Fabrication of near- or mid-infrared wire-grid polarizers with WSi wires

Abstract

We fabricated a subwavelength-grating structure on the Y2O3 ceramic substrate, which has higher transparency than silicon in the mid-infrared range. After coating a photoresist on this substrate, we formed a grating pattern of 350-nm pitch by the two-beam interference of the He-Cd laser (325-nm wavelength). By using this photoresist grating as a mask, WSi was etched with reactive SF6 ions. The transmittance of the transverse magnetic (TM) polarization was greater than 70% in the 3-7-μm wavelength range without antireflection films and the extinction ratio was over 20 dB in the 2.5-5-μm wavelength range. In addition, we also fabricated near-infrared wire-grid polarizer consisting of a 230-nm pitch WSi grating on a SiO2 substrate. The TM polarization transmittance of the fabricated polarizer exceeded 80% in the 1000-1600-nm wavelength range. The extinction ratio was higher than 20 dB in the 650-1500-nm wavelength range.