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Dr. BC Choudhary, Professor
National Institute of Technical Teachers’ Training & Research (NITTTR), Sector-26, Chandigarh
Fiber Optics Technology
An Overview
LECTURE CONTENTS
What is Fiber Optic Technology?
Why Optical Transmission and Optical
Fibers?
OFC Systems & Potential
Fiber Optic Sensor Technology
Special Class of Optical Fibers.
* * *
Fiber Optics Technology - 1980s
Fiber Optics Technology uses light as the primary medium to carry information.
Light often is guided through optical fibers.
Most applications use invisible light (infrared) LEDs or LDs.
Also called Lightwave Technology
NEAR ZERO LOSS & INFINITE BANDWIDTH
Invention of LASER (1960) and low loss Optical Fiber
Waveguides (1970) An edge toward making the dream of
carrying huge amount of information, a reality.
Lightwave Technology: Application Areas
Majority Applications:
– Telephone Networks
– Data Communication Systems
– Cable TV distribution
Niche Applications:
– Optical Sensors
– Medical Equipment
Telecommunication
Developments & Issues
Communication – Exchange of information
Telecommunication – Exchange of information over
a distance – using some type of equipment
• Generally three basic types of information to be exchanged
Voice, Video and Data – Analog or Digital ?
Information is often carried by an EM carrier - frequency
varying from few MHz to several hundred THz.
1896 2016
Transmitter
Receiver
Link Information Information
Transmission
medium
Telecom Systems of 1970s
Transmission Medium
• Twisted pair
• Coaxial cable
• Radio and Microwave
• Satellite
Signal Type • Analog—continuous
• Digital-- discrete
• High Attenuation 20 dB/km
• Limited Bandwidth KHz to MHz
Attenuation and BW
limitations
Why Fiber Optic Communication?
• A phenomenal increase in voice, data
and video communication - demands for
larger capacity and more economical
communication systems.
• Lightwave Technology: Technological
route for achieving this goal
Most cost-effective way to move huge amounts of information (voice, video, data) quickly and reliably.
During past three decades, remarkable and dramatic changes
took place in the electronic communication industry.
Why Optical Transmission ? Capacity ! Capacity ! and More Capacity !
A technical revolution in Electronic Communication Industry to
explore for large capacity, high quality and economical systems
for communication at Global level.
Radio-waves and Trrestrial Microwave systems have long
since reached their capacity
Satellite Communication Systems can provide, at best, only a
temporary relief to the ever-increasing demand.
extremely high initial cost of launching
The geometry of suitable orbits,
available microwave frequency allocations and
if needed repair is nearly impossible
Next option: OPTICAL COMMUNICATION SYSTEMS !
The Electromagnetic Spectrum
Optical Region THz range
Potential of Optical Transmission ?
Information carrying capacity of a communications system is
directly proportional to its bandwidth;
Wider the bandwidth, the greater its information carrying capacity.
• Theoretically; BW is 10% of the carrier frequency
Communication System with light as the carrier of information A great deal of attention.
Signal Carrier Bandwidth
VHF Radio system; 100 MHz. 10 MHz
Microwave system; 6 GHz 0.6 GHz.
Lightwave system; 106 GHz 105 GHz.
A system with light as carriers has an excessive bandwidth (more than 100,000 times than achieved with microwave frequencies)
Meet the today’s communication needs or that of the foreseeable future
C= BWlog2(1+SNR);
Shanon-Hartley theorem
Major Difficulties
Transmission of light wave for any useful distance through the earth’s
atmosphere is impractical because of attenuation and absorption of ultra
high light frequencies by water vapors, oxygen and air particulate.
Consequently, the only practical type of optical communication
system that uses a fiber guide.
What is an optical fiber ?
A strand of glass or plastic material
with special optical properties, which
enable light to travel a large distance
down its length.
Powerful & Intense Optical Sources
Invention of LASER (1960) and low loss Optical Fiber Wave
guides (1970) – An edge toward making the dream of carrying
huge amount of information, a reality.
Fiber Optic Timeline 1930: Scanning & transmitting television images through uncoated fiber cables.
1951: Light transmission through bundles of fibers- flexible fibrescope used in medical field.
1957 : First fiber-optic endoscope tested on a patient.
