Dispersion-Engineered Surface Phonon Polariton Metasurfaces for Tunable and Efficient Polarization Conversion.

Metasurfaces offer compact control of light polarization, which is vital for imaging, sensing, and communications. However, cost-effective efficient polarization conversion in the mid-infrared (IR) remains challenging due to reliance on high-resolution lithography. We demonstrate that dispersion engineering of surface phonon polariton (SPhP) metasurfaces overcomes these limitations, enabling efficient and tunable polarization conversion in the mid-IR. By integrating a dielectric layer with the SiC-based metasurface, we control hybrid SPhP and SPhP-like waveguide resonances, achieving up to 61% experimental and 82% simulated conversion efficiency across the Reststrahlen band. Our design avoids SiC etching, enhancing compatibility with hard-to-etch materials. Bandwidth tunability is achieved by varying the grating pitch, with full width at half-maximum ranging from 146.82 to 52.2 cm (∼15% to 5% of design frequency), enabling versatile applications ranging from broadband spectroscopy to narrow band thermal sensing. This platform is transferable to other SPhP materials, offering new avenues for reflective polarizers in the mid-IR and terahertz ranges.