Periodically patterned photoconductive-silicon-incorporated dual-functional, optically reconfigurable terahertz device

In this work, we present an optically reconfigurable dual-functional terahertz (THz) metasurface that integrates broadband absorption and polarization conversion within a single ultrathin architecture. A wheel-like photoconductive-silicon pattern integrated onto a PTFE substrate enables switching between the two operating states through optical modulation of the Si conductivity. Here, we demonstrate broadband absorption exceeding 90% over 3.40–5.824 THz, thanks to the optical illumination-induced conductivity modulation of the silicon layer. The periodic grooves in the wheels cause strong entrapment of the THz wave, thereby contributing to obtaining a wider bandwidth. The principal illuminated-state full-wave response is further reproduced using a physics-guided eigenmode equivalent-circuit model. As a polarization converter, our proposed device transforms the incident linearly polarized electromagnetic signal into its cross-polarized component from 3.523 THz to 5.394 THz. The converter also achieves a maximum LP-to-CP bandwidth of 1.654 THz (1.864–3.518 THz). The performance exhibits robust angular stability, maintaining efficiency under TE polarization, for incidence angles up to 30° for the absorber and 10° for the polarization converter. A steady-state thermal analysis was performed to demonstrate a modest, manageable temperature rise under continuous optical excitation across realistic cooling conditions.