High modulation depth 3-bit graphene encoder and multi-channel optical switch based on double plasmon-induced transparency

In this paper, we propose a novel structure based on a single-layer patterned graphene all-dielectric metasurface, which achieves the double plasmon-induced transparency (PIT) through triple bright mode interactions through near-field coupling. This innovative approach can be further developed into high-performance terahertz devices by dynamic modulation of the Fermi energy level and polarization sensitivity. The research results show that the 3-bit encoding function is achieved through the independent modulation of the Fermi energy level in the graphene strip. The maximum modulation depth of the encoder is 98.8 %, the minimum insertion loss is 0.11 dB, and the extinction ratio is as high as 19.1 dB. Through the synchronous modulation of the Fermi energy levels in the three sets of graphene strips, a six-frequency asynchronous optical switch is constructed. The maximum modulation depth is 97.78 % and the minimum insertion loss is 0.26 dB. To support multi-band parallel signal processing in adverse hot weather conditions, we design a four-pass-channel optical switch utilizing polarization anisotropy. By varying the polarization direction of the incident light within the range of 2.31–7.82 THz, stable switching is accomplished. In comparison to existing encoders and optical switches, the structure proposed in this paper significantly enhances coding capacity, modulation depth, extinction ratio, and insertion loss, thereby offering innovative insights for designing terahertz devices.