by use of a He-Ne laser,” Optics Letters,
30(6), 592-594 (2005).
146. A. Fratalocchi, R. Asquini, G. Assanto, “Integrated electro-optic switch in liquid
crystals,” Optics Express, 13(1), 32-37 (2005).
147. M. S. Alam, M. A. Karim, “Biometric recognition systems: introduction,”
Applied Optics, 44(5), 635-636 (2005).
148. V. A. Sautenkov, Y. V. Rostovtsev, C. Y. Ye, G. R. Welch, O. Kocharovskaya,
M. O. Scully, “Electromagnetically induced transparency in rubidium vapor
prepared by a comb of short optical pulses,” Physical Review A, 71(6), 063804
(2005).
149. C. Yu, L. Christen, T. Luo, Y. Wang, Z. Pan, L. S. Yan, A. E. Willner, “All
optical XOR gate using polarization rotation in single highly nonlinear fiber”,
IEEE Photonics Technology Letters, 17(6), 1232-1234 (2005).
150. E. Tangdiongga, X. Yang, Z. Li, Y. Liu, D. Lenstra, G-D. Khoe, H. J. S. Dorren,
“Optical flip-flop based on two coupled mode-locked ring lasers,” IEEE
Photonics Technology Letters, 17(1), 208-210(2005).
151. R. Clavero, F.Ramos, J.M. Martinez, J. Marti, “All-optical flip-flop based on a
single SOA-MZI,” IEEE Photonics Technology Letters, 17(4), 843-845(2005).
152. Y. Wu, “All-optical logic gates by using multibranch waveguide structure with
localized optical nonlinearity,” IEEE Journal of Selected Topics in Quantum
Electronics, 11(2), 307-312(2005).
153. M. Borda, I. Nafornita, D. Isar, A. Isar, “New instantaneous frequency
estimation method based on image processing techniques,” Journal of
Electronic Imaging, 14(2), 023013(2005).
154. S. H. Kim, J. H. Kim, B. G. Yu, Y. T. Byun, Y. M. Jeon, S. Lee, D. H. Woo, S.
H. Kim, “All-optical NAND gate using cross-gain modulation in semiconductor
optical amplifiers,” Electronics Letters, 41(18), 1027-1028 (2005).
155. Z. Li, Y. Liu, S. Zhang, H. Ju, H. de Waardt, G. D. Khoe, H. J. S. Dorren, D.
Lenstra, “All-optical logic gates using semiconductor optical amplifier assisted
by optical filter,” Electronics Letters, 41(25), 1397-1399 (2005).
~ 155 ~
156. L. Qian, H. J. Caulfield, “Abstract passive interferometers with applications to
conservative logic,” Optik – International Journal for Light and Electron
Optics, 116(8), 404-408 (2005).
157. Y. Zhou, J. Wu, J. Lin, “Novel ultrafast all-optical XOR scheme based on
Sagnac interferometric structure,” IEEE Journal of Quantum Electronics, 41(6),
823-827 (2005).
158. X. Yang, C. Zhang, S. Qi, K. Chen, J. Tian, G. Zhang, “All-optical Boolean
logic gate using azo-dye doped polymer film,” Optik – International Journal for
Light and Electron Optics, 116(6), 251-254 (2005).
159. G. Y. Chen, Z. X. Guo, K. Chen, C. P. Zhang, J. G. Tian, Q. W. Song, “Time-
dependent all-optical logic-gates with bacteriorhodopsin film,” Optik –
International Journal for Light and Electron Optics, 116(5), 227-231 (2005).
160. M. Takenaka, M. Raburn, Y. Nakano, “All-optical flip-flop multimode
interference bistable laser diode,” IEEE Photonics Technology Letters, 17(5),
968-970 (2005).
161. S. Medhekar, R. K. Sarkar, “All-optical passive transistor,” Optics Letters,
30(8), 887-889 (2005).
162. A. Bogoni, L. Poti, R. Proietti, G. Meloni, F. Ponzini, P. Ghelfi, “Regenerative
and reconfigurable all-optical logic gates for ultra-fast applications,” Electronics
Letters, 41(7), 435-436 (2005).
163. A. K. Das, P. P. Das, S. Mukhopadhyay, “A new approach of binary addition
and subtraction by nonlinear material based switching technique,” Pramana,
64(2), 239-247 (2005).
164. C. G. Lee, Y. J. Kim, C. S. Park, H. J. Lee, C. S. Park, “Experimental
demonstration of 10 Gb/s data format conversions between NRZ and RZ using
SOA loop mirror,” Journal of Lightwave Technology, 23(2), 834-841 (2005).
165. M. Fleischhauer, A. Imamoglu, J. P. Marangos, “Electromagnetically induced
transparency: optics in coherent media,” Reviews of Modern Physics, 77, 633-
673 (2005).
166. N. Pahari, S. Mukhopadhyay, “New method of all-optical data comparison with
nonlinear material using 1‟s compliment method,” Optical Engineering, 45(1),
015201 (2006).
~ 156 ~
167. N. Pahari, S. Mukhopadhyay, “New scheme for image edge detection using the
switching mechanism of nonlinear optical material,” Optical Engineering,
45(3), 037003 (2006).
168. A. Shinya, S. Mitsugi, T. Tanabe, M. Notomi, I. Yokohama, H. Takara, S.
Kawanishi, “All-optical flip-flop circuit composed of coupled two-port resonant
tunneling filter in two-dimensional photonic crystal slab,” Optics Express,
14(3), 1230-1235 (2006).
