Silicon slot waveguide ring resonators: Can we target high Q factors?

We present our analysis and optimization of slot ring resonators by investigating the slotted coupler properties in order to achieve high Q ring resonators. Firstly, different ring resonators loaded by conventional straight bus ring resonator couplers with different gaps were fabricated with a cavity length of 828 μm and a bending radius of 50 μm. They were measured with an average Q-factor around 85,000 and proved to present large intrinsic coupler losses. We then proposed a new symmetric racetrack ring resonator coupler to reduce coupler loss thanks to a smoothed transition in coupling region between the coupled supermodes and achieved Q factor above 120,000 with total intrinsic loss around 2.2 dB/cm in a 50 μm radius ring resonator with total cavity length 326 μm by this approach. These optimized slot ring resonators could bring a new progress towards low loss silicon slot waveguiding structures for hybrid Si photonics including on-chip nonlinear optics and sensing in future.