Theoretical and computational study of a quad-band optical switch and three-bit encoder based on a graphene metasurface

To address the issues of insufficient tunability and high losses in existing metamaterial devices, this study proposes a tunable metamaterial device based on graphene. Coupling effects among these units under normal-incidence x-polarized terahertz irradiation result in the emergence of four transmission dips and three electromagnetically induced transparency resonances, the latter achieving transmittance values above 90%. Under Fermi level adjustment in graphene, the device exhibits excellent quad-band optical switching performance, achieving a maximum modulation depth of 92.1%, alongside an insertion loss of only 0.01 dB alongside an 11 dB extinction ratio. Furthermore, the proposed device can also realize 3-bit encoding functions at 3.18, 4.8, and 6.38 THz. The structure demonstrates remarkable slow-light tunability, with the group refractive index peaking at 623. This research provides a novel device design approach for terahertz communications, wide-field imaging, and multifunctional sensing applications.