1960 : Invention of Laser (development, T Maiman)
1966: Charles Kao; proposed cladded fiber optic cables with lower losses as a communication medium.
1970: (Corning Glass, NY) developed fibers with losses below 20 dB/km.
1972: Semiconductor Injection laser diodes (room temp.) were developed
1977: GT&E in Los Angeles and AT&T in Chicago sends live telephone signals through fiber optics (850nm, 4dB/km, MMF, 9km) World’s first FO link
1980s: 2nd generation systems; 1300nm, SM, 0.5 dB/km, O-E-O
3rd generation systems; 1550nm, SM, 0.2 dB/km, EDFA, 5Gb/s
1993 : Bell Labs sends 10 Billion bits/s through 20,000 km of fibers using a WDM systems and Soliton pulses.
1996 : NTT, Bell Labs and Fujitsu able to send one Trillion bits per second through single optical fiber.
2000s : Towards achieving, Tb/s, Pb/s of data, All Optical Networks
The Nobel Prize in Physics 2009
Charles K. Kao
(b. 1933 Shanghai, China)
1/2 of the prize
Standard Telecommunication Laboratories,
Harlow, UK;
Chinese University of Hong Kong,
Hong Kong, China
"For ground breaking achievements
concerning the transmission of light in
fibers for optical communication"
"For the invention of an imaging
semiconductor circuit – the CCD
sensor"
Willard S. Boyle George E. Smith
b. 1924 b. 1930
1/4 of the prize 1/4 of the prize
Bell Laboratories, Murray Hill, NJ, USA
Kao’s Experiment (1966)
Dr. Narinder S Kapany Born in Moga (Punjab) in October 1926
Basic Fiber Optic Link
TRANSMITTER
DRIVER LIGHT
SOURCE
• Converts Electrical signal to light
• Driver modifies the information into
a suitable form for conversion into
light (Modulation)
• Source is LED or ILDs whose output
is modulated.
OPTICAL FIBER
MEDIUM FOR CARRYING LIGHT
DETECTOR
RECIEVER
• Detector accepts light, converts
it back to electrical signal.
• Detector is PIN diode or APD
• Elect. Signal is demodulated to
separate out the information
Fiber-Optic System Devices
• Transmitter (Laser diode or LED).
• Fiber-Optic Cable (MMF, SMF)
• Receiver (PIN diode or APDs).
Backbone of an OFC System : OPTICAL FIBER
acts as transmission channel for carrying light beam
loaded with information
Transmit data as light pulses (first converting electronic signals
to light pulses then finally
converting back to electronic
signals)
Optical Fiber as Transmission Medium
Light propagate by means of Total Internal Reflection (TIR)
Structure of Optical Fiber
A dielectric core (doped silica) of high refractive index
surrounded by a lower refractive index cladding (SCS, PCS).
Basic Structure of a Step-Index Optical Fiber
• Single mode: 5-10 m
• Multimode: 50/62.5 m
NECESSARY CONDITION FOR TIR: n1 > n2
Step Index Profile
Graded Index Profile
• 1970, First Optical
Fiber: Loss 20 dB/km
at 633nm
• 1977, losses reduced to
5dB/km at 850nm
• 1980s, Loss reduced to
0.2 dB/km at 1550 nm
Transmission Loss in Optical Glass
Dramatic reduction in transmission loss in optical glass
Highly pure; Transmitting light through 3 mile thick slab of glass
ATTENUATION (Power loss)
Attenuation is signal loss over distance. The light pulses loose
their energy and amplitude falls as they travel down the cable.
Puts distance limitation on long- haul networks.
Two Major Communication Issues
DISPERSION (Pulse broadening)
Dispersion is the broadening of pulse as it travels down.
