No abstract

The asymmetric transmission of electromagnetic waves can be flexibly manipulated by chiral metamaterials hybridized with tunable materials or active components. Here, we propose the concept of a direction-reversible tunable asymmetric transmission effect realized by chiral metamaterials. As the proof-of-concept, twisted metallic meta-sheets consisting of split-ring resonators incorporated with active diodes is designed for linearly polarized operation in the microwave region. The direction of asymmetric transmission depending on the working states of the loaded diodes can be switched by the external bias voltage in real-time. At the same time, the reconfigurable metamaterial also shows ability to control the polarization of the transmitted wave. Both the simulation and experimental results demonstrate that this direction-reversible chiral metamaterial can dynamically adjust the propagating direction of waves, showing potential uses for full-space wave manipulation and versatile modulation devices.

Polarization is one of the key characteristics of light; hence its versatile manipulation plays a pivotal role in wave‐matter interaction, communication, detection, etc. Although metasurfaces have emerged as a promising platform for polarization optics, most of them only support limited polarization controls even in reconfigurable fashion. Here, an on‐demand dynamic polarization meta‐transformer operating for full Poincaré sphere by means of an ultrathin transmissive time‐varying metasurface is proposed. By temporally and independently modulating co‐polarized transmission coefficients of the metasurface for a pair of orthogonal linearly polarized incidence, the effective transmission metasurface anisotropy can be modified to mimic the desired arbitrary birefringence, thus enacting the polarization transformation between incidence and transmission waves with arbitrary polarization states. Experiments have been conducted in the microwave region to verify the design theory. This study may provide a new architecture in polarization optics and may advance the applications in vectorial polarimetry imaging, polarimetry radars, and optical/wireless communications.

The independent tailoring of electromagnetic waves with different circular-polarized (CP) wavefront in both reflection and transmission channels is of broad scientific and technical interest, offering ultimate degrees of freedom in designing advanced devices with the merits of functionality integration and spatial exploitation. However, most metasurfaces only provide dependent wavefront control of dual-helicity in a single channel, restricting their applications to limited practical scenarios. Herein, we propose a full-space dual-helicity decoupled metasurface and apply it to assemble a multi-folded reflective antenna (MFRA) in the microwave regime. A multilayered chiral meta-atom is designed and optimized to reflect a particular helical wave while allowing the orthogonal helical wave to penetrate through, with simultaneous full span of phase modulations in both channels. When a uniform reflection and a hyperbolic transmission phase profile is imposed simultaneously on the metasurface in a polarization-selective manner, it can be engineered to conduct specular reflection for one helical wave and convergent transmission of the other helical wave. Combining the proposed metasurface with a metallic plate as a bottom reflector and an integrated microstrip patch antenna in the center of metasurface as a feed, a MFRA is realized with a low profile, high efficiency, and high polarization purity in a broad frequency band. The proposed design method of the dual-helicity decoupled metasurface and its antenna application provide opportunities for high-performance functional devices, promising more potential in future communication and detection systems.

Janus metasurfaces, a category of two-faced twodimensional (2D) materials, are emerging as a promising platform for designing multifunctional metasurfaces by exploring the intrinsic propagation direction (k-direction) of electromagnetic waves. Their out-of-plane asymmetry is utilized for achieving distinct functions selectively excited by choosing the propagation directions, providing an effective strategy to meet the growing demand for the integration of more functionalities into a single optoelectronic device. Here, we propose the concept of directionduplex Janus metasurface for full-space wave control yielding drastically different transmission and reflection wavefronts for the same polarized incidence with opposite k-directions. A series of Janus metasurface devices that enable asymmetric full-space wave manipulations, such as integrated metalens, beam generators, and fully direction-duplex meta-holography, are experimentally demonstrated. We envision the Janus metasurface platform proposed here to open new possibilities toward a broader exploration of creating sophisticated multifunctional meta-devices ranging from microwaves to optical systems.