The High Optical Performance of a Polymeric Sulfur-Based Mid-Wavelength Infrared Linear Polarizer

The elemental sulfur, a by-product from the petroleum refining process, has a great potential for low-cost polymeric mid-wavelength infrared (MWIR, 3-5 μm) optics owing to its high transmittance in the IR spectrum regime. For applying polymeric sulfur to a high-performance optical polarizer, the optical simulation must be preceded for investigating geometries dependent optical properties including the transmission of transverse magnetic field (T_TM) and extinction ratio. However, in the nano-fabrication point of view, the realization of simulated design remains a challenge for polymeric sulfur via thermal nanoimprinting due to the high viscosity of polymeric sulfur in conjunction with the large surface tension of nanostructures originating from their high surface area-to-volume ratio. Herein, we demonstrate high fidelity 1D nano-gratings patterned and spacer thickness controlled polymeric sulfur-based MWIR polarizer (SM-polarizer) as a result of the conjunction with simulation and investigation of processing conditions. Before considering the processing conditions, a theoretical analysis is conducted to investigate optimal spacer thickness, width, height, pitches, and gold layer thickness for high T_TM and extinction ratio. For realizing the simulated geometries of SM-polarizer, we investigate thermal nanoimprinting lithography (thermal NIL) conditions including pressure, temperature, and time for high fidelity nano-feature of SM-polarizer. Then, the spacer thickness, where the Fabry-Perot resonance occurs, is tailored via a spin-coating process by adjusting concentrations of polymeric sulfur solution. Finally, the SM-polarizer demonstrates high T_TM with a high extinction ratio, measured by using the FT-IR method and confirmed by simulations.