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Chiral metasurfaces have great potential in various applications such as polarimetric imaging and biomedical recognition. However, simultaneous broadband and high circular dichroism (CD) with high polarization extinction ratio (PER) remains a challenge. Here, we present a novel approach to realize simultaneous broadband and high CD with high PER in the optical communication band using a two-dimensional all-dielectric chiral metasurface. The structure is formed by a two-level chiral structure of split cross (first-order) and trapezoid-shaped (second-order) of Si nano ribs, respectively, in which constructively coupled first- and second-order of chirality occurs, resulting in the broad chiral response in the far field of multipoles excited by incident light of different chiralities. Theoretical results show that a CD in transmission reaching 0.9 (up to 0.993) and a PER exceeding 20 dB (up to 35 dB) over the entire wavelength range from 1.39 to 1.61 μm can be achieved simultaneously, consistent with the experimental results of CD ∼0.9 and PER of 10 dB (up to 19.7 dB). Our design paves the way for chiral metasurfaces toward practical applications in terms of working bandwidth, high CD and PER as well as integrality of the devices in many fields.

We propose and experimentally demonstrate a single chip metasurface for simultaneous chiral and achiral imaging and polarimetric detecting using a high efficiency three dimensional plasmonic metalens (3D-PM) with capability of designed separation of different circular polarizations. The proposed 3D-PM combines both propagating and geometric phases so that two orthogonal circular polarization components of the incidence can be precisely separated and imaged into two channels and the incident polarization state can be detected with differentiation of the two channels. One single set of an array of Au layer covered anisotropic polymethyl methacrylate elliptical nanopillars is employed, in which height of each nanopillar is added as a new design degree of freedom to realize both full phase manipulation (0–2π) and high efficiency (>0.85) with coupled equivalent Fabry–Pérot cavity and localized surface plasmons. At design wavelength of 1550 nm, experimental results show that optical resolution of both chiral and achiral images approaches the diffraction limit, extinction ratio of circular polarizations in two channels is ∼33:1, and the energy efficiency reaches ∼63 %. The proposed 3D-PM provides a new and simple way for chiral/achiral imaging and polarimetric measurement, and can be applied in integrated optics, optical communication, and biomolecule detection.

As an alternative electron transport material to the chemically unstable ZnO nanoparticles (NPs), SnO2 NPs exhibit a great potential to construct high‐performance quantum dot light‐emitting diodes (QLEDs). However, only moderate device performance has been obtained for SnO2‐based QLEDs due to the low electron mobility, unfavorable energy band, and massive defects of SnO2 NPs. Herein, a strategy of transition metal doping is reported to achieve high‐quality manganese‐doped SnO2 (Mn‐SnO2) NPs to address the above problems. Specifically, the large bond energy of Mn─O bonds reduces the oxygen vacancy defects, prompting an effective suppression of the interfacial exciton quenching for massive radiative recombination. Moreover, the favorable energy band and high electron mobility for Mn‐SnO2 promote efficient electron injection and transportation. The good optoelectronic properties for Mn‐SnO2 NPs contribute to a great enhancement in device efficiency from 8.2 to 11.4% and a remarkable improvement in lifetime (T95) from 565.3 to 1009.2 h at 1000 cd−2, among the best performing ZnO‐free QLEDs. Notably, the Mn‐SnO2 based QLEDs show a very superior shelf stability to the QLEDs based on SnO2 and ZnO analogs. Consequently, this work reports an effective approach to achieve high‐quality SnO2 NPs for efficient and stable QLEDs. [ABSTRACT FROM AUTHOR]

2D chiral metasurface have been widely used for planar circular dichroism (CD) devices. However, the design of 2D metasurfaces usually means a time‐consuming search of effective structures, which are typically limited to regular geometries and compromised performances. Here, an efficient method for 2D chiral metasurfaces with pixelated topological structure based on machine learning (ML) is proposed and demonstrated from which simultaneous high CD and extinction ratio (ER) either over broadband or at specific wavelength can be efficiently achieved. The proposed ML method combines both advantages of high efficiency of neural network (NN) and superior goal evolution ability of microbial genetic algorithm (MGA). Unlike traditional empirical‐driven methods, the hybrid framework and pixelated topologically deformable structures can fully exploit the potential of design space and push design capability to its physical limit. An average CD of 94.7% and ER of 15 dB over wavelength from 1.45–1.65 µm and a CD of >90%/ER of >27 dB at freely‐selected wavelength of 1.54 and 1.616 µm are obtained. Experiments with fabricated topological structures validate the theoretical predictions. The proposed pixelated structures with ML provide a universal method for precise tailoring of optical properties of metasurfaces which is otherwise unattainable with conventional regular geometries. [ABSTRACT FROM AUTHOR]

We report on an all‐dielectric cut‐off perfect absorber and an optical long‐pass filter using a gallium arsenide multi‐nanocylinder array grown on SiO2 in the wavelength from ultraviolet to infrared. A high average absorption of 0.985 is realized in the absorption band and there is a sharp cut‐off between the absorption band and the non‐absorption band, where the extinction ratio is 12.17 dB, the extinction difference is 0.88, and the cut‐off slope is 0.0047 nm−1. Based on the cut‐off absorption mechanism, a transmissive long‐pass cut‐off filter is proposed with extinction ratio of 21.56 dB, extinction difference of 0.86 and cutoff slope of 0.0049 nm−1. The average transmission of only 0.006 in the stop band and 0.967 in the pass band is realized. The demonstrated devices suggest an efficient way of designing cut‐off perfect absorbers and optical filters with metasurface, which is of important applications in advanced nanophotonic devices and integrated photonic systems. [ABSTRACT FROM AUTHOR]

A snapshot imaging spectrometer is a powerful tool for dynamic target tracking and real-time recognition compared with a scanning imaging spectrometer. However, all the current snapshot spectral imaging techniques suffer from a major trade-off between the spatial and spectral resolutions. In this paper, an integral field snapshot imaging spectrometer (TIF-SIS) with a continuously tunable spatial-spectral resolution and light throughput is proposed and demonstrated. The proposed TIF-SIS is formed by a fore optics, a lenslet array, and a collimated dispersive subsystem. Theoretical analyses indicate that the spatial-spectral resolution and light throughput of the system can be continuously tuned through adjusting the F number of the fore optics, the rotation angle of the lenslet array, or the focal length of the collimating lens. Analytical relationships between the spatial and spectral resolutions and the first-order parameters of the system with different geometric arrangements of the lenslet unit are obtained. An experimental TIF-SIS consisting of a self-fabricated lenslet array with a pixelated scale of 100×100 and a fill factor of 0.716 is built. The experimental results show that the spectral resolution of the system can be steadily improved from 4.17 to 0.82 nm with a data cube ( N x × N y × N λ ) continuously tuned from 35×35×36 to 40×40×183 in the visible wavelength range from 500 to 650 nm, which is consistent with the theoretical prediction. The proposed method for real-time tuning of the spatial-spectral resolution and light throughput opens new possibilities for broader applications, especially for recognition of things with weak spectral signature and biomedical investigations where a high light throughput and tunable resolution are needed.