Phase-change metasurface for switchable terahertz edge detection and bright-field imaging based on quasi-bound states in the continuum.

Metasurfaces are confined to static functionalities and lack reconfigurability-a key characteristic urgently needed for their practical applications in dynamic environments. To address the critical challenges of traditional metasurfaces, including fixed functions, polarization dependence, bulky imaging systems, difficulties in integrating edge detection with bright-field imaging, and the requirement for additional digital post-processing, we propose to leverage the dynamic reconfigurability enabled by phase change materials, combining it with polarization insensitivity and omnidirectional dynamic switching between high-resolution edge extraction and clear bright-field imaging. In this paper, we propose a dual-polarization Laplacian differentiator operating in the terahertz band based on a nonlocal perforated metasurface, with dynamic function switching achieved by regulating the phase transition of vanadium dioxide (VO2). When VO2 is in the insulating state, the device can directly perform two-dimensional second-order image edge detection. When VO2 transitions to the metallic state, it switches to bright-field imaging mode. The Optical Transfer Function (OTF) required for Laplacian operations is achieved by exciting the Quasi-Bound States in the Continuum (Q-BIC) mode under p- and s-polarized terahertz wave illumination, which endows the device with an angular dispersive response matching the Laplacian operator's requirements. This differentiator offers dual-polarization-compatible edge detection, and its efficient, high-performance function switching-coupled with the benefits of dual-polarization imaging-provides robust technical support for terahertz-band applications including machine vision, biomedical detection, and image processing.