A fiber-to-waveguide edge coupler assisted by silicon-nitride waveguide with large fabrication tolerance

A fiber-to-waveguide edge coupler assisted by silicon-nitride subwavelength grating (SWG) structure is proposed on silicon-on-insulator (SOI) platform with large fabrication tolerance. The SWG structure silicon nitride waveguide is designed in the upper layer of the inversed taper silicon waveguide with SWG structure. The two waveguides and cantilever structure work together to reduce the polarization dependent loss (PDL) and improve coupling efficiency. The coupling efficiency of the structure reach up to 98% (0.08dB) when it couples with 10.4 μm SMF-28 fiber. The structure has the advantages of large fabrication tolerance, large alignment tolerance, insensitive polarization and high coupling efficiency etc. The silicon nitride waveguide assisted fiber to waveguide edge coupler is compatible with complementary metal oxide semiconductor (CMOS) process and the fabrication tolerance is also analyzed for future fabrication and measurement.