Design of antireflective subwavelength grating structure for infrared medical imaging

A subwavelength grating (SWG) structure was designed and simulated on a germanium substrate to reduce the Fresnel reflection of transmissive optical elements. Three different grating structures were compared and analyzed by solving Maxwell's equations using rigorous coupled wave analysis (RCWA) method. The designed antireflective SWG of 2 dimensional sinusoidal structure has pitch of 2.3 µm and pattern height of 3.3 µm for maximum sensitivity of infrared medical camera at wavelength ranging from 8 µm to 12 µm. The 2D photoresist sinusoidal grating structure, to be used as etching barrier for fabrication of antireflective germanium grating structure, was fabricated by laser interference lithography.