Advances in Widely Tunable Lasers

Advances in Widely Tunable LasersRichard SchatzLaboratory of PhotonicsRoyal Institute of Technology• Tunability of common semiconductor lasers• Widely tunable laser types• Syntune MGY laser: tuning principle & performance• Tunable modulation and wavelength conversion• The tunable transmitter of tomorrow1Why tunability?• Inventory reduction, sparing purposes(cost premium around 20% compared to DFB)• Spectroscopy• Measurement equipment• Tomorrow: Wavelength routing?21

Common Semiconductor Laser TypesFPFabry-Perot+ very simple- multimodeDBR BDFBDistributedBraggReflectorDistributedFeed-Back+ single mode+ electric tunability ~ 10 nm- two waveguide materials- two contacts+ simple- thermal tunability ~4 nm- inherently double modePS-DFBPhase-ShiftedDistributedFeed-BackVCSEL VerticalCavitySurfaceEmittingLaserTunability limited byΔλΔn≈ Γ < 1⋅10λn g−2+ single mode- thermal tunability ~4 nm- more complicated than DFB- needs antireflection coating+ on wafer testing: low cost- thermal tunability~2 nm-low power- difficult transverse single mode- difficult >1.2 μm3DFB arrayWidely Tunable LasersNTT (8 DFB)Fujitsu (8 DFB)Furukawa (12 DFB)Santur (MEMS-switch12 DFB)+ DFB technology+ stable λ- coupler loss- chip size- powe consumptionExternalcavitylaserTunable mirror or filterIolon, Nec,Pirelli, Fujitsu,Intel+ tuning range+ spectral properties- size- tuning speed- modulation speedMonolithicDBR laserwith sampledgratingSG-DBRDS-DBRJDSU (Agility)BookhamSyntune+ monolitic (incl. SOA &modulator)+ size+ tuning speed+ power consumption+ control- electrically induced- phase noiseMGY-laserJens Buus and Edmond J. Murphy, Tunable Lasers in OpticalNetworks,Journal of Lightwave Technology, Vol. 24, Issue 1, pp. 542

Modulated Grating Y-branch Laserfabricated by SyntuneWide tuning by additive Verniereffect using two slightly differentmulti-peak reflectorsUpperLowerUpper reflectorMMILower reflectorCommonphaseGainFrontfacet540 nm tunability with high side modesuppression ratio and output powerSMSR > 40 dBOutput power > 10 dBmPower variation < 1.5 dB withoutcompensation63

Direct Modulation vs ModulatorI bias +ΔI+I bias+ -V bias +ΔV+ Simpler+ Higher Output Power+ Inherently Linear Modulation(Radio over fiber applications)+ Lower Chirp+ Higher Extinction Ratio+ Higher Modulation Bandwidth7Syntune S4500 C-band tunable 10 Gb/stransmitter• Monolithically integrated MGY+SOA+MZM• Full C-band tuning (89 channels at 50 GHz spacing)• 40dB SMSR• 4dBm output power•

Directly Modulated MGY-laser using chirpmanaged transmissionChirp adjusted so that azero cause a π phaseshift,”101” becomes ”10-1”→ dispersion tolerantExternal filter utilizes thechirp to enhanceextinction ratioMatsui et al.,Widely Tunable Modulated Grating Y-branch Chirped Managed Laserpostdeadline ECOC 2009910 Gb/s over 200 km standard fiber using directmodulation and chirp managed transmission• 18 GHz bandwidthdt• Error free 10 Gbit/stransmission over 200 km• 10-18 mW output power atall wavelengths• 11-12 dB Extinction ratioMatsui et al.,Widely Tunable Modulated Grating Y-branch Chirped Managed Laserpostdeadline ECOC 2009105

Tunable wavelength conversion (1530-1560 to 1530-1560)at 10 Gb/s with MGY-laser integrated with SOASOA IFRGainMMIRight reflectorCommonphaseLeft reflector•Utilising cross-gain modulation in SOA•Conversion efficiency 20-70%•Collaboration with University of GhentChacinski et al. OFC 200711Recent Advances in Widely TunableLasersRichard Schatz• Tunability of common semiconductor lasers• Widely tunable laser types• Syntune MGY laser: tuning principle & performance• Tunable modulation and wavelength conversion• The tunable transmitter of tomorrow126

