Polarization-Selective Modulation of Meandered-Line Metamaterials with Graphene Surface Plasmonics

Abstract

Periodic metal lines are the first kind of metamaterials, which typically exhibit resonance to the incident transverse magnetic (TM) waves polarized perpendicularly. Meandered lines can obtain bidirectional resonances for both TM and transverse electric (TE) incidences and have found important applications in chirality and polarization conversion. The modulation methods reported recently have rarely provided polarization-dependent control to the meandered lines, and thus simultaneously tune both TE and TM resonances. In this work, hybrid meandered-line metamaterials with graphene plasmonic dipoles are designed with 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 strip pairs are patterned symmetrically along the TE polarization direction and asymmetrically along the TM polarization direction, which produce even dipole and odd coupling modes under TE and TM incident waves, respectively. These surface plasmonic modes with various field concentrations exhibit considerable difference to the graphene conductivity variation. As graphene conductivity increases, 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.

Keywords: meandered-line metamaterials, polarization-selective modulation, graphene, surface plasmonics, terahertz