Inverse Taper Waveguides for Low-Loss Mode Converters

A mode converter fabrication method comprising:

• obtaining a mode converter comprising:
• a substrate;
• a silicon waveguide disposed on the substrate and comprising a sidewall and a first adiabatic tapering;
• and
• a hard mask disposed on the silicon waveguide and comprising a silicon dioxide (SiO2) layer, wherein the hard mask does not cover the sidewall;
• and
• oxidizing the silicon waveguide and the hard mask, wherein oxidizing the silicon waveguide and the hard mask encloses the silicon waveguide within the silicon dioxide layer.

A mode converter fabrication method comprising:

• fabricating onto a substrate a silicon waveguide that comprises a first adiabatic tapering and a sidewall, wherein a hard mask is disposed on the silicon waveguide and does not cover the sidewall, and wherein the hard mask comprises silicon dioxide (SiO2) material;
• fabricating a second waveguide onto the substrate, wherein the second waveguide comprises a second hard mask enclosing the second waveguide;
• and
• oxidizing the silicon waveguide and the second waveguide until the silicon waveguide is enclosed within the silicon dioxide material.