Optical All-Pass Filter Based on Dual-Injection MRR With Arbitrary Coupling Coefficients

An optical all-pass filter (APF) has unified amplitude response and varied phase response, enabling phase manipulation without causing amplitude degradation. Therefore, the APF is significantly important to phase manipulation occasions. However, the implementation of optical APFs requires extremely stringent coupling coefficients matching between different couplers of the microring resonator (MRR). In actual fact, the matching of coupling coefficients is difficult due to the thermal crosstalk and adjusting accuracy of coupling coefficients. Here, we proposed and demonstrated an optical APF that can be realized under arbitrary coupling coefficients of the MRR by interfering the output lights from the MRR and a straight waveguide. We designed and fabricated the chip based on the silicon-on-insulator (SOI) platform. Experimental results show that the implemented optical APF has a phase change of 1.85π while the amplitude variation is within 1.3 dB from 5 to 40 GHz. Meanwhile, tunable time delay and microwave photonic phase shift based on the optical APF are also demonstrated.