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?