Fig. 1. Principle of the ultrahigh rejection MRR. (a) The schematic diagram of the MRR. (b) The frequency responses of the cascaded APF and MRR-based bandpass filter. (c) The principle of the ultrahigh rejection MRR. APF, all-pass filter (the blue solid curve shows the amplitude response and the red dashed curve shows the phase response).

Fig. 2. Schematic diagram of the proposed ultrahigh rejection ratio MRR assisted by the APF. GC, grating coupler; MZI, Mach–Zehnder interferometer; MRR, microring resonator; MMI, multimode interferometer.

Fig. 3. Simulated results of the proposed device. (a) The amplitude (black solid curve) and the phase (yellow dashed curve) frequency responses of the APF. (b) The amplitude-frequency responses of HDrop (blue dashed curve) and HDrop×HAPF (green solid curve). (c) The phase frequency responses of HDrop (blue dashed curve) and HDrop×HAPF (green solid curve). (d) The amplitude frequency responses at the drop port of MRR2 without (blue dashed curve) and with (red solid curve) APF.

Fig. 4. Micrograph of the fabricated device. GC, grating coupler; MZI, Mach–Zehnder interferometer; MRR, microring resonator; MMI, multimode interferometer; APF, all-pass filter.

Fig. 5. The experimental setup for precisely measuring the amplitude and phase responses of the fabricated device. TLS, tunable laser source; OC, optical coupler; PC, polarization controller; PM, phase modulator; OBPF, optical bandpass filter; EDFA, erbium-doped fiber amplifier; VOA, variable optical attenuator; PD, photodetector; VNA, vector network analyzer.

Fig. 6. Experimental results. (a) The amplitude (black solid curve) and phase (red dashed curve) frequency responses of the APF. (b) The amplitude-frequency response of MRR2 without (black dashed curve) and with (red solid curve) the assistance of APF. (c) Tuning the center frequency of the MRR2 with the assistance of APF.