Infrared Polarizer Fabrication by Imprinting on Sb–Ge–Sn–S Chalcogenide Glass

Abstract

We fabricated infrared wire-grid polarizers consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb–Ge–Sn–S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5–9 µm wavelength range, and an extinction ratio greater than 20 dB in 3.5–11 µm wavelength range. The extinction ratio of the element with Al wires of 180-nm thickness reached 27 dB at 5.4-µm wavelength. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

Infrared Wire-Grid Polarizer with Antireflection Structure by Imprinting on Both Sides

“…To enhance the extinction ratio further, increase in the Al grating thickness is effective, since it reduces the TE transmittance. 12,16) Another reason for the TE transmission leakage may be the misalignment of the Al grating direction; i.e., the direction of the AR grating was not completely parallel to the wire direction in the current sample. Therefore, we have to consider the effect of the structured birefringence; i.e., as this AR grating acted as a wave plate, TE polarization might have been transmitted slightly.…”

“…In an earlier study, the processes of two-beam interference exposure and the direct glass imprinting were used to fabricate wire-grid polarizers consisting of a low-toxicity chalcogenide glass substrate (Sb-Ge-Sn-S system) and an Al grating with a subwavelength period. 11,12) These polar-izers exhibited high extinction ratios in the infrared range. However, the reflection loss of these polarizers was very high ($35%), since the glass had a high refractive index (2.7).…”

“…A novel chalcogenide glass that we use in the current experiment (Isuzu Glass IIR-SF Ò 1) has a wide transmission range of 0.85-11 m, a low glass transition temperature (230 C), and low toxicity (Sb-Ge-Sn-S system). 11,12,14) Glass imprinting was conducted with a pressing machine (Toshiba Machine GMP-415V). The SiC plate with a carbon film for demolding, which had a grating of 500 nm period, was set as the upper mold in the pressing machine, and the GC plate with a grating of 3 m period was set as the lower mold.…”