Design of a photo-excited switchable broadband reflective linear polarization conversion metasurface for terahertz waves

We present a photo-excited switchable broadband reflective linear polarization conversion metasurface for terahertz waves. The unit-cell structure of the switchable polarization conversion metasurface is composed of metallic disk and split-ring resonator (together named as DSRR) integrated with semiconductor photoconductive silicon (Si) placed over the continuous films. The electric response of the photoconductive Si filled in the gap of the DSRR can be tunable through a pump beam with different optical power. The simulation results indicate that the polarization conversion ratio (PCR) of the compound metasurface without pump beam is greater than 80% in the frequency range of 0.65-1.58 THz, and the PCR is up to 99% at resonances frequencies of 0.69 THz, 1.01 THz and 1.42 THz, respectively. The numerical simulation results are in good agreement with the theoretical predictions based on the interference theory. Furthermore, the broadband PCR can be tunable continuously with the changes of Si conductivity by adjusting the pump optical power. Moreover, the surface current distributions of the unit-cell structure with different Si conductivity at the resonance frequency are discussed to illustrate its physics mechanism. Thus, our design can find potential applications in many areas, such as remote sensors, reflector antennas, and radiometers in terahertz region.