光波技术基础无源器件发送器和接收器光放大器等.ppt

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1、LW Technology(Passive Components).PPT-1 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Passive Components,LW Technology,LW Technology(Passive Components).PPT-2 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Patchcords,“Jumper cables”to connect devices and instrument

2、s“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 Tec

3、hnologies,Revision 1.1February 2,2023,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 compo

4、nent,LW Technology(Passive Components).PPT-4 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 optic

5、al 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 2,2023,Isolators,Main application:To protect

6、 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(Passive Co

7、mponents).PPT-6 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Filter Characteristics,PassbandInsertion lossRippleWavelengths(peak,center,edges)Bandwidths(0.5 dB,3 dB,.)Polarization dependenceStopbandCrosstalk rejectionBandwidths(20 dB,40 dB,.),LW Technology(Passive Components).PPT-

8、7 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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)Insertion

9、 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 2,2023,Tunable Fabry-Perot Filters,Filter shapeRepetitive passband with Lorentzian shapeFree Spectral Range FSR=c/2 n l(l:cavit

10、y 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 1.1February 2,2

11、023,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 dispersion

12、,LW Technology(Passive Components).PPT-10 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 port devi

13、cePort 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 2,2023,Add/Drop Nodes,Filter reflects l i,Add l i,Add/Drop,Dielectric thin-film filter design,Circulator with FBG design,Common,Passband,Drop l i,

14、LW Technology(Passive Components).PPT-12 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Multiplexers(MUX)/Demultiplexers(DEMUX),Key component of wavelength-division multiplexing technology(DWDM)Variety of technologiesCascaded dielectric filtersCascaded FBGsPhased arrays(see later)Hi

15、gh crosstalk suppression essential for demultiplexing,LW Technology(Passive Components).PPT-13 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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,l,1b,l,3d,l,

16、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 2,2023,Review Questions,1.What is the difference between a WIC and a W

17、DM?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 2,2023,Transmitters&Receivers,LW Technology,LW Technology(Passive Components).PPT-16 Copyright 1999,Agilent Technologies,Revision 1.1

18、February 2,2023,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(poor coupling int

19、o fiber),LW Technology(Passive Components).PPT-17 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Fabry-Perot(FP)Laser,Multiple longitudinal mode(MLM)spectrum“Classic”semiconductor laserFirst fiberoptic links(850 or 1300 nm)Today:short&medium range linksKey characteristicsMost common

20、 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 1.1February 2,2023,Distribu

21、ted 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 suppression ratio

22、(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 2,2023,Vertical Cavity Surface Emitting Lasers(VCSEL),Distributed Bragg Reflector(DBR)MirrorsAlternating layers of semiconductor

23、 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-20 Copyright 1999,Ag

24、ilent Technologies,Revision 1.1February 2,2023,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 input signalWavelen

25、gth 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,Agilent Technologies,

26、Revision 1.1February 2,2023,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 sequences of 1s or 0s(re

27、duced 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 2,2023,Modulation Principles,Direct(laser current)InexpensiveCan

28、 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,Agilent Technologies,Revis

29、ion 1.1February 2,2023,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 2,2023,Photodiodes,PIN(p-layer,intrinsic layer,n-layer)Highly l

30、inear,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 currentResponsivity(current vs.L

31、),Bias Voltage,APD Gain,LW Technology(Passive Components).PPT-25 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Material Aspects,Silicon(Si)Least expensiveGermanium(Ge)“Classic”detectorIndium gallium arsenide(InGaAs)Highest speed,Wavelength nm,500,1000,1500,Silicon,Germanium,InGaAs,

32、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 2,2023,Basic Receiver Design,Optimized for one particular Sensitivity rangeWavelengthBit rate Can include circuitsfor telemetry,LW Technology(Passive C

33、omponents).PPT-27 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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,noise from optical amplifiers,

34、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 2,2023,Regenerator,Receiver followed by a transmitterNo add or drop of trafficDesigned for one bit rate&

35、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,LW Technology(Passive Compon

36、ents).PPT-29 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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,RX,TX,ProtectionPath,Inter-l

37、eaving,.,.,Inter-leaving,SONET/SDHStreams,LW Technology(Passive Components).PPT-30 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Review Questions,1.What are the differences between an LED,FP,and DFB lasers?2.Which photodiode do you use forData communication?Speed longhaul traffic?3

38、.How do you define receiver sensitivity?,LW Technology(Passive Components).PPT-31 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Optical Amplifiers,LW Technology,LW Technology(Passive Components).PPT-32 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Erbium:rare elem

39、ent 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 wavelength&phase areidentical to incide

40、nt one,Erbium Properties,LW Technology(Passive Components).PPT-33 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Basic EDF Amplifier Design,Erbium-doped fiber amplifier(EDFA)most commonCommercially available since the early 1990sWorks best in the range 1530 to 1565 nmGain up to 30 d

41、B(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 2,2023,Amplified Spontaneous Emission,Amplifiedspontaneous emission(ASE),Random spontaneous emission(

42、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 amplified spontaneous emissionInput sign

43、al(s)consume metastable electrons much less ASE,LW Technology(Passive Components).PPT-35 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,Output Spectra,ASE spectrum when no input signal is present,Amplified signal spectrum(input signal saturates the optical amplifier),1575 nm,-40 dBm

44、,1525 nm,+10 dBm,LW Technology(Passive Components).PPT-36 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 Signal,on,on,LW Technology(Passive C

45、omponents).PPT-37 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 power and wavelength ofincoming sign

46、al,Wavelength(nm),LW Technology(Passive Components).PPT-38 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 bandwidth Hzof OSAInput signal dependentIn a

47、 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 2,2023,Gain Compression,Total output power:Amplifi

48、ed 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,-30,-10,Gain,LW Technology(Passive Compon

49、ents).PPT-40 Copyright 1999,Agilent Technologies,Revision 1.1February 2,2023,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 independent of the state of polarization

50、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 the input signal,LW Technology(Passive