• Intermodal (Modal) dispersion
• Intramodal (Chromatic) dispersion
Puts data rate limitation on networks
Fiber Attenuation
Attenuation in Silica Optical Fibers
0.5 dB/km at 1310 nm
0.2 dB/km at 1550 nm
Limit SNR / distance
Fiber Dispersion
Dispersion is
minimum in SMFs
Limit Data Rate
Wavelengths of Operation
Attenuation in Silica Fibers
900 1100 1300 1500 1700
0.5
1.0
1.5
2.0
2.5
Att
en
ua
tio
n (
dB
/km
)
Wavelength (nm)
“ Optical
Windows”2 3
1
850 nm 1310 nm 1550 nm
Both 1310 and
1550 nm are
active windows
Communication Channel Capacity
Communication
Medium
Carrier
Frequency
Bandwidth 2 way voice
Channels
Copper Cable
Coaxial Cable
Optical Fiber
Cables
1 MHz
100 MHz
100 –1000 THz
100 kHz
10 MHz
40 THz
< 2000
13,000
>3,00,000 or
90,000 Video
signals
Attenuation in silica OFC 0.2dB/km at 1550nm
Pulse Broadening 16 ps/km at 1550 nm
Practical Optical Fiber Cable
OPTICAL SOURCES
LEDs (GaAs, GaAlAs) • 850 nm, 1310 nm
• Low cost easy to use
• Used for multimode fibers
• Special “edge-emitting “ LEDs for SMFs
Laser Diodes (InGaAsP, InGaAsSb)
• 850nm, 1310nm, 1550nm
• Very high power output
• Very high speed operation
• Specialized power supply & circuitry
• Very expensive
OPTICAL DETECTORS
PIN Diodes (Si, Ge, InGaAs) • 850nm, 1310nm, 1550 nm
• Low cost
APDs (Avalanche Photodiodes, GaAlAs)
• 850nm, 1310nm, 1550 nm
• High sensitivity- operate at very low
power levels
• Expensive
Advantages of Optical Fiber
Wide Bandwidth: Extremely high information carrying
capacity (~GHz)
3,00,000 voice channels on a pair of fiber
Voice/Data/Video Integrated Service
2.5 Gb/s systems from NTT, Japan; 5 Gb/s System, Siemens
Low loss : Information can be sent over a large distance. Losses ~ 0.2 dB/km
Repeater spacing >100 km with bit rates in Gb/s
Interference Free Immune to Electromagnetic interference: No cross talk between fibers
Can be used in harsh or noisy environments
Higher security : No radiations, Difficult to tap signal Attractive for Defense, Intelligence and Banks Networks
Advantages of Optical Fiber: Contd..
Compact & light weight
Smaller size : Fiber thinner than human hair
Can easily replace 1000 pair copper cable of 10 cm dia.
Fiber weighs 28gm/km; considerably lighter than copper
Light weight cable
Environmemtal Immunity/Greater safety
Dielectric- No current, No short circuits – Extremely safe for hazardous environments; attractive for oil & petrochemicals
Not prone to lightning
Wide temperature range
Long life > 25 years
Abundant Raw Material: Optical fibers made from Silica (Sand)
Not a scarce resource in comparison to copper.
Some Practical Disadvantages
Optical fibers are relatively expensive.
Connectors very expensive: Due to high degree of precision involved
Connector installation is time consuming and highly skilled operation
Jointing (Splicing) of fibers requires expensive equipment and skilled operators
Connector and joints are relatively lossy.
Difficult to tap in and out (for bus architectures) - need expensive couplers
Relatively careful handling required
OFC- Systems
Installed Systems: operating at 1310 nm
• Low loss; minimum pulse broadening
• Transmission rate 2-10 Gb/s
• Regeneration of Signal after every 30-60 km
Conversion of O-E-O signal
Current OFC Systems: 1550nm wavelength band
• Silica has lowest loss, increased dispersion
Design of Dispersion Shifted Fibers
Lowest loss and Negligible dispersion
Signal amplification after 80-100 km
Direct amplification of signal in optical domain
Erbium Doped Fiber Amplifier (EDFA)
EDFA : Fiber Amplifier
Erbium Doped Fiber Amplifier
Direct amplification of optical signal
Flat gain around 1550nm low loss window
BW 12,500 GHz ; Enormous potential
Increasing Network Capacity Options
Faster Electronics
(TDM)
Higher bit rate, same fiber
Electronics more expensive
More Fibers
(SDM)
Same bit rate, more fibers
Slow Time to Market
Expensive Engineering
Limited Rights of Way
Duct Exhaust
W
D
M
Same fiber & bit rate, more ls
Fiber Compatibility
Fiber Capacity Release
Fast Time to Market
Lower Cost of Ownership
Utilizes existing TDM Equipment
WDM/DWDM OFC- Systems
Coincidence of low-loss window & wide-BW EDFA
Possibilities of WDM Communication Systems
Capable of carrying enormous rates of information
Typical WDM network containing various types of optical amplifiers.
