Theoretical analysis of a thermal-optical tunable filter based on Vernier effect of cascade microring resonators

A thermal-optical tunable filter based on the Venier effect of cascade microring resonator, which can expand the Free-Spectrum-Range (FSR) and the tuning range, is designed and simulated. The FSR of the filter with a radius of 48 m for the first order and 50 m for the second order microring can be expanded to 76.5 nm, which is at present the largest FSR to our best knowledge. A tuning range covering all of the above mentioned FSR can be reached under 103.1 mW heating power, which is also the largest one for silicon based thermal-optic tunable microring resonator filers. The response time, calculated by finite-element-method, of the designed tunable filter with 50 m radius ring is 3.5 s for the rise edge and 0.8 s for the fall edge.