169. Y. D. Jeong, J. S. Cho, Y. H. Won, H. J. Lee, H. Yoo, “All-optical flip-flop
based on the bistability of injection locked Fabry-Perot laser diode,” Optics
Express, 14(9), 4058-4063 (2006).
170. Y. A. Zaghloul, A. R. M. Zaghloul, “Complete all-optical processing
polarization based binary logic gates and optical processors”, Optics Express,
14(21), 9879-9895(2006).
171. Y. A. Zaghloul, A. R. M. Zaghloul, “Unforced polarization-based optical
implementation of Binary logic,” Optics Express, 14(16), 7252-7269(2006).
172. P. Li, D. Huang, X. Zhang, G. Zhu, “Ultrahigh-speed all-optical half adder
based on four-wave mixing in semiconductor optical amplifier,” Optics Express,
14(24), 11839-11847(2006).
173. W. B. Fraga, J.W. M. Menezes, M. G. da Silva, C. S. Sobrinho, A. S. B.
Sombra, “All optical logic gates based on an asymmetric nonlinear directional
coupler,” Optics Communications, 262(1), 32-37(2006).
174. S. Medhekar, P. P. Paltani, “Proposal for optical switch using nonlinear
refraction,” IEEE Photonics Technology Letters, 18(15), 1579-1581(2006).
175. Q. Wang, H. Dong, G. Zhu, H. Sun, J. Jaques, A. B. Piccirilli, N. K. Dutta, “All
optical logic OR gate using SOA and delayed interferometer,” Optics
Communication, 260(1), 81-86 (2006).
176. H. J. Caulfield, C. S. Vikram, A. Zavalin, “Optical logic redux,” Optik-
International Journal for Light and Electron Optics, 117, 199-209 (2006).
177. J. Zhang, J. Wu, C. Feng, G. Zhou, K. Xu and J. Lin, “40 Gbit/s all-optical logic
NOR gate based on a semiconductor optical amplifier and a filter,” Optical
Engineering, 45(8), 080503(2006).
178. J. Wang, J. Sun, Q. Sun, “Experimental observation of a 1.5 μm band
wavelength conversion and logic NOT gate at 40 Gbit/s based on sum-
frequency generation,” Optics Letters, 31(11), 1711-1713 (2006).
~ 157 ~
179. T. K. Liang, L. R. Nunes, M. Tsuchiya, K. S. Abedin, T. Miyazaki, D. Van
Thourhout, W. Bogaerts, P. Dumon, R. Baets, H. K. Tsang, “High speed logic
gate using two-photon absorption in silicon waveguides,” Optics
Communications, 265(1), 171-174 (2006).
180. Y. Liu, E. Tangdiongga, Z. Li, S. Zhang, H. de Waardt, G. D. Khoe, H. J. S.
Dorren, “Error-free all-optical wavelength conversion at 160 Gb/s using a
semiconductor optical amplifier and an optical bandpass filter,” Journal of
Lightwave Technology, 24(1), 230-236 (2006).
181. J. Oksanen, J. Tulkki, “Coherent optical logic by laser amplifiers with
feedback,” Journal of Lightwave Technology, 24(12), 4918-4924 (2006).
182. S. Kumar, A. E. Willner, “Simultaneous four-wave mixing and cross-gain
modulation for implementing an all-optical XNOR logic gate using a single
SOA,” Optics Express, 14(12), 5092-5097 (2006).
183. T. Kawazoe, K. Kobayashi, K. Akahane, M. Naruse, N. Yamamoto, M. Ohtsu,
“Demonstration of nanophotonic NOT gate using near-field optically coupled
quantum dots,” Applied Physics B: Lasers and Optics, 84(1-2), 243-246 (2006).
184. J. S. Sanghera, I. D. Aggarwal, L. B. Shaw, C. M. Florea, P. Pureza, V. Q.
Nguyen, F. Kung, I. D. Aggarwal, “Nonlinear properties of chalcogenide glass
fibers,” Journal of Optoelectronics and Advanced Materials, 8(6), 2148-2155
(2006).
185. J. Oksanen, J. Tulkki, “Fast coherent all-optical flip-flop memory,” Applied
Physics Letters, 88, 181118 (2006).
186. L. Q. Guo, M. J. Connelly, “All-optical AND gate with improved extinction
ratio using signal induced nonlinearities in a bulk semiconductor optical
amplifier,” Optics Express, 14(7), 2938-2943 (2006).
187. P. Mondal, S. Mukhopadhyay, “Method of conducting an all-optical NAND
logic operation controlled from a long distance”, Optical Engineering, 46(3),
035009 (2007).
188. J. Zhang, J. Wu, C. Feng, K. Xu, J. Lin, “All-optical logic OR gate exploiting
nonlinear polarization rotation in an SOA and red-shifted sideband filtering,”
IEEE Photonics Technology Letters, 19(1), 33-35 (2007).
189. J. Dong, S. Fu, X. Zhang, P. Shum, L. Zhang, J. Xu, D. Huang, “Single SOA
based all-optical adder assisted by optical bandpass filter: theoretical analysis
~ 158 ~
and performance optimization,” Optics Communications, 270(2), 238-246
(2007).
190. H. J. Caulfield, R. A. Soref, L. Qian, A. Zavalin, J. Hardy, “Generalized optical
logic elements –GOLEs,” Optics Communications, 271(2), 365-376 (2007).
191. J. Hardy, J. Shamir, “Optics inspired logic architecture,” Optics Express, 15(1),
150-165 (2007).
192. Q. Xu, M. Lipson, “All-optical logic based on silicon micro-ring resonators,”
Optics Express, 15(3), 924 (2007).
