Broadband Linear-to-Circular Polarization Conversion Enabled by Birefringent Off-Resonance Reflective Metasurfaces

Circularly polarized light in the terahertz (THz) regime is essential for a variety of scientific research and technological applications. However, it is challenging to achieve broadband circular polarization at these long wavelengths due to the dispersion of common birefringent materials. Here we propose and demonstrate the broadband linear-to-circular polarization conversion with up to 80% fractional bandwidth and near-unity power conversion efficiency based on the coupled-mode theory using reflective birefringent metasurfaces [1]. The arbitrary rotation of a linear polarization can also be achieved by leveraging the design parameters of the unit cell. This novel design approach can be further expanded to the mid-infrared and visible regimes by simply scaling the size of the structure. The realization of the polarization converter and rotator may significantly enrich the polarization-based optical probe of matter, including circular dichroism spectroscopy at THz regime and studies of the rising quantum materials.
[1] C.C. Chang*, Z. Zhao*, D. Li*, A.J. Taylor, S. Fan, and H.T. Chen, “Broadband Linear-to-Circular Polarization Conversion Enabled by Birefringent Off-Resonance Reflective Metasurfaces”. Accepted by Phys. Rev. Lett. (2019)