Tunable optical filter design with ring resonator based Sagnac loop

We theoretically investigate an advanced tunable photonic filter implemented by a novel structure, termed ring resonator based Sagnac loop reflector (RR-SLR). The ring resonator is rotated by electrostatic actuation to provide Sagnac phase shift and hence tunability. We investigate mode splitting in this filter and demonstrate its high performance in achieving diverse filtering functions. By changing the reflectivity of the Sagnac loop reflector, and ring resonator power coupling and tuning the phase shift through actuator, we tailor coherent mode interference to achieve resonance mode splitting with high extinction ratio, low insertion loss, and wide free spectral range. A detailed analysis of the impact of the structural parameters is presented to facilitate device optimization and design. The filtering performance is compared with other reported works. These results theoretically confirm the effectiveness of using RR-SLR as a multifunctional photonic filter for flexible spectral engineering.