Broadband mirrors in the near-infrared based on subwavelength gratings in SOI

We describe the design, fabrication, and characterization of high-reflectivity broadband mirrors operating in the near-infrared (700-1000 nm) wavelength range. The mirrors consist of 1-D and 2-D subwavelength resonant gratings (SWGs) fabricated on a silicon-on-insulator (SOI) wafer. A very good agreement between numerical and experimental results is obtained. The mirror response can be tailored by adjusting the geometrical parameters of the gratings, with the grating period as the main parameter. The optimized mirrors reflect strongly (> 95%) over a fractional optical bandwidth Delta lambda/lambda of about 12% and 7.5% for 1-D and 2-D gratings, respectively. The important and somewhat surprising feature of these gratings is that high reflectivities have been achieved, despite the fact that silicon exhibits significant absorption in this wavelength range.