193. J. Wang, J. Sun, Q. Sun, “Single PPLN based simultaneous half-adder, half –
subtracter and OR logic gate: proposal and simulation,” Optics Express, 15(4),
1690-1699 (2007).
194. R. Salem, M. A. Foster, A. C. Turner, D. F. Geraghty, M. Lipson, A. L. Gaeta,
“All-optical regeneration on a silicon chip,” Optics Express, 15(12), 7802-7809
(2007).
195. Y. Zhang, Y. Zhang, B. Li, “Optical switches and logic gates based on self-
collimated beams in two-dimensional photonic crystals,” Optics Express,
15(15), 9287-9292 (2007).
196. J. Yang, L. Han, H. Zhang, Y. Guo, “Function-lock strategy in OR/NOR optical
logic gates based on cross-polarization modulation effect in semiconductor
optical amplifier,” Chinese Optics Letters, 5(10), 566-568 (2007).
197. C. Leyder, T. C. H. Liew, A. V. Kavokin, I. A. Shelykh, M. Romanelli, J. Ph.
Karr, E. Giacobino, A. Bramati, “Interference of coherent polariton beams in
microcavities: polarization controlled optical gates,” Physical Review Letters,
99(19), 196402 (2007).
198. C. Emary, L. J. Shanm, “Optically controlled logic gates for two spin qubits in
vertically coupled quantum dots,” Physical Review B, 75(12), 125317 (2007).
199. H. Jung, “2×2, 1×4 Ti:LiNbO3 digital optical switches,” Optical Engineering,
46(3), 034602 (2007).
200. Y. Wang, X. Zhang, J. Dong, D. Huang, “Simultaneous demonstration on all-
optical digital encoder and comparator at 40 Gb/s with semiconductor optical
amplifiers,” Optics Express, 15(23), 15080-15085 (2007).
201. X. Li, J. W. M. Chon, S. Wu, R. A. Evans, M. Gu, “Rewritable polarization-
encoded multilayer data storage in 2, 5-dimethyl-4-(p-nitrophenylazo) anisole
doped polymer,” Optics Letters, 32(3), 277-279 (2007).
~ 159 ~
202. Y. Park, J. Azana, R. Slavik, “Ultrafast all-optical first and higher order
differentiators based on interferometers,” Optics Letters, 32(6), 710-712 (2007).
203. J. N. Roy, D. K. Gayen, “Integrated all-optical logic and arithmetic operations
with the help of a TOAD-based interferometer device – alternative approach,”
Applied Optics, 46(22), 5304-5310 (2007).
204. J. D. Franson, T. B. Pittman, B. C. Jacobs, “Zeno logic gates using
microcavities,” Journal of the Optical Society of America B, 24(2), 209-213
(2007).
205. B. RayChaudhuri, S. Bhattacharyya (Bhaumik), “Molecular level all-optical
logic with chlorophyll absorption spectrum and polarization sensitivity,”
Applied Physics B: Lasers and Optics, 91(3-4), 545-550 (2008).
206. Y. Miyoshi, K. Ikeda, H. Tobioka, T. Inoue, S. Namiki, K. Kitayama, “Ultrafast
all-optical logic gate using a nonlinear optical loop mirror based multi-periodic
transfer function,” Optics Express, 16(4), 2570-2577 (2008).
207. M. Waldow, T. Plotzing, M. Gottheil, M. Forst, J. Bolten, T. Wahlbrink, H.
Kurz, “25ps all-optical switching in oxygen implanted silicon-on-insulator
microring resonator,” Optics Express, 16(11), 7693-7702 (2008).
208. K. Huybrechts, G. Morthier, R. Baets, “Fast all-optical flip-flop based on a
single distributed feedback laser diode,” Optics Express, 16(15), 11405-11410
(2008).
209. K. Huybrechts, G. Morthier, R. Baets, “Experimental demonstration of all-
optical flip-flop operation with a single distributed feedback laser diode,”
International Conference on Photonics in Switching, Hokkaido University,
Japan, 4-7 August, 2008.
210. K. Huybrechts, W. D‟Oosterlinck, G. Morthier, R. Baets, “Proposal for an all-
optical flip-flop using a single distributed feedback laser diode,” IEEE
Photonics Technology Letters, 20(1), 18-20 (2008).
211. S. C. Kong, A. Sahakian, A. Taflove, V. Backman, “Photonic nanojet-enabled
optical data storage,” Optics Express, 16(18), 13713-13719 (2008).
212. F. Liu, T. Wang, L. Qiang, T. Ye, Z. Zhang, M. Qiu, Y. Su, “Compact optical
temporal differentiator based on silicon microring resonator,” Optics Express,
16(20), 15880-15886 (2008).
~ 160 ~
213. R. Slavik, Y. Park, N. Ayotte, S. Doucet, T. J. Ahn, S. LaRochelle, J. Azana,
“Photonic temporal integrator for all-optical computing,” Optics Express,
16(22), 18202-18214 (2008).
214. D. M. Lai, C. H. Kwok, K. K. Wong, “All-optical picoseconds logic gates based
on a fiber optical parametric amplifier,” Optics Express, 16(22), 18362-18370
(2008).
215. Q. Liu, Z. Ouyang, C. J. Wu, C. P. Liu, J. C. Wang, “All-optical half adder
based on cross structures in two-dimensional photonic crystals,” Optics Express,
16(23), 18992-19000 (2008).
216. J. Wang, J. Sun, X. Zhang, D. Huang, M. M. Fejer, “Ultrafast all-optical three-
input Boolean XOR operation for differential phase-shift keying signals using
periodically poled lithium niobate,” Optics Letters, 33(13), 1419-1421 (2008).
