Si3N4-Based Narrowband and High Peak Rejection Microwave Photonic Filter With Adjustable Bandwidth

A narrowband notch microwave photonic filter (MPF) with adjustable bandwidth and ultra-high rejection ratio is proposed and experimentally demonstrated leveraging a Mach–Zehnder interferometer (MZI) coupled Si
₃
N
₄
ring resonator. The ring is designed with two interferometric coupling waveguides so as to tune the effective coupling coefficients between the bending waveguides and the resonator. Consequently, the bandwidth and the extinction ratio of the resonator could be adjusted. Leveraging the MZI-coupled Si
₃
N
₄
ring, the experimental results illustrate that the 3dB-bandwidth of the notch microwave filters can be effectively adjusted. Furthermore, during the bandwidth tuning process, the rejection ratios of the notch MPFs could obtain high values by utilizing the interference cancellation. To our knowledge, with maintaining ultra-high rejections beyond 60 dB, the 3dB-bandwidth of the Si
₃
N
₄
-based notch MPFs is firstly verified with an adjustable range from tens of MHz to GHz level. The proposed narrowband MPF schemes with superior bandwidth tunability and ultra-high rejection ratios have various important applications in integrated radio frequency systems.