Design of polarization-insensitive ring resonators in silicon-on-insulator using MMI couplers and cladding stress engineering

A novel silicon-on-insulator (SOI) ring resonator design is described that uses a 2 × 2 multimode interference coupler to achieve polarization-independent coupling, and cladding stress induced birefringence control to eliminate the difference in round-trip phase accumulation between the transverse-electric and transverse-magnetic polarized modes. The design parameters are determined for polarization-independent SOI ring resonators with couplers having a 50 : 50 or 15 : 85 splitting ratio, and 1.5-μm ridge height and width. As designed, the resonators offer a polarization-independent free-spectral range of 0.5 nm for a ring radius of 200 μm, and a quality factor Q as high as 55 000.