Abstract

We propose and experimentally demonstrate sub-gigahertz microwave photonic filters (MPFs) with widely tunable bandwidths and ultra-high rejection ratios based on a silicon add-drop Mach–Zehnder interferometers (MZI) coupled ring array. To realize a ring filter with a widely tunable bandwidth and a flexibly adjustable extinction ratio, the two coupling waveguides of the silicon resonator are designed as bending waveguides and are both fabricated with microheaters. Consequently, the effective coupling coefficients between the add-drop ring and the coupling waveguides could be significantly manipulated, resulting in tunable bandwidths and extinction ratios. Capitalizing the designed resonators with broadly adjustable bandwidth, the experimental results show that the 3dB-bandwidth of the MPF could be widely tuned from 0.178 GHz to 22.7 GHz. What's more, owing to the ring flexibly tunable extinction ratios and the complete interference cancellation technology, the maximum MPF rejection ratios could realize beyond 75 dB. To the best of our knowledge, it is the first time to realize the notch MPFs with widely tunable 3dB-bandwidths ranging from sub-gigahertz to tens of gigahertz while maintaining the ultra-high rejection ratios. The proposed scheme paves a way for the notch MPFs with the dominant advantages of narrow bandwidths, wide bandwidth tuning ranges, ultra-high rejection ratios and complementary metal-oxide semiconductor (CMOS)-compatibility, which is competent to process dynamic radio frequency (RF) signals in on-chip microwave systems.

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