Enhanced Frequency Stability Over Fiber Link With Improved Phase Discrimination Scheme

We demonstrate a phase-stability radio-frequency (RF) dissemination system via fiber link with direct phase discrimination. The phase fluctuation of the RF signal is identically transferred to a 10 MHz intermediate frequency (IF) by using dual-heterodyne phase error transfer. It guarantees that the phase discrimination of the IF signals and the atomic clock frequency signal can be directly performed without the frequency division or multiplication. This scheme can enhance the frequency stability of the dissemination system by mean of higher precision phase detection and high noise suppression capability. Experimentally, the residual phase noise of compensated system with improved phase detection scheme is -50 dBc/Hz and -67 dBc/Hz at 0.01 Hz and 1 Hz frequency offset, respectively, the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches about 50 fs. Compared with the frequency division and multiplication methods, the frequency stability is improved nearly one orders of magnitude to 5 × 10
^-17
at 2000 s averaging time.