Phase Stability Measurement of an Optical Two-Tone Signal Applied to a Signal Reference Source for Millimeter and Sub-Millimeter Wave Interferometer

摘要

Localsignalgenerationwithhighphasestabilityisoneofthekeyelementsofaninterferometersystem.IntheALMA(AtacamaLargeMillimeter/submillimeterArray)project,wehaveplanstogenerateandtransmitamicro/millimeter-waveLO(LocalOscillator)referencesignalasanopticaltwo-tonesignal.Torealizethis,weintroduceamethodtogenerateanopticaltwo-tonesignalbydoublesidebandsuppressedcarriermodulationwithalithiumniobate($$mathrm{LiNbO}_3$$)Macha€“Zehnderopticalmodulator.ThephaseinstabilityoftheLOsignalcausesalossofcoherenceintheinterferometer.WemeasuredthephaseinstabilityandestimatedthecoherencelosswhileassumingthehighestfrequencyofALMALO.TheobservedAllanstandarddeviationfor22a€‰GHzwas$$1.9 imes10^{-14}$$at1a€‰s.Additionalnoisewasfoundatalongertimescalethan4a€‰s;however,thereasonisnotwellunderstoodatthisstage.Ifthisadditionalnoisewasclassifiedaswhitefrequencynoise,theestimatedcoherencelosswas5.2%when938a€‰GHzfrequencyanda100-sintegrationtimewereassumed.Ontheotherhand,ifthisadditionalnoisewascausedbysomeothereffect,forexamplephasefluctuationoftheamplifier,thecoherencelosswasestimatedtobe0.33%at938a€‰GHzfrequency(100a€‰s).