Broadband Achromatic Metalens in the Visible Light Spectrum Based on Fresnel Zone Spatial Multiplexing

Full-Color Imaging System Based on the Joint Integration of a Metalens and Neural Network

Lenses have been a cornerstone of optical systems for centuries; however, they are inherently limited by the laws of physics, particularly in terms of size and weight. Because of their characteristic light weight, small size, and subwavelength modulation, metalenses have the potential to miniaturize and integrate imaging systems. However, metalenses still face the problem that chromatic aberration affects the clarity and accuracy of images. A high-quality image system based on the end-to-end joint optimization of a neural network and an achromatic metalens is demonstrated in this paper. In the multi-scale encoder-decoder network, both the phase characteristics of the metalens and the hyperparameters of the neural network are optimized to obtain high-resolution images. The average peak-signal-to-noise ratio (PSNR) and average structure similarity (SSIM) of the recovered images reach 28.53 and 0.83. This method enables full-color and high-performance imaging in the visible band. Our approach holds promise for a wide range of applications, including medical imaging, remote sensing, and consumer electronics.

Four-channel meta-hologram enabled by a frequency-multiplexed mono-layered geometric phase metasurface

In recent years, frequency-multiplexed metasurfaces have received extensive attention due to the increasing demand for multifunction integration and communication capacity. However, multi-channel studies achieved with a mono-layered frequency-multiplexed metasurface are limited. Herein, a universal design strategy for a frequency-multiplexed mono-layered geometric phase metasurface is proposed by utilizing Pancharatnam-Berry (PB) phase modulations. The elementary meta-atom is judiciously designed to transmit the cross-polarized component of a circularly polarized incident wave at four distinct frequencies with independent 360° phase shifts and a constant amplitude of 0.48, close to the theoretical limit of 0.5. As a proof-of-concept demonstration, a four-channel meta-hologram is designed to achieve distinct holographic images of "three foci", "five foci", "J" and "X" at 7.2 GHz, 9.1 GHz, 10.9 GHz, and 15.2 GHz respectively. The images are projected in the desired azimuth planes by exploiting the time-shifting properties of the Fourier transform. The experimental and full-wave simulation results are in good agreement, which indicates that the proposed strategy has great potentials in various applications, such as multi-channel imaging and information encryption technology.