Microwave photonic transversal filters based on microcombs with feedback control

Abstract: Feedback control plays a crucial role in improving system accuracy and stability for a variety of scientific and engineering applications. Here, we theoretically and experimentally investigate the implementation of feedback control in microwave photonic (MWP) transversal filter systems based on optical microcomb sources, which offer advantages in achieving highly reconfigurable processing functions without requiring changes to hardware. We propose four different feedback control methods including (1) one stage spectral power reshaping, (2) one stage impulse response reshaping, (3) two stage spectral power reshaping, and (4) two stage synergic spectral power reshaping and impulse response reshaping. We experimentally implement these feedback control methods and compare their performance. The results show that the feedback control can significantly improve not only the accuracy of comb line shaping as well as temporal signal processing and spectral filtering, but also the systems long term stability. Finally, we discuss the current limitations and future prospects for optimizing feedback control in microcomb based MWP transversal filter systems implemented by both discrete components and integrated chips. Our results provide a comprehensive guide for the implementation of feedback control in microcomb based MWP filter systems in order to improve their performance for practical applications.