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Design and fabrication of a linear polarizer in the 8–12μm infrared region with multilayer nanogratings

The design and fabrication of a ZnSe-based linear polarizer operating in the 8–12 μm infrared region with multilayer nanogratings is demonstrated. The multilayer structure is formed by a low- and a high-refractive index thin layer that are evaporated successively on a ZnSe substrate, followed by a dielectric nanograting that is etched into the high-refractive index thin layer, and then a double-layer metallic nanograting that sits on the dielectric nanograting. Polarization characteristics of the proposed polarizer on structural parameters are investigated and an optimized multilayer structure is obtained. Experimental fabrication of the multilayer nanograting structure using UV lithography and thin-film deposition is conducted in a way in which no ion etching process is needed for the formation of metallic nanogratings. An extinction ratio (ER) of 35 dB and TM-transmission (TMT) of averagely higher than 80% are obtained experimentally in the whole 8–12 μm waveband with 250-nm-period multilayer nanogratings. The ZnSe-based multilayer structure shows the possibility of achieving large-area and high-performance polarization in the 8–12 μm infrared region with relatively easy fabrication.