Dielectric chiral metasurface is a new type of planar and efficient chiral optical device that shows strong circular dichroism or optical activity, which has important application potential in optical sensing and display. However, the two types of chiral optical responses in conventional chiral metasurfaces are often interdependent, as their modulation of the amplitudes and phases of orthogonal circularly polarized components is correlated, which limits the further progress of chiral meta-devices. Here we propose a new scheme for independently designing the circular dichroism and optical activity of chiral metasurfaces to further control the polarization and wavefront of transmitted waves. Inspired by mixtures of chiral molecular isomers, we use the dielectric isomer resonators to form “super-units” instead of single meta-atoms for chiral responses in terahertz band, which is called racemic metasurface. By introducing two levels of Pancharatnam-Berry phases between meta-atoms and “super-units”, the polarization rotation angle and wavefront of the beam can be designed without the far-field circular dichroism. We demonstrate the strong control ability on terahertz waves of this scheme through simulation and experiments. In addition, this new type of device with near-field chirality but no far-field circular dichroism may also have important value in optical sensing and other technologies.

Diatomic metasurfaces designed for interferometric mechanisms possess significant potential for the multidimensional manipulation of electromagnetic waves, including control over amplitude, phase, frequency, and polarization. Geometric phase profiles with spin-selective properties are commonly associated with wavefront modulation, allowing the implementation of conjugate strategies within orthogonal circularly polarized channels. Simultaneous control of these characteristics in a single-layered diatomic metasurface will be an apparent technological extension. Here, spin-selective modulation of terahertz (THz) beams is realized by assembling a pair of meta-atoms with birefringent effects. The distinct modulation functions arise from geometric phase profiles characterized by multiple rotational properties, which introduce independent parametric factors that elucidate their physical significance. By arranging the key parameters, the proposed design strategy can be employed to realize independent amplitude and phase manipulation. A series of THz metasurface samples with specific modulation functions are characterized, experimentally demonstrating the accuracy of on-demand manipulation. This research paves the way for all-silicon meta-optics that may have great potential in imaging, sensing and detection.

The manipulation of polarization states is crucial for tailoring light–matter interactions and has great applications in fundamental science.

Vortex beams, characterized by orbital angular momentum (OAM), hold significant potential in optical communications, quantum information processing, and optical manipulation. However, existing metasurface designs are largely confined to single‐degree‐of‐freedom control, such as static OAM generation or fixed focal points, which limiting their ability to integrate polarization multiplexing with dynamic focal tuning. To address this challenge, we propose a tunable multifunctional cascaded metasurface that synergizes polarization‐sensitive phase engineering with interlayer rotational coupling, overcoming conventional device limitations. The designed metasurface independently generates distinct OAM states in orthogonal circular polarization channels under right‐handed circularly polarized (RCP) incidence, that is, a vortex beam with topological charge ℓ = −1 in the left‐handed circularly polarized (LCP) channel and a superimposed vortex state (ℓ = +1, −1) in the RCP channel. Continuous focal tuning is achieved via interlayer rotation in the axis‐direction, with experimental validation at target frequency. Experimental results demonstrate the focal length modulation range from 25.9λ to 9.5λ as the interlayer rotation angle varies between 90° and 240°. This multi‐degree‐of‐freedom control strategy establishes a new method for high‐capacity optical communications, dynamic holography, and quantum state manipulation, while advancing the development of intelligent metasurfaces for 6G networks and integrated photonic systems.

In recent years, continuous bound states in the continuum (BIC) have gained significant attention for their practical applications in optics, chip technology, and modern communication. Traditional approaches to realizing and analyzing BIC typically rely on magnetic dipole models, which have limitations in quantitative analysis and integration. This creates a gap in understanding how to efficiently harness BIC with higher Q-factors for enhanced performance in real-world applications, particularly in scenarios involving terahertz imaging and multi-channel communication. In this study, we introduce a novel approach using a metallic resonator model that leverages toroidal dipole moments to generate symmetry-protected BIC with high Q-factors. By systematically varying the asymmetry parameters of the metasurface, we gradually break its symmetry, achieving a transition from the BIC mode to the quasi-BIC mode and facilitating the gradual release of stored electromagnetic energy. Our theoretical analysis confirms the existence and generation of BIC, and experimental measurements of the transmission response spectrum validate these theoretical predictions. The results indicate that terahertz metasurface with high Q-factors can produce strong resonances at specific frequencies, enhancing resistance to electromagnetic interference and ensuring stable imaging quality in complex environments. Additionally, this study suggests the potential for an integrated plasmonic ruler to achieve high-resolution and efficient biological imaging. These findings bridge the gap by demonstrating how high Q-factor BIC can be effectively utilized for multi-channel terahertz dynamic imaging and biosensing applications. This advancement lays a new foundation for developing robust systems in multi-channel communication and biomedical sensing, offering significant potential for future technological and medical innovations.