Silicon microring resonators with 1.5-μm radius

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 mu m and effective mode volumes around 1.0 mu m(3) that are critically coupled to a waveguide with coupled Q's up to 9,000. The radius of 1.5 mu m 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. (c) 2008 Optical Society of America.