The refractive-lens technique has been well developed over a long period of evolution, offering powerful imaging functionalities, such as microscopes, telescopes, and spectroscopes. Nevertheless, the ever-growing requirements continue to urge further enhanced imaging capabilities and upgraded devices that are more compact for convenience. Metamaterial as a fascinating concept has inspired unprecedented new explorations in physics, material science, and optics, not only in fundamental researches but also novel applications. Along with the imaging topic, this paper reviews the progress of the flat lens as an important branch of metamaterials, covering the early superlens with super-diffraction capability and current hot topics of metalenses including a paralleled strategy of multilevel diffractive lenses. Numerous efforts and approaches have been dedicated to areas ranging from the new fascinating physics to feasible applications. This review provides a clear picture of the flat-lens evolution from the perspective of metamaterial design, elucidating the relation and comparison between a superlens and metalens, and addressing derivative designs. Finally, application scenarios that favor the ultrathin lens technique are emphasized with respect to possible revolutionary imaging devices, followed by conclusive remarks and prospects.
Microscopy is very important in research and industry, yet traditional optical microscopy suffers from the limited field-of-view (FOV) and depth-of-field (DOF) in high-resolution imaging. We demonstrate a simultaneous large FOV and DOF microscope imaging technology based on a chip-scale metalens device that is implemented by a SiNx metalens array with a co- and cross-polarization multiplexed dual-phase design and dispersive spectrum zoom effect. A 4-mm × 4-mm FOV is obtained with a resolution of 1.74 μm and DOF of 200 μm within a wavelength range of 450 to 510 nm, which definitely exceeds the performance of traditional microscopes with the same resolution. Moreover, it is realized in a miniaturized compact prototype, showing an overall advantage for portable and convenient microscope technology.
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