Low-drift and low-jitter microwave signal synthesis from mode-locked lasers

The conversion of optical signals into electronic signals is the major bottleneck in transfer of timing stability. Excess phase noise and drift in the photodetection processes limits the achievable microwave signal quality. We report on the microwave signal synthesis from mode-locked lasers using a new type of an optoelectronic phase-locked loop (PLL). This PLL is based on the phase detection between optical pulse trains and microwave signals in a differentially-biased Sagnac loop interferometer. The measured out-of-loop timing jitter in a 1 MHz bandwidth integrated over 10 hours is 6.8 fs (rms). The relative timing stability in the microwave signal read-out process reaches 1.9times10^-19 in 36000 seconds.