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Dr. BC Choudhary
Professor & Head
Applied Science Department,
NITTTR, Sector-26, Chandigarh-160019.
COURSE CONTENTS
What Fiber Optic Technology?
Why Fiber Optic Technology?
Need for Optical Transmission ?
Why Optical Fibers?
OFC- Systems : Present & Future ?
* * * * *
Communication 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
Information is often carried by an EM carrier - frequency
varying from few MHz to several hundred THz.
1896 2010s
Transmitter
Receiver
Link Information Information
Transmission
medium
General Communication Link
Information Source: Electrical signal, derived from a massage signal
(sound, video, data)- Analog/digital
Transmitter: Electronic module – convert signal into suitable form for
propagation over the transmission medium- Modulating the carrier.
Transmission Medium: Pair of wires, coaxial cable or radio link through
free space down which signal is transmitted to the receiver - channel.
Receiver: Signal transformed into original electrical signal (demodulation)
before being passed onto the destination.
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
What is Fiber Optic Technology?
Fiber Optic Technology uses light as the primary medium to carry information.
The light often is guided through optical fibers.
Most applications use invisible (infrared) light.
Also called Lightwave Technology
“NEAR ZERO LOSS & NEAR INFINITE
BANDWIDTH”
Optical Fiber Communication System
Transmitter : Electrical signal converted into Optical signal (E/O)
using an optical source (optical modulation).
Transmission Medium: Modulated optical signal transmitted through
optical fibers to the receiver.
Receiver : Optical signal reconverted to the electrical signal (O/E) for
further processing (demodulation) before passing onto destination.
TRANSMITTER
RECIEVER
Why Fiber Optic Technology?
• A phenomenal increase in voice, data
and video communication
demands for larger capacity & more
economical communication systems.
During past three decades, remarkable and dramatic changes in
electronic communication industry.
Most cost-effective way to move huge amounts of information (voice, video, data) quickly and reliably.
Lightwave Technology: Technological route for achieving
this goal
Why Optical Transmission ? Capacity ! Capacity ! and More Capacity !
A technical revolution in 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. But
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
How Optical Transmission fulfill the need?
Information carrying capacity of a communications system is directly proportional to its bandwidth;
C= BWlog2(1+SNR); Shanon-Hartley theorem
Wider the bandwidth, greater its information carrying capacity.
Communication Systems with light as the carrier A great deal of attention
Excessive bandwidth (100,000 times than achieved with microwave
frequencies)
Meets communication needs of present and that of foreseeable future.
Signal Carrier Bandwidth
VHF Radio system; 100 MHz. 10 MHz
Microwave system; 10 GHz 1.0 GHz
Lightwave system; 1015 Hz or 106 GHz 105 GHz
Theoretically; BW is 10% of the carrier frequency
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
90 THz
< 2000
13,000
>3,00,000 or
90,000 Video
signals
Major Difficulties
Transmission of light wave for any useful distance through the earth’s
atmosphere is impractical high 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.
Optical fiber ?
A strand of glass or plastic material
with special optical properties, which
enable light to travel a large distance
down its length.
Invention of LASER (1960) and Optical Fiber Waveguides
(1970) – An edge toward making the dream of carrying huge
amount of information, a reality.
An Intense Light Source
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 diode laser was 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 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
Video – Charles Kao
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
• Source is LED or Laser diode
whose output is modulated.
OPTICAL FIBER
MEDIUM FOR CARRYING LIGHT
DETECTOR
RECIEVER
• Detector accepts light, convert 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 or SMF)
• Receiver (PIN or Avalanche photodiode)
Foundation 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 Cladding of lower refractive index.
Basic Structure of a Step-Index Optical Fiber • Single mode: 5-10 m
• Multimode: 50/62.5 m
NECESSARY CONDITION FOR TIR: n1 > n2
• 1970, First Optical
Fiber: Loss 20 dB/km
at 633nm
• 1980s, Loss reduced to
0.2 dB/km at 1550 nm
Transmission Loss in Optical Glass
Dramatic reduction in transmission loss in
optical glass
Two Major Communication Issues
z=0 z=L Attenuation- signal loss over distance
Attenuation puts distance limitations on long- haul networks.
z=0 z=L
Dispersion- broadening of pulses
Dispersion puts BW / Data rate limitation on networks
Fiber Attenuation
Attenuation in Silica Optical Fibers
2.0 dB/km at 850nm
0.5 dB/km at 1310nm
0.2 dB/km at 1550nm
Fiber Dispersion
Dispersion is
minimum in SMFs
1310 nm
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
OPTICAL SOURCES
LEDS (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
• Very expensive
• Need specialized power supply and circuitry
OPTICAL DETECTORS
PIN Diodes (Si, Ge, InGaAs)
• 850nm, 1310nm, 1550 nm
• Low cost
APDs (Avalanche Photodiodes, GaAlAs)
• 850nm, 1310nm, 1550 nm
• High sensitivity- can operate at very low power levels
• Need high bias supply (40-50 V)
• 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 Attractive for Defense, Intelligence and Banks Netwroks
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
Environmental 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 > 30 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
Typical Long-haul Telecom System
• Amplifier spans: 30 to 120 km • Regenerator spans: 50 to 600 km • Terminal spans: 600 km (without regenerators) 9000 km (with regenerators)
Terminal Equipment
Amplifier Unit
Regenerator Unit
Terminal Equipment
Amplifier Unit
Amplifier Unit
Two pairs of single-mode fiber
OFC- Systems
Existing Systems: operating at 1310 nm wavelength
• 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
Presently installed Systems: 1550 nm wavelength band
• Silica has lowest loss, Increased dispersion
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
Optical Fiber Amplifiers: EDFA
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 Concept
Typical WDM network containing various types of optical amplifiers.
Technology of combining a number of wavelengths onto the
same fiber – Wavelength Division Multiplexing (WDM)
A unique feature of OFC Technology
Ability to put multiple services onto a single wavelength
POTENTIAL OF WDM NETWORK Sub-wavelength Multiplexing or Muxponding
Future OFC- Systems
Coincidence of low-loss 1550 nm window &
wide-BW EDFA
WDM/DWDM OFC Systems – multi channel
Soliton pulse transmission – Non dispersive
Capable of carrying enormous rates of information
Examples:
• 1.1 Tb/s over 150 km ; 55 wavelengths WDM
• 2.6 Tb/s over 120 km ; 132 wavelengths DWDM
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
Optical Fiber Platform
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
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 fiber cable
Next Step is FTTx?
FTTH: fiber to the home
FTTP: fiber to the premises
FTTC: fiber to the curb
FTTN: Fiber to the node
FTTx: for those who can’t decide what to call it or are referring to all varieties!
Fiber-To-The-Premises (FTTP)
Optical
Amplifier
Optical Fiber
ONT
DWDM
Coupler 1490nm
1310nm
1550nm
Video
OLT
Splitter
1490nm
1310nm
1550nm
Cable
Tx
Tx
Rx
Tx
Rx Rx
Fifty Years of Fiber Optics
The first quarter of 21st century will see a continued growth in
the demand for Photonics and fiber optic components.
Silicon Photonics_Intel
Questions?
