Three-Dimensional Tapered Spot-Size Converter Based on (111) Silicon-on-Insulator

A novel method is presented to realize a three- dimensional (3-D) spot-size converter (SSC) by standard silicon micromachining techniques, for efficient coupling from single-mode fiber to silicon photonic chip. The SSC is comprised of input-output waveguides and a 3-D tapered coupler on silicon-on-insulator (SOI) substrate. The dimensions are decreased linearly in both vertical and horizontal directions from input facet to output facet. The slope in the vertical direction is originated from the angle between the surface of (111) SOI wafer and the real (111) crystal plane. Fabrication of the device has large process tolerance and its effectiveness was conformed by optical loss measurement.