217. H. L. Yan, W. He, J. Huan, G. Y. Li, Z. H. Yi, “All-optical AND logic gate
without additional input beam by utilizing cross polarization modulation effect,”
Chinese Physics Letters, 25(11), 3901 (2008).
218. S. Dolev, T. Haist, M. Oltean, “Optical supercomputing,” 1st International
workshop OSC 2008 proceedings, Vienna, Austria, 26 August, 2008.
219. H. Zou, G. Q. Liang, H. Z. Wang, “Efficient all-optical dual-channel switches,
logic gates, half-adder and half-subtracter in a one-dimensional photonic
heterostructure,” Journal of the Optical Society of America B, 25(3), 351-360
(2008).
220. C. Pistol, C. Dwyer, A. R. Lebeck, “Nanoscale optical computing using
resonance energy transfer logic,” IEEE Micro, 28(6), 7-18 (2008).
221. L. Q. Guo, M. J. Connelly, “A novel approach to all-optical wavelength
conversion by utilizing a reflective semiconductor optical amplifier in a co-
propagation scheme,” Optics Communications, 281(17), 4470-4473 (2008).
222. M. A. Foster, A. C. Turner, M. Lipson, A. L. Gaeta, “Nonlinear optics in
photonic nanowires,” Optics Express, 16(2), 1300-1320 (2008).
223. D. K. Gayen, J. N. Roy, “All-optical arithmetic unit with the help of terahertz-
optical asymmetric-demultiplexer-based tree architecture,” Applied Optics,
47(7), 933-943 (2008).
224. I. Fushman, D. Englund, A. Faraon, N. Stoltz, P. Petroff, J. Vuckovic,
“Controlled phase shifts with a single quantum dot,” Science, 320(5877), 769-
772 (2008).
~ 161 ~
225. K. RoyChowdhury, A. Sinha, S. Mukhopadhyay, “An all-optical comparison
scheme between two multi-bit data with optical nonlinear material,” Chinese
Optics Letters, 6(9), 1-4 (2008).
226. A. Babinski, J. Borysiuk, S. Kret, M. Czyz, A. Golnik, S. Raymond, Z. R.
Wasilewski, “Natural quantum dots in the InAs/ GaAs wetting layer,” Applied
Physics Letters, 92, 171104 (2008).
227. I. B. Akca, A. Dana, A. Aydinli, M. Rossetti, L. Li, A. Fiore, N. Dagli, “Electo-
optic and electro-absorption characterization of InAs quantum dot waveguides,”
Optics Express, 16(5), 3439-3444 (2008).
228. A. K. Ghosh, A. Basuray, “Trinary flip-flops using Savart plate and spatial light
modulator for optical computation in multivalued logic,” Optoelectronics
Letters, 4(6), 443-446 (2008).
229. K. Roychowdhury, S. Mukhopadhyay, “An all-optical scheme of signed digit
binary addition based on optical nonlinear material,” Optoelectronics Letters,
4(6), 447-451 (2008).
230. P. Kuila, A. Sinha, S. Mukhopadhyay, “An all-optical remote controlled XNOR
logic using soliton pulse,” Optoelectronics Letters, 4(5), 365-368 (2008).
231. P. Ginzburg, A. Hayat, V. Vishnyakov, M. Orenstein, “Photonic logic by linear
unidirectional interference,” Optics Express, 17(6), 4251-4256 (2009).
232. J. Dong, X. Zhang, D. Huang, “A proposal for two-input arbitrary Boolean logic
gates using single semiconductor optical amplifier by picoseconds pulse
injection,” Optics Express, 17(10), 7725-7730 (2009).
233. P. Andalib, N. Granpayeh, “All-optical ultracompact photonic crystal AND gate
based on nonlinear ring resonators,” Journal of the Optical Society of America
B, 26(1), 10-16 (2009).
234. J. Wang, Q. Sun, J. Sun, “Ultrafast all-optical logic AND gate for CSRZ signals
using periodically poled lithium niobate,” Journal of the Optical Society of
America B, 26(5), 951-958 (2009).
235. B. M. Isfahani, T. A. Tameh, N. Granpayeh, A. R. M. Javan, “All-optical NOR
gate based on nonlinear photonic crystal microring resonators,” JOSA B, 26(5),
1097-1102 (2009).
~ 162 ~
236. T. Chattopadhyay, J. N. Roy, “All-optical conversion scheme: binary to
quaternary and quaternary to binary number,” Optics & Laser Technology,
41(3), 289-294 (2009).
237. A. S. Clark, J. Fulconis, J. G. Rarity, W. J. Wadsworth, J. L. O‟Brien, “All-
optical fiber polarization based quantum logic gate,” Physical Review A, 79,
030303(R) (2009).
238. F. A. Bovino, M. C. Larciprete, M. Giardina, A. Belardini, M. Centini, C.
Sibilia, M. Bertolotti, A. Passaseo, V. Tasco, “Optical polarization based logic
function (XOR or XNOR) with nonlinear gallium nitride nanoslab,” Optics
Express, 17(22), 19337-19344 (2009).
239. D. K. Gayen, R. K. Pal, J. N. Roy, “All-optical adder/ subtractor based on
terahertz optical asymmetric demultiplexer,” Chinese Optics Letters, 7(6), 530-
533 (2009).
240. M. Khorasaninejad, S. S. Saini, “All-optical logic gates using nonlinear effects
in silicon-on-insulator waveguides,” Applied Optics, 48(25), F31-F36 (2009).
