Efficient mid-infrared linear-to-circular polarization conversion using a nanorod-based metasurface

Abstract

In this work we numerically and experimentally characterize a nanorod-based metasurface, demonstrating efficient linear-to-circular polarization conversion in the technologically important mid-infrared region of the spectrum. Measurement of the Stokes parameters confirms a very high degree of circular polarization (with a value of axial ratio between 0.9 to 1) of reflected light over the wavelength range from 3.8µm to 4.8µm, with an average conversion efficiency of 80% and a maximum value of 91%. Such metasurfaces, which have subwavelength thickness, could potentially replace conventional quarter wave plates, but could also be used for circular dichroism spectroscopy in the mid-infrared region, allowing the relative easy characterization of important molecules such as proteins.