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A chiral metasurface, which obtains chirality through a subwavelength artificial structure, is essential for realizing asymmetric transmission in the application of enantioselective sensing, spin-dependent light emission, and other polarization control systems. Here, we studied a split Archimedean spiral metasurface, which can control the propagating wave from asymmetric transmission to symmetric transmission for linear polarized light. As a proof of concept, a dual-band asymmetric transmission is demonstrated in the GHz region using the coupling of the split spiral structures. The maximum asymmetric transmission parameter reaches 53%. By manipulating the height of the split spiral structures using microfluidic technology, a broadband asymmetric transmission is obtained with the bandwidth of 25.9%. Meanwhile, the asymmetric transmission can be controlled from 50% to 0%, enabling the propagation wave from asymmetric transmission to symmetric transmission. Furthermore, the asymmetric transmission is maintained when the metasurface is bent into different curvatures, promising high potential applications for optical isolation, one-way glass, and optical interconnects.

We demonstrate a multilayered microfluidic system with a flexible substrate, which has tunable optical chirality within THz spectrum range. The optical properties of the multilayered microfluidic system can be tuned by either changing the liquid pumped into each layer or stretching the flexible substrate. In experiment, the polarization rotation angle is tuned from zero (non-chiral structure) to 16.9° (strong-chiral structure). Furthermore, the tuning resolution can be well controlled due to the fine refractive index change of the liquid with different concentrations. It is feasible for the multilayered microfluidic structure to be integrated to an optofluidic system, where strong or tunable optical chirality are needed, which not only can be used as traditional optical components such as THz polarizers and filters but also has potential applications on imaging and sensor of bio-materials.

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