Temperature-Controlled and Photoexcited Multitasking Janus Metasurface in the Terahertz Region

In this paper, a photoexcited multitasking Janus metasurface (MJM) based on the phase-changed material vanadium dioxide and the photosensitive materials silicon and germanium in the terahertz (THz) region is proposed, which also exploits the directionality feature of electromagnetic waves. The MJM can switch its functionalities between working band shifting and full-space polarized wave control, and six functions can be implemented by exciting the switchable materials. By regulating the power of the incident pump beam, it is feasible to complete band adjustment in terms of normal incidence, i.e. the band range of polarization conversion ratio >0.9 changing from 1.23 THz-1.91 THz to 0.98 THz-1.91 THz in the reflection state and axial ratio (AR) <3 dB band range toggling between 0.69 THz-1.08 THz and 0.67 THz-0.96 THz in the transmission state. However, for the backward incidence,, it presents reflective linear-to-circle (LTC) polarization conversion (PC), with AR <3 dB domain of 0.99 THz-1.63 THz. The multiple reflection interference theory and electric field distributions are introduced to interpret the high performance. Moreover, the designed device exhibits a high angular tolerance for achieving LTC PC. The integration of numerous functions in a single structure endows the MJM with the great benefit for efficient polarization-controlled applications.