High-efficiency terahertz dual-function devices based on the dielectric metasurface

The multifunctional optical device has attracted great interests due to the wide range of modern optical applications. However, conventional optical devices are single function and bulky structure, thereby hindering the practicality and miniaturization of the optical systems. Here, we present the basic theory, simulated demonstration, and in-depth analysis of a novel type of dielectric metasurface based on crystal Si to simultaneously convert and focus an incident linear polarization into other linear polarization or circular polarization with high efficiency and high numerical aperture (NA). Additionally, we have also achieved a quart wave-plate (QWP) based deflector that enables both arbitrary anomalous beam deflection and the polarization conversion. Simulation results show that the invertible QWP based deflector, including the linear-to-circular (LTC) and circular-to-linear (CTL) conversions, demonstrate around 80% deflection efficiency at 1.0 THz. With similar concept, a half wave-plate (HWP) combined with beam steering has also been achieved. Taking into account the considerable manipulation efficiency and cost-efficient sample fabrication technique, our designs show the great potentials of metasurfaces as a versatile platform for designing practical functional devices in the THz range.