Wideband infrared metal wire grating polarizer using holographic lithography and lift-off process

In this work we design a wire grid polarizer(WGP) with silver nanowire grids on a germanium(Ge) substrate with 550nm period and 200nm thickness double-layer and single-layer wire grids based on FDTD method, which can achieve an average TM transmittance(TMT) over 70% and 48% and an extinction ratio(ER) over 76dB and 32dB respectively in the range of 3~15μm waveband. The photoresist grating was made by the Lloyd’s mirror interferometer interference lithography (IL) systems and the metal silver was deposited by thermal evaporation, which avoid the high cost of electron beam lithography and the difficult process of wet etching or dry etching. The fabrication shows that method is proved to be easy implement in the fabrication of sub-wavelength metal gratings. The experiment results show the polarizer has uniform polarization characteristics in the wide infrared band that the average TMT and ER of the doublelayer polarizer are 72.6% and 27.5dB in 3~15μm with single side antireflection coating. The average TMT and ER of the single-layer polarizer are 59.1% and 25.1dB in 3~15μm.