Chiral terahertz metasurface with asymmetric transmission, polarization conversion and circular dichroism.

A tri-layer chiral metasurface with multi-functions of asymmetric transmission (AT), polarization conversion (PC) and circular dichroism (CD) is proposed in the terahertz (THz) range. Simulation results show that the metasurface is able to realize AT with more than 90% efficiency and PC fractional bandwidth of 80% over a frequency range of 0.15 to 0.35 THz. At 0.33 THz, it showcases the utmost CD of 58%. Through experimental measurements, the fabricated device demonstrate that the AT parameters exceed 35% in the frequency range of 0.24-0.33 THz. This broad frequency range represents a PC fractional bandwidth of 69% and reveals a prominent peak at 0.28 THz, wherein the transmission attains a value of 0.62. The proposed configuration exhibits CD, achieving 14% at 0.24 THz. Furthermore, the functionalities of AT, PC and CD are stable for changes in incident angle up to 60° for both linearly polarized and circularly polarized incident waves. Moreover, the experimental and measured results demonstrate that the proposed multilayer chiral metamaterial achieves multifunctionality for THz incident waves, offering promising implications for advancing THz communication bands.