Active Terahertz-Beam Deflection in a Double-Sided All-Dielectric Metadevice Modulated by both Polarization Rotation and Optical Pumping

Abstract

Active manipulation of the terahertz (THz) beam, especially beam deflection, is urgently required for wide THz applications. Although Pancharatnam-Berry (PB) metasurfaces can flexibly control the spatial phase distribution of circularly polarized waves, active power distribution and modulation between two conjugate spin beams are still challenging. Here, we demonstrate an all-dielectric metadevice consisting of an anisotropic metasurface layer and a PB metasurface layer etched on both sides of a silicon wafer. This structure develops a photonic spin-decoupling mechanism for spin-beam manipulation, which actively controls the power distribution between the two deflected spin beams by rotating the incident linearly polarized direction. The power-distribution ratio reaches 14.9:1 in the experiment. Moreover, the deflected beam can also be modulated by active switching via a laser pump, achieving an intensity-modulation depth of over 90%. The experimental modulation depth of the metadevice is 52% higher than that of the bare silicon wafer at the same pump power, which originates from the THz localized field enhancement and the strong dispersion effect of the PB structures. Therefore, this work provides a scheme for actively manipulating THz-beam deflection, realizing controllable wave-division multiplexing, power distribution, polarization control, and modulation.