FPGA-Driven Soliton Locking for Reduced Manual Intervention in Microcombs

In this article, we propose and demonstrate a soliton locking structure based on FPGA control. The FPGA integrates all necessary control modules for power-kicking control and incorporates additional techniques to simplify the locking process and reduce the need for manual intervention. These techniques include decoupling the PZT driving voltage from the laser frequency through pre-distortion, using reinforcement learning to elongate the soliton, and implementing automatic soliton tracking to cancel the relative frequency drift between the pump laser and the microresonator. In our experiment, each locking attempt requires only 8.24 ms. On average, approximately 10 attempts are sufficient to re-lock single soliton after an abrupt vibration induced by beating the optical table, resulting in an average locking time of 82 ms. The FPGA-based system automatically detects and re-locks without manual intervention, ensuring reliable soliton locking. The results show that this structure effectively locks single solitons in silica microcombs for both 17 GHz and 22 GHz microresonators with a Q factor above 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup>, showing a state-of-the-art stability and robustness.