Tri-state reconfigurable terahertz metasurface integrating VO 2 , InAs, and GST

Many tuneable electromagnetic metasurfaces rely on a single active material, limiting their functional versatility. We propose a tri-state reconfigurable terahertz metasurface that integrates VO2, InAs, and GST within a metal-dielectric-metal architecture. VO2, InAs, and GST respond to thermal, optical, and pulsed-laser excitation, respectively, enabling selection among three pre-encoded phase profiles. At 0.97 THz, the simulated unit cell achieves a polarization conversion ratio close to unity. In-plane rotation of the anisotropic unit cell provides a full 360° Pancharatnam-Berry phase range. The encoded phase profiles produce conventional foci at 500 and 1000 µm and a vortex-focused beam with orbital angular momentum (OAM) order l = 1. The same platform also reconstructs the pre-encoded holographic patterns ‘H’, ‘R’, and ‘B’ near z = 2100 µm. Full-wave simulations reproduce the intended focal and holographic field distributions, demonstrating multiple pre-encoded wavefront functions within a single metasurface aperture.