基于双焦点聚焦的偏振无关可变焦光纤超表面

Polarization-Independent Varifocal Metafiber Based on Bifocal Focusing

摘要: 传统光纤在引导光方面具有优异的性能，已广泛应用于长距离光通信。虽然光纤可以有效地传输光，但其功能受到铁芯和包层材料(如锗掺杂硅和硅玻璃)介电性能的限制。光纤通过在光纤尖端集成超表面，正在成为纳米光子学和光纤领域的重要光耦合平台。为了提高对自旋电磁波的控制，本研究设计了一种可直接在光纤端面集成的超表面。在1550 nm波长的入射光照射下，可实现偏振无关的双焦点聚焦，焦距为10 um。同时，通过改变超表面周围的介质折射率还可以实现连续变焦功能，使得空间光场的连续调制成为可能。随着通信能力的提高，具有多自旋光束的独立操控光纤超表面能够在多目标探测雷达系统和多目标多输入多输出(MIMO)通信中得到实际应用。

Abstract: Conventional optical fiber has excellent performance in guiding light and has been widely employed for long-distance optical communication. Although the optical fiber is efficient for transmitting light, its functionality is limited by the dielectric properties of the core’s and cladding’s materials (e.g., germanium-doped silicon and silica glasses). Metafibers, by integrating metasurface at the optical fiber tip, are emerging as significant optical coupling platforms for nanophotonics and fiber-optic communities. To enhance the control over spin electromagnetic waves, here we have designed a metasurface that can be directly integrated into the end face of an optical fiber. Under the illumination of incident light with a wavelength of 1550 nm, polarization-independent bifocal focusing can be achieved with a focal length of 10 μm. Meanwhile, by changing the refractive index of the medium surrounding the metasurface, the continuous zoom function can also be realized, making it possible to continuously modulate the spatial light field. With the improvement of communication capabilities, the metafiber with independent manipulation of multi-spin beams can find practical applications in multi-target detection radar systems and multi-target multiple-input multiple-output (MIMO) communication.