超透镜是基于超表面对光场调控的成像器件，由于其具有体积小型化、工艺流程化的优势，在器件轻量化、便携性方面具有很好的应用前景。针对当前市场对透镜的体积需求，使用时域有限差分法模拟了一种新型结构的超透镜，它是基于光子晶体的平板超透镜，尺寸为长2 μm，宽1 μm，工作波长在717 nm可见光波段。该平板超透镜以TiO₂波导作为衬底，由Au和GaP两组周期相同的光子晶体呈相切的结构共同蚀刻在TiO₂波导上，模拟研究透镜成像效果。此外通过引入一系列不同形状的缺陷，研究其对平板透镜成像结果的影响，结果表明，当缺陷结构为矩形尺寸：Lx = 0.5 μm，Ly = 0.8 μm时，该平板超透镜呈现出最好的成像效果，达到了0.556 λ数值的超分辨，极大地提高了成像质量。未来该平板超透镜在可便携的成像设备，AR，VR以及小型医疗设备等各个领域具有极大的发展潜力。

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.

In this Letter, a Gabor superlens with variable focus is presented. This configuration uses tunable liquid lenses in the third microlens array of the Gabor superlens. By applying voltage, the radius of curvature of the micro-tunable doublet arrays changes, and the Gabor conditions are fulfilled at different focal planes. As a consequence, the magnification of the image at the focal planes changes, and a zoom effect is observed. The marginal depth plane for this system goes from 0.86 to 0.89 mm. The optical simulation, calculations, and results of the simulated optical system performance are presented.