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.
We demonstrate a stable coherent dual comb generator with two phase/intensity-modulated combs. The optical fiber path induced phase fluctuation results in the coherent dual comb beating phase noise. We transfer this phase noise to a 40MHz intermediate frequency with dual-heterodyne phase error transfer, decreasing by a phase-locked loop and optical phase locked loop. Under the scheme, stable coherent dual comb with slightly different repetition rates and offset frequency is generated.
We have demonstrated an optical generation of highly stable millimeter-wave signal distribution system, which transfers a 300GHz signal to two remote ends over different optical fiber links for signal stability comparison. The transmission delay variations of each fiber link caused by temperature and mechanical perturbations are compensated by high-precise phase-correction system. The residual phase noise between two remote end signals is detected by dual-heterodyne phase error transfer and reaches -46dBc/Hz at 1 Hz frequency offset from the carrier. The relative instability is 8×10-17 at 1000s averaging time.