An advanced digital controller with automatic design for laser frequency stabilization in space.

We present an advanced digital controller developed for laser frequency stabilization systems. A fully digital Pound-Drever-Hall (PDH) control scheme is implemented through direct digitization of the modulated optical signal, which is then demodulated in the digital domain and employs an inner-outer loop control module to lock the laser frequency to the cavity resonance. The design features automatic locking and relocking, where complex logic for signal verification and time-consuming monitoring is implemented using a state machine, thus enabling the system to automatically recover and prevent the locking procedure from getting stuck in a particular step. We also introduce a locked-state determination method based on spectral characteristic of closed-loop noise. Using fast Fourier transform (FFT) analysis and in-loop noise power evaluation, the locking state can be accurately determined within 8 milliseconds, eliminating the need for threshold selection. This research significantly advances autonomous optical control systems by demonstrating a highly efficient, reliable, and versatile PDH control system with strong potential for future space applications.