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1、LW Technology(Passive Components).PPT-1 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Passive Components,LW Technology,LW Technology(Passive Components).PPT-2 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Patchcords,“Jumper cables”to connect devices and instrume
2、nts“Adapter cables”to connect interfaces using different connector stylesInsertion loss is dominated by the connector losses(2 m fiber has almost no attenuation)Often yellow sheath used for single-mode fiber,orange sheath for multimode,LW Technology(Passive Components).PPT-3 Copyright 1999,Agilent T
3、echnologies,Revision 1.1February 21,2023,Wavelength-Independent Couplers,Wavelength-Independent coupler(WIC)types:couple light from each fiber to all the fibers at the other side50%/50%(3 dB)most common 4 port type1%,5%or 10%taps(often 3 port devices)Excess Loss(EL):Measure of power“wasted”in the co
4、mponent,LW Technology(Passive Components).PPT-4 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Wavelength-Dependent Couplers,Wavelength-division multiplexers(WDM)types:3 port devices(4th port terminated)1310/1550 nm(“classic”WDM technology)1480/1550 nm and 980/1550 nm for pumping o
5、ptical amplifiers(see later)1550/1625 nm for network monitoringInsertion and rejection:Low loss(1 dB)for path wavelengthHigh loss(20 to 50 dB)for other wavelength,LW Technology(Passive Components).PPT-5 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Isolators,Main application:To pr
6、otect lasers and optical amplifiers from light coming back(which otherwise can cause instabilities)Insertion loss:Low loss(0.2 to 2 dB)in forward directionHigh loss in reverse direction:20 to 40 dB single stage,40 to 80 dB dual stage)Return loss:More than 60 dB without connectors,LW Technology(Passi
7、ve Components).PPT-6 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Filter Characteristics,PassbandInsertion lossRippleWavelengths(peak,center,edges)Bandwidths(0.5 dB,3 dB,.)Polarization dependenceStopbandCrosstalk rejectionBandwidths(20 dB,40 dB,.),LW Technology(Passive Components
8、).PPT-7 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Dielectric Filters,Thin-film cavitiesAlternating dielectric thin-film layers with different refractive indexMultiple reflections cause constructive&destructive interferenceVariety of filter shapes and bandwidths(0.1 to 10 nm)In
9、sertion loss 0.2 to 2 dB,stopband rejection 30 to 50 dB,1535 nm,1555 nm,0 dB,30 dB,LW Technology(Passive Components).PPT-8 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Tunable Fabry-Perot Filters,Filter shapeRepetitive passband with Lorentzian shapeFree Spectral Range FSR=c/2 n l
10、(l:cavity length)FinesssF=FSR/BW(BW:3 dB bandwidth)Typical specifications for 1550 nm applicationsFSR:4 THz to 10 THz,F:100 to 200,BW:20 to 100 GHzInsertion loss:0.5 to 35 dB,Optical Frequency,FSR,1 dB,30 dB,LW Technology(Passive Components).PPT-9 Copyright 1999,Agilent Technologies,Revision 1.1Febr
11、uary 21,2023,Fiber Bragg Gratings(FBG),Single-mode fiber with“modulated”refractive indexRefractive index changed using high power UV radiationRegular interval pattern:reflective at one wavelengthNotch filter,add/drop multiplexer(see later)Increasing intervals:“chirped”FBGCompensation for chromatic d
12、ispersion,LW Technology(Passive Components).PPT-10 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Circulators,Circulator&chirped FGB configured to compensate CD,Optical crystal technology similar to isolatorsInsertion loss 0.3 to 1.5 dB,isolation 20 to 40 dB Typical configuration:3
13、 port devicePort 1-Port 2Port 2-Port 3Port 3-Port 1,Fast l,Slow l,LW Technology(Passive Components).PPT-11 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Add/Drop Nodes,Filter reflects l i,Add l i,Add/Drop,Dielectric thin-film filter design,Circulator with FBG design,Common,Passban
14、d,Drop l i,LW Technology(Passive Components).PPT-12 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Multiplexers(MUX)/Demultiplexers(DEMUX),Key component of wavelength-division multiplexing technology(DWDM)Variety of technologiesCascaded dielectric filtersCascaded FBGsPhased arrays(
15、see later)High crosstalk suppression essential for demultiplexing,LW Technology(Passive Components).PPT-13 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Array Waveguide Grating(AWG),l,1a,l,3a,l,2a,l,4a,l,1b,l,3b,l,2b,l,4b,l,1c,l,3c,l,2c,l,4c,l,1d,l,3d,l,2d,l,4d,l,1a,l,3c,l,2d,l,4b
16、,l,1b,l,3d,l,2a,l,4c,l,1c,l,3a,l,2b,l,4d,l,1d,l,3b,l,2c,l,4a,Rows.,.translate into.,.columns,If only one input is used:wavelength demultiplexer!,LW Technology(Passive Components).PPT-14 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Review Questions,1.What is the difference between
17、 a WIC and a WDM?2.What are the losses of a 10%tap?3.What does a demultiplexer do?,LW Technology(Passive Components).PPT-15 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Transmitters&Receivers,LW Technology,LW Technology(Passive Components).PPT-16 Copyright 1999,Agilent Technologi