Examples: 1.1 Tb/s over 150 km ; 55 wavelengths WDM
2.6 Tb/s over 120 km ; 132 wavelengths WDM
Fiber Optics Communication
Expressway
• CISCO raising the speed limit
• LUCENT adding more lanes
• NORTEL providing faster transport
equipments
Lightwave Communication Systems Employing DWDM,
EDFA and Soliton pulses
“ZERO LOSS & NEAR INFINITE BANDWIDTH “
Provide with a network capable of handling almost
all our information needs.
FORESIGHT…
All-Optical Network
(Terabits Petabits)
TDM DWDM
0
5
10
15
20
25
30
35
40
Ba
nd
wid
th
8l @OC-48
4l @OC-192
4l @OC-48
2l @OC-48
2l @1.2Gb/s
(1310 nm, 1550 nm)
10 Gb/s
2.4 Gb/s 1.2 Gb/s 565 Mb/s
1.8 Gb/s 810 Mb/s 405 Mb/s
Enablers
EDFA + Raman Amplifier
Dense WDM/Filter
High Speed Opto-electronics
Advanced Fiber
1982
1984
1988
1994
1996
1998
2000
2002
1990
1986
1992
16l @OC-192
40 Gb/s
32l @OC-192
176l @OC-192
2004
2006
TDM (Gb/s)
EDFA
EDFA +
Raman Amplifier
80l @ 40Gb/s
Bandwidth Evolutionary Landmarks
• Fiber is deployed at a rate of 2000
miles every hour
Optical
Fiber
Optical Fiber Platform
Bands in Light Spectrum
700 1300 1100 900 1700 nm 1500
Visible Infrared
“E” Band ~ 1370 - 1440 nm
“S” Band ~ 1470 - 1500 nm
“C” Band ~ 1530 - 1565 nm
“L” Band ~ 1570 - 1610 nm
“O” Band ~ 1270-1350 nm
Approximate Attenuation of Single Mode
silica fiber cable
All Wave Optical Fiber
LUCENT
CORNING
OFS
HUAWEI
Photonic Crystal Fibers (PCFs)
Solid core PCF Hollow core PCF
PCFs are optical fibers with a periodic
arrangement of low-index material in a
background with higher refractive index.
The background material is usually undoped
silica & the low index is typically provided by
air-holes running along their entire length.
www.crystal-fiber.com
PCF: around since 1996 (JC Knight et al, OFC (1996) paper PD3
Important facts regarding PCFs
• Photonic crystal fibers have a range of properties that can be
dramatically different from those of conventional fibers.
• Index-guiding PCFs can be endlessly single-mode, highly
nonlinear and/or have a wide range of dispersion properties
• Transparency window: UV to mid-IR region
• Band gap-guiding PCFs can guide light through air or other gases
• Hollow core PCFs have allowed significant advances in chemical
sensing, gas-based non linear optics, high power delivery, pulse
compression…
• PCFs can also be the basis for new generation of practical and
compact gas-based laser sources and fiber devices etc...
Multicore fiber for SDM – Pb/s Transmission
• NTT Japan (2012)
Videos\SDM NTTT Peta bit system of future
Optical Fibres Beyond Telecom
Optical fibres can also have applications in:
Fiber Optic Sensing
Medicine – Light guidance
Biological and genetics research
Defence/Guidance
Industrial materials processing
Next generation lasers
Optical data processing
Transmitting light beyond the near-IR
Fiber Optic Sensors
An offshoot of fiber optic communication research
Realization of high sensitivity of optical fibers to external
perturbations (phase modulation, micro bending loss in cabling,
modal noise etc) and its exploitation for development of sensors.
(An Alternate School of Thought, 1975)
High sensitivity of fibers due to long interaction length of light with
the physical variable is the attraction.
FOS: Any device in which variations in the transmitted
power or the rate of transmission of light in optical fiber are
the means of measurement or control to measure physical
parameters such as strain, pressure, temperature, velocity,
and acceleration etc.
