Notes on Optical Fiber CommunicationsCourse : Optics and Laser CommunicationText Book : Optical Fiber Communication: Senior Optical Fiber Communication: Gerd Keiser Fiber Optic Communication System: Govind Agarwal

Historical DevelopmentOptical CommunicationFree 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 jet1873-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 waveguide1951-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 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

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 Optical TelegraphyElectrical Telegraphy

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 Transmitter 1880 - Photophone Receiver 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 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 FiberDuring 1920-1950, thin, flexible rods of glass or plastic were used to guide lightSuch bare fibers require air outside each fiberImage from Wikipedia

Fiber With CladdingDeveloped in 1954 by Van Heel, Hopkins & KapanyCladding is a glass or plastic cover around the coreProtects the total-reflection surface contaminationReduces cross-talk from fibers in bundles

Medical ImagingBy 1960, glass-clad fibers were available for medical instruments, to look inside the bodyThe glass was unable to transmit light far enough for communications, because of impuritiesAttenuation (loss of light) was 1 decibel per meter

DecibelsDecibels are a logarithmic scale of powerAbbreviated dBA loss of 10 decibels means only 10% of the light gets throughA loss of 20 dB means 1% of the light gets throughSunglasses stop 99% of light, so they cause a loss of 20 dBFor communications, loss must be no more than 10 or 20 decibels per kilometer

Important BreakthroughKao and Hockham in 1966 The 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 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 nmIn 1985 ~0.25 dB/km1970 I. HayashiSemiconductor Laser

Optical Fiber in 1977Telephone signals used infrared light with a wavelength of 850 nm to send data at 6.2 Mbps Loss was 2 dB per kmRepeaters were required every few kilometersThe repeaters were electro-optical converting the light to electricity and then back to light

History of Attenuation

123GenerationFirst Generation (1974-1980) Mutimode fibers Intermodal dispersion and fiber loss quite high 45 140 Mb/s Repeater Spacing: 10 kmSecond Generation (-1987-) Single mode 152 - 622 Mb/s - 1.7 Gb/s Repeater Spacing: 40 kmThird Generation (-1996-) Dispersion shifted fibers 2.5 Gb/s 10 Gb/s Rep. Spacing: 90 km (undersea)

Fourth Generation (2000) WDM: Wavelength divison multiplexing : Multiple sources operating at slightly different wavelength to transmit several independent information, Combination of EDFA and WDM boosted fiber capacity10 Tb/s Higher than 90 km SEA-ME-WE3 Cable : Runs from Germany to Singapore Erbium Doped Fiber AmplifierFifth Generation (Today) Solitons: 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/s over a single 160 km line using optical amplifiers

WDM:An Analogy with Multiple lane highway

Optical Fiber Link : An Overview

Different Ways of Installation

SEA-ME-WE3 Undersea WDM cable network

Advantages: Comparison with Electrical transmissionEnormous Wide Bandwidth: Optical carrier frequency : 1014 Hz/105 GHzOptical bandwidth ~ (1013 Hz ) around 104 times higher than the bandwidth of highest microwave transmissionLow Transmission Loss : 0.2 dB/kmImmunity to Interference and Cross talkFree 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 mannerElectrical isolationIdeally suited for communication in electrically hazardous environmentsRuggedness and flexibilityBent, twisted without any damageSmall size and weightPotential low cost

Advantages of Electrical TransmissionElectrical transmission is often preferred forShort DistanceLow Bandwidth applicationsBecause Lower material cost, where large quantities are not requiredLower cost of transmitters and receiversEase of splicingCapability to carry electrical power as well as signalsIn 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

**The first semaphore was devceloped by Robert Hooke in 1684. This is Optical Telegraph of France by Claude Chappe on Litermont near Nalbach, Germanyin 1790sIt used sunlight reflected from a thin voice-modulated mirror to carry conversation. At the receiver the modulated sunlight fell on a photoconducting selenium cell, which converted the message to electrical current. A telephone receiver completed the system**Summary form only given. At the beginning of 1997, the contracts for the provision of the Sea-Me-We 3 Cable System have been signed; the total budget of the project is 1,300 M$. Owned by more than 90 Telecommunication companies, with a length of 38,000 km and 39 landing points in 33 countries, Sea-Me-We 3 is the most important submarine cable project ever launched. It will link Europe, Far East Asia, and Australia. Commercial service will begin in December 1998 and be completed in March 1999. The system will be initially equipped, in the cable stations, at half its maximum capacity. Sea-Me-We 3 will use the most advanced submarine amplified technology together with state-of-the-art SDH network management