AUTHOR=Ma Xiaoyue , Hu Heming , Liu Shiping , Dong Runyu , Fang Qing , Chen Hua 

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

JOURNAL=Frontiers in Physics

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2022.1018624

DOI=10.3389/fphy.2022.1018624

ISSN=2296-424X

ABSTRACT=<p>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 SiO<sub>2</sub> waveguide, the amorphous silicon (α-Si) nano taper and the crystal silicon (c-Si) nano tapers. The thin α-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 SiO<sub>2</sub> waveguide, then coupled into the α-Si nano taper at the center of the SiO<sub>2</sub> 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 μm. 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 ±2.0 μm in both horizontal and vertical directions. Besides, potential hybrid optical integration could also be allowed with this results in the future.</p>