ECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 1Lecture 11: WavelengthConversionECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 2Optical Wavelength Conversion Process of transferring data from one optical wavelength toanother without modifying the content of the data Two main approaches Optical electronic Optoelectronic optical (OEO) Optoelectronic IC (OEIC) All-Optical Each approach employs one or a combination of physical“nonlinear” process to transfer data between wavelengths Free carrier modulation (governed by carrier dynamics) Bound carrier modulation (ultra-fast response time > 1THz) Field modulationECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 3Optical Wavelength Conversion MetricsAddition of chirp or RIN to output signal relative to input signalChirp and RIN PenaltyAbility to convert input wavelength to same wavelength at outputSelf-ConversionRatio of input to output SNRNoise FigureInverting and/or non-inverting digital operationPolarity1R, 2R or 3R regenerative or regenerative capableRegenerative CapabilityMinimum optical power at input to achieve minimum required BERSensitivitySensitivity in optical output signal (efficiency, etc.) to changes in input polarization statePolarization DependenceRange of optical input power at original wavelength that achieves required performanceInput Dynamic RangeRange of output wavelengths (converted)Output Optical BandwidthRange of input wavelengths over which required optical performance at output can beachievedInput Optical BandwidthRatio of the power in the “one” bit to the “zero” bit at the output converted wavelengthModulation Extinction RatioRatio of the average power in the original and new wavelengths at outputConversion Extinction RatioAverage power in the output wavelength relative to the input wavelengthConversion EfficiencyThe range of bit rates (hi and low) that the converter will operate without major adjustmentsBit Rate TransparencyThe range of modulation techniques and bit formats that can be transferred from the input tothe output (incoherent, coherent, multi-level, RZ, NRZ, etc)Modulation and FormatTransparencyDescriptionMetricECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 4Wavelength Conversion ProcessesOEO OEICFree Carrier ModulationBound CarrierModulationField ModulationAll-OpticalFree Carrier ModulationSemiconductor Optical Amplifiers (SOA)Cross GainModulation (XGM)Cross Phase Modulation(XPM)Injection Locked LasersOptical FibersCross Phase Modulation(XPM)OEFour-Wave Mixing(FWM)Four-Wave Mixing(FWM)Lithium NiobateDifference FrequencyGeneration (DFG)Field ModulationElectro-AbsorptionModulators (EAM)Cross AbsorptionModulation (XAM)Cross PhaseModulation (XPM)Photocurrent AssistedModulation (PAM)ECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 5Wavelength Converter FunctionLaser Laser SourceSourceData modulated Data modulated λλininWavelength selectWavelength selectif tunableif tunableOptically orOptically orElectricallyElectricallyDriven Driven ModulatorModulatorOpticalOpticalFilteringFilteringElementElementλλoutoutλλoutout••Optically driven requiresOptically driven requiressome form of nonlinearsome form of nonlinearoptical mediumoptical medium••Electrically driven requiresElectrically driven requiresOEOOEO••Optical filtering requiredOptical filtering requiredif signals are mixed in co-if signals are mixed in co-propagating geometry andpropagating geometry andcan be located in variouscan be located in variousplaces in converterplaces in converterλλinin+ + λλoutoutECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 6OEO Data is fully converted toelectronics Electronic thresholding is usedto re-shape the data (2R) and/orclock recovery is used to re-shape and re-time (3R) Laser and external modulator (ordirect modulation) is used to re-transmit regenerated data onnew wavelength Digital logic largely decouplesdesign requirements for detectorand modulatorλλininReceiverReceiverLaserLaserModulatorModulatorλλoutoutλλininReceiverReceiverLaserLaserModulatorModulatorClock andClock andData Rec.Data Rec.λλoutout2R OEO2R OEO3R OEO3R OEOAmplifierAmplifierECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 7OEIC This technique involves a back-to-back detector/externally modulated laser. Data is converted(as in OEO) to electronic domain and used to re-modulate as laser. The difference is that noelectronics are placed in between the detector and laser. The design of the detector and modulator each have unique set of constraints. Hardwiring thetwo together means there has to be a balancing of the requirements for optimal detection andmodulation.PDLaserBias 1Pre AmpSOABias 2Bias 3Bias 4Post AmpCurrent monitorDirect Drive ConfigurationExternal Modulator ConfigurationPDBias 1Pre AmpSOABias 2ModulatorBias 4Post AmpLaserBias 3λinλoutλoutλinECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 8OEIC Issues Optical pre-amplification critical to boost input signal in shot noise limit forphotodetector Optical-preamplifier must be linear (no distortion, no bit-patterning) Photodetector must be designed to balance speed, responsivity and ability to drive largeenough photocurrent with output load. ApproachesSGDBROn chip amplifiersQCSE EAMPIN-PDIntegrated uni-traveling carrier photodiodes, highsaturation power SOAs, tunable laser and EAMM. Sysak et. al. (UCSB)Receiver SOASOAsSGDBRQW DetectorMZPhaseMach-ZehnderM. Sysak et. al. (UCSB)Hybrid SOA preamplified receiver and MZ Interfermeter(MZI) tunable transmitterECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 9Free Carrier All-Optical: SOAs Semiconductor Optical Amplifiers (SOAs) Intensity of data modulation produces changes in gain (and phase viaKramers-Kronig) in the SOA Input driven changes in gain (phase) in SOA can be used to modulateinformation onto new optical carrier supplied by local laser source(can be tunable).ECE228B, Prof. D. J. Blumenthal Lecture 11, Slide 10SOA Cross Gain Modulation (XGM) Input data is intensity modulated on λin (probe). Induceds gain compression in the SOA that is seen by λout(signal). Data is inverted Extinction ratio at output is lower than at input Asymmetry in wavelength up-conversion vs. down-conversion due to wavelength dependent saturationpower Co-propagating probe and signal need for high bit rate (>10Gbps) operation. Therefore need filter forsignal separation.EcEvPinGPin+ PASEAstAstAspASEASE + SignalSOA Power Spectrum