Tapered self-written waveguide for a silicon photonic chip I/O.

An optical coupling method with high alignment tolerance by self-written waveguide (SWW) formation is a promising candidate for co-packaged optics (CPO) by silicon photonics (SiPh). However, conventional SWWs cannot be used with Si waveguides because visible light for SWW formation cannot radiate from the waveguide facet. Here, we devised a new, to the best of our knowledge, optical circuit with SiON waveguides for SWW formation from an SiPh chip. With our circuit, we achieved optical coupling between an SiPh chip and a standard single-mode fiber (SSMF) with a tapered SWW (TSWW). The lowest excess coupling loss compared to butt coupling with a high-numerical aperture (NA) fiber is approximately 0.6 dB over the C-band with the TSWW. In addition, our coupling method has higher alignment tolerances than butt coupling with a high-NA fiber (HNF).