High-precision fiber-optic time transfer with an unlimited compensation range

We present a fiber-optic time transfer system with high transfer stability and an unlimited compensation range of the delay variation. We first stably transmit a frequency signal from a voltage-controlled oscillator to the remote site. The time signal is then embedded in the frequency signal by simply selecting its one cycle per second with a tunable gate signal. Therefore, the proposed time transfer system inherits both the stability and the unlimited adjustment range of the frequency transfer yet with no need for demodulation. The time deviation of 1.93 ps is achieved at 1000-s averaging. This simple and demodulation-free time transfer system is applicable for scalable distributed applications that require high-precision time synchronization and wide-range delay compensation.