Revolutionary meta-imaging:from superlens to metalens

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.

Neural network assisted high-spatial-resolution polarimetry with non-interleaved chiral metasurfaces

Polarimetry plays an indispensable role in modern optics.Nevertheless,the current strategies generally suffer from bulky system volume or spatial multiplexing scheme,resulting in limited performances when dealing with inhomogeneous polarizations.Here,we propose a non-interleaved,interferometric method to analyze the polarizations based on a tri-channel chiral metasurface.A deep convolutional neural network is also incorporated to enable fast,robust and accurate polarimetry.Spatially uniform and nonuniform polarizations are both measured through the metasurface experimentally.Distinction between two semblable glasses is also demonstrated.Our strategy features the merits of compactness and high spatial resolution,and would inspire more intriguing design for detecting and sensing.

Chip-scale metalens microscope for wide-field and depth-of-field imaging

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 SiNxmetalens 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 1.74μm and DOF of200μm 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.

Large-scale achromatic flat lens by light frequency-domain coherence optimization

Flat lenses,including metalens and diffractive lens,have attracted increasing attention due to their ability to miniaturize the imaging devices.However,realizing a large scale achromatic flat lens with high performance still remains a big challenge.Here,we developed a new framework in designing achromatic multi-level diffractive lenses by light coherence optimization,which enables the implementation of large-scale flat lenses under non-ideal conditions.As results,a series achromatic polymer lenses with diameter from 1 to 10mm are successfully designed and fabricated.The subsequent optical characterizations substantially validate our theoretical framework and show relatively good performance of the centimeter-scale achromatic multi-level diffractive lenses with a super broad bandwidth in optical wavelengths(400-1100 nm).After comparing with conventional refractive lens,this achromatic lens shows significant advantages in white-light imaging performance,implying a new strategy in developing practical planar optical devices.

Bandpass-filter-integrated multiwavelength achromatic metalens

The design of large-scale,high-numerical-aperture,and broadband achromatism is a big challenge in metalens research. In fact,many colorful imaging systems have RGB color filters,which means the achromatism only for RGB lights would be sufficient. Avoiding broadband achromatism is expected to greatly improve the working efficiency of metalenses. Nevertheless,a proper bandpass filter is necessary under a white light illumination in the metalens integrated imaging system. Here we propose a bandpass-filter-integrated multiwavelength achromatic metalens (NA=0.2),which is designed using a searching optimization algorithm to achieve the achromatism of RGB lights with high efficiencies. The bandpass filter is implemented by composite DBRs and defect layers,by which three desired wavelengths are selected out. The simulations and experiments on the filter-integrated metalens definitely show a good RGB achromatism. Further imaging experiments demonstrate a higher signal-to-noise ratio and resolution compared with the one without the filter. Our approach provides not only an RGB achromatic meta-imaging device but also a new route to access a highly efficient spectrum tailoring metasystem by incorporating bandpass filter designs.