| Summary: | Over the last decade, photonics in the mid-infrared (mid-IR) frequency range had major advances in both generation and detection of light. However, efficient manipulation of the mid-IR light still faces many challenges. Spatially inhomogeneous control over the wavefront and polarization of mid-IR radiation is particularly difficult. Many standard techniques used for visible and near-infrared frequencies, such as liquid crystal-based spatial light modulation, are not applicable in the mid-IR due to unfavorable material properties in that spectral range. Here, we demonstrate spatially inhomogeneous polarization control of the mid-infrared light using custom-designed vortex retarders. Vortex retarders, while being widely used in the near-infrared and visible spectral ranges for generation of cylindrical vector beams, have been missing in the mid-infrared spectral range. Our implementation of mid-infrared vortex retarders is based on the concept of metasurfaces. We demonstrate metasurface-based vortex retarders at the wavelengths of 2.9 and 3.5 μm. We compare the performance of all-dielectric metasurface vortex retarders with the elements arranged in square and hexagonal lattices [Arbabi et al., Nat. Nanotechnol. 10, 937–943 (2015) and Arbabi et al., Nat. Commun. 6, 7069 (2015)]. Our work could accelerate the adoption of metasurfaces for the development of novel classes of mid-infrared optical components.
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