Research

14 pages, 4597 KiB

Open AccessArticle

Simulation Analysis of an Atmospheric Turbulence Wavefront Measurement System

by Gangyu Wang, Laian Qin, Yang Li, Yilun Cheng, Xu Jing, Gongye Chen and Zaihong Hou

Photonics 2024, 11(4), 383; https://doi.org/10.3390/photonics11040383 - 18 Apr 2024

Viewed by 394

In this paper, a turbulent wavefront measurement model based on the Hartmann system structure is proposed. The maximum recognizable mode number of different lens units is discussed, and the influence of different lens array arrangements on the accuracy of turbulent wavefront reconstruction is [...] Read more.

In this paper, a turbulent wavefront measurement model based on the Hartmann system structure is proposed. The maximum recognizable mode number of different lens units is discussed, and the influence of different lens array arrangements on the accuracy of turbulent wavefront reconstruction is analyzed. The results indicate that the increase in the aberration order of the turbulent wavefront has a certain influence on the reconstruction ability of the system. Different lens arrangements and number of lens units will lead to the effective reconstruction of different final mode orders. When using a 5 × 5 lens array arrangement and a hexagonal arrangement of 19 lenses, the maximum order of turbulent wavefront aberrations allowing for effective reconstruction was 25. When the sparse arrangement of 25 lenses or the sparse arrangement of 31 lenses was used, the maximum order allowing for effective reconstruction was 36. If the aberration composition of the turbulent wavefront contained higher-order aberrations, the system could not accurately measure the turbulent wavefront. When the order of the aberrations of the turbulent wavefront was low, the turbulent wavefront could be measured by the lens arrangement with fewer lens units, and the wavefront reconstruction accuracy was close to the measurement results obtained when more lens units were used. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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13 pages, 12542 KiB

Open AccessArticle

A Deep Learning-Based Preprocessing Method for Single Interferometric Fringe Patterns

by Xueliang Zhu, Di Zhang, Yilei Hao, Bingcai Liu, Hongjun Wang and Ailing Tian

Photonics 2024, 11(3), 226; https://doi.org/10.3390/photonics11030226 - 29 Feb 2024

Viewed by 599

Abstract

A novel preprocessing method based on a modified U-NET is proposed for single interference fringes. The framework is constructed by introducing spatial attention and channel attention modules to optimize performance. In this process, interferometric fringe maps with an added background intensity, fringe amplitude, [...] Read more.

A novel preprocessing method based on a modified U-NET is proposed for single interference fringes. The framework is constructed by introducing spatial attention and channel attention modules to optimize performance. In this process, interferometric fringe maps with an added background intensity, fringe amplitude, and ambient noise are used as the input to the network, which outputs fringe maps in an ideal state. Simulated and experimental results demonstrated that this technique can preprocess single interference fringes in ~1 microsecond. The quality of the results was further evaluated using the root mean square error, peak signal-to-noise ratio, structural similarity, and equivalent number of views. The proposed method outperformed U-NET, U-NET++, and other conventional algorithms as measured by each of these metrics. In addition, the model produced high-quality normalized fringes by combining objective data with visual effects, significantly improving the accuracy of the phase solutions for single interference fringes. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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16 pages, 18828 KiB

Open AccessArticle

Dark Light Image-Enhancement Method Based on Multiple Self-Encoding Prior Collaborative Constraints

by Lei Guan, Jiawei Dong, Qianxi Li, Jijiang Huang, Weining Chen and Hao Wang

Photonics 2024, 11(2), 190; https://doi.org/10.3390/photonics11020190 - 19 Feb 2024

Viewed by 859

Abstract

The purpose of dark image enhancement is to restore dark images to visual images under normal lighting conditions. Due to the ill-posedness of the enhancement process, previous enhancement algorithms often have overexposure, underexposure, noise increases and artifacts when dealing with complex and changeable [...] Read more.

