Modelling of back reflection in optical ring resonators

Modelling of back reflection in silicon ring resonators is presented, together with a simulation to extract the values of reflection coefficients. Back reflection in ring resonators is induced by the sidewall roughness of silicon waveguides and is the main cause of response splitting at resonance. Calculation of the ring resonator frequency response without consideration of back reflection yields inaccurate results. Simulation results show that the resonance shape is strongly affected by back reflection and each resonance has a different response from the others in the same ring. Analytically, this manifests as a change in reflection coefficient at each resonant frequency. This paper proposes an analytical model that characterises back reflection and calculates the reflection coefficient.