Efficiency adjustable terahertz circular polarization anomalous refraction and planar focusing based on a bi-layered complementary Z-shaped graphene metasurface

Abstract

Metasurfaces (MSs) have received great attention due to their wide application potentials in terahertz (THz) wavefront manipulation. Although great achievements have been obtained in MSs so far, the functionalities are almost static. The active adjustable MS-based devices are far less explored. In this paper, an efficiency adjustable MS composed of a dielectric substrate sandwiched with bi-layered complementary Z-shaped (CZS) structure graphene is proposed and investigated theoretically, which can control the THz circular polarization (CP) wavefront in transmission mode. The simulation results show that the MS structure under a Fermi energy level of 1.0 eV can realize CP conversion with efficiency of about 0.9, and the full range of a 2 π phase shift also can be achieved by changing the rotation angle of the CZS structure graphene along the wave propagation direction. More importantly, the transmission CP conversion efficiency is positively correlated with the Fermi energy levels of graphene. The anomalous refraction and planar focusing effect can be realized by the specific design of a spatial phase profile of the graphene MS, and the corresponding efficiencies can be adjusted by changing the Fermi energy level of the graphene. Adjustable graphene MSs have wide application prospects in the fields of communication, imaging, and other THz wavefront manipulation devices.

Ultrathin and Ultra‐Broadband Terahertz Single‐Layer Metasurface Based on Double‐Arrow‐Shaped Resonator Structure for Full‐Space Wavefront Manipulation

“…Through the ultrathin MS meta‐lens, the incident LCP(RCP) wave will be converted into an RCP(LCP) wave and then converge into a focus point after reflection and transmission. To realize the focusing effect for both reflection and transmission, the compensation phase profile generated by each unit‐cell of the MS‐based meta‐lens at position ( x,y ) should be satisfied as: [ 26–28 ] $$$$\begin{equation}\varphi (x,y,F) = \frac{{2\pi }}{\lambda }\left( {\sqrt {{x}^2 + {y}^2 + {F}^2} - {F}^2} \right) + {\varphi }_0\end{equation}$$$$where φ ( x , y , F ) is the compensation phase of the each unit‐cell in position ( x , y ), λ is the operation wavelength, F is the focal length between the MS‐based meta‐lens and focusing plane, and φ 0 is the initial phase in the center ( x = y = 0) position.…”

“…The anisotropical design of the DASR is very important and a key to achieve the highefficient cross-polarization conversion, which has been used to construct various polarization convertor either in reflection or transmission mode. [16,[26][27][28]45] The 𝛼 is the oriented angle of the DASR structure respect to the x-axis direction, as shown in Figure 1a. The 0-2𝜋 phase shifts of the reflected and transmitted orthogonal CP wave can be realized independently by adjusting 𝛼.…”

“…The most of the currently MSs can operate well only in reflection or transmission mode. [21][22][23][24][25][26][27][28][29] For the practical miniaturization and integration THz applications, the design and realizations of the multifunctional MS for both reflection and transmission are highly desirable and necessary. [30][31][32][33][34][35][36] For example, Wu et al, reported a novel digital MS by multi-layered structures based on the concept of reflection-transmission code, which can achieve EM manipulations in full-space [31] .…”

Broadband Graphene-Based Electro-Optic Chiral Polarization Conversion for Terahertz Pulse Shaping

“…Despite important advances in the exploration of the active control of polarization, electrical control of THZ chiral polarization remains largely elusive and suffers from a limited dynamic range of polarization conversion and limited response frequency bandwidth. − Because of the highly tunable conductivity in the THz region, two-dimensional (2D) materials (e.g., graphene and black phosphorus) show great potential in THz modulation. − Combining graphene with metamaterials/metasurface, electrical modulation of the polarization state of THz beams has been widely demonstrated. − However, the working frequency is limited at a certain narrowband because of the resonance nature of metamaterials.…”

Terahertz Transmission‐Type Metasurface for the Linear and Circular Polarization Wavefront Manipulation

“…Multiple beam generation and multifocal lenses have been demonstrated numerically. [42,43] All of the above MSs can control the wavefront at different frequencies [44][45][46][47][48][49][50][51] but they can only operate well for LP or CP wave.…”