Terahertz programmable metasurface for phase modulation based on free carrier plasma dispersion effect

Active metasurfaces utilize semiconductor carrier modulation, offering an approach for spatial light modulation with advantages in speed, efficiency, and power consumption. Here, we present a method for designing programmable metasurfaces that leverage the plasma dispersion effect of semiconductors to tune terahertz wave phase. By integrating the PN junction into the metasurface unit and adjusting the relative permittivity of the PN junction through voltage control, the reflected wave phase can be effectively manipulated. The designed metasurface enables continuous phase modulation of up to 270° around 0.4 THz, with an average reflection efficiency of 30% and potential modulation speed in the GHz range. Additionally, by configuring different phase distributions, the metasurface can steer terahertz beams at different angles, achieving a far-field radiation peak gain of 13 dB. This proposed programmable metasurface shows great potential for applications in terahertz communication and imaging.