Reconfigurable Bandpass Microwave Photonic Filter With Ultrahigh Spectral Selectivity Based on Cascaded High-Q Silicon Microdisk Resonators

Abstract

As a cornerstone of radio frequency (RF) signal processing, microwave photonic filters (MPFs) with flexible reconfigurability and high spectral selectivity play a pivotal role in high-resolution radar and 6G wireless communication networks, where precise spectral grooming is of paramount importance. In this work, we propose a reconfigurable bandpass MPF with ultrahigh selectivity based on cascaded high- $Q$ silicon microdisk resonators (MDRs). The MDR unit leverages an add-drop configuration integrated with a slab waveguide surrounding both the disk and bus waveguides. This design is strategically engineered to enhance optical confinement and minimize propagation loss, thereby enabling a high $Q$ -factor. Metallic microheaters are patterned atop the MDRs to facilitate thermo-optic tuning of the resonance wavelength. Through precise optical-to-electrical mapping, the high- $Q$ spectral characteristics of the MDRs are faithfully replicated in the RF domain, enabling microwave filtering with exceptional selectivity. For experimental validation, a cascaded high- $Q$ silicon MDR chip is designed and fabricated. With the use of the fabricated chip, a high-performance bandpass MPF is implemented, exhibiting a narrow 3-dB bandwidth (BW) of 172.9 MHz, a wide frequency tuning range spanning 2.77–20.52 GHz, a high rejection ratio (RR) of 60.2 dB, and a sharp roll-off rate (ROR) of 75.5 dB/GHz. Moreover, the proposed MPF facilitates flexible BW tunability, manifesting as flat-top passband responses with adjustable 3-dB BWs ranging from 210.3 to 540.7 MHz, consistently sustaining high RRs exceeding 49.3 dB. Featuring a compelling combination of narrow passband, ultrahigh RR, wide frequency tuning range, sharp ROR, and flexible BW reconfigurability, the proposed bandpass MPF paves the way for high-fidelity spectral manipulation in modern RF signal processing systems.