A novel method of fabricating 3D spot-size converter on (111) SOI

We present a novel method to realize 3D adiabatically Spot-Size Converter (SSC) structures by standard silicon micromachining technics, for efficient coupling from single-mode fiber or free-space to silicon photonic chip. The SSC is comprised of I/O waveguides and a 3D 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 vertical direction was 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.