Chinese Version Light学术出版中心
Latest Issue
Issue 15 ， 2022
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Application of metasurfaces in three-dimensonal imaging and display
Abstract：Three-dimensional （3D） imaging and display technology can obtain and save the three-dimensional information of objects and present stereoscopic realistic pictures. It has broad application prospects in consumer electronics， autonomous driving， robot vision， and augmented reality/virtual reality （AR/VR）. The existing three-dimensional imaging and display devices are limited by the performance defects of traditional optical elements， and it is difficult to simultaneously meet the performance requirements of wide field of view， large numerical aperture， high resolution， continuous parallax and miniaturization， etc. As a new type of planar optical element composed of subwavelength structural unit， metasurfaces can flexibly control the light field， and have the advantage of easy integration， thinness， and compactness. It is expected to break through the bottleneck of traditional optical elements and provide the possibility for realizing multi-functional compact three-dimensional imaging and display equipment. Herein， we review the research progress of metasurfaces in three-dimensional imaging and display technology. The application and performance of metasurfaces in active and passive three-dimensional imaging technologies and three-dimensional display technologies such as holographic display， light field display， and near-eye display are discussed in detail. Finally， the challenges and future development directions of metasurfaces in the field of three-dimensional imaging and display are summarized and prospected.Keywords：metasurfaces;optical elements;three-dimensional imaging;three-dimensional display;multifunction;compactness- 706
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Published：2022-08-16 -
Multifunctional lab on fiber tips based on metasurface
Abstract：Multifunctional and highly integrated all-fiber devices has promoted the development of lab-on-fiber technology. The rapid progress in the manufacturing technology has opened up a new avenue for the multifunctional plug-and-play fiber-optic platform. Researchers are committed to exploring and optimizing the onboard laboratory preparation technology to show the potential of onboard laboratory components in many application scenarios. First， we review the classification of fiber-on-lab technology and describe the preparation process of nanostructure at the fiber end facet， including physical and chemical processing methods. Then， we discuss the research progress of lab-on-fiber preparation technology based on the metasurface on the fiber end facet and the difficulties in the process of technology development. Finally， we clarify the strategy of constructing multi-functional， highly integrated， and multi-application scenarios of fiber sensing devices. The remarkable achievements of lab-on-fiber technology clearly show that multifunctional， highly integrated all-fiber devices can play a vital role in many scenarios related to physical and biochemical parameter monitoring， particle capture， and light field regulation.Keywords：fiber-optic sensing;metasurface;lab on fiber;nano fabrication- 208
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Published：2022-08-16 -
Research progress on complete fabrication technology of diffractive optical elements
Abstract：The key fabrication technology for diffractive optical elements （DOE） was systematically investigated from the following four aspects： graphic data processing， advanced lithography， pattern transfer， and large-area integration with high reliability. Based on the standard CMOS process， a complete set of manufacturing technologies for DOE with high precision， multi-functionality （high fidelity， high aspect ratio， high surface flatness， multiple substrates， etc.）， and large area was proposed. A data processing system with precision greater than 2 nm is developed for complex pattern lithography. Moreover， a hybrid lithography method was proposed and two types of basic pattern transfer techniques and four different processes are established， including additive processes （lift-off and electroplating） and subtractive processes （drying etching and low-temperature metal assisted chemical etching）. Importantly， we demonstrate the pattern generation from micron to sub-10 nm scale， pattern transfer of 25 nm gold structures with aspect ratio of 12∶1， and 30 nm Al2O3 nanotubes with aspect ratio up to 500∶1. Based on various substrates， including fused quartz， multilayer film， SiC self-supporting membrane， and wafer with high surface flatness， various large-area DOEs are integrated. The maximum area is 142 mm×142 mm， the maximum self-supporting aperture is 70 mm， and the highest surface flatness is 0.03λ peak to valley. Our proposed framework can meet the manufacturing requirements of various DOEs， covering the spectral bands ranging from visible light to hard X-rays. Various DOEs are used in four major optical projects， including advanced lithography， synchrotron radiation， laser fusion， and X-ray astronomy， as well as more than 1 000 domestic and foreign universities， scientific research institutes， and high-tech enterprises.Keywords：diffractive optical elements;advanced lithography;standard CMOS process;data processing system for GDSII data;pattern transfer- 196
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Published：2022-08-16 -
Optimization of large-aperture micro-nano structure planar optical element
