Actively tunable bi-functional metamirror in a terahertz band

Area of Science:

• Metamaterials and Nanophotonics
• Terahertz (THz) Technology
• Graphene-based Devices

Background:

• Metamaterials offer unique electromagnetic properties.
• Active tunability and bi-functionality are crucial for advanced optical devices.
• Graphene's tunable conductivity makes it suitable for active metamaterial applications.

Purpose of the Study:

• To propose and demonstrate an actively tunable bi-functional metamirror.
• To achieve spin-selective absorption and polarization conversion functionalities.
• To explore applications in terahertz integrated devices.

Main Methods:

• Fabrication of a bi-layer graphene structure.
• Utilizing voltage-controlled conductivity of graphene for active tuning.
• Characterization of optical response under circularly and linearly polarized incidence.

Main Results:

• Demonstrated a metamirror with giant circular dichroism, acting as a spin-selective absorber (near-perfect absorption for RCP, reflection for LCP).
• Achieved polarization conversion, transforming linearly polarized waves into left circularly polarized waves.
• Showcased active switching (ON/OFF) and frequency control via applied voltages.
• Confirmed angle insensitivity for stable operation.

Conclusions:

• The proposed bi-layer graphene metamirror offers active tunability and bi-functionality.
• This design enables stable, single-mode spin-selective absorption and polarization conversion.
• Potential applications include active spin detectors, absorbers, and quarter-wave plates in the terahertz regime.