Notes on Optical Fiber Communications

Course : Optics and Laser CommunicationCourse : Optics and Laser CommunicationText Book : Optical Fiber Communication: Senior

Optical Fiber Communication: Gerd KeiserFiber Optic Communication System: Govind Agarwal

Historical Development

Optical Communication

Free Space(FSO)

Guided Waves(Fibre Optics)

Important MilestonesCirca 2500 B.C. Earliest known glassRoman times-glass drawn into fibersVenice Decorative Flowers made of glass fibers1609-Galileo uses optical telescope1626-Snell formulates law of refraction1668-Newton invents reflection telescope1840-Samuel Morse Invents Telegraph1841-Daniel Colladon-Light guiding demonstrated

in water jet1870-Tyndall observes light guiding in a thin water jet

1951-Heel, Hopkins, Kapany image transmission using fiber bundles1957-First Endoscope used in patient1958-Goubau et. al. Experiments with the lens guide1958-59 Kapany creates optical fiber with cladding1960-Ted Maiman demonstrates first laser in Ruby1960-Javan et. al. invents HeNe laser1962-4 Groups simultaneously make first semiconductor lasers1961-66 Kao, Snitzer et al conceive of low loss single 1870-Tyndall observes light guiding in a thin water jet

1873-Maxwell electromagnetic waves1876-Elisha Gray and Alexander Bell Invent Telephone1877-First Telephone Exchange1880-Bell invents Photophone1888-Hertz Confirms EM waves and relation to light1880-1920 Glass rods used for illumination1897-Rayleigh analyzes waveguide1899-Marconi Radio Communication1902-Marconi invention of radio detector1910-1940 Vacuum Tubes invented and developed1930-Heinrich Lamb experiments with silica fiber1931-Owens-Fiberglass1936-1940 Communication using a waveguide

1961-66 Kao, Snitzer et al conceive of low loss single mode fiber communications and develop theory1970-First room temp. CW semiconductor laser-Hayashi & PanishApril 1977-First fiber link with live telephone traffic-

GTE Long Beach 6 Mb/sMay 1977-First Bell system 45 mb/s links

GaAs lasers 850nm Multimode -2dB/km lossEarly 1980s-InGaAsP 1.3 m Lasers

- 0.5 dB/km, lower dispersion-Single modeLate 1980s-Single mode transmission at 1.55 m -0.2 dB/km1989-Erbium doped fiber amplifier1 Q 1996-8 Channel WDM4th Q 1996-16 Channel WDM1Q 1998-40 Channel WDM

Optical Telegraphy Electrical Telegraphy

A semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc

Alexander Graham Bell patented an optical telephone system, which he called the Photophone, in 1880, but his earlier invention, the telephone, proved far more practical. He dreamed of sending signals through the air, but the atmosphere didn't transmit light as reliably as wires carried electricity.

Bells Photophone1880 - Photophone Receiver

1880 - Photophone Transmitter

The ordinary manwill find a little difficulty in comprehending how sunbeams are to be used. Does Prof. Bell intend to connect Boston and Cambridgewith a line of sunbeams hung on telegraph posts, and, if so, what diameter are the sunbeams to be?will it be necessary to insulate them against the weather?until (the public) sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Prof. Bells photophone which places a tremendous strain on human credulity.

New York Times Editorial, 30 August 1880

Do you know !?!

William Wheeling, in 1880, patented a method of light

transfer called piping light. Wheeling believed that by

using mirrored pipes branching off from a single source

of illumination, i.e. a bright electric arc, he could send

the light to many different rooms in the same way that

water, through plumbing, is carried throughout

buildings today. Due to the ineffectiveness of

Wheelings idea and to the concurrent introduction of

Edisons highly successful incandescent light bulb, the

concept of piping light never took off.

IDEA !?!In 1870, John Tyndall, using a

jet of water that flowed from one

container to another and a beam

of light, demonstrated that light

used internal reflection to follow

a specific path. As water poured a specific path. As water poured

out through the spout of the

first container, Tyndall directed

a beam of sunlight at the path of

the water. The light, as seen by

the audience, followed a zigzag

path inside the curved path of

the water. This simple

experiment, illustrated in

Figure, marked the first

research into the guided

transmission of light.