Abstract：The metalens constructed by the micro-nano structure array is not only small and lightweight， but also has a multi-functional design that can be realized through a composite structure. The existing metalens diameters are generally in the order of micrometers. For a metalens such as a centimeter-level diameter， the number of micro-nano structure units contained in it can reach billions. If these massive micro-nano structures are drawn by modeling them sequentially， the layout file will inevitably be too large， such that the drawing time is so long that the layout cannot be opened. To solve this problem， this study proposes a circular layout metalens design method based on the layout design software L-Edit. This method uses binary coding to divide the metalens into blocks to compress the layout file. Numerical simulation results show that the designed metalens achieves sub-wavelength focusing. For the 50 mm diameter metalens， the layout file size obtained using the proposed layout drawing method is 176 MB. This is much smaller than the layout file size （3.70 TB） generated by the one-by-one modeling and drawing method. This study proves that an efficient compression of massive data of a large-aperture metalens in the layout design ensures the manufacturability of the design of large-aperture metalens elements.Keywords：metalens;Large-aperture;layout design;Data compression- 197
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Published：2022-08-16 -
Interference lithography of space-variant grating structures by phase modulation
Abstract：The modulation of the phase wavefront of geometric phase metasurface lenses does not depend on the cumulative phase of the propagation process. However， it affects the local polarization state through the space-variant unit structure and introduces the conjugate additional phase that focuses the incident beam， which differs from the characteristics of traditional refractive lenses. For interference lithography fabrication of geometric phase metalens structures， an optical Fourier transform system modulated by a space-variant phase element is proposed in this study. Subsequently， the orientation and frequency-variant micron structures were prepared using interference lithography. Based on the Fourier transform theory of optical lens and geometric propagation principle of light diffraction， the influence of light field on image plane based on the inserted sub-phase-elements with different frequencies， orientations， and relative positions was analyzed. Therefore， a method was proposed for multi-interference light fields with sectionalized modulation of space-variant phase elements on incident light. Moreover， the preparation of orientation and period-variant micron structure based on multiple simultaneously generated light fields were illustrated. Accordingly， utilizing the designed and fabricated space-variant phase element， interference light fields with circle and ring distributions were simultaneously generated. The experimental results demonstrate that space-variant grating structures with orientations of 0°， 125°， and 235°， periods of 7.22， 6.51， and 5.78 μm， and micron pattern structure with radius of 1 892 μm can be obtained simultaneously. The proposed optical system is simple and easy to be combined with a projection exposure system and has great potential for manufacturing geometric phase metalens devices based on a space-variant micro-nano unit cell.Keywords：interference lithography;4f optical system;space-variant structure;phase modulation- 187
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Published：2022-08-16 -
Efficient adaptive flying cutting for infrared optics micro-structured surfaces
Abstract：In the processing of infrared optical microstructured surfaces， the hard， brittle， and difficult-to-machine properties of infrared optical materials and the complex geometric properties of microstructured surfaces lead to uneven and brittle fractures in the processed microstructured surfaces and reduce the face shape accuracy. Small feeds are now commonly used to suppress surface fragmentation but are inefficient. To achieve efficient， high-precision， and low-damage machining of infrared optical microstructured surfaces， an ultra-precise adaptive flying cutting method was proposed and experimentally validated in this study. First， based on the kinematic characteristics of flying cutting， a flying cutting plasticity machining model was established. Second， based on the principle whereby the maximum chip thickness was always less than the brittle-plastic transition threshold， an iterative algorithm was used to plan a tool trajectory with dynamically varying feed rates based on the local morphological characteristics of the microstructured surface. Finally， the effectiveness of the proposed adaptive flying cutting method was verified by comparing it with the conventional flying cutting method in experiments. Experiments show that microgrooves are successfully machined without brittle fracture on single-crystal silicon materials and that a surface roughness of 18 nm is achieved. Compared with conventional flying tool cutting methods， the proposed ultra-precision adaptive flying cutting method avoids brittle breakage without reducing feed rates and achieves 2.5 times the machining efficiency of conventional methods.Keywords：infrared optical material;ultra-precision flying cutting;Microstructures;adaptive tuning;machining efficiency- 169
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Published：2022-08-16 -
Magnetic-assisted polishing of fused silica optics with high efficiency and low defects
