Fabrication and characterization of three-dimensional silicon tapers

We present the fabrication of 3D adiabatically tapered structures, for efficient coupling from an optical fiber, or free-space, to a chip. These structures are fabricated integrally with optical waveguides in a silicon-on-insulator wafer. Fabrication involves writing a single grayscale mask in HEBS glass with a high-energy electron beam, ultra-violet grayscale lithography, and inductively coupled plasma etching. We also present the experimentally determined coupling efficiencies of the fabricated tapers using end-fire coupling. The design parameters of the tapered structures are based on electromagnetic simulations and are discussed in this paper.