Recent advances in metasurface lenses (metalenses) have shown great potential for opening a new era in compact imaging, photography, light detection, and ranging (LiDAR) and virtual reality/augmented reality applications. However, the fundamental trade-off between broadband focusing efficiency and operating bandwidth limits the performance of broadband metalenses, resulting in chromatic aberration, angular aberration, and a relatively low efficiency. A deep-learning-based image restoration framework is proposed to overcome these limitations and realize end-to-end metalens imaging, thereby achieving aberration-free full-color imaging for mass-produced metalenses with 10 mm diameter. Neural-network-assisted metalens imaging achieved a high resolution comparable to that of the ground truth image.
In our study, we introduce wavelength-multiplexed orbital angular momentum meta-holography, aiming to expand holographic information channels by leveraging light's wavelength and orbital angular momentum (OAM). We selectively employed red, green, and blue as primary colors, and incorporated four unique OAM channels (-2, -1, 1, and 2). Through the utilization of a metasurface comprising three distinct types of wavelength-selective meta-atoms, we successfully encoded the twelve holographic images onto a single metasurface. This advancement holds significant potential for applications in various fields, providing opportunities for advanced holography and augmented reality systems.
Optical resolution photoacoustic microscopy (OR-PAM) provides high optical contrast and lateral resolution. However, the resolution of a typical OR-PAM using an objective lens is limited to not exceeding Abbe's optical diffraction limit. In this study, a lensless shear force scanning PAM is presented. Instead of a lens, the system uses an imaging probe that combines a non-coated tapered fiber with a quartz tuning fork (QTF). A shear force feedback mechanism is used to maintain a tens of nm (near-field) distance between the fiber tip and the sample. With the system, PA signals generated in the near field of a gold sputtered glass sample were successfully acquired. We also performed 2D PA scanning experiments and obtained PA images of gold cube samples with high lateral resolution. This study demonstrates the existence of a near field PA signal and shows its potential for super-resolution scanning PAM.
Metasurfaces have attracted great attention due to their ability to manipulate the phase, amplitude, and polarization of light in a compact form. Tunable metasurfaces have been investigated recently through the integration with mechanically moving components and electrically tunable elements. Two interesting applications, in particular, are to vary the focal point of metalenses and to switch between holographic images. We present the recent progress on tunable metasurfaces focused on metalenses and metaholograms, including the basic working principles, advantages, and disadvantages of each working mechanism. We classify the tunable stimuli based on the light source and electrical bias, as well as others such as thermal and mechanical modulation. We conclude by summarizing the recent progress of metalenses and metaholograms, and providing our perspectives for the further development of tunable metasurfaces.
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