Field-programmable gate array-based residual amplitude modulation suppression and control for compact atomic clocks

We designed a field-programmable gate array (FPGA) fabric to provide phase modulation techniques to lock lasers to optical frequency references. The method incorporates an active residual amplitude modulation (RAM) suppression scheme that relies on complex modulation. All the required servos to construct an optical atomic clock are incorporated into the same low-cost, commercial FPGA chip. We demonstrate a reliable, long-term RAM suppression of 60 dB with the remaining RAM level at −100 dBc and an improved stability of three decades when applied on a two-photon rubidium clock.