Highly Reconfigurable All-Pass Microwave Photonic Filters using Optical Microcombs

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 MWP APFs based on a microcomb-driven finite-impulse-response (FIR) transversal filter system, enabling high reconfigurability and sharp phase transitions with high group delays. We experimentally demonstrate both 1st- and 2nd-order APFs, achieving maximum amplitude variations (MAVs) down to ~1.95 dB and maximum group delays (MGDs) up to ~580 ps for the former, and MAVs down to ~2.01 dB and MGDs up to ~1740 ps for the latter. In addition, by simply programming the tap coefficients without changing any hardware, we experimentally demonstrate a high degree of filter reconfigurability with respect to filter order, group delay, center frequency, and independent control of multiple APF parameters. 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.