Multi-frequency polarization and electro-optical modulator based on triple plasmon- induced transparency in monolayer graphene metamaterials

In this paper, a dynamically tunable triple plasmon-induced transparency (PIT) is numerically investigated in a simple monolayer graphene- patterned structure. The structure is composed of five graphene strips and a silicon substrate. Electric field distributions show that the triple PIT effect is originated from the strong destructive interference between three bright modes and one dark mode, coupled mode theory (CMT) is utilized to confirm the finite-difference-time-domain (FDTD) simulation. Results show the maximum figure of merit (FOM) and sensitivity can reach 15.88 and 0.91 THz/RIU. A on-to-off electro-optical modulator is realized by tuning the Fermi levels of the graphene, the modulation degrees of amplitude are 79.3 %, 87.1 %, 70.5 %, 79.2 %, and 84.3 %, corresponding to 2.35 terahertz (THz), 3.12THz, 3.58 THz, 3.91THz, and 4.31 THz, respectively. In addition, the effect of polarized angle on the transmission spectra was studied in detail. A multi-frequency polarization modulator can also be realized with modulation degrees of amplitude (MDA) of 77.6 %, 85.9 %, and 93.7 % at 2.09 THz, 2.82 THz, and 3.59 THz, respectively, and the corresponding polarization extinction ratio (PER) are 6.5 dB, 8.5 dB, and 12.1 dB, respectively. Therefore, the results of the paper are significant to the design of multi-frequency, terahertz sensors, slow light, and modulators.