241. B. S. Ham, J. Hahn, “Observations of ultraslow light-based photon logic gates:
NAND/ OR,” Applied Physics Letters, 94(10), 101110-101110-3 (2009).
242. M. Suzuki, H. Uenohara, “Investigation of all-optical error detection circuit
using SOA-MZI-based XOR gates at 10 Gbit/s,” Electronics Letters, 45(4), 224-
225 (2009).
243. B. Li, D. Lu, M. I, Memon, G. Mezosi, Z. Wang, M. Sorel, S. Yu, “All-optical
digital logic AND and XOR gates using four-wave-mixing in monolithically
integrated semiconductor ring lasers,” Electronics Letters, 45(13), 698-700
(2009).
244. B. Chakraborty, S. Mukhopadhyay, “Alternative approach of conducting phase-
modulated all-optical logic gates,” Optical Engineering, 48(3), 035201 (2009).
245. A. Bogoni, X. Wu, I. Fazal, A. E. Willner, “160 Gb/s time-domain channel
extraction/insertion and all-optical logic operations exploiting a single PPLN
waveguide,” Journal of Lightwave Technology, 27(19), 4221-4227 (2009).
246. J. Xu, X. Zhang, Y. Zhang, J. Dong, D. Liu, D. Huang, “Reconfigurable all-
optical logic gates for multi-input differential phase-shift keying signals: design
and experiments,” Journal of Lightwave Technology, 27(23), 5268-5275 (2009).
~ 163 ~
247. J. N. Roy, “Mach-Zehnder interferometer-based tree architecture for all-optical
logic and arithmetic operations,” Optik – International Journal for Light and
Electron Optics, 120(7), 318-324 (2009).
248. M. Nazarathy, Z. Zalevsky, A. Rudnitsky, B. Larom, A. Nevet, M. Orenstein, B.
Fischer, “All-optical linear reconfigurable logic with nonlinear phase erasure,”
Journal of Optical Society of America A, 26(8), A21-A39 (2009).
249. J. Wang, Q. Sun, J. Sun, X. Zhang, “Experimental demonstration on 40 Gbit/s
all-optical multicasting logic XOR gate for NRZ-DPSK signals using four-wave
mixing in highly nonlinear fiber,” Optics Communications, 282(13), 2615-2619
(2009).
250. J. Hwang, M. Pototschning, R. Lettow, G. Zumofen, A. Renn, S. Gotzinger, V.
Sandoghdar, “A single-molecule optical transistor,” Nature, 460, 76-80 (2009).
251. D. Miller, “Device requirements for optical interconnects to silicon chips,”
Proceedings of the IEEE, 97(7), 1166-1185 (2009).
252. S. Medhekar, P. P. Paltani, “All-optical passive transistor using counter-
propagating beams in a nonlinear Mach-Zehnder interferometer,” Fiber and
Integrated Optics, 28(4), 268-274 (2009).
253. J. Zhang, H. Xu, “Optical computation based on nonlinear total reflectional
optical switch at the interface,” Pramana, 72(3), 547-554 (2009).
254. H. J. Caulfield, S. Dolev, “Why future supercomputing requires optics,” Nature
Photonics, 4, 261-263 (2010).
255. A. Rostami, H. Nejad, R. M. Qartavol, H. R. Saghai, “Tb/s optical logic gates
based on quantum-dot semiconductor optical amplifiers,” IEEE Journal of
Quantum Electronics, 46(3), 354-360 (2010).
256. M. Belotti, M. Galli, D. Gerace, L. C. Andreani, G. Guizzetti, A. R. M. Zain, N.
P. Johnson, M. Sorel, R. M. D. L. Rue, “All-optical switching in silicon-on-
insulator photonic wire nano-cavities,” Optics Express, 18(2), 1450-1461
(2010).
257. S. Ma, Z. Chen, H. Sun, N. K. Dutta, “High speed all optical logic gates based
on quantum dot semiconductor optical amplifiers,” Optics Express, 18(7), 6417-
6422 (2010).
258. A. Bogoni, X. Wu, Z. Bakhtiari, S. Nuccio, A. E. Willner, “640 Gbit/s photonic
logic gates,” Optics Letters, 35(23), 3955-3957 (2010).
~ 164 ~
259. S. K. Garai, S. Mukhopadhyay, “A method of optical implementation of
frequency encoded different logic operations using second harmonic and
difference frequency generation techniques in nonlinear material,” Optik –
International Journal for Light and Electron Optics, 121(8), 715-721 (2010).
260. D. A. B. Miller, “Are optical transistors the logical next step?” Nature
Photonics, 4, 3-5 (2010).
261. L. Zhang, R. Ji, L. Jia, L. Yang, P. Zhou, Y. Tian, P. Chen, Y. Lu, Z. Jiang, Y.
Liu, Q. Fang, M. Yu, “Demonstration of directed XOR/XNOR logic gates using
two cascaded microring resonators,” Optics Letters, 35(10), 1620-1622 (2010).
262. J. Wang, J. Sun, “All-optical logic XOR gate for high-speed CSRZ-DPSK
signals based on cSFG/DFG in PPLN waveguide,” Electronics Letters, 46(4),
288-290 (2010).
263. S. Zeng, Y. Zhang, B. Li, E. Y. B. Pun, “Ultrasmall optical logic gates based on
silicon periodic dielectric waveguides,” Photonics and Nanostructures -
Fundamentals and Applications, 8(1), 32-37 (2010).
264. C. Taraphdar, T. Chattopadhyay, J. N. Roy, “Mach – Zehnder interferometer-
based all-optical reversible logic gate,” Optics & Laser Technology, 42(2), 249-
259 (2010).