18、es,Revision 1.1February 21,2023,Light-emitting Diode(LED),Datacom through air&multimode fiberVery inexpensive(laptops,airplanes,lans)Key characteristicsMost common for 780,850,1300 nmTotal power up to a few WSpectral width 30 to 100 nmCoherence length 0.01 to 0.1 mm Little or not polarizedLarge NA(p
19、oor coupling into fiber),LW Technology(Passive Components).PPT-17 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Fabry-Perot(FP)Laser,Multiple longitudinal mode(MLM)spectrum“Classic”semiconductor laserFirst fiberoptic links(850 or 1300 nm)Today:short&medium range linksKey character
20、isticsMost common for 850 or 1310 nmTotal power up to a few mwSpectral width 3 to 20 nmMode spacing 0.7 to 2 nmHighly polarizedCoherence length 1 to 100 mmSmall NA(good coupling into fiber),I,P,Threshold,LW Technology(Passive Components).PPT-18 Copyright 1999,Agilent Technologies,Revision 1.1Februar
21、y 21,2023,Distributed Feedback(DFB)Laser,Single longitudinal mode(SLM)spectrumHigh performance telecommunication laserMost expensive(difficult to manufacture)Long-haul links&DWDM systemsKey characteristicsMostly around 1550 nmTotal power 3 to 50 mwSpectral width 10 to 100 MHz(0.08 to 0.8 pm)Sidemode
22、 suppression ratio(SMSR):50 dBCoherence length 1 to 100 mSmall NA(good coupling into fiber),LW Technology(Passive Components).PPT-19 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Vertical Cavity Surface Emitting Lasers(VCSEL),Distributed Bragg Reflector(DBR)MirrorsAlternating laye
23、rs of semiconductor material40 to 60 layers,each l/4 thickBeam matches optical acceptance needs of fibers more closelyKey propertiesWavelength range 780 to 980 nm(gigabit ethernet)Spectral width:-10 dBmCoherence length:10 cm to10 mNumerical aperture:0.2 to 0.3,LW Technology(Passive Components).PPT-2
24、0 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Other Light Sources,White light sourceSpecialized tungsten light bulbWavelength range 900 to 1700 nm,Power density 0.1 to 0.4 nw/nm(SM),10 to 25 nw/nm(MM)Amplified spontaneous emission(ASE)source“Noise”of an optical amplifier without
25、 input signalWavelength range 1525 to 1570 nmPower density 10 to 100 w/nmExternal cavity laserMost common for 1550 nm band(some for 1310 nm)Tunable over more than 100 nm,power up to 10 mwSpectrum similar to DFB laser,bandwidth 10 kHz to 1 MHz,LW Technology(Passive Components).PPT-21 Copyright 1999,A
26、gilent Technologies,Revision 1.1February 21,2023,Basic Transmitter Design,Optimized for one particular bit rate&wavelengthOften temperature stabilized laserInternal(direct)or external modulationDigital modulationExtinction ratio:9 to 15 dBForward error correctionScrambling of bits to reduce long seq
27、uences of 1s or 0s(reduced DC and low frequency spectral content)Analog modulationModulation index typically 2 to 4%Laser bias optimized for maximum linearity,LW Technology(Passive Components).PPT-22 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Modulation Principles,Direct(laser
28、current)InexpensiveCan cause chirp up to 1 nm(wavelength variation caused by variation in electron densities in the lasing area)External2.5 to 40 gb/sAM sidebands(caused by modulation spectrum)dominate linewidth of optical signal,DC,MOD,RF,LW Technology(Passive Components).PPT-23 Copyright 1999,Agil
29、ent Technologies,Revision 1.1February 21,2023,External Modulators,Mach-Zehnder Principle,Lasersection,Modulationsection,DFB laser with external on-chip modulator,LW Technology(Passive Components).PPT-24 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Photodiodes,PIN(p-layer,intrinsi
30、c layer,n-layer)Highly linear,low dark currentAvalanche photo diode(APD)Gain up to x100 lifts detected optical signal above electrical noise of receiverBest for high speed and highly sensitive receiversStrong temperature dependenceMain characteristicsQuantum efficiency(electrons/photon)Dark currentR
31、esponsivity(current vs.L),Bias Voltage,APD Gain,LW Technology(Passive Components).PPT-25 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Material Aspects,Silicon(Si)Least expensiveGermanium(Ge)“Classic”detectorIndium gallium arsenide(InGaAs)Highest speed,Wavelength nm,500,1000,1500,
32、Silicon,Germanium,InGaAs,Quantum,Efficiency=1,0.1,0.5,1.0,Responsivity(A/W),LW Technology(Passive Components).PPT-26 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Basic Receiver Design,Optimized for one particular Sensitivity rangeWavelengthBit rate Can include circuitsfor telemet
33、ry,LW Technology(Passive Components).PPT-27 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Receiver Sensitivity,Bit error ratio(BER)versus input power(pi)Minimum input power depends on acceptable bit error ratePower margins important to tolerate imperfections of link(dispersion,noi