FOS: A Boon in Disguise
Light Wave Parameters
1. Amplitude / Intensity
2. Phase
3. Wavelength
4. Polarization
5. Time / Frequency
Variation in any of these
parameters due to external
influence will form the
working principle of the
sensor.
Supporting Technology
Kapron (1970) demonstrated that the attenuation of light in fused silica fiber was low enough that long transmission links were possible
Procedure in Fiber optic sensor systems:
Transmit light from a light source along an optical fiber to a sensor, which sense only the change of a desired environmental parameter.
The sensor modulates the characteristics (intensity, wave length, amplitude, phase) of the light.
The modulated light is transmitted from the sensor to the signal processor and converted into a signal that is processed in the control system.
The properties of light involved in fiber optic sensors: reflection, refraction, interference and grating
Basic Elements of a Fiber Optic Sensor
Light source
Beam conditioning
optics
Transducer
Modulator
Detector
Optical Fiber
Type of Fiber Optic Sensors
Fiber optic sensors can be divided by:
Places where sensing happens
Extrinsic or Hybrid fiber optic sensors
Intrinsic or All-Fiber fiber optic sensors
Characteristics of light modulated by environmental effect
Intensity-based fiber optic sensors
Spectrally-based fiber optic sensors
Interferometeric fiber optic sensors
ADVANTAGES
Immunity to electromagnetic interference (EMI) and radio
frequency interference (RFI)
All-passive dielectric characteristic: elimination of conductive
paths in high-voltage environments
Inherent safety and suitability for extreme vibration and
explosive environments
Tolerant of high temperatures (>1450 oC) and corrosive
environments
Light weight, and small size
High sensitivity
What Does F.O.S. Look Like?
Various Fiber Optic Sensors
GENERAL USES
Measurement of physical properties such as strain, pressure,
displacement, temperature, velocity, and acceleration in
structures of any shape or size
Monitoring the physical health of structures in real time (SHM).
Damage detection
Used in multifunctional structures, in which a combination of
smart materials, actuators and sensors work together to
produce specific action
“Any environmental effect that can be conceived of can be
converted to an optical signal to be interpreted”;
Eric Udd, Fiber Optic Sensors
Monitoring in Structural Engineering
Buildings and Bridges: concrete monitoring during setting, crack (length, propagation speed) monitoring, prestressing monitoring, spatial displacement measurement, neutral axis evolution, long-term deformation (creep and shrinkage) monitoring, concrete-steel interaction, and post-seismic damage evaluation
Tunnels: multipoint optical extensometers, convergence monitoring, shotcrete / prefabricated vaults evaluation, and joints monitoring Damage detection
Dams: foundation monitoring, joint expansion monitoring, spatial displacement measurement, leakage monitoring, and distributed temperature monitoring
Heritage structures: displacement monitoring, crack opening analysis, post-seismic damage evaluation, restoration monitoring, and old-new interaction
General Purpose FOS
Fiber Optic Probe Colorimeter
Optical fibers in Textiles Smart Beds
Fly by Light System-Airframe & Engine
MEDICAL APPLICATIONS
Small, Flexible
Non Toxic
Chemically Inert
Intrinsically Safe
Low Maintenance
Ease of Use
Advantages of Optical Fibers
• Thin/Small size
• Flexible
• Non Toxic
• Chemically Inert
• EM Inert
• No Cross talk
• Wide Bandwidth
• Reliable
• Ease of Use
Image Transmission by Fiber Bundle
Medical Illumination Products
Fibers are Everywhere
Fifty Years of Fiber Optics
First quarter of the 21st century will see a continued growth in
the demand for fiber optic components.
Bibliography:
1. John M. Senior “Optical Fiber Communications: Principles and Practice,
2nd edn., PHI, 2001.
2. Gerd Keiser, “Optical Fiber Communica tion” 3rd edn., Mc Graw Hill ,
2000.
3. www.google.co.in
4. www.youtube/OFC videos
5. www.FO4sale.com
6. Govind P. Agrawal, “Fiber-Optic Communication Systems” John Wiley
& sons (Asia) Pte Ltd , 3rd Edn., 2005.
7. Bishnu P. Pal, “Fundamentals of Fibre Optics in Telecommunication and
Sensor Systems”, New Age International Publishers, 2005.
The excerpts of this lecture are based on the information drawn
from following reference.
Questions?