基于电磁超表面的透镜成像技术研究进展

电磁超表面属于超材料的一种,是由许多亚波长纳米结构单元组成的二维功能性平面结构.根据惠更斯原理,超表面阵列可以任意调控光波的相位、振幅和偏振.与传统器件相比,基于这种超材料设计的光学功能器件最大的优势是其具有极薄的厚度.本文首先介绍了广义斯涅耳定律以及纳米单元结构调控相位的基本原理,重点归纳了电磁超表面在透镜成像技术方面的研究进展,包括等离子体超表面、全介质超表面以及金属/介质混合式超表面在成像方面的应用,最后指出了超表面在成像方面尚未解决的前沿问题以及与实际应用接轨的重要问题,希望能为以后的深入研究提供一定的参考和借鉴.

Research progress of imaging technologies based on electromagnetic metasurfaces

Electromagnetic metamaterials are artificial structures engineered on a subwavelength scale to have optical properties that are not observed in their constituent materials and may not be found in nature either, such as negative refractive index. They have enabled unprecedented flexibility in manipulating light waves and producing various novel optical functionalities. Since the beginning of this century, with the development of nanofabrication and characterization technologies, there has been aroused a tremendous growing interest in the study of electromagnetic metamaterials and their potential applications in different fields including super-resolution imaging, optical biosensing, electromagnetic cloaking, photonic circuits and data storage. Electromagnetic metasurfaces are two-dimensional metamaterials composed of subwavelength planar building blocks. Although metasurfaces sacrifice some functionalities compared with their bulk counterparts, they provide us with distinct possibility to fully control light wave with ultrathin planar structures. Based on Huygens principle, the metasurfaces are able to arbitrarily manipulate the phases, amplitudes or polarizations of optical waves. For example, metasurfaces made of gold nanoantenna-arrays are able to create phase discontinuities for light propagating through the interfaces and drastically change the flows of reflected and refracted light at infrared frequencies. Comparing traditional dielectric optic elements, the thickness values of metasurface-based optical devices are much smaller. In addition to the control of free-space incident light, metasurfaces can also be used to precisely control and manipulate surface electromagnetic waves. In this review, we introduce the generalized Snell's law and the fundamental principles to modulate phase by using metasurfaces. Research progress of a variety of imaging technologies based on metasurfaces is then presented, including plasmonic metasurface, all-dielectric metasurface and metal/insulator hybrid metasurface. Finally, we summarize several frontier problems associated with metasurface, which maybe provide some references for the future researches and applications.