Fischer, U.H.P.U.H.P.FischerGladisch, A.A.GladischGiehmann, L.L.Giehmann2022-03-032022-03-031996https://publica.fraunhofer.de/handle/publica/18951710.1006/ofte.1996.0019The relative optical frequency stabilities of three optical reference units at 1547.825 nm were examined. The reference units were located at different places in Berlin and connected via several kilometres of optical fiber. The three optical signals were heterodyned to measure the frequency stabilities, which were better than 2*10-11 at 1000 s sample time.endemodulationfrequency stabilitymeasurement standardsoptical fibre subscriber loopswavelength division multiplexingoptical frequency referenceshdwdm systemsfield conditionsrelative optical frequency stabilitiesoptical reference unitsberlinoptical fiber subscriber loopsheterodynedfrequency stability measurementsample time1547.825 nm621journal article