Polarization-selective modulation of meandered-line metamaterials with graphene surface plasmonics

Abstract

Periodic metal lines are the first kind of metamaterials, which typically exhibit plasmonic resonances to the normally incident waves polarized perpendicularly to them, i.e., transverse magnetic (TM) waves. Meandered lines can obtain resonances for both TM and transverse electric (TE) incidences and have found important applications in chirality and polarization conversion. Recently, several stimuli have been investigated to dynamically modulate the optical properties of periodic lines, which simultaneously tune both TE and TM resonances and show little polarization dependence. In this work, metal-graphene hybrid meandered-line metamaterials are designed for polarization-selective modulation at terahertz frequencies for the first time. The periodic lines meandered in S-shape resonate at 103 GHz for TE waves and at 195 and 320 GHz for TM waves, respectively. Graphene strips are patterned in pairs right at the bending corners along the polarization direction of TE waves, which produce even plasmonic dipole mode for TE incidence. In contrast, they are asymmetric with respect to the TM waves and generate odd coupling mode under TM incidence. These modes with various field concentrations exhibit considerable modulation difference to the graphene conductivity variation. As the graphene chemical potential sweeps, TE transmittance is modulated from 0.7 to 0.47 at 100 GHz, and TM transmittance is modulated just from 0.4 to 0.39 at 190 GHz and from 0.57 to 0.52 at 289 GHz, respectively. The corresponding modulation axial ratio is as large as 23 and 4.6 under a low bias from -1.2 to 1.2 V. This work paves a new way to control terahertz waves polarization-selectively.