Tunable polarization-independent plasmonically induced transparency based on metal-graphene metasurface

A tunable polarization-independent dual-band plasmonically induced transparency (PIT) device based on metal-graphene nanostructures is proposed theoretically and numerically at mid-infrared frequencies, which is composed of two kinds of center-symmetric metallic nanostructure array with different sizes and element numbers placed on separate graphene interdigitated finger sets, respectively. The coupled Lorentz oscillator model is used to explain the physical mechanism of PIT effect at multiple frequency domains. The finite-difference time-domain (FDTD) solutions are employed to simulate the characteristics of the polarization-independent metal-graphene PIT device, which is consistent with the theoretical analysis. The PIT peaks, obtained at two frequency domains, are separately and dynamically modulated by varying the Fermi energy of corresponding graphene finger set without changing the geometrical parameter of the metallic nanostructure. By the carefully selected element numbers of nanostructure arrays, the resonance strength of the PIT peaks at two frequency domains are nearly close. And the PIT device has identical response to the various polarized incident field due to the center symmetry of the metallic nanostructure, which have advantages in practical applications with no polarization-dependent loss.