A highly precise fiber delay fluctuation measurement with a wide range

We propose a time delay fluctuation measurement method with high precision and wide range. The round-trip time delay fluctuation of a 40 km optical fiber link from the phase of a transmitted 20.02 GHz signal is transferred into the one of an intermediate frequency by using dual heterodyne phase error transfer. It allows a precise measurement of the time delay fluctuation by measuring the phase of the RF signal. Frequency division of the intermediate frequency is applied to realize the wide range of delay fluctuation measurement. The resolution of the measurement can be reached at 27 fs and the range can be 6.25 ns.