Dual-frequency unidirectional reflectionless propagation in a non-Hermitian graphene plasmonic waveguide-cavity...

Area of Science:

• Photonics and Plasmonics
• Condensed Matter Physics
• Nanotechnology

Background:

• Graphene surface plasmon polaritons (GSPPs) offer unique light-matter interactions at the nanoscale.
• Exceptional points (EPs) in non-Hermitian systems exhibit exotic phenomena like enhanced sensitivity and asymmetric transport.
• Controlling light propagation unidirectionally is crucial for integrated photonic devices.

Purpose of the Study:

• To theoretically investigate controllable dual-frequency unidirectional reflectionlessness at EPs in a graphene plasmonic waveguide system.
• To explore the tunability of this phenomenon via external voltage and graphene Fermi level.
• To verify the existence of double EPs and analyze the system's non-Hermitian characteristics.

Main Methods:

• Theoretical investigation of a graphene waveguide coupled with two resonators.
• Utilizing COMSOL simulations to model GSPP mode reflection.
• Employing a non-Hermitian scattering matrix approach to identify EPs.

Main Results:

• Achieved near-zero reflection for forward incidence at 24.418 THz and backward incidence at 20.865 THz.
• Demonstrated significant reflection asymmetry: 24.71% for backward and 22.945% for forward incidence.
• Verified the existence of double EPs and confirmed tunability of unidirectional reflectionlessness by adjusting graphene's Fermi level.

Conclusions:

• The proposed graphene plasmonic system enables controllable dual-frequency unidirectional reflectionlessness at EPs.
• External voltage and Fermi level tuning offer practical methods for manipulating light propagation.
• This work paves the way for novel non-reciprocal devices in integrated photonics.