The metasurface is a platform with a small footprint and abundant functionalities. With propagation phase and geometric phase, polarization multiplexing is possible. However, different response behaviors of propagation phase and geometric phase to wavelength have not been fully employed to widen the capabilities of metasurfaces. Here, we theoretically demonstrate that metasurfaces can achieve near-field and far-field decoupling with the same polarization at two wavelengths. First, we found a set of pillars whose propagation phase difference between two wavelengths covers the full range of 2π. Then, by rotating pillars to control the geometric phase, the phase at both wavelengths can cover the full range of 2π. Finally, by means of interference principle, arbitrary independent coding for the near field and far field of dual wavelengths is realized. In addition, when the far-field function is focusing, the focused spot is close to the diffraction limit, and, when the NA of the lens is very small, the final output focal length is four times of initial input focal length. This work circumvents the strong wavelength-dependent limitation of planar devices and paves the way toward designing multi-wavelength and multi-functional metadevices for scenarios such as AR applications, fluorescence microscopy, and stimulated emission depletion microscopy.

超构表面是由精心设计和排布的亚波长纳米单元组成的平面元件，其可以在微观尺度下调制电磁场，从而实现波前的任意调控。目前，它已被用来灵活地操纵相位、偏振、振幅等各种光学参数。超构透镜是超构表面中相当重要且非常活跃的一个研究方向，由于其厚度在波长量级，与传统光学透镜相比，能够显著增加光学器件的集成度并且降低结构复杂度。但是，单元结构材料的固有色散以及结构几何形状衍射效应导致的色差会严重影响超构透镜的成像质量，从而限制了其在光电子器件中的潜在应用。本文首先讨论超构透镜控制色差的原理。随后回顾了几种重要的成像应用，包括分立波长消色差，宽带聚焦成像，光场成像等重要的成像系统。最后，本文对超构透镜未来的发展方向和应用前景做出展望。

近年来，超构表面在经典光场调控领域受到了广泛的关注，获得了优异的成果。同时，超构表面在非线性光学和量子光学方面的应用也引起了人们越来越多的兴趣。文中分别介绍了非线性超构表面和量子超构表面的基本原理和应用，总结了近几年的相关报道，包括谐波产生和增强，谐波产生和对称性的关系，非线性相位调控和全息成像，以及基于超构表面的纠缠光子对产生，测量和调控。最后，对超构表面在这两个领域的进一步应用和前景进行了展望。

We report an observation of the second-order correlation between twin beams generated by amplified spontaneous parametric down-conversion operating above threshold with kilowatt-level peak power, from a periodically poled LiTaO₃ crystal via a single-pass scheme. Photocurrent correlation was measured because of the bright photon streams, with raw visibility of 37.9% or 97.3% after electronic filtering. As expected in our theory, this correlation is robust and insensitive to parametric gain and detection loss, enabling important applications in optical communications, precision measurement, and nonlocal imaging.

The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth (8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications.