2-D taper for low-loss coupling between polarization-insensitive microwaveguides and single-mode optical fibers

This paper reports modeling and simulation of low-loss coupling between polarization-insensitive silicon-on-insulator (SOI) microwaveguides and single-mode optical fiber, using a two-dimensional taper. The proposed structure is a reduction of both sizes of a square-strip waveguide from a 350×350-nm² cross section to about 155×155-nm² cross section. At the output facet, the guided mode is spread out and has a non-Gaussian profile, but low-loss coupling can be achieved by optimizing the overlap integral between the submicrometer waveguide mode and the optical fiber one. The calculated coupling losses are lower than 0.2 dB, the alignment tolerance is larger than 4 μm at ±1 dB for the coupling losses, and the total length is about 10 μm.