Broadband focusing grating couplers for suspended-membrane waveguides

We propose and demonstrate broadband focusing grating couplers for suspended-membrane waveguides on silicon-on-insulator both in near-infrared (near-IR) and in mid-IR wavelength range. Finite-difference time-domain simulation predicts similar to 100 nm 3 dB bandwidth with -1.7 dB coupling efficiency for an apodized grating in near-IR. -3.5 dB maximum coupling efficiency and similar to 90 nm 3 dB bandwidth are realized experimentally. In mid-IR, -5.5 dB maximum coupling efficiency from a uniform focusing grating is measured at 2.75 mu m, and similar to 500 nm 3 dB bandwidth is predicted theoretically. (C) 2012 Optical Society of America