Abstract Background. The aim of this work is a numerical investigation of linear dichroism in graphene nanoribbon (GNR) metasurfaces in transmission, reflection, and absorption regimes in the terahertz (THz) frequency range as an important property for controlling and characterizing polarization in THz devices based on them, which are dynamically tunable by gating the chemical potential of graphene (by applying an electric field). Materials and methods. An effective way to achieve dynamic dichroism control is the integration of 2D materials (including graphene) into metasurfaces. Their surface conductivity ensures dynamic control over a broad THz frequency band using electrical biasing or chemical doping. Surface plasmon polaritons in graphene exhibit high spatial localization and ensure the manipulation of THz radiation at extreme nanoscales. A numerical investigation of dichroism in GNR metasurfaces has been performed based on automated modeling methods by using the CST Microwave Studio software. The Floquet channel method has been chosen to solve the electrodynamic problem of diffraction of linearly polarized plane waves with the p‑ and s-polarization on a GNR metasurface. The boundary value problem of electrodynamics in CST MWS is solved using the numerical finite element method (FEM) in the frequency domain. Results. The spectral dependences of the transmission, reflection, and absorption coefficients of linearly polarized normally and obliquely incident p- and s-polarized plane waves on a GNR metasurface have been calculated for different values of chemical potential µc and wave incidence angle α in the THz frequency range. The spectral dependences of the linear dichroism coefficients (LDC) of the GNR metasurface have been calculated in the absorption, transmission, and reflection regimes, and analysis of the dichroism controllability has been performed with varying chemical potential µc (0.2–1 eV) and wave incidence angle α (from 0° to 80°) in the THz range. Conclusions. The numerical investigation results show that the LDC maxima are attained at the resonant frequencies of the graphene metasurface. The resonant frequencies and the LDC magnitude are controlled by varying the chemical potential µсh of graphene; with increasing µc (0.2–1 eV), the LDC increases. By varying the chemical potential (in the range of µс = 0.2–1 eV), it is possible to tune (for the given geometric parameters of the metasurface (period d = 1 μm) based on a GNR (width w = 0.5 μm)) the LDC function in the range of 0.37–0.52 in the frequency range of 7.24–16.58 THz (at normal incidence). The linear dichroism coefficient depends on incidence angle α and reaches a maximum value of LDC = 0.56 at oblique incidence (α = 80°) at frequency fres = 7.6 THz and µс = 0.2 eV. GNR metasurfaces exhibit polarization modulation and polarization-selective absorption based on linear dichroism at normal (α = 0°) and oblique (α = 80°) incidence of orthogonally polarized THz waves (with p- and s-polarization) most effectively at LDC maxima at resonant frequencies. The operating frequencies of polarization THz modulators and polarization-selective THz absorbers based on GNR metasurfaces, as well as the maximal values of LDC at resonant frequencies, which determine the efficiency of THz radiation polarization conversion, are dynamically controlled by changing the chemical potential of graphene (by applying an electric field) in a wide range of THz frequencies.

Electrically Tunable Linear Dichroism in Graphene Nanoribbon-Based Metasurfaces for Controlling the Polarization of Terahertz Radiation

期刊论文
发表日期：

2026年2月1日

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G. S. Makeeva,
M. S. Nikitin

摘要

Abstract

Background. The aim of this work is a numerical investigation of linear dichroism in graphene nanoribbon (GNR) metasurfaces in transmission, reflection, and absorption regimes in the terahertz (THz) frequency range as an important property for controlling and characterizing polarization in THz devices based on them, which are dynamically tunable by gating the chemical potential of graphene (by applying an electric field). Materials and methods. An effective way to achieve dynamic dichroism control is the integration of 2D materials (including graphene) into metasurfaces. Their surface conductivity ensures dynamic control over a broad THz frequency band using electrical biasing or chemical doping. Surface plasmon polaritons in graphene exhibit high spatial localization and ensure the manipulation of THz radiation at extreme nanoscales. A numerical investigation of dichroism in GNR metasurfaces has been performed based on automated modeling methods by using the CST Microwave Studio software. The Floquet channel method has been chosen to solve the electrodynamic problem of diffraction of linearly polarized plane waves with the p‑ and s-polarization on a GNR metasurface. The boundary value problem of electrodynamics in CST MWS is solved using the numerical finite element method (FEM) in the frequency domain. Results. The spectral dependences of the transmission, reflection, and absorption coefficients of linearly polarized normally and obliquely incident p- and s-polarized plane waves on a GNR metasurface have been calculated for different values of chemical potential µ_c and wave incidence angle α in the THz frequency range. The spectral dependences of the linear dichroism coefficients (LDC) of the GNR metasurface have been calculated in the absorption, transmission, and reflection regimes, and analysis of the dichroism controllability has been performed with varying chemical potential µ_c (0.2–1 eV) and wave incidence angle α (from 0° to 80°) in the THz range. Conclusions. The numerical investigation results show that the LDC maxima are attained at the resonant frequencies of the graphene metasurface. The resonant frequencies and the LDC magnitude are controlled by varying the chemical potential µ_сh of graphene; with increasing µ_c (0.2–1 eV), the LDC increases. By varying the chemical potential (in the range of µ_с = 0.2–1 eV), it is possible to tune (for the given geometric parameters of the metasurface (period d = 1 μm) based on a GNR (width w = 0.5 μm)) the LDC function in the range of 0.37–0.52 in the frequency range of 7.24–16.58 THz (at normal incidence). The linear dichroism coefficient depends on incidence angle α and reaches a maximum value of LDC = 0.56 at oblique incidence (α = 80°) at frequency f_res = 7.6 THz and µ_с = 0.2 eV. GNR metasurfaces exhibit polarization modulation and polarization-selective absorption based on linear dichroism at normal (α = 0°) and oblique (α = 80°) incidence of orthogonally polarized THz waves (with p- and s-polarization) most effectively at LDC maxima at resonant frequencies. The operating frequencies of polarization THz modulators and polarization-selective THz absorbers based on GNR metasurfaces, as well as the maximal values of LDC at resonant frequencies, which determine the efficiency of THz radiation polarization conversion, are dynamically controlled by changing the chemical potential of graphene (by applying an electric field) in a wide range of THz frequencies.