Abstract
We investigate the optical exceptional points (EPs) in the graphene incorporated multilayer metamaterial manifesting Fano resonance. The system is non-Hermitian and possesses EPs where both the eigenvalues and eigenvectors of the Hamiltonian coalesce. In the aid of Fano resonance, the reflection may reach minimum approaching to zero, resulting in the degeneration of both eigenvalues and eigenvectors and thus the emergence of EPs. The transmission and reflection of light through the metamaterial change sharply by varying slightly the incident wavelength and chemical potential of graphene in the parameter space when encircling the EPs. In addition, the unidirectional invisibility can be achieved at EPs. The study paves a way to precisely controlling the transmission and reflection through metamaterials and may find applications in optoelectronic switches, modulators, absorbers, and optical sensors.
Highlights
In an open quantum system with parity-time symmetry, the Hamiltonian is non-Hermitian but possesses purely real eigenvalues
The exceptional points (EPs) associated with Fano resonance show unidirectional reflections and the resonance wavelength change with the optical parameters, which may find applications in optical sensors and environment detection [26]
The results indicate that this metamaterial structure may find applications in optical switches by encircling one EP or two in the parameter space
Summary
In an open quantum system with parity-time symmetry, the Hamiltonian is non-Hermitian but possesses purely real eigenvalues. Dembowski et al have observed experimentally the topological structure of EPs in microwave cavities [7], where anti-crossing (crossing) of the real and imaginary parts of eigenvalues is presented and the eigenvalues and eigenvectors are interchanged from one state to another while encircling an EP. The photon trapping annihilates the reflection on one side of the system [15], resulting in unidirectional zero reflection and the realization of EPs. Fano resonance can be applied to graphene metamaterials to realize EPs by employing the highly tunable property of graphene. Instead of changing the dielectric constant or structural parameters of the system, the chemical potential of graphene is tuned to adjust the valleys of Fano-type reflection. The EPs associated with Fano resonance show unidirectional reflections and the resonance wavelength change with the optical parameters, which may find applications in optical sensors and environment detection [26]
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