FPGA-based residual amplitude modulation suppression and control for compact atomic clocks

Abstract

We designed an 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 onto the same low-cost, commercial FPGA chip. We demonstrate a reliable, long-term RAM suppression 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.