Ultra-High Peak Rejection, Sub-Gigahertz Narrowband and Bandwidth Tunable Microwave Photonic Filter Based on Silicon Racetrack Resonators

We propose and experimentally demonstrate a notch microwave photonic filter (MPF) with optimized performance (including the sub-gigahertz narrowband, ultra-high rejection ratio and tunable bandwidth) based on two cascaded silicon Mach–Zehnder interferometers (MZI) coupled microring resonators (MRRs). The MRR structure is optimized to obtain a high quality (Q) factor (corresponding to a sub-gigahertz 3dB-bandwidth), adjustable bandwidths and extinction ratios. One ring is designed as the over-coupled state with a π resonant peak phase shift while the other ring performs the under-coupled state with 0 peak phase shift. Under the intensity modulation, an extremely high MPF rejection ratio could be obtained capitalizing the complete interference cancellation technology. Moreover, the MPF bandwidth and central frequency could be flexibly tuned by adjusting the MRR bandwidths and resonant wavelengths, respectively. The experimental results demonstrate the notch MPF response with a narrow 3dB-bandwidth of 185 MHz, an extremely high rejection ratio beyond 70 dB and a 3dB-bandwidth tuning range from 185 MHz to 1.263 GHz. To the best of our knowledge, it is the first time to realize the silicon-based notch narrowband MPFs with the ultra-high rejection ratio (>70 dB) and a 3dB-bandwidth tuning range from sub-gigahertz to gigahertz level. The proposed silicon-on-insulator-based MPF with competitive performance paves a way for on-chip high-quality microwave signal processing.