The purpose of dark image enhancement is to restore dark images to visual images under normal lighting conditions. Due to the ill-posedness of the enhancement process, previous enhancement algorithms often have overexposure, underexposure, noise increases and artifacts when dealing with complex and changeable images, and the robustness is poor. This article proposes a new enhancement approach consisting in constructing a dim light enhancement network with more robustness and rich detail features through the collaborative constraint of multiple self-coding priors (CCMP). Specifically, our model consists of two prior modules and an enhancement module. The former learns the feature distribution of the dark light image under normal exposure as an a priori term of the enhancement process through multiple specific autoencoders, implicitly measures the enhancement quality and drives the network to approach the truth value. The latter fits the curve mapping of the enhancement process as a fidelity term to restore global illumination and local details. Through experiments, we concluded that the new method proposed in this article can achieve more excellent quantitative and qualitative results, improve detail contrast, reduce artifacts and noise, and is suitable for dark light enhancement in multiple scenes. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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18 pages, 8493 KiB

Open AccessArticle

Investigation of the Space-Variance Effect of Imaging Systems with Digital Holography

by Xingyu Yang, Rong Zhao, Huan Chen, Yijun Du, Chen Fan, Gaopeng Zhang and Zixin Zhao

Photonics 2023, 10(12), 1350; https://doi.org/10.3390/photonics10121350 - 07 Dec 2023

Viewed by 707

Abstract

In classical Fourier optics, an optical imaging system is regarded as a linear space-invariant system, which is only an approximation. Especially in digital holography, the space-variance effect has a great impact on the image quality and cannot be ignored. Therefore, it is comprehensively [...] Read more.

In classical Fourier optics, an optical imaging system is regarded as a linear space-invariant system, which is only an approximation. Especially in digital holography, the space-variance effect has a great impact on the image quality and cannot be ignored. Therefore, it is comprehensively investigated in this article. Theoretical analyses indicate that the space-variance effect is caused by linear frequency modulation and ideal low-pass filtering, and it can be divided into three states: the approximate space-invariance state, the high-frequency distortion state, and the boundary-diffraction state. Classical Fourier optics analysis of optical imaging systems only considers the first. Regarding the high-frequency distortion state, the closer the image field is to the edge, the more severe the distortion of high-frequency information is. As for the boundary-diffraction state, in addition to the distortion of high-frequency information in the margin, a prominent boundary-diffraction phenomenon is observed. If the space-variance effect of the imaging lens is ignored, we predict that no space-variance effect in image holography will occur when the hologram is recorded at the back focal plane of the imaging lens. Simulation and experimental results are presented to validate our theoretical prediction. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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13 pages, 3408 KiB

Open AccessArticle

Analysis of Coaxiality Error Induced by the Cube Corner Retro-Reflector Geometrical and Assembly Errors of an Acquisition, Pointing, and Tracking System

by Daquan Li, Zhaoyong Mao, Lijuan Sun, Haifeng Zhang and Furui Zhang

Photonics 2023, 10(10), 1176; https://doi.org/10.3390/photonics10101176 - 23 Oct 2023

Viewed by 746

Abstract

Satellite laser communication is a promising technology for the next-generation communication system. Its communication performance is subject to the APT beam-pointing accuracy. One of the most important problems is reducing the coaxiality error before the APT starts working. However, the coaxiality error is [...] Read more.

Satellite laser communication is a promising technology for the next-generation communication system. Its communication performance is subject to the APT beam-pointing accuracy. One of the most important problems is reducing the coaxiality error before the APT starts working. However, the coaxiality error is difficult to correct effectively owing to the lack of empirical guidance based on qualitative analysis. We study the inducement that will generate coaxiality errors. The mathematical model of the influence of the CCR dihedral angle error and planeness error on the spot centroid measurement are built, and an analysis is performed. The model of the beam-pointing error induced by the APT element’s assembly error is built, and the pointing error change rule is explored. Furthermore, the coaxiality performance simulation is performed in the presence of a CCR geometrical error while considering the assembly error. The results show that the coaxiality error has a nonlinear characteristic. The CCR planeness error has a greater influence on coaxiality deviation than that of dihedral angle error under certain conditions. This research is relevant to the design and test work of the APT system. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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9 pages, 5327 KiB

Open AccessEditor’s ChoiceCommunication

Single-Shot Phase-Contrast Imaging with a Single Grating

by Xin Liu, Lang Liu, Jianheng Huang, Yaohu Lei and Ji Li

Photonics 2023, 10(9), 968; https://doi.org/10.3390/photonics10090968 - 24 Aug 2023

Cited by 1 | Viewed by 866

Abstract

In the field of X-ray phase-contrast imaging, a time-saving approach and preservation of details are crucial factors for obtaining phase-contrast images. In this manuscript, a single grating imaging system is proposed to perform the X-ray phase-contrast imaging. Instead of the time-consuming phase-stepping method, [...] Read more.

