Femtosecond-level laser-microwave synchronization based on an all-fiber optical-microwave phase detector

Abstract A laser-microwave synchronization system using an all-fiber optical-microwave phase detector (AFOM-PD) has been developed and experimentally validated at the Institute of High Energy Physics (IHEP). A Yb-doped fiber amplifier (YDFA) was employed to suppress the relative intensity noise (RIN) of the reference laser. And the root-mean-square (RMS) integrated RIN was reduced from 7.78 × 10 -4 before suppression to 6 × 10 -5 after suppression in the interval of 1 Hz to 1 MHz. The performance of this system has been demonstrated using a mode-locked fiber laser with a repetition rate of 29.1 MHz, in conjunction with L-band and S-band microwave signals. Residual phase noise levels of -118 dBc/Hz and -116 dBc/Hz at the 1-Hz offset frequency have been achieved for the L-band and S-band microwave signals, respectively. The integrated RMS timing jitters measured within the frequency range of 1 Hz to 1 MHz during the same experiments are 18.6 fs for the L-band signals and 6.0 fs for the S-band signals. Tests conducted over a 6-hour period have shown that this system can achieve a long-term RMS timing drift of less than 16 fs. This system has potential applications in the plasma wakefield accelerator currently being developed at IHEP.