Active switching of chirality at exceptional points in terahertz metasurface and its multifunctional sensing applications.

The missing dimensionality in the parameter space of non-Hermitian systems endows exceptional points (EPs) with inherent chirality, making EPs particularly valuable for ultrasensitive sensing, asymmetric optical transmission, and laser directional emission. Here we demonstrate dynamic chirality switching at three EPs in a single metasurface through temperature-controlled conductivity modulation of vanadium dioxide (VO₂). Depending on the resonant field distributions of VO₂ patches under low- and high-conductivity states, the system is modeled as either a tri-mode dual-port or bi-mode dual-port configuration. The Hamiltonian is constructed via coupled mode theory, and the eigenvalue and eigenstate evolution in polarization space are systematically analyzed. Based on EP in metasurface, three sensing schemes are designed for chiral enantiomer discrimination, refractive index, and temperature sensing, respectively. The proposed method provides a novel perspective for multi-EP design, chiral switching, and multifunctional sensing in metasurfaces, which can be extended to various non-Hermitian systems from microwave, infrared to visible light.