Bare Fiber During 1920-1950,

thin, flexible rods of glass or plastic were used to guide lightused to guide light

Such bare fibers require air outside each fiber

Image from Wikipedia

Fiber With Cladding Developed in 1954 by

Van Heel, Hopkins & Kapany

Cladding is a glass or plastic cover around the coreplastic cover around the core

Protects the total-reflection surface contamination

Reduces cross-talk from fibers in bundles

Medical Imaging By 1960, glass-clad fibers were available

for medical instruments, to look inside the body

The glass was unable to transmit light far The glass was unable to transmit light far enough for communications, because of impurities Attenuation (loss of light) was 1 decibel per

meter

Decibels Decibels are a logarithmic scale of power

Abbreviated dB A loss of 10 decibels means only 10% of the

light gets throughlight gets through A loss of 20 dB means 1% of the light gets

through Sunglasses stop 99% of light, so they cause a loss of

20 dB For communications, loss must be no more than

10 or 20 decibels per kilometer

Important Breakthrough

Kao and Hockham in 1966The breakthrough came when Dr Kao worked out that the loss of light was not an inherent property of the glass, but was due to imperfections in the material. If the glass could be improved so that imperfections improved so that imperfections were removed, leaving an acceptable rate of light loss at 20 decibels per kilometre, then many of the hurdles to optical communication would fall. [ before loss was ~1000 dB/km]

In 1970 Kapron, Keck and Maurer (Corning Glass Corporation) were successful in producing silica fibers with a loss of about 17 dB/km at a wavelength of 633 nm

In 1985 ~0.25 dB/km

1970 I. HayashiSemiconductor Laser

Optical Fiber in 1977 Telephone signals used infrared light with

a wavelength of 850 nm to send data at 6.2 Mbps

Loss was 2 dB per km Loss was 2 dB per km Repeaters were required every few

kilometers The repeaters were electro-optical

converting the light to electricity and then back to light

History of Attenuation

1 2 3 GenerationFirst Generation (1974-1980) Mutimode fibers Intermodal dispersion and fiber loss quite high 45 140 Mb/s Repeater Spacing: 10 km

Second Generation (-1987-)Second Generation (-1987-) Single mode 152 - 622 Mb/s - 1.7 Gb/s Repeater Spacing: 40 km

Third Generation (-1996-) Dispersion shifted fibers 2.5 Gb/s 10 Gb/s Rep. Spacing: 90 km (undersea)

Fourth Generation (2000) WDMWDM: Wavelength divison multiplexing

: Multiple sources operating at slightly different wavelength to transmit several independent information,

Combination of EDFAEDFA and WDMWDM boosted fiber capacity10 Tb/s Higher than 90 km

Erbium Doped Fiber Amplifier Higher than 90 km SEA-ME-WE3 Cable : Runs from Germany to Singapore

Fifth Generation (Today) SolitonsSolitons: Non dispersive optical pulse that preserve their shape by counteracting the effects of dispersion with the nonlinear effect of the fiber by using pulses of a specific shape. Increasing the range of WDM from C band (1.53-1.57 um) to 1.30 to 1.65 um 14 Tb/s14 Tb/s over a over a single 160 kmsingle 160 km line using optical amplifiersline using optical amplifiers

WDM:An Analogy with Multiple lane highwayWDM:An Analogy with Multiple lane highwayWDM:An Analogy with Multiple lane highwayWDM:An Analogy with Multiple lane highway

Optical Fiber Link : An Overview

Different Ways of InstallationDifferent Ways of InstallationDifferent Ways of InstallationDifferent Ways of Installation

SEA-ME-WE3 Undersea WDM cable network

Advantages: Comparison with Electrical transmission

Enormous Wide Bandwidth:Optical carrier frequency : 1014 Hz/105 GHzOptical bandwidth ~ (1013 Hz ) around 104 times higher than the bandwidth of highest microwave transmission

Low Transmission Loss : 0.2 dB/km Immunity to Interference and Cross talk

Free from Electromagnetic Interference (EMI), radiofrequency interference Free from Electromagnetic Interference (EMI), radiofrequency interference (RFI) or switching transients giving electromagnetic pulses (EMP)

Signal securityUnlike the situation with copper cables, a transmitted optical signal cannot be obtained from a fiber in a noninvasive manner

Electrical isolationIdeally suited for communication in electrically hazardous environments

Ruggedness and flexibilityBent, twisted without any damage

Small size and weight Potential low cost

Advantages of Electrical Transmission

Electrical transmission is often preferred for Short Distance Low Bandwidth applicationsBecause Lower material cost, where large quantities are not required Lower cost of transmitters and receivers Ease of splicing Capability to carry electrical power as well as signals

In certain situations fiber may be used even for short distance or low bandwidth applications because of immunity to electromagnetic interference, high electrical resistance, lighter weight, electromagnetically not radiating and much smaller cable size