Demonstration of A Tunable Microwave-Photonic Notch Filter Using Low Loss Silicon Ring Resonators

Abstract: We present a fully-tunable multi-stage narrowband optical pole-zero notch filter that is fabricated in a silicon complementary metal oxide semiconductor (CMOS) foundry. The filter allows for the reconfigurable and independent tuning of the center frequency, null depth, and bandwidth for one or more notches simultaneously. It is constructed using a Mach- Zehnder interferometer (MZI) with cascaded tunable all-pass filter (APF) ring resonators in its arms. 

Measured filter nulling response exhibits ultra-narrow notch 3-dB BW of 0.6350 GHz, and nulling depth of 33 dB. This filter is compact and integrated in an area of 1.75 mm2. Using this device, a novel method to cancel undesired bands of < 910 MHz in microwave-photonic systems is demonstrated. The ultra-narrow filter response properties have been realized based on our developed low propagation loss silicon channel waveguide and tunable ring resonator designs. Experimentally, they yielded a loss of 0.25dB/cm and 0.15 dB/round trip, respectively.