Fiber Optics Technology
An Overview
Dr. BC Choudhary, Professor
National Institute of Technical Teachers’ Training &
Research (NITTTR), Sector-26, Chandigarh
CONTENT OUTLINES
 What is Fiber Optic Technology?
 Why Optical Transmission?
 Why Optical Fibers?
 OFC Systems & Potential
 Fiber Optics Sensing & Medical Applns
***
What is Fiber Optic Technology?
 Also called Lightwave 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; LEDs or LDs
Why Fiber Optic Technology?
 During past three decades, remarkable and dramatic changes
took place in the electronic communication industry.
• 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.
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 global demand.




extremely high initial cost of launching
geometry of suitable orbits,
available microwave frequency allocations and
if needed repair is nearly impossible
Next option: Optical Communication Systems !

Optical Frequencies
Optical Region
The Electromagnetic Spectrum
Potential of Optical Transmission ?
 The
information carrying capacity of a communications system is
directly proportional to its bandwidth;
C = BW×log2(1+SNR)
 Wider the bandwidth, greater the information carrying capacity.
• Theoretically; BW is 10% of the carrier frequency
Signal Carrier
 VHF Radio system; 100 MHz.
 Microwave system; 6 GHz
 Lightwave system; 106 GHz
Bandwidth
10 MHz
0.6 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

Communication System with light as the carrier of information
 A great deal of attention.
Major Difficulties

Transmission of light wave for any useful distance through earth’s
atmosphere  Impractical : Attenuation and Absorption of ultra high light
frequencies by water vapors, oxygen and air particulate.
 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.

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.
Dr. N. S. Kapany
Fiber Optics Timeline
• 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 et al; proposed cladded fiber cables with lower losses as a
communication medium.
• 1970: (Corning Glass, NY) developed fibers with losses below 20 dB/km.
• 1972: First Semiconductor diode laser was developed
• 1977: GT&E in Los Angeles and AT&T in Chicago send live telephone
signals through fiber optics (850nm, MMF, 6 Mbps, 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
• 1990s : Bell Labs sends 10 Billion bits through 20,000 km of fibers using a
Soliton system & WDM Techniques.
• 2000s : NTT, Bell Labs and Fujitsu are able to send Trillion bits per second
through single optical fiber  All optical networks.
The Nobel Prize in Physics 2009
"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"
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
Willard S. Boyle
b. 1924
1/4 of the prize
George E. Smith
b. 1930
1/4 of the prize
Bell Laboratories, Murray Hill, NJ, USA
Basic Fiber Optic Link
RECIEVER
TRANSMITTER
DRIVER
LIGHT
SOURCE
OPTICAL FIBER
DETECTOR
MEDIUM FOR CARRYING LIGHT
 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.
 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.
• Receiver (PIN or APD).
Backbone of an OFC System : OPTICAL FIBER
 acts as transmission channel for carrying light beam
loaded with information
Optical Fiber as Transmission Medium
 Transmit data as light pulses
(first converting electronic signals
to light pulses then finally
converting back to electronic
signals)
 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.
Basic Structure of a Step-Index Optical Fiber
•
•
Single mode: 5-10 m
Multimode: 50/62.5 m
NECESSARY CONDITION FOR TIR: n1 > n2
Transmission Loss in Optical Glass
• 1970,
First
Optical
Fiber: Losses  20 dB/km
at 633nm
• 1977, losses reduced to
5dB/km at 850nm
• 1980s, Losses reduced to
 0.2 dB/km at 1550 nm
Dramatic reduction in transmission loss in
optical glass
Communication Channel Capacity
Communication
Medium
Carrier
Frequency
Bandwidth
2 way voice
Channels
Copper Cable
1 MHz
100 kHz
< 2000
Coaxial Cable
100 MHz
10 MHz
13,000
Optical Fiber
Cables
100 –1000 THz
40 THz
>3,00,000 or
90,000 Video
signals
TWO MAJOR COMMUNICATION ISSUES
 ATTENUATION
Attenuation is signal loss over distance  Light pulses loose their energy
and amplitude falls as they travel down the cable.
 Attenuation puts distance limitations on long- haul networks.
 DISPERSION
Dispersion is the broadening of a light pulse as it travels down the cable.
• Intermodal (Modal) dispersion
• Intramodal (Chromatic) dispersion : (Material & Waveguide )
 Puts data rate limitation on networks
Fiber Attenuation
 4dB/km at 850 nm
 0.5 dB/km at 1310 nm
 0.2 dB/km at 1550 nm
Attenuation in Silica Optical Fibers
Fiber Dispersion
 Dispersion is
minimum in SMFs
Step Index / Graded Index
Wavelengths of Operation
Attenuation (dB/ km )
Attenuation in Silica Fibers
2.5
2
2.0
1.5
3
“ Optical
Windows”
1
1.0
0.5
900
850 nm
1100
1300
1500
1700
Wavelength (nm )
1310 nm
1550 nm
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
• 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
OFC- Systems
 Firstly 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
Future OFC Systems: 1550 nm Wavelength band
• Silica has lowest loss, increased dispersion
• Design of Dispersion Shifted Fibers
 Lowest loss and Negligible dispersion
 Erbium Doped Fiber Amplifier (EDFA)
Direct amplification of optical signal
Flat gain around 1550nm low loss window
BW 12,500 GHz ; Enormous potential
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
Same bit rate, more fibers
Slow Time to Market
Expensive Engineering
Limited Rights of Way
Duct Exhaust
More Fibers
(SDM)
W
D
M
Faster Electronics
(TDM)
Same fiber & bit rate, more ls
Fiber Compatibility
Fiber Capacity Release
Fast Time to Market
Lower Cost of Ownership
Utilizes existing TDM Equipment
Higher bit rate, same fiber
Electronics more expensive
Future 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
Bandwidth Evolutionary Landmarks
Optical Fiber
All-Optical Network
(Terabits  Petabits)
TDM (Gb/s)
• Fiber is deployed at a rate of 2000 miles every hour
80l @ 40Gb/s
40
176l @OC-192
35
25
20
EDFA +
Raman Amplifier
15
32l @OC-192
16l @OC-192
8l @OC-48
4l @OC-192
EDFA
10 Gb/s
10
2l @1.2Gb/s
(1310 nm, 1550 nm)
5
4l @OC-48
2l @OC-48
2.4 Gb/s
565 Mb/s 1.2 Gb/s
0
TDM
DWDM
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
810 Mb/s 1.8 Gb/s
1986
1984
405 Mb/s
1982
Bandwidth
30
Enablers
EDFA + Raman Amplifier
Dense WDM/Filter
High Speed Opto-electronics
Advanced Fiber
40 Gb/s
Bands in Light Spectrum
Approximate Attenuation
of Single Mode fiber cable
Infrared
Visible
700
900
“O” Band ~ 1270-1350 nm
“E” Band ~ 1370 - 1440 nm
“S” Band ~ 1470 - 1500 nm
“C” Band ~ 1530 - 1565 nm
“L” Band ~ 1570 - 1610 nm
1100
1300
1500
1700 nm
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 information needs of the society.
Next Step is FTTx?

