Highly Reconfigurable Microwave Photonic All-Pass Filters based on Optical Microcombs

<title>Abstract</title> <p>Microwave photonic (MWP) all-pass filters (APFs), which enable phase manipulation without altering signal amplitudes, are essential for phase engineering in high-bandwidth microwave signal processing. However, achieving a high degree of reconfigurability in the filter order and characteristic parameters of APFs remains challenging for conventional methods. Here, we propose and experimentally demonstrate a new strategy for realizing MWP APFs based on a microcomb-driven transversal filter system, enabling high reconfigurability, sharp phase transitions with high group delays, and low loss. We experimentally demonstrate both 1st - and 2nd -order APFs, achieving a maximum amplitude variation (MAV) of ~ 1.95 dB and a maximum group delay (MGD) of ~ 580 ps for the former, and a MAV of ~ 2.01 dB and an MGD of ~ 1740 ps for the latter. In addition, both independent and joint tuning of APF characteristic parameters are demonstrated by simply programming the tap coefficients without changing any hardware, enabling highly reconfigurable filter response for diverse phase-engineering functionalities. These results highlight the potential of our approach for implementing MWP APFs with both high performance and reconfigurability for practical applications requiring dynamic and versatile phase control.</p>