Optical_frequency_transfer

Opticalfrequencytransferviatelecommunicationfibres20.11.2012,„OpticalNetworksforAccurateTimeandFrequencyTransfer“Internationalworkshop,EMRP-projectNEAT-FT.Hoofddorp,TheNetherlands.viatelecommunicationfibresGesineGrosche,PTBBraunschweig,Germany*LUHHannover,Germany,#MPQGarching,GermanyS.M.F.Raupach,O.Terra,U.Sterr,H.Schnatz,A.Pape*,J.Friebe*,M.Riedmann*,E.M.Rasel*,S.Droste#,K.Predehl#,Th.Udem#,R.Holzwarth#a)disseminationoftheunitoflength/remotecalibration:δλ/λ=δν/ν≈10-6…10-10b)compareopticalfrequencystandards(overlongdistances)fundamentalconstants(mp/me,α)δν/ν≈10-13…10-18TransferthestabilityandaccuracyofafrequencyreferencetoadifferentlocationApplicationsoffrequencydisseminationpeδν/ν≈10-13…10-18c)useoneultra-stable„master“-laserformanyexperimentsremotespectroscopy,remoteμ-wavesynthesis:short-terminstabilityσν10-15(1s)d)remotesensing&synchronization–telescopes,accelerators,geodesy,LIGO;frequencyasa„probe“-GR,SRδν/ν≈10-12…10-20…?BasicsBasicsOpticalfibrenetworks:advantages
existinginfrastructure:fibrenetworksacrossEurope,opticallytransparent;amplifiers
lowattenuation:25dB/100kmforradiationat1,55μm(200THz)
protected,lownoise:4
manyactiveandpassivecomponentsopticaltelecommunications
femtosecondmodelockedlasers:frequencycombsat1,55μm
protected,lownoise:buried,undergroundfibrebroadcasting-DCF77=29EFTF2012-Tutorial©GesineGrosche,PTBChallenge1:delayvariations,„phasenoise“Problem:thermalvariationandmechanicalperturbationschangepathlength:refractiveindexnchangesU(τ)~4nsforL=100kmandΔT=1K(τ=500μs)dtdnLnLdtdtdtdtfibreλλϕπν≈=Δ=Δ)(21)(dn/dT~10-5/K5(τ=500μs)
mirroratremoteend
“repeater”,slavelaserlockedtoincomingsignal
two-wayapproach:simultaneoustransmissioninbothdirectionsSolution:bi-directionallinkstodetectandcorrectnoisedtdtλλEFTF2012-Tutorial©GesineGrosche,PTBAsymmetry?!Challenge2:signaltonoiseratioProblem
attenuation25dB/100km400km100dB
reflectionsatsplices/connectors
scattering(Brillouin,Rayleigh)6
amplify–Erbiumdopedfibreamplifiers,FibreBrillouinamplification,…
regenerate–“repeater”,slavelaserlockedtoincomingsignal
filter–opticalfilters,heterodynedetection,phase-locked-loops…SolutionsEFTF2012-Tutorial©GesineGrosche,PTBAmplifiednoise?!)(tfibreϕΔLaserνoνremotedtdnLmechλν≈Δ)(21)(tdtdtfibreϕπνΔ=Δkm100=LmechHz1000/1010811=×≈Δ-sνservo*Compensationofphasefluctuations7Similaridea:LSMa,etal.Opt.Lett.1777(1994);s/mK1/K/10/147.1μm5.1km1005≈≈===-dtdTdTdnnnLmechλ0)(21)(=Δ=Δtdtdtfibreϕπν*•acousto-opticmodulator(AOM)atinput•short(2m…toafewkm)fibrelinksbasedonopticalcarrierareroutinelyusedinmanymetrologylabswith10-16resolutionEFTF2012-Tutorial©GesineGrosche,PTB[Ros08],...FiberUnderTest2.NoisesuppressionExperimentalimplementation2/synth0remotef+=ννfigureadaptedO.Terra,G.Grosche,K.Predehletal.Appl.PhysB97,541(2009)146kmlink:„delaylimit“offibrenoisesuppression10-310-1101103theoreticallimit4π2/3*(fτD)2Δν=100HzΔν=1Hzunstabilized146km,remoteend(rad2/Hz)Δν=πSν100m1101001k10k10-710-510stabilized146km,remoteendSϕ(f)Fourierfrequencyf(Hz))()(3/4)(22fSffSfiberDremote⋅⋅=τπ[1][1]P.A.Williamsetal.JOSAmB251284(2008)goodPASSIVEstabilityoffibreisimportant![2]G.Grosche,O.Terra,K.Predehletal.Opt.Lett.(2009)figureadaptedfrom[2]FirstsectionofGermanfibrenetworkPTB→UniHanover→PTB,146kmstabilizedlink10-1710-1510-13146kmstabilizedlink20munstabilizedfiberopticalclocks:Al+/Hg+ratio[1]Allandeviationσy(τ)GPS-carrierphase[9]10kHzBW11010010001000010-2110-19noisefloor[6]convertedtoADEVinterferometernoisefloorAllandeviationintegrationtimeτ(s)fig.adaptedfromG.Grosche,O.Terra,K.Predehletal.Opt.Lett.34,2270(2009)σy=3×10-15/τs-1=Application:73kmlinktoIQlabsrel.uncertainty:10-19σy~L3/2L=fiberlengthequiv.timingjitter~3fs=estimateσy=5×10-14/τs-1for900km10kHzBWApplicationsApplications3.Remotemeasurements-viaBraunschweig-Hanoverfibrelink•Mgopticalfrequencystandardmeasurement–longtermaccuracy•Mgclocklaserimprovement–shortterminstability•Hydrogenmaser„calibration“;referenceforGNSS„Remotefrequencymeasurementofthe1S0-3P1transitionin…“JanFriebe,…GG,..E.M.Rasel;NewJ.Phys.13,125010(2011)„Long-distanceremotecomparisonofultrastableoptical…“AndrePape…GG;Opt.Exp.18,21477(2010)fig.adaptedfromO.Terra,PhDDissertation,LUHanover2010FiberfromPTBMg-clockatIQ,UniversityHanoverPTB,BraunschweigRemotespectroscopy:improvinganopticalclocklaser74kmfibrelink+twofs-combs1Hzbeatsignal(:4)914nmlaser(„Mg2“Hanover)vs657nmlaser(„Ca“PTB)O.Terra,G.Grosche,W.Ertmer,J.Friebe,T.Legero,B.Lipphardt,A.Pape,K.Predehl,E.Rasel,M.Riedmann,U.Sterr,T.WübbenaundH.Schnatz:“Frequencymeasurementofamagnesiumfrequencystandardusingacommercialtelecommunicationfiberlink”,Proc.SPIE,Vol.7431,74310B(2009);A.Pape,O.Terra,J.Friebe,M.Riedmann,T.Wübbena,E.M.Rasel,K.Predehl,T.Legero,B.Lipphardt,H.Schnatz,andG.Grosche,Long-distanceremotecomparisonofultrastableopticalfrequencieswith10-15instabilityinfractionsofasecond,Opt.Express18,21477-21483(2010):4Futureapplication:remotespectroscopySeveralclockswithonelasersource1.Onemasterlaser2.Fibrelinkstransportlighttoop