Progress of micro-nano fabrication technologies for optical metasurfaces

The metasurface is composed of carefully arranged sub-wavelength units in a two-dimensional plane, which provides a new paradigm for designing ultra-compact optical elements and shows great potential in miniaturizing optical systems. In less than ten years, metasurfaces have caused extensive concern in multidisciplinary fields due to their advantages of being ultra-light, ultra-thin and capable of manipulating various parameters of light waves to achieve multi-functional integration. However, in the optical band, high-degree-of-freedom, aperiodic, and densely arranged metaunits put forward many extreme parameter requirements for fabrication, such as extremely small size, extremely high precision, high aspect ratio, difficult-to-process materials, cross-scale, etc. This poses a great challenge for metasurfaces from laboratory to practical applications. Here, the principles, characteristics and latest developments for micro-nano fabrication of metasurfaces in recent years were summarized, including small-area direct writing methods, large-area template transfer methods, and some emerging fabrication methods. Finally, the current challenges and future development trends of metasurface fabrication were summarized and prospected.