High optical performance of Polymeric Sulfur Based Mid-Wavelength Infrared Linear Polarizers

초록

The elemental sulfur, by-product from 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 high performance optical polarizer, the optical simulation must be preceded for investigating geometries dependent optical properties including transmission of transverse magnetic field (TTM) and extinction ratio. However, in the nano-fabrication point of view, realization of simulated design remains as a challenge for polymeric sulfur via thermal nanoimprinting due to high viscosity of polymeric sulfur in conjunction with large surface tension [JJW1] 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 TTM 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-Ferot resonance occurs, is tailored via spin-coating process by adjusting concentrations of polymeric sulfur solution. Finally, the SM-polarizer demonstrates high TTM with high extinction ratio, measured by using FT-IR method and confirmed by simulations.