265. A. Villafranca, I. Garces, M. Cabezon, J. J. Martinez, D. Izquierdo, J. Pozo,
“Multiple-bit all-optical logic based on cross-gain modulation in a
semiconductor optical amplifier,” 12th
International Conference on Transparent
Optical Networks (ICTON), Munich, June 27 –July 1, 1-4, 2010.
266. S. Dutta, S. Mukhopadhyay, “An all optical approach of frequency encoded
NOT based Latch using semiconductor optical amplifier,” Journal of Optics,
39(1), 39-45 (2010).
267. Y. Liu, F. Qin, Z. M. Meng, F. Zhou, Q. H. Mao, Z. Y. Li, “All-optical logic
gates based on two-dimensional low-refractive index nonlinear photonic crystal
slabs,” Optics Express, 19(3), 1945-1953 (2011).
268. M. P. Fok, P. R. Prucnal, “All-optical XOR gate with optical feedback using
highly Ge-doped nonlinear fiber and a terahertz optical asymmetric
demultiplexer,” Applied Optics, 50(2), 237-241 (2011).
~ 165 ~
269. Q. Xu, R. Soref, “Reconfigurable optical directed-logic circuits using
microresonator-based optical switches,” Optics Express, 19(6), 5244-5259
(2011).
270. L. Zhang, R. Ji, Y. Tian, L. Yang, P. Zhou, Y. Lu, W. Zhu, Y. Liu, L. Jia, Q.
Fang, M. Yu, “Simultaneous implementation of XOR and XNOR operations
using a directed logic circuit based on two microring resonators,” Optics
Express, 19(7), 6524-6540 (2011).
271. S. Dutta, S. Mukhopadhyay, “Alternating approach of implementing frequency
encoded all-optical logic gates and flip-flop using semiconductor optical
amplifier,” Optik – International Journal for Light and Electron Optics,
122(12), 1088-1094 (2011).
272. X. Chen, Y. Yu, X. Zhang, “All-optical logic minterms for three-input
demodulated differential phase-shift keying signals at 40 Gb/s,” IEEE Photonics
Technology Letters, 23(2), 118-120 (2011).
273. B. Nakarmi, M. Rakib-Uddin, T. Q. Hoai, Y. H. Won, “Demonstration of all-
optical NAND gate using single-mode Fabry-Perot laser diode,” IEEE
Photonics Technology Letters, 23(4), 236-238 (2011).
274. J. Ma, M. L. Povinelli, “Mechanical Kerr nonlinearities due to bipolar optical
forces between deformable silicon waveguides,” Optics Express, 19(11), 10102-
10110 (2011).
275. B. Nakarmi, M. Rakib-Uddin, Y. H. Won, “Realization of all-optical multi-logic
functions and a digital adder with input beam power management for multi-
input injection locking in a single-mode Fabry-Perot laser diode,” Optics
Express, 19(15), 14121-14129 (2011).
276. B. Nakarmi, M. Rakib-Uddin, Y. H. Won, “All-optical exclusive-NOR and
exclusive-OR logic gate based on multi-input injection locking in single mode
Fabry-Perot laser diode,” Optical Engineering, 50(7), 075201 (2011).
277. A. Bogoni, L. Poti, A. E. Willner, P. Ghelfi, C. Porzi, M. Scaffardi, G. Meloni,
G. Berrettini, F. Fresi, E. Lazzeri, X. Wu, “Optical logic elementary circuits,”
IET Circuits, Devices & Systems, 5(2), 76-83 (2011).
278. N. Mitra, S. Mukhopadhyay, “A method of developing all-optical mono-stable
multivibrator system exploiting the Kerr nonlinearity of medium,” Optik –
International Journal for Light and Electron Optics, 122(2), 92-94 (2011).
~ 166 ~
279. P. Phongsanam, S. Mitatha, C. Teeka, P. P. Yupapin, “All optical half
adder/subtractor using dark-bright soliton conversion control,” Microwave and
Optical Technology Letters, 53(7), 1541-1544 (2011).
280. B. Ghosh, R. R. Pal, S. Mukhopadhyay, “A new approach to all-optical half-
adder by utilizing semiconductor optical amplifier based MZI wavelength
converter,” Optik - International Journal for Light and Electron Optics,
122(20), 1804-1807 (2011).
281. T. D. Vo, R. Pant, M. D. Pelusi, J. Schroder, D. Y. Choi, S. K. Debbarma, S. J.
Madden, B. L. Davies, B. J. Eggleton, “Photonic chip-based all-optical XOR
gate for 40 and 160 Gbit/s DPSK signals,” Optics Letters, 36(5), 710-712
(2011).
282. Y. Zhang, Y. Chen, X. Chen, “Polarization-based all-optical logic controlled
NOT, XOR and XNOR gates employing electro-optic effect in periodically
poled lithium niobate,” Applied Physics Letters, 99(16), 161117-161117-3
(2011).
283. S. K. Pal, S. Mukhopadhyay, “Analytical approach of using the squeezed state
formation of light for conducting all-optical noise free XOR and NOT logic
operation,” Optik – International Journal for Light and Electron Optics, 122(5),
411-414 (2011).
284. A. Bahrami, A. Rostami, F. Nazari, “MZ-MMI-based all-optical switch using
nonlinear coupled waveguides,” Optik – International Journal for Light and
Electron Optics, 122(20), 1787-1790 (2011).
285. X. Ma, S. John, “Quantum-dot all-optical logic in a structured vacuum,”
Physical Review A, 84(1), 013830 (2011).
