Design and fabrication of biperiodic AR gratings for the infrared

摘要

We have designed and fabricated a silicon grating which shows antireflection properties in the [4μm ; 6μm] spectral region. It is shown both theoretically and experimentally that, even if the refractive index and the grating period are in the extend that a simple homogenization theory can not be used, a substantial broadband antireflection effect can be obtained. The grating was made using a wet anisotropic etching technique. The reflectance was calculated with a modal method and compared successfully with the experimental results. It is shown that the grating reduces the silicon substrate reflectance in the whole [4μm; 6μm] spectral domain by a factor greater than 10.