Optical All-Pass Filter Realized by Optical Interference

Optical all-pass filters (APFs) are key devices to manipulate phase without introducing amplitude degradation. Here, we proposed to achieve an APF by interfering the two output lights from a dual-injection microring resonator (MRR) and a straight waveguide. The APF can be implemented under arbitrary coupling coefficients of the MRR, which relax the design and adjustment of the device. In experiment, the APF achieve a phase change of 1.8π from 5 to 40 GHz with an amplitude variation of only 1.6 dB. A microwave photonic phase shifter based on the APF is also demonstrated.