Tunable Terahertz Wavefront Modulation Based on Phase Change Materials Embedded in Metasurface

Abstract

In the past decades, metasurfaces have shown their extraordinary abilities on manipulating the wavefront of electromagnetic wave. Based on the ability, various kinds of metasurfaces are designed to realize new functional metadevices based on wavefront manipulations, such as anomalous beam steering, focus metalens, vortex beams generator, and holographic imaging. However, most of the previously proposed designs based on metasurfaces are fixed once design, which is limited for applications where light modulation needs to be tunable. In this paper, we proposed a design for THz tunable wavefront manipulation achieved by the combination of plasmonic metasurface and phase change materials (PCMs) in THz region. Here, we designed a metal-insulator-metal (MIM) metasurface with the typical C-shape split ring resonator (CSRR), whose polarization conversion efficiency is nearly 90% for circular polarized light (CPL) in the range of 0.95~1.15 THz when PCM is in the amorphous state, but the conversion efficiency turns to less than 10% in the same frequency range when PCM switches into the crystalline state. Then, benefiting from the high polarization conversion contrast of unit cell, we can achieve tunable wavefront manipulation by utilizing the Pancharatnam–Berry (PB) phase between the amorphous and crystalline states. As a proof-of-concept, the reflective tunable anomalous beam deflector and focusing metalens are designed and characterized, and the results further verify their capability for tunable wavefront manipulation in THz range. It is believed that the design in our work may pave the way toward the tunable wavefront manipulation of THz waves and is potential for dynamic tunable THz devices.

Recent Advances in Terahertz Manipulations Using C‐Shape‐Split‐Ring‐Resonator Metasurfaces (Review)

“…For example, in its amorphous state, GST can achieve a polarization conversion efficiency of nearly 90% for circularly polarized light within the frequency range of 0.95–1.15 THz. [ 143 ] However, this efficiency drops to <10% within the same frequency range when GST transitions into its crystalline state. The ability to switch between the amorphous and crystalline states in GST allows for tunable wavefront manipulation.…”

Recent Advances in Reconfigurable Metasurfaces: Principle and Applications

“…Zhang et al realized terahertz wavefront manipulation using a GST embedded metasurface. As is shown in Figure 3 c [ 169 ], the unit cell is a metal–GST–metal structure where a C-shape split ring resonator is embedded on a GST layer and a metal ground is on the back of the GST layer. Here, the genetic algorithm is applied to optimize the geometric parameters of the unit cell to obtain high polarization conversion efficiency at an amorphous state of GST and low conversion efficiency at the crystalline state.…”