Multifunctional optical switching and slow light based on tunable triple plasmon-induced transparency in a terahertz patterned graphene metasurface

In the current study, a reconfigurable multifunctionality and compact graphene metasurface consisting of a graphene block, a rectangular graphene ring, and four L-shaped graphene patches is proposed, which can generate triple plasmon-induced transparency (triple-PIT) through interactions between one dark mode and three bright modes in the terahertz band. Its physical mechanism is revealed through comparisons of coupled mode theory (CMT) calculations with finite-difference time-domain (FDTD) simulations. Penta-frequency and hexa-frequency asynchronous optical switching are achieved via modulation of the graphene Fermi levels and carrier mobility; the maximum modulation depth is 98.29%, the minimum insertion loss is 0.06 dB, and the maximum extinction ratio is 17.67 dB. For slow-light applications, the triple-PIT system achieves a group index of up to 1402, indicating a strong slow-light effect. In addition, this structure not only exhibits clear temperature insensitivity but also a certain fabrication tolerance for the critical component. Consequently, the present work provides a basis for designing high-performance optical switches, slow light devices, and modulators based on graphene metasurfaces.