Silicon waveguide grating coupler for perfectly vertical fiber based on a tilted membrane structure

A grating coupler for interfacing between a silicon-on-insulator waveguide and a single-mode fiber located at a perfectly vertical direction is demonstrated based on a tilted membrane structure. The proposed design is compatible with that of conventional grating couplers for oblique fibers and facilitates mass production. A peak coupling efficiency of 28.5% and 1 dB bandwidth of 38 nm are obtained experimentally for transverse-electrics polarized light. Back reflection in the SOI waveguide is also estimated to be 1.4%. The present grating coupler for perfectly vertical fiber exhibits similar performances to the conventional grating coupler for oblique fiber concerning coupling efficiency, bandwidth, and back reflections.