Subwavelength Grating Structures in Silicon‐on‐Insulator Waveguides

First implementations of subwavelength gratings (SWGs) in silicon‐on‐insulator (SOI) waveguides are discussed and demonstrated by experiment and simulations. The subwavelength effect is exploited for making antireflective and highly reflective waveguide facets as well as efficient fiber‐chip coupling structures. We demonstrate experimentally that by etching triangular SWGs into SOI waveguide facets, the facet power reflectivity can be reduced from 31% to <2.5%. Similar structures using square gratings can also be used to achieve high facet reflectivity. Finite difference time‐domain simulations show that >94% facet reflectivity can be achieved with square SWGs for 5 μm thick SOI waveguides. Finally, SWG fiber‐chip couplers for SOI photonic wire waveguides are introduced, including design, simulation, and first experimental results.