Highly Efficient Mid-Wavelength Infrared (MWIR) Polarizer by ORMOCHALC Composite With Improved Thermomechanical Stability and Spectral Selectivity

Mid-wavelength infrared (MWIR, λ = 3–5 μm) materials are of great importance due to their applications in optical sensors and devices for military, industry, and non-invasive medical diagnostics. Specifically, MWIR polarimetry has significantly improved biometric recognition and camouflaged detection. Most commercial polarizers are based on expensive inorganic materials that are heavy, fragile, and brittle. Thus a suitable polymeric material for MWIR optics is highly desired. Herein, sulfur-based organically modified chalcogenides (ORMOCHALC) polymers have been utilized to fabricate MWIR polarizers by a simple thermal imprinting method followed by Ay deposition. A parametric study to choose suitable geometry for the polarizer was conducted, and highly efficient devices were designed that possess competitive extinction coefficients to the commercial polarizers. However, a significant limitation of the ORMOCHALC polymer is that to increase the refractive index of the polymer, the chalcogenide (i.e., S) content needs to be increased, which results in reduced Young’s modulus and lower glass transition temperature. This decayed thermomechanical stability compromises the structural integrity of ORMOCHALC optical devices. In addition to polymeric MWIR polarizer fabrication, composite materials were also synthesized and characterized for future MWIR device fabrications. Poly(S-r-DIB) was reinforced with zinc sulfide nanoparticles to simultaneously improve the refractive index and the thermomechanical properties. The addition of ZnS nanoparticles significantly improved the glass transition temperature (Tg) of the ORMOCHALC (9.6 °C to 31.4 °C), and the refractive index (Δn = 6.6 %). Then, a figure of merit subwavelength wire-grid polarizers was also analyzed based on the optically and mechanically reinforced composites. If fabricated, nanoparticles reinforced polarizers will possess superior structural integrity due to higher glass transition temperature. Moreover, the polarizers show a spectral selectivity as the resonance wavelength of the transmitted-reflected curve was redshifted to larger wavelengths for ZnS reinforced ORMOCHALC composite. These polarizers with superior extinction coefficient, spectral selectivity, and improved thermomechanical stability demonstrate a border implementation opportunity in the MWIR optics.