Nanoholes Grating Couplers for Coupling Between Silicon-on-Insulator Waveguides and Optical Fibers

Simulation and experimental results of grating couplers composed of arrays of nanoholes are presented. The use of an array of holes instead of a conventional waveguide grating provides an additional degree of freedom in the design of the coupler, thus enabling fabrication using the same photolithography mask and etching process as used for the silicon-on-insulator (SOI) waveguides. A grating coupler with coupling efficiency as high as 34% for coupling between the TE mode of the silicon nanophotonic wire waveguide and a single-mode optical fiber and with 3-dB bandwidth of 40 nm was fabricated. A theoretical model is presented, and 3-D finite-difference time-domain simulations are used to optimize the coupler design.