FPGA-Integrated Digital Locking Scheme for Mode-Locked Fiber Lasers

This work demonstrates a simplified and compact locking scheme for a mode-locked laser (MLL) operating at a repetition rate of 111.13 MHz, using a rubidium (Rb) clock as the reference. The proposed system eliminates the need for bulky frequency synthesizers and commercial equipment by employing fully digital signal processing on an field programmable gate array. Using this locking system enclosed in the 13.5 × 10.5 cm case, experimental results show that an Allan deviation of 1.8 × 10⁻¹² at 1 s can be achieved, representing a five-order-of-magnitude improvement over the free-running MLL. The system also supports agile frequency tuning within the tuning range of the MLL. This design paves the way for cost-effective, compact solutions for precision frequency comb stabilization.