Simulation of dynamically tunable broadband and polarization-insensitive electromagnetically induced transparency in Dirac semimetal

Abstract

The structure proposed in this paper is composed of an outer circular ring resonator (CRR) and four L-shaped resonators (LSRs) in the middle. The destructive interference between bright modes produces a broadband electromagnetically induced transparency (EIT) with a maximum transmission efficiency of 97.6% in both vertical polarization directions. The field distributions and the three-level Λ-type system clarify the physical mechanism of the coupling process between bright modes. The calculated transmission spectrum based on the two-particle model is consistent with the simulated transmission spectrum, which proves the correctness of the results. By introducing hybridization bandgap (HBG) to the structure, the bandwidth of EIT-like effect expands. This structure has a fourfold (C4) rotational symmetry; thus, it is insensitive to the polarization angle. In addition, the transparency window undergoes a redshift as the Fermi energy of Dirac semimetal decreases. Meanwhile, the group delay is also controlled. Due to the wide bandwidth, a large delay bandwidth product (DBP) is obtained. Our work provides a new method for the production of slow-light devices and broadband filters.