平面超透镜的远场超衍射极限聚焦和成像研究进展

突破瑞利衍射极限,实现纯光学的远场超衍射极限聚焦和成像在科学和工程的各个领域都有重要意义.现有光学超分辨技术都存在一些固有的限制因素,如工作距离短、适用领域窄、不利于集成等问题.平面超透镜由于理论上的创新、设计灵活、效率高、方便集成等优势,成为实现超衍射极限的有效途径.本文综述了平面超透镜的物理原理及其在超衍射极限聚焦和成像方面近年来的研究进展,并讨论了该领域面临的问题和未来的研究重点和方向.

Advances in the far-field sub-diffraction limit focusing and super-resolution imaging by planar metalenses

Due to the fundamental laws of wave optics, the spatial resolution of traditional optical microscopy is limited by the Rayleigh criterion. Enormous efforts have been made in the past decades to break through the diffraction limit barrier and in depth understand the dynamic processes and static properties. A growing array of super-resolution techniques by distinct approaches have been invented, which can be assigned to two categories: near-field and far-field super-resolution techniques. The near-field techniques, including near-field scanning optical microscopy, superlens, hyperlens, etc., could break through the diffraction limit and realize super-resolution imaging by collecting and modulating the evanescent wave. However, near-field technique suffers a limitation of very short working distances because of the confined propagation distance of evanescent wave, and certainly produces a mechanical damage to the specimen. The super-resolution fluorescence microscopy methods, such as STED, STORM, PALM, etc., could successfully surpass the diffractive limit in far field by selectively activating or deactivating fluorophores rooted in the nonlinear response to excitation light. But those techniques heavily rely on the properties of the fluorophores, and the labelling process makes them only suitable for narrow class samples. Developing a novel approach which could break through the diffraction limit in far field without any near-field operation or labelling processes is of significance for not only scientific research but also industrial production. Recently, the planar metalenses emerge as a promising approach, owing to the theoretical innovation, flexible design, and merits of high efficiency, integratable and so forth. In this review, the most recent progress of planar metalenses is briefly summarized in the aspects of sub-diffractive limit focusing and super-resolution imaging. In addition, the challenge to transforming this academic concept into practical applications, and the future development in the field of planar metalenses are also discussed briefly.