Electromagnetic metasurfaces with excellent electromagnetic wave regulation properties are promising for designing high-performance polarization control devices, while the application prospect of electromagnetic metasurfaces is limited because of the current development situations of the complex structure, low conversion efficiency, and narrow working bandwidth. In this work, we design a type of reflective terahertz metasurface made of a simple structure that can achieve multiple polarization modulation with high efficiency. It is shown that the presented metasurface can realize ultra-broadband, cross-polarization conversion with the relative working bandwidth reaching 94% and a conversion efficiency of over 90%. In addition, the proposed metasurface can also efficiently accomplish different polarization conversion functions, such as linear-to-linear, linear-to-circular, or circular-to-linear polarization conversion in multiple frequency bands. Due to the excellent properties, the designed metasurface can be used as a high-efficiency multi-functional polarization modulation device, and it has important application value in terahertz imaging, communication, biological detection, and other fields.

Polarization is a fundamental property of electromagnetic waves that plays a key role in many physical phenomena and applications. Schemes to manipulate it are revisited with the emergence of metasurfaces, which have brought multi-functionalities straightforwardly. However, this has come at the expense of design complexity that relies strongly on field theory. Here, an ingenious strategy of modular design is proposed to construct subwavelength multifunctional polarization control devices. Chiral metasurfaces with different handedness are first proposed and regarded as modules. The versatile polarization controller can thus be obtained with the combination of different modules. These experiments demonstrate that the well-designed polarization controller possesses reconfigurable functionality, and various broadband polarization and amplitude regulation functions with high efficiency including arbitrary linear polarization rotation, asymmetric transmission effect, neutraldensity-like filter, polarization beam splitter, etc., can be readily realized just by changing the cascaded modules. The physical mechanisms of the versatile polarization controller and chiral metasurface modules are both guaranteed by the Fabry-Pérot-like resonances, which are theoretically verified via the transfer matrix method. It is envisioned that the modular concept will be of great benefit to designing compact multifunctional polarization controllers.

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Multifunctional polarization controllers are highly desirable in numerous fields due to their potential applications. Although the emergence of metasurfaces provides a powerful platform for manipulating the polarization of electromagnetic waves, metasurfaces have not yet enabled multifunctional controllers. Here, this work demonstrates an effective strategy to design a multifunctional polarization controller through the integration of frequency and angular multiplexing. As an experimental proof, a non‐planar dual‐multiplexed metadevice composed of a chiral metagrating array and an anisotropic metasurface is fabricated by printed circuit board technology. The experiments show that at least five distinct functions, including ultra‐broadband linear‐to‐circular polarization conversion in 2.5–6.3 GHz, ultra‐broadband linear‐to‐linear polarization conversion in 6.6–11.0 GHz, strong optical activity between 11.4 and 12.2 GHz, giant linear and circular dichroism ≈5.96 and 12.97 GHz, respectively, can be accomplished by the proposed meta‐multiplexer. Hence, the proposed metadevice can act as high‐efficiency bifunctional waveplate, polarization rotator, linear polarizer, chiral metamirror, and so on, enabling more application flexibility. The concept of integrating multidimensional multiplexing proposed here will be of great benefit to the design of novel multifunctional polarization controllers.