286. D. K. Gayen, A. Bhattacharyya, C. Taraphdar, R. K. Pal, J. N. Roy, “All-optical
binary-coded decimal adder with a terahertz optical asymmetric demultiplexer,”
Computing in Science & Engineering, 13(1), 50-57 (2011).
287. A. Srivastava, S. Medhekar, “Switching of one beam by another in a Kerr type
nonlinear Mach-Zehnder interferometer,” Optics & Laser Technology, 43(1),
29-35 (2011).
288. I. S. Maksymov, “Optical switching and logic gates with hybrid plasmonic-
photonic crystal nanobeam cavities,” Physics Letters A, 375(5), 918-921 (2011).
~ 167 ~
289. A. Rudnitsky, A. Shahmoon, M. Nathan, M. Nazarathy, B. Larom, J. Jasieniak,
A. Martucci, L. Businaro, A. Gerardino, Z. Zalevsky, “All-optical integrated
micro logic gate,” Microelectronics Journal, 42(2), 472-476 (2011).
290. C. J. Wu, C. P. Liu, Z. Ouyang, “Compact and low-power optical logic NOT
gate based on photonic crystal waveguides without optical amplifiers and
nonlinear materials,” Applied Optics, 51(5), 680-685 (2012).
291. M. Sahafi, A. Rostami, A. Sahafi, “All-optical high speed logic gates using
SOA,” Optics Communications, 285(9), 2289-2292 (2012).
292. J. F. Tao, J. Wu, H. Cai, Q. X. Zhang, J. M. Tsai, J. T. Lin, A. Q. Liu, “A
nanomachined optical logic gate driven by gradient optical force,” Applied
Physics Letters, 100(11), 113104 (2012).
293. J. Han, B. Yao, P. Gao, L. Chen, M. Huang, “All-optical logic gates based on
photoinduced anisotropy of bacteriorhodopsin film,” Journal of Modern Optics,
59(7), 636-642 (2012).
294. Y. Tian, L. Yang, L. Zhang, R. Ji, J. Ding, P. Zhou, W. Zhu, Y. Lu, “Directed
optical half-adder based on two cascaded microring resonators,” IEEE
Photonics Technology Letters, 24(8), 643-645 (2012).
295. S. Lin, Y. Ishikawa, K. Wada, “Demonstration of optical computing logics
based on binary decision diagram,” Optics Express, 20(2), 1378-1384 (2012).
296. J. Wang, S. R. Nuccio, J. Y. Yang, X. Wu, A. Bagoni, A. E. Willner, “High-
speed addition/subtraction/ complement/ doubling of quaternary numbers using
optical nonlinearities and DQPSK signals,” Optics Letters, 37(7), 1139-1141
(2012).
297. M. Morris Mano, “Digital design,” Prentice Hall India, 3rd
edition.
298. A. P. Malvino, D. P. Leach, “Digital principles and applications”, Tata
McGraw-Hill Edition (New Delhi), 4th
edition, 14th
reprint, (1998).
299. M. A. Karim, A. A. S. Awwal, “Optical computing: an introduction”, John
Wiley & Sons, Inc., (2003).
300. R. Arrathooon, “Optical computing”, Marcel Dekker Inc., (1989).
301. S. Mukhopadhyay, “Optical computation and parallel processing” Classique
Books (9, Radhanath Mallick Lane, Kolkata 700012, India), (2000).
~ 168 ~
302. P. Ghosh, S. Mukhopadhyay, “Some digital approaches in optical computation,”
Premier Books (32/3 Old Ballygunge First Lane, Kolkata -19, India), (2004).
303. A. N. Matveev, “Optics,” Mir Publishers, Moscow, 427- 428 (1988).
304. M. J. Connelly, “Semiconductor optical amplifiers,” Kluwer Academic
Publishers, (2004).
305. J. N. Roy, A. K. Maity, D. Samanta, S. Mukhopadhyay, “Tree-net architecture
for integrated all-optical arithmetic operations and data comparison scheme with
optical nonlinear material,” Optical Switching and Networking, 4, 231-
237(2007).
306. D. Samanta, S. Mukhopadhyay, “A new scheme of implementing all-optical
logic systems exploiting material nonlinearity and polarization based encoding
technique,” Optoelectronics Letters, 4(3), 172-176 (2008).
307. D. Samanta, S. Mukhopadhyay, “All-optical method for maintaining a fixed
intensity level of a light signal in optical computation” Optics Communications,
281(19), 4851-4853(2008).
308. A. Ghatak, K. Thyagarajan, “Optical electronics,” Cambridge University Press,
Cambridge, 461-477 (2002).
309. M. C. Gupta, J. Ballato, “The handbook of photonics,” CRC Press, 2nd
edition.
310. D. Samanta, S. Mukhopadhyay, “A method of generating single optical pulse in
nanosecond range with the joint uses of electro-optic modulator and nonlinear
material” Optik - International Journal for Light and Electron Optics, 121,
1129-1132 (2010).
~ 169 ~
List of My Publications and Presentations
Journal papers-
1. Jitendra Nath Roy, Anup Kumar Maity, Debajyoti Samanta and Sourangshu
Mukhopadhyay, “Tree-net architecture for integrated all-optical arithmetic
operations and data comparison scheme with optical nonlinear material,”
Optical Switching and Networking, 4, 231-237(2007).
doi:10.1016/j.osn.2007.08.003
2. Debajyoti Samanta, Sourangshu Mukhopadhyay, “A method of maintaining
the intensity level of a polarization encoded light signal,” Journal of Physical
Sciences (VU), 11, 87-91(2007).
