光纤通信课程设计课件Class3-03.pptx
Class 3Class 3Chromatic dispersion effectDispersion compensating techniquesOptimization of residual dispersion or its map010011timefcarrierfreq.ViVjVkFourier Information Bandwidth of Data Temporal Spreading f(distance,(bit rate)2)(ps/nm)/kmtimeFibertimePhoton Velocity(f)=Speed of Light in VacuumIndex of Refraction(f)Control Packet(C.P.),not payload,is regenerated at every node C.P.has lower bit-rate(C.D.effect (bit-rate)2)There is higher chance for payload to be degradedNodeNodeNodeNodettttPayloadC.P.Polarization-mode-dispersion(PMD)Polarization dependent loss(PDL)Degradation based onnon-catastrophicevents Random polarizationcouplingStatistically varies with timeBit-rate andwavelengthdependentPolarization state generally unknown and wanderscross sectionElliptical Fiber Coreside view PMD induces randomly changing degradations.Critical limitation at 10 Gbit/s payload data rates.The 2 polarization modes propagate at different speeds.1st-order PMD=DGD(A)(B)DGD PMDHow many segments will beenough to emulate PMD?Ans.=12Principle State of PolarizationProved 1986 Bell Labs C.D.Poole&R.E.WagnerTwo PSP perpendicular to each other independent of wavelength to the first-orderPSPin 球面上的每一个点都代表了一种椭圆偏振态，在两极演化为右旋、左旋圆球面上的每一个点都代表了一种椭圆偏振态，在两极演化为右旋、左旋圆偏振光，在赤道退化为线偏振光，北半球为右旋偏振态，南半球为左旋偏偏振光，在赤道退化为线偏振光，北半球为右旋偏振态，南半球为左旋偏振态。所以，偏振光在光纤传输过程中的任意偏振态的变化都可以表示成振态。所以，偏振光在光纤传输过程中的任意偏振态的变化都可以表示成邦加球上的邦加球上的某一条运动轨迹某一条运动轨迹 PMD temporal changes more rapidly with the fiber length and average DGDFrequency of occurrence induced by PMD fluctuationTime Span(ms)Occurrence52 km fiber=2.8 ps(b)Fast Fluctuation Mechanical vibrations:milliseconds to minutesH.Bulow,et al.,OFC 1999Time Rate of PMD ChangePMD(ps)1.52.02.5101418Temp.(C)Time(min)040080048.8 km buried cable(a)Slow Fluctuation PMD variations due to temperature changes:hours to daysJ.Cameron,et al.,OFC 1998PMD Monitoring Techniques Requires high-speed devices(demonstrated for 160 Gb/s RZ signal)Affected by other distortion sources+Can be integrated with electronic equalizationA.Eye opening measurementB.RF spectrum analysis+No high speed electronics+Depends only on PMD+Bit-rate independent+Unaffected by other distortion sources Pulse-width dependentC.Degree of polarization(DOP)measurement+Simple Affected by other distortion sources Sensitivity and DGD range depends on monitored frequencyGoalTo gain an understanding of the temporal and spectral characteristics of PMD on an installed fiber link.ApproachMake long-term measurements of the differential group delay(DGD or)over a range of wavelengths and assess its rates of change with time and .Desired outcomeProvide network operators with knowledge to evaluate techniques for mitigating PMD-induced outages when channel dataPC forRemote Control&Data StorageTunable Laser Source(TLS)(1510 1625 nm)=0.1 nmPolarization Analyzer(PA)(Jones Matrix Eigen Analysis)Instrument Controller Fiber loopback:95-km span of slotted-core,direct buried fiber-optic cable made available by Sprint.Over 86 days(from November 9,2001 thru February 2,2002)692 measurements were made on the 1150 discrete wavelengths.Measurements were repeated about every 3 hours.86 days of data795,800 data ptsObservationsDGD depends on both time and.DGD varies slowly with time.DGD varies rapidly with.Instances of high DGD are spectrally localized.PMD characterization:Probability density function ObservationsMeasured data show good agreement with Maxwellian distribution.There is a low probability of high DGD events(i.e.,DGD 3 mean DGD).Theoretical results from outage model:Rx Threshold 3 3.7 Span 1MTBO6.39 years1648 years!Outage duration 136 minutes 108 minutesMTBOs:mean time between outagesFiberSim:SMF/Leaf Comparison75 km75 km10 Gb/s per channel25 channels75 kmDCF/EDFADCF/EDFA.DCF/EDFARxTxDifferent Fibers:Eye Diagrams vs.Distance 75km 450km 750km 1050kmSSMF LinkNZDSF LinkCompensation ConfigurationsOutputInputSqueezers(00)Squeezers(450)Optical FiberABCDEPMFEfficient optical modulation formats:WDM+SCMOptical MUXAdd/dropTransmitter 1f1Sf2ch.2fnch.n.1LDch.1m1f1Sf2ch.2fnch.n.Receiver 1ch.1Optical DMUXf1Sf2ch.2fnch.n.Receiver mch.1Transmitter mf1Sf2ch.2fnch.n.mch.1LDEfficient optical modulation formats:Combat PMD-induced signal fadingusing diversity SCM receiverTxPolarization controllerRF detectionSLPFAmp.Control algorithmTo decision circuitSpliterPBSRF detectionPD 1(b)PD 2(a)PD 1PD 2What are we going to use to reduce PMD?Optical Delay LineEffect of compensationScan thru delay length(time)Homework:Two-staged compensationWe tested this setup in a installed fiber link before!Homework:Two-staged compensationMeasurement Instruments
