Fiber Optics Technology
An Overview
Dr. BC Choudhary, Professor
National Institute of Technical Teachers’ Training &
Research (NITTTR), Sector-26, Chandigarh
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

Also called Lightwave Technology
 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.

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.
 NEAR ZERO LOSS & INFINITE BANDWIDTH
Lightwave Technology: Application Areas

Majority Applications:
– Telephone Networks
– Data Communication Systems
– Cable TV distribution
 Niche Applications:
– Optical Sensors
– Medical Equipment
Telecommunication
Developments & Issues
1896
2016
 Communication – Exchange of information
 Telecommunication – Exchange of information over
a distance – using some type of equipment
Information
Link
Transmitter
Transmission
medium
Receiver
Information
• 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.
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?
 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 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 !
Optical Region
THz range
The Electromagnetic Spectrum
Potential of Optical Transmission ?
 Information
carrying capacity of a communications system is
directly proportional to its bandwidth; C= BWlog2(1+SNR);
Shanon-Hartley theorem
 Wider the bandwidth, the greater its 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 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
"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
Kao’s Experiment (1966)
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
Dr. Narinder S Kapany
Born in Moga (Punjab) in October 1926
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 (Modulation)
• Source is LED or ILDs 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 (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
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 (SCS, PCS).
Basic Structure of a Step-Index Optical Fiber
• Single mode: 5-10 m
 Step Index Profile
• Multimode: 50/62.5 m
 Graded Index Profile
NECESSARY CONDITION FOR TIR: n1 > n2
Transmission Loss in Optical Glass
• 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
Dramatic reduction in transmission loss in optical glass

Highly pure; Transmitting light through 3 mile thick slab of glass
Two Major Communication Issues
 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.
 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
 0.5 dB/km at 1310 nm
 0.2 dB/km at 1550 nm
Attenuation in Silica Optical Fibers
 Limit
SNR / distance
Fiber Dispersion
 Dispersion is
minimum in SMFs
 Limit Data Rate
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
Both 1310 and
1550 nm are
active windows
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

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
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
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
FORESIGHT…

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.
Bandwidth Evolutionary Landmarks
Optical
Fiber
All-Optical Network
(Terabits  Petabits)
TDM (Gb/s)
40
• Fiber is deployed at a rate of 2000
miles every hour
80l @ 40Gb/s
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
Optical Fiber Platform
Bands in Light Spectrum
Approximate Attenuation of Single Mode
silica 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
All Wave Optical Fiber




LUCENT
CORNING
OFS
HUAWEI
Photonic Crystal Fibers (PCFs)
PCF: around since 1996 (JC Knight et al, OFC (1996) paper PD3
 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
Solid core PCF
Hollow core PCF
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
Variation in any of these
parameters due to external
5. Time / Frequency 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
Beam conditioning
optics
Modulator
Optical Fiber
Light source
Transducer
Detector
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, 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
Fiber Optic Probe Colorimeter
Smart Beds
Optical fibers in Textiles
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
Medical Illumination Products
Image Transmission by Fiber
Bundle
•
•
•
•
•
•
•
•
•
Thin/Small size
Flexible
Non Toxic
Chemically Inert
EM Inert
No Cross talk
Wide Bandwidth
Reliable
Ease of Use
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:
The excerpts of this lecture are based on the information drawn
from following reference.
1.
2.
3.
4.
5.
6.
7.
John M. Senior “Optical Fiber Communications: Principles and Practice,
2nd edn., PHI, 2001.
Gerd Keiser, “Optical Fiber Communica tion” 3rd edn., Mc Graw Hill ,
2000.
www.google.co.in
www.youtube/OFC videos
www.FO4sale.com
Govind P. Agrawal, “Fiber-Optic Communication Systems” John Wiley
& sons (Asia) Pte Ltd , 3rd Edn., 2005.
Bishnu P. Pal, “Fundamentals of Fibre Optics in Telecommunication and
Sensor Systems”, New Age International Publishers, 2005.
Questions?