34、se from optical amplifiers,etc.)Theoretical curve well understoodMany receivers designed for 1E-12 or better BER,Pi(dBm),BER,LW Technology(Passive Components).PPT-28 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Regenerator,Receiver followed by a transmitterNo add or drop of traff
35、icDesigned for one bit rate&wavelengthSignal regenerationReshaping&timing of data streamInserted every 30 to 80 km before optical amplifiers became commercially availableToday:reshaping necessary after about 600 km(at 2.5 Gb/s),often done by SONET/SDH add/drop multiplexers or digital cross-connects,
36、LW Technology(Passive Components).PPT-29 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Conceptual Terminal Diagram,TransmissionPath,2488.32 Mb/s,PDH Streams(Tributaries),.,.,.,1.5 Mb/s,51.84 Mb/s,Monitoring&Management,Synchronous ContainerMapping,Synchronous ContainerMapping,RX,TX
37、,RX,TX,ProtectionPath,Inter-leaving,.,.,Inter-leaving,SONET/SDHStreams,LW Technology(Passive Components).PPT-30 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Review Questions,1.What are the differences between an LED,FP,and DFB lasers?2.Which photodiode do you use forData communic
38、ation?Speed longhaul traffic?3.How do you define receiver sensitivity?,LW Technology(Passive Components).PPT-31 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Optical Amplifiers,LW Technology,LW Technology(Passive Components).PPT-32 Copyright 1999,Agilent Technologies,Revision 1.1F
39、ebruary 21,2023,Erbium:rare element with phosphorescent propertiesPhotons at 1480 or 980 nm activate electrons into a metastable stateElectrons falling back emit light in the 1550 nm rangeSpontaneous emissionOccurs randomly(time constant 1 ms)Stimulated emissionBy electromagnetic waveEmitted wavelen
40、gth&phase areidentical to incident one,Erbium Properties,LW Technology(Passive Components).PPT-33 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Basic EDF Amplifier Design,Erbium-doped fiber amplifier(EDFA)most commonCommercially available since the early 1990sWorks best in the ran
41、ge 1530 to 1565 nmGain up to 30 dB(1000 photons out per photon in!)Optically transparent“Unlimited”RF bandwidthWavelength transparent,LW Technology(Passive Components).PPT-34 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Amplified Spontaneous Emission,Amplifiedspontaneous emission
42、(ASE),Random spontaneous emission(SE),Amplification along fiber,Erbium randomly emits photons between 1520 and 1570 nmSpontaneous emission(SE)is not polarized or coherent Like any photon,SE stimulates emission of other photonsWith no input signal,eventually all optical energy is consumed into amplif
43、ied spontaneous emissionInput signal(s)consume metastable electrons much less ASE,LW Technology(Passive Components).PPT-35 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Output Spectra,ASE spectrum when no input signal is present,Amplified signal spectrum(input signal saturates the
44、 optical amplifier),1575 nm,-40 dBm,1525 nm,+10 dBm,LW Technology(Passive Components).PPT-36 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Time-Domain Properties,Turn-On Overshoot,Gain x Signal,ASE level(signal present),ASE level(signal absent),10.50 s,0.2.0.8 ms,off,on,off,Input
45、Signal,on,on,LW Technology(Passive Components).PPT-37 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Optical Gain(G),G=S Output/S InputS Output:output signal(without noise from amplifier)S Input:input signalInput signal dependentOperating point(saturation)ofEDFA strongly depends on
46、 power and wavelength ofincoming signal,Wavelength(nm),LW Technology(Passive Components).PPT-38 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Noise Figure(NF),NF=P ASE/(h G B OSA)P ASE:ASE power measured by OSA h:Planks constant:Optical frequencyG:Gain of EDFA B OSA:Optical bandwi
47、dth Hzof OSAInput signal dependentIn a saturated EDFA,the NFdepends mostly on thewavelength of the signalPhysical limit:3.0 dB,Noise Figure(dB),1540,1560,1580,1520,7.5,10,Wavelength(nm),5.0,LW Technology(Passive Components).PPT-39 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Gain
48、 Compression,Total output power:Amplified signal+ASEEDFA is in saturation if almost all Erbium ions are consumed for amplificationTotal output power remains almost constantLowest noise figurePreferred operating point Power levels in link stabilize automatically,P in(dBm),Total P out,-3 dB,Max,-20,-3
49、0,-10,Gain,LW Technology(Passive Components).PPT-40 Copyright 1999,Agilent Technologies,Revision 1.1February 21,2023,Polarization Hole Burning(PHB),Polarization Dependent Gain(PDG)Gain of small signal polarized orthogonal to saturating signal 0.05 to 0.3 dB greater than the large signal gainEffect i
50、ndependent of the state of polarization of the large signalPDG recovery time constant relatively slowASE power accumulationASE power is minimally polarized ASE perpendicular to signal experiences higher gainPHB effects can be reduced effectively by quickly scrambling the state of polarization(SOP)of
