A fiber-to-chip coupler based on Si/SiON cascaded tapers for Si photonic chips

This paper reports a fiber-to-chip coupler consisting of a silicon inverted taper and a silicon oxynitride (SiON) double stage taper, where the cascaded taper structure enables adiabatic mode transfer between a submicron silicon waveguide and a single mode fiber. The coupler, fabricated by a simplified process, demonstrates an average coupling loss of 3.6 and 4.2 dB for TM and TE polarizations, respectively, with a misalignment tolerance of ± 2.2 µm for 1 dB loss penalty.