Realization of circular-polarized asymmetric transmission and wavefront modulation with terahertz metasurfaces based on composite phases

Polarization filtering and shaping occupy crucial positions in optical systems, finding extensive applications across diverse domains such as optical imaging, detection, communication, and numerous other fields. Among them, metasurfaces, as a novel type of optical element, possess unique advantages in electromagnetic manipulation, enabling precise control over the phase, amplitude, polarization, and propagation direction of electromagnetic waves. Specifically in the terahertz band, the metasurfaces provide innovative solutions for polarization filtering and polarization conversion. To simultaneously regulate the transmission and reflection of circularly polarized light, this paper proposes and experimentally demonstrates a terahertz spin-selective metasurface, which can achieve circular polarization selection and wavefront manipulation. The metasurface is composed of split-ring resonators and realizes independent manipulation of these two types of circularly polarized light by combining transmission phase modulation and geometric phase modulation. When circularly polarized light is incident, the metasurface can achieve arbitrary wavefront modulation while simultaneously achieving the polarization selection, permitting only one type of circularly polarized light to transmit while reflecting the other type of polarized light. At the operating frequency, the cross-polarization efficiency exceeds 80%, exhibiting excellent performance. Through continuous optimization of the geometric parameters of each layer of the metasurface, we have achieved precise modulation of the phase and polarization state of the transmitted wave. Based on this metasurface, the designed deflectors and focusing lenses are demonstrated, and simulation results have verified the effectiveness and practicality of this approach. This metasurface holds tremendous potential for applications in optical information security, optical communications, and other fields.