Multifunctional THz chiral metasurfaces for optical dichroism and wavefront shaping

Chiral terahertz (THz) metasurfaces offer compact platforms for polarization and wavefront control, but most existing designs are passive and limited to a single function. This work proposes a reflective VO 2 -based chiral metasurface that combines tunable circular dichroism (CD), linear dichroism (LD), and Pancharatnam–Berry phase wavefront shaping within a single device. The unit cell consists of a gold split-ring resonator partially filled with vanadium dioxide (VO 2 ), patterned on a polyimide spacer backed by a gold ground plane. The thermally driven insulator–metal transition of VO 2 reconfigures both the amplitude and phase of the reflected THz waves, enabling active control of the device response. Under circularly polarized illumination with VO 2 in the insulating state, the metasurface exhibits CD exceeding 40% from 0.60 to 0.72 THz, with a peak value of 64% at 0.66 THz. For linearly polarized incidence, it maintains LD above 30% from 0.61 to 0.74 THz and reaches a maximum of 54% at 0.69 THz. By rotating the resonator to implement a geometric phase profile, the same platform realizes tunable wavefront manipulation, numerically demonstrating a helicity-dependent anomalous beam deflector, a vortex beam generator carrying orbital angular momentum, and a reflective focusing metalens operating at 0.502 THz and 0.841 THz. These results demonstrate that the proposed VO 2 -based chiral metasurface provides a compact and multifunctional solution for thermally reconfigurable polarization control and wavefront shaping in THz imaging and communication systems.