Switchable dichroism in VO 2 -GST225 terahertz metasurfaces

Traditional metasurfaces suffer from limited flexibility in integrating circular dichroism (CD) and linear dichroism (LD), as well as structural complexity. Addressing these challenges, we propose an ultracompact VO 2 /Ge 2 Sb 2 Te 5 (GST225) hybrid metasurface that dynamically switches between CD and LD modes. The device sequentially achieves CD−, LD, and CD+ modes through the reversible VO 2 phase transition and the nonvolatile GST225 phase change. Each mode exhibits dual-band spectral responses. In CD− and CD+ modes, the device generates CD signals with opposite signs. Both CD+ and CD− modes exhibit dual-band CD responses at identical frequencies: 1.3151 and 1.6689 THz, with corresponding peak values of (0.821, 0.7086) for CD+ and (−0.7943,−0.6649) for CD−, respectively. To our knowledge, this is the first realization of spectrally overlapped dual-band CD with opposite signs in a single metasurface. Conversely, in the LD mode, the device exhibits pronounced LD peaks reaching values of 0.822 and 0.7697 at frequencies of 0.3117 and 1.2571 THz, respectively. All three modes exhibit enhanced absorption for left-circularly polarized (LCP), right-circularly polarized (RCP), and y-linearly polarized (YLP) waves compared with their respective orthogonally polarized waves. This work achieves, for the first time, the integration of dual-band switchable CD and high-efficiency LD responses in a single streamlined device—outperforming conventional designs in both functionality and simplicity. The three operational modes of this device unlock new opportunities for image encryption and polarization-selective detection systems.