Dr. BC Choudhary, Professor

National Institute of Technical Teachers’ Training & Research (NITTTR), Sector-26, Chandigarh

Fiber Optics Technology

An Overview

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?

• 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

Also called Lightwave Technology

Why Fiber Optic Technology?

• 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 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

The Electromagnetic Spectrum

Optical Region

Potential of Optical Transmission ?

The information carrying capacity of a communications system is

directly proportional to its bandwidth;

Wider the bandwidth, greater the 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 than100,000 times than achieved with microwave frequencies)

meet the today’s communication needs or that of the foreseeable future

C = BW×log2(1+SNR)

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 secondthrough single optical fiber 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

Basic Fiber Optic Link

TRANSMITTER

DRIVERLIGHT

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, 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

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.

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: 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

Transmission Loss in Optical Glass

Dramatic reduction in transmission loss in

optical glass

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

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.

TWO MAJOR COMMUNICATION ISSUES

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

Attenuation in Silica Optical Fibers

4dB/km at 850 nm

0.5 dB/km at 1310 nm

0.2 dB/km at 1550 nm

Fiber Dispersion

Dispersion is

minimum in SMFs

Step Index / Graded Index

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

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

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

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

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/s1.2 Gb/s565 Mb/s

1.8 Gb/s810 Mb/s405 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 13001100900 1700 nm1500

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

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?

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

Coupler1490nm

1310nm

1550nm

Video

OLT

Splitter

1490nm

1310nm

1550nm

Cable

Tx

Tx

Rx

Tx

RxRx

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

Fiber optic SHM

systems are mandated

on new civil and

aerospace structures

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

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

Light source

Beam conditioning

optics

Transducer

Modulator

Detector

Optical Fiber

Optical fiber

Light sources

Beam conditioning optics

Modulators

Detectors

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, 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

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