Reconfigurable terahertz metasurface based on photoconductive silicon and vanadium dioxide for broadband absorption and multiband polarization conversion

A terahertz multifunctional metasurface based on photoconductive silicon (PSi) and vanadium dioxide (VO 2 ) is proposed. By tuning the conductivity state of PSi via external optical pumping, the metasurface can switch between broadband absorption and multiband polarization conversion. When PSi is in the metallic state, the metasurface operates as a broadband absorber with absorptance exceeding 90% over 4.17–9.60 THz, corresponding to a 5.43 THz bandwidth. When PSi is in the insulating state, the metasurface operates as a polarization converter, and the polarization conversion response can be further tuned through the phase transition of VO 2 under temperature tuning. In the insulating state of VO 2 , dual-band linear-to-linear (LTL) polarization conversion is achieved in the ranges of 4.58–5.36 THz and 8.17–8.34 THz; right-hand circular polarization (RHCP) is obtained over 2.87–4.06 THz and 8.4–8.52 THz, while left-hand circular polarization (LHCP) is achieved across 5.71–8.05 THz. In the metallic state of VO 2 , broadband LTL polarization conversion is realized over 2.60–4.98 THz, yielding a bandwidth of 2.38 THz, and RHCP and LHCP are obtained within 2.19–2.42 THz and 5.50–8.37 THz, respectively. This work elucidates the underlying multifunctional mechanism using impedance matching and analyses of the electromagnetic-field and surface current distributions. By integrating broadband absorption and multiband polarization conversion into a single compact platform, the proposed metasurface shows potential for compact multifunctional terahertz devices in imaging and sensing.