Catenary metasurface has been widely used in fields such as wild-angle imaging, spectral detection, and broadband absorbers, due to its advantages of high efficiency and broadband. In our previous studies, perfect wavefront control of catenary metasurface is achieved via field-driven optimization (FDO). However, the proposed method focuses solely on the performance of catenary metasurfaces at a specific wavelength. Here, considering the broadband and multifunctional of the catenary and catenary-like metasurfaces, multi-objectives FDO is proposed. With 30 iterations, the average diffraction efficiency of the catenary metasurface increases to ~96% at the wavelength of 9-13 μm. In addition, considering the functionality, the catenary and catenary-like metasurfaces are optimized with a pair of orthogonal polarized light incidences. The optimization process preserves the chiral nature of the catenary metasurface. After 30 iterations, the diffraction efficiency of the catenary metasurface is improved from 96.4% to 99.2%. For catenary-like metasurfaces, the diffraction efficiencies exceed 90% for both left-handed and right-handed elliptically polarized light incidences. Our work provides a methodology for designing multifunctional complex continuous metasurfaces, which may further promote catenary optics.
As a type of computational optical imaging technology, Fourier ptychography (FP) imaging technology combines phase recovery algorithm with the idea of synthetic aperture. It is oriented towards a large field of view and high resolution. However, there are still two issues that need to be addressed. First, there is the problem of slow speed of image acquisition and long acquisition time. The large synthetic aperture and high overlap rate between adjacent images significantly increase the number of collected images. Second, for the transmissive FP imaging, when the intensity of the illumination source is constant, the theoretical synthetic aperture size cannot increase unlimited with the increase of the scanning range of the camera array in the focal plane. Therefore, in this paper, we adopt a 3×3 camera array for data acquisition, reducing the data acquisition speed to one-ninth under the same conditions, greatly improving the imaging speed; research was conducted on the transmissive FP imaging experiment, which achieved a 7-fold resolution improvement; At the same time, through system simulation and reverse derivation of experimental results, the actual effective synthetic aperture size was determined under certain lighting source power conditions. Our work has laid the foundation for further imaging distances in the future and contributed new methods for fast subdiffraction computed imaging.
Simultaneously achieving a large field of view (FOV) and high-resolution imaging has always been the goal in the design of optical systems. Although traditional optical systems can switch from large-FOV to high-resolution imaging by adjusting the focal length, this method relies on complex mechanical structures and multi-lens combinations, leading to slow switching speed and bulky volume. Planar metasurfaces composed of subwavelength structures can achieve arbitrary wavefront manipulation, but their phase distributions are usually fixed once fabricated. In this paper, we propose a strategy for large-scale pixel-level active control of local phase on demand via cascaded bilayer metasurfaces. This method enables fast switching between the quadratic phase and hyperbolic phase by globally translating one of two layers at a one-lattice interval. Simulation results indicate that the full FOV for the quadratic phase exceeds 80°, and the point spread functions for the hyperbolic phase at various focal lengths closely approach the diffraction limit. Such multifunctional metalenses may find many potential applications, such as surveillance, unmanned vehicles, and medical science.
The geometric phase concept has profound implications in many branches of physics, from condensed matter physics to quantum systems. Although geometric phase has a long research history, novel theories, devices, and applications are constantly emerging with developments going down to the subwavelength scale. Specifically, as one of the main approaches to implement gradient phase modulation along a thin interface, geometric phase metasurfaces composed of spatially rotated subwavelength artificial structures have been utilized to construct various thin and planar meta-devices. In this paper, we first give a simple overview of the development of geometric phase in optics. Then, we focus on recent advances in continuously shaped geometric phase metasurfaces, geometric–dynamic composite phase metasurfaces, and nonlinear and high-order linear Pancharatnam–Berry phase metasurfaces. Finally, conclusions and outlooks for future developments are presented.
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