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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)
ONT
OLT
Tx
1490nm
DWDM
Coupler
1310nm
Rx
Video
Cable
Optical Fiber
Splitter
Tx
1550nm
Optical
Amplifier
1550nm
Rx
1490nm Rx
1310nm Tx
Optical Fiber Platform
Lightwave Technology: Application Areas

Majority Applications:
– Telephone networks
– Data communication systems
– Cable TV distribution
 Niche Applications:
– Optical sensors
– Medical equipment
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
FO Sensors: A Boon in Disguise
FIBER OPTIC SENSORS?

Dictionary: 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, temperature,
pressure, velocity, and acceleration etc.

Optical fibers: strands of glass that transmit light over long
distances (wire in electrical systems)

Light: transmitted by continuous internal reflections in optical
fibers (electron in electrical systems)
Light Wave Parameters
1. Amplitude / Intensity
2. Phase
3. Wavelength
4. Polarization
5. Time / Frequency
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
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
Extrinsic or Hybrid Fiber Optic Sensors

Consist of optical fibers that lead up to and out of a “black
box” that modulates the light beam passing through it in
response to an environmental effect.

Sensing takes place in a region outside the fiber.
Intrinsic or All-Fiber Optic Sensors

Sensing takes place within the fiber itself.

The sensors rely on the properties of the optical fiber itself
to convert an environmental action into a modulation of
the light beam passing through it.
Fiber Optic Sensor Capabilities
• Rotation, acceleration
• Electric and magnetic fields
• Temperature and pressure
• Acoustics and vibration
• Strain, humidity, and viscosity
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
Fiber Optic Sensors Historical Trends
Few, high-priced
components, laser
diodes, microoptics
Low-cost basic
components, laser
diodes pigtailed, fiber
beamsplitters
Low-cost complex
components, mass
produced integrated
optics
Niche markets - RF
temperature
Mass markets emerge fiber gyros, medical, lab
instruments,
manufacturing
Fiber optic systems fiber optic smart
structures, industrial
systems
Fiber Optic Sensors What’s Next?
Fiber optic health and
structural monitoring
systems on about 100
bridges, aerospace
SHM technology
moves toward level 6
Hundreds of civil
structure installations,
aerospace fiber optic
SHM moves to level 8
and 9 with initial
deployments
Oil and gas
deployments start to
appear
Hundreds of oil and gas
wells uses downhole fiber
optic sensor systems,
platforms begin to use
fiber optic SHM systems
Fiber optic SHM
systems are mandated
on new civil and
aerospace structures
Thousands of systems
are deployed for many
high value oil and gas
wells, fiber optic SHM
mandated on some oil
platforms
Basic Elements of a Fiber Optic Sensor
Beam conditioning
optics
Modulator
Optical Fiber
Light source
Transducer
 Optical fiber
 Light sources
 Beam conditioning optics
 Modulators
 Detectors
Detector
What Does F.O.S. Look Like?
Various Fiber Optic Sensors
GENERAL USES

Measurement of physical properties such as strain,
displacement, temperature, pressure, velocity, and acceleration
in structures of any shape or size

Monitoring the physical health of structures in real time

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, longterm 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
Fly by Light System
Fly by Light System-Airframe
Fly by Light System-Engine
MEDICAL APPLICATIONS






Small, Flexible
Non Toxic
Chemically Inert
Intrinsically Safe
Low Maintenance
Ease of Use
Fibers are Everywhere
THANK YOU