Abstract：To achieve high-efficiency and low-defect machining of fused silica optics， the material removal characteristics and surface quality formation mechanism based on magnetically assisted polishing technology were studied. Magnetic polishing fluid with different degrees of polishing clearance and different volume ratios of iron powders was used to conduct magnetically assisted polishing of lapped fused silica optics. The material removal rate， profile of polished spots， surface roughness， and transmittance of samples were evaluated， and the effects of the processing parameters on processing efficiency and surface quality were determined by combining a spatial magnetic flux intensity simulation and polishing pressure analysis. Results show that the material depth removal rate increases as a power function with the magnetic flux intensity and rises significantly with the volume ratio of iron powders in the polishing fluid. In addition， polishing fluid with a low spatial magnetic field intensity and low volume ratio of iron powders can facilitate material removal in the elastic domain， resulting in a smooth surface. A small polishing clearance of 0.5 mm and high iron powder volume ratio of 14.18% in the polishing fluid can obtain maximum depth removal and volume removal rates of 0.439 2 μm/min and 1.49 × 10-4 mm3/min， respectively. A large polishing gap of 1.5 mm and a low volume ratio of iron powders of 9.93% generates a smooth surface with Ra roughness as low as 8.1 nm.Keywords：magnetic-assisted polishing;polishing clearance;volume ratio of iron powders;material removal rate;surface roughness- 165
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Published：2022-08-16
Design，Fabrication and Application of Planar Optical Elements
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Visible light video denoising and FPGA hardware implementation
Abstract：It is difficult to suppress the noise in static state of the existing filtering algorithm. Moreover， motion compensated filtering algorithm fails to effectively suppress noise. To solve these problems， a video denoising algorithm based on spatio-temporal filtering is proposed and implemented on the field programmable gate array （FPGA）. The algorithm mainly uses Gaussian difference filtering to extract image features， and then applies spatial filtering to suppress high-frequency noise. Simultaneously， different denoising strategies are adopted for the segmented image area by feedback. Implementing hardware requires high-level synthesis tools to simplify programming， and is to make DDR3 control module to operate input and output of video stream between modules. Simulation results show that the proposed algorithm can be used for denoising. For different scenes， the peak signal-to-noise ratio can be increased by up to 15 dB in comparison with the denoising algorithm based on a non-subsampled contourlet （NSCT）. After transplanting the algorithm to FPGA， the difference between PSNR and MATLAB simulation program was approximately 0.3 dB， and the running time was shortened by over 71.5%. Considering the real-time performance， PSNR achieves a better visible video denoising effect.Keywords：image processing;video denoising;visible light;FPGA;motion compensation;Gaussian difference filtering- 205
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Published：2022-08-16 -
Removing mixed noise from remote sensing images by wavelet multifractal method
Abstract：To remove the mixed noise from remote sensing images， a wavelet multifractal denoising algorithm was developed. The algorithm mainly uses wavelet analysis for signal decomposition and multifractal to extract image features. First， image decomposition was performed by wavelet decomposition， and additive noise was preliminarily processed using the exponential decay threshold method of the wavelet semi-soft threshold. Second， using the multifractal theory， the multifractal spectrum of the noisy image was found， and an offset operator is constructed to process the additive noise twice. Then， the sparse gradient set was obtained by multiplying the direction gradient with the two-dimensional mask layer pixel by pixel， and the denoised image is reconstructed. Finally， the evaluation index value of the denoised image was calculated， and the denoising effect was evaluated according to the numerical analysis. The experimental results show that the method can effectively remove the mixed noise of remote sensing images. The maximum peak signal-to-noise ratio of the denoised images is 26.700 dB by denoising six randomly added noise images. Moreover， the highest edge preservation index is 0.449. It can meet the requirements of the visibility and detail preservation of mixed denoising of remote sensing images and provide a reliable basis for subsequent analysis.Keywords：image processing;remote sensing image denoising;multifractal;semi-soft threshold;wavelet analysis- 148
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Published：2022-08-16 -
Semi-supervised dual path network for hyperspectral image classification
Abstract：To extract the deep discrimination features from hyperspectral images， many labeled samples are often required； however， it is difficult to label samples in hyperspectral image. By using the characteristic of combining image with hyperspectral information， a semi-supervised dual path network （SSDPNet） based on deep-manifold learning was proposed. In this network， convolution and neural networks were used to extract the spatial-spectrum joint features from few labeled samples and many unlabeled samples， respectively. Then， the manifold reconstruction graph models based on supervised and unsupervised graphs were constructed to explore the manifold structure in hyperspectral images. In addition， a joint loss function based on mean square error and manifold learning was developed to jointly measure manifold boundary and spatial-spectral probability residuals to realize integrated feedback and optimize the dual path network； this results in land cover classification. The overall classification accuracies of experiments on WHU-Hi-Longkou and Heihe hyperspectral data sets reach 97.53% and 96.79% respectively， which effectively improves the ability to classify land covers.Keywords：hyperspectral remote sensing;land cover classification;feature extraction;graph embedding;manifold learning;semi supervised learning- 174
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Published：2022-08-16
Information Sciences
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