The edge-coupler of fiber-to-chip with ultra-low coupling loss based on double-layer silicon waveguides

The edge-coupler of fiber-to-chip with ultra-low coupling loss is demonstrated on SOI platform. The edge-coupler is consisted of the cantilevered SiO2 waveguide, the amorphous silicon (alpha-Si) nano taper and the crystal silicon (c-Si) nano tapers. The thin alpha-Si layer is deposited on the c-Si layer to improve the pattern matching with fiber. The optical input signal from the optical fiber is launched into the suspended SiO2 waveguide, then coupled into the alpha-Si nano taper at the center of the SiO2 waveguide, and finally coupled into the c-Si nano taper. We characterized the cantilevered edge-coupler using cleaved single-mode optical fiber with a mode field diameter of 10.5 mu m. The measured coupling loss is as low as -1.7 dB per facet for TE mode without index matching liquid at 1550 nm. The 1 dB bandwidth is more than 100 nm with 1 dB alignment tolerances of & PLUSMN;2.0 mu m in both horizontal and vertical directions. Besides, potential hybrid optical integration could also be allowed with this results in the future.