Silicon microring vertical coupler

Silicon microring vertical couplers are proposed and fabricated to efficiently couple light into silicon-on-insulator waveguides for silicon photonic integration. A specific mode is excited to match the effective index of the silicon-on-insulator guided mode by oblique incidence. The vertical leakage from the microring forms gradual coupling into the silicon-on-insulator slab. Coupling efficiency up to 91% is demonstrated using the three-dimensional finite-difference time-domain method. A semi-disk and lateral taper can be used to convert the lateral mode size for coupling light into a single mode silicon-on-insulator waveguide.