Highly Integrated Silicon Cascaded Dual-Microring Microwave Photonic Bandpass Filter with Wide Bandwidth Tunability

Compared to traditional microwave filters, microwave photonic filters (MPFs), due to their advantages such as high reconfigurability and immunity to electromagnetic interference, hold promising applications in future broadband communications, microwave photonic radar, and electronic warfare systems. With the urgent need for miniaturization in system applications, integrated MPFs are increasingly gaining attention. Among various integration platforms, the SOI platform offers advantages such as high integration density and CMOS process compatibility. Crucially, it enables the fabrication of MPF chips incorporating all device components except the light source, thus attracting considerable research interest. Due to the limitations imposed by the Lorentzian filtering spectral shape and the limited bandwidth tunability of the microring resonator (MRR), it is difficult for an integrated microwave photonic bandpass filter based on silicon MRR to achieve a large bandwidth tuning range and a high out-of-band rejection ratio simultaneously through direct mapping of MRR’s filter response from the optical domain to the microwave domain. To address this, we proposed and demonstrated a highly integrated silicon MPF chip, which contains a phase modulator, a cascaded tunable dual-MRR, and a photodetector. The MPF chip employs two MRRs to independently process the two modulated optical sidebands followed by spectral synthesis in the microwave domain. By implementing a collaborative tuning strategy that simultaneously increases the MRR’s optical bandwidth and optimizes the optical carrier detuning, the highly integrated bandpass MPF overcomes the constraints imposed by the intrinsic optical bandwidth of MRR on bandwidth tuning range and out-of-band rejection ratio. This approach achieves continuous bandwidth tunability of ∼9 GHz, a frequency tuning range of ∼20 GHz, and an out-of-band rejection ratio of ∼26 dB, which surpasses that of existing highly integrated solutions. Furthermore, analysis indicates that the performance of this integrated MPF is primarily limited by the bandwidth of the on-chip modulator. By employing an external lithium niobate phase modulator, the bandwidth tuning range, frequency tuning range, and out-of-band rejection ratio can be further enhanced to 1–12.5 GHz, 1–40 GHz, and 35 dB, respectively. This work presents a robust solution for highly integrated signal processing, holding great promise for future applications in microwave photonic radar, wireless communications, and electronic warfare systems.