Spin-multiplexed full-space trifunctional terahertz metasurface [Invited]

The widespread use of multifunctional metasurfaces has started to revolutionize conventional electromagnetic devices due to their unprecedented capabilities and exceedingly low losses. Specifically, geometric metasurfaces that utilize spatially varied single-celled elements to impart arbitrary phase modulation under circularly polarized (CP) waves have attracted more attention. However, the geometric phase has intrinsically opposite signs for two spins, resulting in locked and mir-rored functionalities for the right-handed and left-handed CP beams. Additionally, the demonstrated geometric metasur-faces so far have been limited to operating in either transmission or reflection modes at a single wavelength. Here, we propose a double-layered metasurface composed of complementary elliptical and reversal ring resonator structures to achieve simultaneous and independent control of the reflection and transmission of CP waves at two independent terahertz frequencies, which integrates three functions of reflected beam deflection, reflected Bessel beam generation, and trans-mitted beam focusing on the whole space. The high efficiency and simple design of our metasurface will open new avenues for integrated terahertz metadevices with advanced functionalities.

Automated summary

The use of multifunctional metasurfaces is revolutionizing conventional electromagnetic devices, with their unprecedented capabilities and low losses. The attention has been drawn towards geometric metasurfaces that use single-celled elements to modulate the phase of circularly polarized waves. However, the opposite signs of geometric phase for two spins have limited its functionality. Moreover, the current geometric metasurfaces operate at a single wavelength in either transmission or reflection modes. To overcome these limitations, a double-layered metasurface composed of complementary elliptical and reversal ring resonator structures is proposed for simultaneous and independent control of reflected and transmitted circularly polarized waves at two terahertz frequencies, offering advanced functionalities.