Packaged DFB-laser integrated with Trawelling-Wave Electroabsorption Modulator for 100 GbE• 100 Gb/s NRZ PRBS 2 31 -1• 0 dBm average power• 4.3 dB extinction ratio13Fiber DispersionDispersive fiberDistance ∝ 1/(Bitrate) 210 Gbit/s: 65 km40 Gbit/s: 4 km100 Gbit/s: 650 m!The solution?Adaptive dispersioncompensation needed butstill difficult to reach e.g. 65km with 100 Gbit/s!147

Radio Evolution vs Photonic Evolution1887Spark gapTransmitterOn-Offkeying1903First arctransmitterwithcontinuosradio wavesFSK keying1906First radiobroadcast ofvoice andmusicAMmodulation1914FirstcoherentradiotransmitterAMmodulation.1915FM stereoBroad-casting1918Superhetero-dynereceiver1961SSBmodul-ation1933FMmodul-ation.SubcarrierFMmodulation.1962First pulsed1970First CW1970First low loss1975First DFB1985-1989Research onsemiconductor semiconductor optical fiber singlemode coherentlaser laser laser opticalreceivers1987First ErbiumdopedFiberAmplifierToday fiber-optic systems for telecom still utilize simple on-offkeying and direct detection (Morse code and crystal receiver)15Radio systems today are the future for photonics1991199119941995199819982001GSMWiFiGPSDVBSADSLDVBTUMTS (3G)GMSKGaussianMinimumShiftKeyingOFDM orCCKOrthogonalfrequency-divisionmultiplexingCDMACodeDivisionMultipleAccessQPSKQuadraturephase shiftkeyingDMTDiscretemultitoneOFDMwith QAMW-CDMANext generation optical transmission i systems will beadvanced digital radio systems at optical frequencies168

Use more advanced modulation formats!DQPSK, QPSK, QAM, OFDM, SCM, SSB...Higher spectral efficiency( lower modulation bandwidth for same bitrate)•Better tolerance to fiber dispersion•More wavelength channels per fiber (or higher bitrate forsame channel grid)•Lower bandwidth demands of electronics and photonics17Different carrier modulation formatsOOK PSK QPSK 16-QAM1bit/symbol 1bit/symbol 2bits/symbol 4bits/symbolPolarization multiplex yields another doubling of capacitywithin same WDM channel189

Optical QPSK system with Polarization Multiplex(one channel in a WDM system)Complex integratedoptical transmitters &receivers will be neededfor low cost!19Subcarrier modulation1-20 subcarriers, RF-generatedMulticarrier modulation formatsOptical CarrierOFDMOrthogonal FrequencyDivision Multiplex100-10000 subcarriers,digitally generated.Carriers orthogonal overbitslot200 THz±k . 10 GHzCDMACode Division Multiple AccessCarriers” consist of orthogonal digital code sequenciesinstead of sinuses200 THz±k . 10 MHz2010

Optical Subcarrier System for 100GbE• Compare with ADSL modem for high speed data over telephone line• High demands on linearity of modulator and detector• Integrated optical components needed for low cost21400km Transmission of 12.5 Gbit/sBaseband and DVBT on 45 GHz SubcarrierIP dataTunableLaserM-ZModulator0-10-20-30-40-501549.5 1550 1550.5 1551λSignal on fiber with IPdata in baseband andDVBT on subcarrierIP dataOther signal,e.g., DVBTMixerSubcarrier@ GHzFBGUpper sidebandfiltered out anddirectly detectedwith low speedPIN detectorλ BOther signal,e.g., DVBTFBGDispersion tolerant since onlyone sideband is usedResidual lowersideband isfiltered away byreceiver filter2211

Final conclusions• Monolithic 10 Gbit/s widely tunable lasers are today integrated withmodulators and manufactured at high volumes and low price• Monolithic devices offers fast tuning