Silicon microring resonators with 1.5-μm radius

Abstract
We demonstrate a junction between a silicon strip waveguide and an ultra-compact silicon microring resonator that minimizes spurious light scattering and increases the critical dimensions of the geometry. We show cascaded silicon microring resonators with radii around 1.5 µm and effective mode volumes around 1.0 µm3 that are critically coupled to a waveguide with coupled Q’s up to 9,000. The radius of 1.5 µm is smaller than the operational wavelength, and is close to the theoretical size limit of the silicon microring ring resonator for the same Q. The device is fabricated with a widely-available SEM-based lithography system using a stitch-free design based on a U-shaped waveguide.