FPGA-Based Optical Cavity Phase Stabilization for Coherent Pulse Stacking
IEEE Journal of Quantum Electronics
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable and distributed digital control system with firmware and software integration for algorithms, to support the coherent pulse stacking application. We model coherent pulse stacking as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection
... e detection algorithm on an FPGA. A 2-stage (2+1 cavities) 15pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5 kHz, and stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg RMS phase errors for Stage 1 and Stage 2 respectively. Optical cavity phase control with nm accuracy ensures 1.2% intensity stability of the stacked pulse over 12 hours. The FPGAbased feedback control system can be scaled to large numbers of optical cavities.