Design and fabrication of silicon-based linear polarizer with multilayer nanogratings operating in infrared region

Abstract

We have proposed and experimentally demonstrated a silicon-based linear polarizer with multilayer nanogratings working in 3 to 5 μm of an infrared region. A dielectric grating is first fabricated in a low-refractive index thin layer on a Si-substrate and then double-layer metallic gratings are formed by evaporating a metallic film onto the dielectric grating. With the designed structure of multilayer nanogratings coupled with a low-refractive-index dielectric layer on the high-refractive index silicon substrate, both high transverse magnetic transmission (TMT) and high extinction ratio (ER) can be effectively achieved across 3- to 5-μm range in the infrared band without the complicated metallic ion etching process that is required in conventional nanowire grids. An ER of 40 dB and TMT of averagely higher than 80% were obtained experimentally from a linear polarizer with a multilayer grating of 280-nm period. The Si-based multilayer grating structure shows possibilities of implementing polarization in a fashion of relatively easy-fabrication, semiconductor process compatible, and high performance.