Wideband subwavelength gratings for coupling between silicon-on-insulator waveguides and optical fibers.

We propose and experimentally demonstrate a novel subwavelength grating coupler on silicon-on-insulator, for coupling to optical fibers with a wide optical bandwidth. Theoretical analysis and design optimization of the coupler are described. About 73 nm 1 dB bandwidth was experimentally demonstrated with -5.6  dB coupling efficiency. Better than -3.4  dB efficiency with 86 nm 1 dB bandwidth is predicted for these structures with optimized buried oxide thickness.