Digital Laser Frequency Stabilization Using an Optical Cavity

Pound-Drever-Hall locking is a high performance technique for laser frequency stabilization. Radio frequency optical modulation combined with electronic demodulation provides a feedback signal to lock a laser's frequency to a cavity resonance. Although the demodulation and feedback system are typically implemented using analog electronics, digital implementations are now possible thanks to recent advances in digital signal processing. Aside from flexibility, digital systems have improved performance at low frequencies where electronic noise may be a problem. In this paper we analyze several noise sources that appear in a digital Pound-Drever-Hall locking loop and estimate their effect on the performance of the stabilization system. Furthermore, we implement a digital Pound-Drever-Hall scheme and characterize the feedback performance by beating two lasers locked to a single cavity. A relative frequency noise floor of 0.2 Hz/¿(Hz) above 3 Hz was measured, giving an upper bound on the noise performance of the digital system.