Basics of Optical Fiber Communications.

1. What are the Basic Elementsofa FiberOptic CommunicationSystem?-
For gigabitsandbeyondgigabitstransmissionof data,the fiberopticcommunicationisthe ideal choice.
Thistype of communicationisusedtotransmitvoice,video,telemetryanddata overlongdistancesand
local area networksorcomputernetworks.A fiberOpticCommunicationSystemuseslightwave
technologytotransmitthe data overa fiberbychangingelectronicsignalsintolight.
Some exceptional characteristicfeaturesof thistype of communication systemlikelarge bandwidth,
smallerdiameter,lightweight,longdistance signaltransmission,low attenuation,transmissionsecurity,
and so onmake thiscommunicationamajor buildingblockinanytelecommunicationinfrastructure.The
subsequentinformationonfiberoptic communicationsystemhighlightsitscharacteristicfeatures,basic
elementsandotherdetails.
How a FiberOptic CommunicationWorks?
Unlike copperwire basedtransmissionwhere the transmissionentirelydependsonelectrical signals
passingthroughthe cable,the fiberopticstransmissioninvolvestransmissionof signalsinthe formof
lightfromone pointto the other.Furthermore,afiberopticcommunicationnetworkconsistsof
transmittingandreceivingcircuitry,alightsource anddetectordeviceslikethe onesshowninthe figure.
Whenthe inputdata, inthe form of electrical signals,isgiventothe transmittercircuitry,itconverts
themintolightsignal withthe helpof alightsource.Thissource is of LED whose amplitude,frequency
and phasesmustremainstable andfree fromfluctuationinordertohave efficienttransmission.The
lightbeamfromthe source is carriedby a fiberopticcable tothe destinationcircuitrywhereinthe
informationistransmittedbacktothe electrical signalbyareceivercircuit.
Workingof Fiberoptic
communication
The Receivercircuitconsistsof a photodetectoralongwithanappropriate electroniccircuit,whichis
capable of measuringmagnitude,frequencyandphase of the opticfield.Thistype of communication
usesthe wave lengthsneartothe infraredband that are justabove the visible range.BothLEDand Laser
can be usedaslightsourcesbasedonthe application.

2. 3 Basic Elementsof a FiberOptic CommunicationSystem –
There are three mainbasicelementsof fiberoptic communicationsystem.Theyare
1. CompactLight Source
2. Low lossOptical Fiber
3. PhotoDetector
Accessorieslikeconnectors,switches,couplers,multiplexingdevices,amplifiersandsplicesare also
essential elementsinthiscommunicationsystem.
1. Compact Light Source
Dependingonthe applicationslikelocal areanetworksandthe longhaul communicationsystems,the
lightsource requirementsvary.The requirementsof the sourcesinclude power,speed,spectral line
width,noise,ruggedness,cost,temperature,andsoon.Two componentsare usedaslightsources:light
emittingdiodes(LED’s) andlaserdiodes.
The lightemittingdiodesare usedforshortdistancesandlow data rate applicationsdue totheirlow
bandwidthandpowercapabilities.TwosuchLEDs structuresinclude Surface andEdge EmittingSystems.
The surface emittingdiodesare simple indesignandare reliable,butdue toitsbroaderline widthand
modulationfrequencylimitationedgeemittingdiode are mostlyused.Edge emittingdiodeshave high
powerandnarrowerline widthcapabilities.
For longerdistancesandhighdatarate transmission,LaserDiodesare preferreddue toitshighpower,
highspeedandnarrowerspectral line widthcharacteristics.Butthese are inherentlynon-linearand
more sensitive totemperature variations.

3. Nowadaysmanyimprovementsandadvancementshave made thesesourcesmore reliable.A few of
such comparisonsof these twosourcesare givenbelow.Boththese sourcesare modulatedusingeither
director external modulationtechniques.
2. Low Loss Optical Fiber
Optical fiberisa cable,whichisalsoknownascylindrical dielectricwaveguide made of low lossmaterial.
An optical fiberalsoconsidersthe parameterslikethe environmentinwhichitisoperating,the tensile
strength,durabilityandrigidity.The Fiberopticcable ismade of highqualityextrudedglass(si) or
plastic,andit isflexible.The diameterof the fiberopticcable isinbetween0.25to 0.5mm (slightly
thickerthana humanhair).
A FiberOptic Cable consists of four parts.
 Core
 Cladding
 Buffer
 Jacket
Core
The core of a fibercable isa cylinderof plasticthatrunsall alongthe fibercable’slength,andoffers
protectionbycladding.The diameterof the core dependsonthe applicationused.Due tointernal
reflection,the light travellingwithinthe core reflectsfromthe core,the claddingboundary.The core
cross sectionneedstobe a circularone for mostof the applications.

4. Cladding
Claddingisanouter optical material thatprotectsthe core.The mainfunctionof the claddingisthat it
reflectsthe lightbackintothe core.Whenlightentersthroughthe core (dense material)intothe
cladding(lessdense material),itchangesitsangle,andthenreflectsbacktothe core.
Buffer
The main functionof the bufferistoprotect the fiberfromdamage andthousandsof optical fibers
arrangedin hundredsof optical cables.These bundlesare protectedbythe cable’soutercoveringthatis
calledjacket.
JACKET
Fiberopticcable’sjacketsare available indifferentcolorsthatcaneasilymake usrecognize the exact
colorof the cable we are dealingwith.The coloryellowclearlysignifiesasingle mode cable,andorange
colorindicatesmultimode.
2 Typesof Optical Fibers
Single-Mode Fibers:Single mode fibersare usedtotransmitone signal perfiber;thesefibersare usedin
telephoneandtelevisionsets.Singlemode fibershave small cores.
Multi-Mode Fibers:Multimode fibersare usedtotransmitmanysignalsperfiber;these signalsare used
incomputerand local area networksthat have largercores.
3. Photo Detectors
The purpose of photodetectorsisto convertthe lightsignal backto an electrical signal.Twotypes
of photodetectors are mainlyusedforoptical receiverinoptical communicationsystem:PN photo
diode andavalanche photodiode.Dependingonthe application’swavelengths,the material
compositionof these devicesvary.These materialsincludesilicon,germanium,InGaAs, etc.
Thisis all aboutthe basic elementsof the fiberopticcommunicationsystem.