3. Debajyoti Samanta, Sourangshu Mukhopadhyay, “A new scheme of
implementing all-optical logic systems exploiting material nonlinearity and
polarization based encoding technique,” Optoelectronics Letters, 4(3), 172-176
(May 2008). doi:10.1007/s11801-008-8018-2
4. Debajyoti Samanta, Sourangshu Mukhopadhyay, “All-optical method for
maintaining a fixed intensity level of a light signal in optical computation”
Optics Communications, 281(19), 4851-4853(2008).
doi:10.1016/j.optcom.2008.06.033
5. Sisir Kumar Garai, Debajyoti Samanta, Sourangshu Mukhopadhyay, “All-
optical implementation of inversion logic operation by second harmonic
generation and wave mixing character of some non-linear material,” Optics &
Optoelectronic Technology, 6(4), 39-42(August, 2008).
6. Debajyoti Samanta, Sourangshu Mukhopadhyay, “Implementation of an
optical S-R flip-flop with polarization encoded light signal”, Optoelectronics
Letters, 5(1), 57-60(1 January, 2009). doi:10.1007/s11801-009-8136-5
7. Debajyoti Samanta, Sourangshu Mukhopadhyay, “A method of generating
single optical pulse in nanosecond range with the joint uses of electro-optic
~ 170 ~
modulator and nonlinear material” Optik - International Journal for Light and
Electron Optics, 121, 1129-1132 (2010). doi: 10.1016/j.ijleo.2008.12.025.
8. Nandita Mitra, Debajyoti Samanta, Sourangshu Mukhopadhyay, “An all-
optical architecture of serial to parallel converter by using Kerr type of non-
linear material,” Journal of Optics, 39, 115-121 (2010). doi: 10.1007/s12596-
010-0010-0.
9. Debajyoti Samanta, Sourangshu Mukhopadhyay, “All-optical method of
developing parity generator and checker with polarization encoded light signal,”
accepted for publication in Journal of Optics.
Conference papers -
1. Debajyoti Samanta, Sourangshu Mukhopadhyay, “A photonic astable
multivibrator with the joint accommodation of LiNbO3 based modulator and
isotropic nonlinear material,” Short term course cum workshop on Physics and
Technology of All Optical Communication Components and Devices,
Department of Physics and Meteorology, IIT, Kharagpur, India, 11th
-16th
October, 2007. FULL paper was published in the proceedings.
2. Debajyoti Samanta, Sourangshu Mukhopadhyay, “All optical method of
implementing integrated logic and arithmetic processor(ILAP) using nonlinear
material,” XXXIII OSI Symposium on Optics and Optoelectronics, Department
of Electronics & Communication Engineering, Tezpur University, Napaam,
Assam-784028, India, 18th
-20th
December, 2007. FULL paper was published
in the proceedings „Contemporary Optics and Optoelectronics‟, Tata
McGraw-Hill Publishing Company Limited, page 118-120.
3. Debajyoti Samanta, Sourangshu Mukhopadhyay, “Optical S-R flip-flop
using polarization encoded light signal, half-wave plate and nonlinear
material,” 15th
West Bengal State Science & Technology Congress, Bengal
Engineering & Science University, Shibpur, Howrah, West Bengal, India, 28th
-29th
February, 2008.
4. Debajyoti Samanta, Sourangshu Mukhopadhyay, “A new scheme to
maintain a fixed intensity level of a polarization encoded light signal,”
National Workshop on Radiation Science and Applications, organized by
~ 171 ~
UGC-DAE Consortium for Scientific Research, Kolkata centre and
Department of Physics, The University of Burdwan, held at Science Centre,
Golapbag, Bardhaman, India, 10th
-12th
November, 2008.
5. Debajyoti Samanta, Sourangshu Mukhopadhyay, “An all optical method for
implementing polarization encoded binary half and full subtractors with the
use of nonlinear material,” 16th
West Bengal State Science & Technology
Congress, The University of Burdwan, India, 28th
February -1st March, 2009.
6. Debajyoti Samanta, Sourangshu Mukhopadhyay, “All optical M-S J-K flip-
flop using polarization encoded light signal,” International Conference on
Optics & Photonics (ICOP-2009), XXXIV Symposium of the Optical Society of
India, Central Scientific Instruments Organisation (CSIO), Sector -30 C,
Chandigarh, India, October 30 – November 1, 2009. FULL paper was
published in the proceedings.
7. Debajyoti Samanta, Sourangshu Mukhopadhyay, “Method of developing a
polarization encoded optical multiplexer,” International Conference on
Radiation Physics and its Applications (ICRPA 2010), organized by
Department of Physics, The University of Burdwan; held at Science Centre,
Golapbag, Bardhaman, India, 16, 17 January, 2010.
8. Debajyoti Samanta, Sourangshu Mukhopadhyay, “An all-optical method for
obtaining polarization encoded data bit from intensity encoded data bit and
vice versa,” 7th
International Conference on Optics-photonics Design &
Fabrication (ODF’10 Yokohama), held at Pacifico Yokohama, Yokohama,
Japan, April 19-21, 2010.
9. Debajyoti Samanta, Sourangshu Mukhopadhyay, “All-optical method of
developing parity generator and checker with polarization encoded light
signal,” XXXV Optical Society of India Symposium and International
Conference on Contemporary Trends in Optics and Optoelectronics, jointly
organized by Indian Institute of Space Science and Technology and OSI, held
at ATF Campus, Veli, Thiruvananthapuram, Kerala, India, January 17-19,
2011. Paper was published in the proceedings.
