Ultra-high performance microwave spectral filters using optical microcombs

Abstract: Microwave photonic (MWP) filters are essential components in microwave systems due to their wide bandwidth, low loss, and immunity to electromagnetic interference. A sharp transition band is critical for precise spectral shaping and interference suppression, yet conventional MWP filters face challenges in achieving both sharp transitions and high reconfigurability. Adaptive MWP filters with sharp transition based on a transversal filter structure using an optical microcomb source are demonstrated in this paper. Four different types of single-band MWP filters with roll-off rates up to ~32.6 dB/GHz and a minimum shape factor of ~1.15 are achieved. In addition, simply through designing tap coefficients, band-pass filters with tunable centre frequencies ranging from 5 GHz to 15 GHz and dual-band MWP filters with various filter response are demonstrated without changing any hardware, where sharp transition is also validated. The adaptive filters with sharp transition presented in this paper offer a stable and highly reconfigurable solution for applications requiring stringent spectral selectivity, such as next-generation wireless networks, high-resolution radar imaging, and advanced biomedical photonic sensing.