Asymmetric off-axis focusing THz metasurface for circularly polarized light waves

Abstract

Metasurfaces can be used to control the phase, amplitude and polarization of light arbitrarily. Here, we design a transmission-type all dielectric metasurface to realize asymmetric off-axis light focusing which can focus transmitted light on different sides of the principal axis with different focal lengths and off-axis light angles. This metasurface works for normally incident waves with left-handed circular polarization (LCP) and right-handed circular polarization (RCP), and can maintain its functionality for obliquely incident waves. Remarkably, in this metasurface, dispersion control is successfully realized in the frequency range from 0.55 THz to 0.85 THz, that is, the focal point moves along a straight line. A monolayer of graphene is further introduced to achieve the dynamical control of the intensity of transmitted waves by tuning the Fermi energy of graphene. The scheme we proposed here provides an effective approach to design asymmetric off-axis optical devices.

Keywords

• Asymmetric off-axis light focusing
• Metasurfaces
• Phase combination
• Dispersion control