Bifunctional sensing based on an exceptional point with bilayer metasurfaces.

Area of Science:

• Non-Hermitian physics
• Metamaterials and Plasmonics
• Terahertz (THz) technology

Background:

• Exceptional points (EPs) are critical phase transition points in non-Hermitian parity-time (PT) systems.
• EPs offer unique physical properties and applications, including ultra-sensitive perturbation detection.
• Metasurfaces provide a versatile platform for manipulating electromagnetic waves.

Purpose of the Study:

• To propose a bilayer metasurface with tunable PT symmetry for observing exceptional points.
• To demonstrate a phase transition of eigenpolarization states by altering vanadium dioxide (VO2) conductivity.
• To develop high-sensitivity sensing schemes for temperature and refractive index in the terahertz range.

Main Methods:

• Design and fabrication of a bilayer metasurface with orthogonally oriented split-ring resonators (SRRs).
• Integration of a vanadium dioxide (VO2) patch into the SRR gap to enable tunable conductivity.
• Observation of exceptional points in polarization space at a specific VO2 conductivity.
• Development of two sensing schemes utilizing the metasurface properties.

Main Results:

• The proposed metasurface exhibits passive PT symmetry.
• An exceptional point in polarization space was observed.
• The metasurface demonstrated potential for high-sensitivity sensing of temperature and refractive index.
• The device operates in the terahertz (THz) frequency range.

Conclusions:

• The developed metasurface effectively demonstrates exceptional points through tunable PT symmetry.
• The device shows promise for ultra-sensitive terahertz sensing applications.
• Potential applications include THz biosensing and advanced polarization manipulation.