Bifunctional metasurface for high-efficiency terahertz absorption and polarization conversion

Area of Science:

• Metasurface technology
• Terahertz (THz) optics
• Advanced materials

Background:

• Development of compact and efficient devices requires reconfigurable metasurfaces with switchable functions.
• Existing metasurfaces often lack broad bandwidth, high efficiency, or ultra-compact size.
• Vanadium dioxide (VO2) and graphene offer tunable electromagnetic properties crucial for reconfigurable devices.

Purpose of the Study:

• To propose and demonstrate a bifunctional metasurface for high-efficiency absorption and polarization conversion in the terahertz range.
• To achieve flexible switching between absorption, cross-polarized conversion, and linear-to-circular polarization conversion (LTC) functionalities.
• To enhance device performance through the integration of an additional dielectric layer.

Main Methods:

• Design of a bifunctional metasurface incorporating vanadium dioxide (VO2) and graphene with an additional dielectric layer.
• Utilizing the phase transition properties of VO2 (metal and insulator states) and the tunable conductivity of graphene.
• Electromagnetic simulations to analyze absorption, polarization conversion (PC) ratio, and ellipticity across various terahertz frequencies and incident angles.

Main Results:

• The metasurface exhibits high-efficiency absorption (over 98.4%) in the 2.0-7.0 THz range (111.1% relative bandwidth) when VO2 is in its metallic state.
• Absorption remains high (>90%) even at a 50° incident angle and can be tuned from 10% to 98.4% by adjusting VO2 conductivity.
• In the insulator state of VO2, the metasurface achieves efficient cross-polarized conversion (>95% PC ratio at 1.8-3.4 THz) and linear-to-circular polarization conversion (LTC) with high ellipticity at specific frequency bands (1.7-2.1 THz and 2.7-3.0 THz).

Conclusions:

• The proposed bifunctional metasurface demonstrates remarkable performance in both absorption and polarization conversion in the terahertz spectrum.
• The integration of VO2 and graphene, along with a dielectric layer, enables flexible, switchable functionalities and enhanced wave coupling.
• This design offers a promising platform for advanced, compact terahertz devices requiring tunable electromagnetic responses.