Reduction of silicon waveguide endface reflection using a taper

In this paper, a method that adds an inverse taper at the endface of the waveguide is analyzed to reduce the silicon waveguide endface reflection (SWER). A high index-contrast optical waveguide on a silicon-on-insulator (SOI) wafer allows for the strong optical confinement, while it also brings in a substantial endface reflection. Most parameters of the taper, such as the length and tip width of the taper, and wavelength of the guided light, even the shape of the taper, have been studied in detail using the three-dimensional finite-difference time-domain (3D-FDTD) method to reduce the SWER. In addition, we have also proposed a new structure that adds the special taper to the straight-through port of the 3-dB directional coupler (DC) to measure the SWER in experiments. The experimental results show good agreement with our simulation results. This taper is useful and small enough that can be applied to many silicon photonic devices and large scale photonic integration circuits (PICs).