Optically switchable multifunctional terahertz geometric phase metasurface

An optically switchable terahertz metasurface was proposed based on the metal-photosensitive silicon combination rings, which could be used to achieve multifunctional wavefront control. The metasurface was composed of double-sided structural layers and an intermediate medium layer, from which the structural layers were metal rings with opposite opening directions, and the opening was filled by photosensitive silicon. At a lower light intensity, the metasurfaces could convert the incident circularly polarized waves into cross-polarized transmitted waves. As the light intensity increasing, the transmitted waves would be completely suppressed. Based on the geometric phase principle, by rotating the metal-photosensitive silicon combination ring, the transmitted cross-polarization wave would carry additional phase factors, and could achieve a complete 2π-range phase coverage. By properly arranging the metasurface unit structure, the wavefront of the transmitted wave could be manipulated arbitrarily. The proposed optically switchable metasurface enabled an efficient anomalous refraction, metalens and orbital angular momentum generator under lower light conditions, while the transmission efficiency was suppressed and the application function could be conditionally selected under higher light conditions, which showed the better flexibility. Therefore, the proposed device has great potential applications in terahertz imaging, communication, radar, and etc.