Abstract
A back-to-back time transfer system based on two integrated microcombs and linear optical sampling is demonstrated, establishing the feasibility of chip-scale microcomb sources for precision time–frequency metrology. Two microcombs with repetition rates near 20 GHz are built and repetition-rate locked before asynchronous heterodyne sampling. By tuning the initial optical-frequency offset between the two combs, the linear–optical–sampling signal is shifted into the bandwidth of low-frequency balanced photodetection and oscilloscope acquisition. In a dual-channel balanced-detection configuration, a time deviation of approximately 11 fs at an averaging time of 1 s is obtained. The results demonstrate coherent mapping of a microwave reference onto microcomb pulse trains and femtosecond-level readout of their relative timing, establishing the feasibility of integrated microcombs for precision time–frequency transfer.