Silicon Photonic Resonator Design with Tunable Multimode Interference Coupling Structures

This paper presents the design and simulation of a tunable silicon on insulator ring resonator using tunable multimode interference (MMI) coupling structures. The new design is aimed to include the tuning capability for enhancing spectral response of the device in post-fabrication. Theoretically, coupling coefficient of between the waveguide and microring, waveguide loss and the resonator round trip length are among the design parameters. Racetrack ring design, consisting of parallel coupler sections, is used to control the coupling coefficient in some devices. However such passive device can suffer from fabrication error which causes the response to deviate from expected values. In addition, in the process with low resolution lithography, the gap between parallel waveguides may be rather large in the order of 0.5 µm or more, thus coupling ratio is not accurate as well as requiring long coupling length. Therefore tunable 2 × 2 MMI couplers are proposed in place of parallel coupler.