State of polarization (SoP) of light is one of the fundamental characteristics of light and has great significance to optical communication, imaging, quantum optics and medical facilities. The generation and maintenance of polarized light have always been research concerns in polarization optics. Polarization-maintaining fibers are frequently used to transmit polarized light without changing its polarization in optical systems, but the high cost and coupling efficiency problems hinder their usage in large-scale light paths. Polarization controllers, which operate arbitrary polarization generation and conversion at the expense of utilizing at least two optical elements such as a half-wave plate and quarter-wave plate, are too bulky for some special applications. Meanwhile, they can only generate desired output polarization of light by transcendentally determining the input polarization, which means that the existing polarization controllers cannot respond in real time. Metasurfaces composed of subwavelength nanoscatterers offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Here, we propose and experimentally demonstrate a real-time polarization controller realized by combining a depolarizer and polarizer into one monolithic metasurface. Arbitrary polarization states can be transferred to the required polarization with no requirement to determine the incident polarization in advance. Through combining with ordinary optical fibers, the proposed metasurface may also replace polarization-maintaining fibers and optical fiber polarizers in some polarization-dependent applications. This versatile concept may settle the problems of arbitrary polarization conversion once and for all.

中文翻译：

---

用于任意偏振光的恒定偏振生成超表面

光的偏振态（SoP）是光的基本特性之一，对光通信、成像、量子光学和医疗设施具有重要意义。偏振光的产生和维持一直是偏振光学的研究热点。保偏光纤在光学系统中常用于在不改变其偏振态的情况下传输偏振光，但高成本和耦合效率问题阻碍了其在大规模光路中的应用。偏振控制器以使用至少两个光学元件（例如半波片和四分之一波片）为代价进行任意偏振生成和转换，对于某些特殊应用来说过于庞大。同时，它们只能通过超验地确定输入偏振来产生所需的光输出偏振，这意味着现有的偏振控制器无法实时响应。由亚波长纳米散射体组成的超表面提供了丰富的功能来控制光的幅度、相位和偏振。在这里，我们提出并通过实验证明了一种实时偏振控制器，该控制器通过将消偏振器和偏振器组合到一个单片超表面中来实现。无需事先确定入射偏振态，即可将任意偏振态转换为所需偏振态。通过与普通光纤相结合，所提出的超表面还可以在一些偏振相关应用中替代保偏光纤和光纤偏振器。