Progress in the design, nanofabrication, and performance of metalenses
Zhenghao WANG, Yongling Wu, Dongfeng Qi, Wenhui Yu, Hongyu Zheng
Abstract
Abstract Metalenses have been shown to overcome the diffraction limit of conventional optical lenses to achieve subwavelength resolution. Due to being lightweight and their planar structure, metalenses have potential applications in the manufacture of flat lenses for cameras and other high-resolution imaging optics. However, currently reported metalenses have low focusing efficiencies: 26%–68% in the THz and GHz range, 1%–91% in the near infrared range, and 5%–91.6% in the visible range. Far-field imaging in visible light is essential for use in cameras and mobile phones, which require a complex metalens structure with multi-layers of alternating metal and dielectric layers. Most of the reported metalenses work in a single wavelength, mainly due to the high dispersion characteristics of the diffractive metalenses. It remains a challenge to realize high-resolution imaging for a wide wavelength band in the visible range in particular. In this review, we report on state-of-the-art metalens design principles, types of nanoscale structures, and various fabrication processes. We introduce femtosecond laser direct writing based on two-photon polymerization as an emerging nanofabrication technology. Finally, we provide an overview of the optical performance of the recently reported metalenses and elaborate on the major research and engineering challenges and future prospects.