Narrowband terahertz metasurface circular polarization beam splitter with large spectral tunability based on lattice-induced chirality

We propose a terahertz metasurface with chirality induced by surface lattice resonance for achieving narrowband circular polarization beam splitter (PBS) with large spectral tunability in both transmission and reflection modes. Results show that strong circular dichroism effects can be observed in two spectrally narrow bands, and thus a dual-band circular PBS can be achieved. We show that surface lattice resonance induces much narrower and stronger circular dichroism effects than localized resonance, resulting in higher polarization extinction ratios, higher quality factors, and more circular polarization states. The narrowband operation frequency of lattice-induced PBS with extinction ratio larger than 10 dB can be tuned over a large spectral range, from 1.6 THz to 2.3 THz, by varying the incidence angle. We expect the proposed strong, narrowband, and spectrally tunable circular PBS will find applications in polarization-dependent systems including imaging, spectroscopy, sensing and telecommunication in the terahertz regime.