Nonreciprocal terahertz wavefront manipulation based on a magneto-optical metasurface with an orthogonal meta-atom pair

Abstract

Active wavefront manipulation and nonreciprocal transmission give key performances in beam steering, unidirectional isolation, and multichannel multiplexing. In this work, we propose a magneto-optical (MO) Pancharatnam–Berry (PB) metasurface, which consists of a pair of orthogonal anisotropic Si and InSb columns. This orthogonal meta-atom pair (OMP) structure leads to destructive interference in the geometric phase so that the wavefront manipulation is in the OFF state without a biased magnetic field (BMF). When the BMF is applied, the nonreciprocal transmission effect for different spin states in InSb breaks the original destructive interference, so the devices provide different geometric phase distribution for different magnetic field directions and spin states, achieving the ON state of the nonreciprocal wavefront manipulation, where cross-polarization circular dichroism is higher than 0.98 and the polarization conversion rate is over 97%. Furthermore, based on this mechanism, a beam deflector and a vortex beam generator are designed by arranging the OMP with different azimuthal angles. Compared with ordinary reciprocal wavefront manipulation, this work shows that this MO PB metasurface with OMP structure has irreplaceable functions in the isolation, selection, and conversion of the two conjugate spin beams, providing a unique path for active THz wavefront manipulation.