In the field of X-ray phase-contrast imaging, a time-saving approach and preservation of details are crucial factors for obtaining phase-contrast images. In this manuscript, a single grating imaging system is proposed to perform the X-ray phase-contrast imaging. Instead of the time-consuming phase-stepping method, this system uses a single-shot algorithm to retrieve the distribution of samples’ attenuation and phase gradient. Unlike the single-shot Fourier transform algorithm, which truncates the high-frequency component of the image and reduces the spatial resolution, our method can retrieve the attenuation and phase information images with the same spatial resolution as the images acquired directly by the X-ray detector used. Furthermore, by using a large-size X-ray detector (29 cm × 23 cm), the imaging system can be configured as either a microscopic instrument or a normal large field-of-view imaging system. Finally, a series of experiments were performed to validate the feasibility of the proposed method. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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15 pages, 7533 KiB

Open AccessArticle

Storage Duration Prediction for Long-Expired Frozen Meat Exceeding State Reserve Time via Swept-Source Optical Coherence Tomography (SS-OCT) under Low-Frequency Electric Field

by Lu Zhang, Ruoxuan Li, Xiaorong Shen, Linkai He, Jie Huang, Chi Song, Zeyu Fan, Hong Zhao, Kejia Li, Meizhen Xie, Jinfeng Peng, Pingping Jia, Xiaojun Deng and Minli Yang

Photonics 2023, 10(9), 956; https://doi.org/10.3390/photonics10090956 - 22 Aug 2023

Viewed by 658

Abstract

Storage duration detection for frozen meat, especially meat exceeding the state reserve time several times, has always been a big challenge in food safety inspection. Under long freezing times, the physical and chemical properties of meat change complexly. In this paper, the SS-OCT [...] Read more.

Storage duration detection for frozen meat, especially meat exceeding the state reserve time several times, has always been a big challenge in food safety inspection. Under long freezing times, the physical and chemical properties of meat change complexly. In this paper, the SS-OCT detection method under a low-frequency electric field is firstly (to our knowledge) applied to the predict storage durations of long-expired frozen meat. The average normalized cross-correlation (ANCC) is put forward as a comprehensive parameter to reflect both the electric–kinetic and optical properties of meat’s biological changes. A monotonically increasing inversion rule between ANCC and the storage duration of frozen meat is found after investigating 3840 pork samples, the frozen storage durations of which were from 1 to 13 months. To verify the correctness and accuracy of our method, nine groups of long-expired frozen pork samples were investigated. The maximum relative error for their storage durations is less than 5.71%, which means that our SS-OCT method under a low-frequency electric field is promising in providing a rapid on-site storage duration detection method without any complicated laboratory pretreatments for food safety inspection. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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15 pages, 11326 KiB

Open AccessArticle

Design of a Large-Format Low-Light Imaging System Based on the RGB Filter Wheel

by Jianwei Peng, Hongtao Yang, Xiaodong Song, Yingjun Ma, Weining Chen and Guangdong Zhang

Photonics 2023, 10(8), 953; https://doi.org/10.3390/photonics10080953 - 21 Aug 2023

Viewed by 715

Abstract

In order to capture true-color information of distant targets under extremely low light, a large-format low-light imaging system is designed based on an RGB filter wheel. By decomposing the system indicators, this study proposes a method for acquiring low-light true-color images using a [...] Read more.

In order to capture true-color information of distant targets under extremely low light, a large-format low-light imaging system is designed based on an RGB filter wheel. By decomposing the system indicators, this study proposes a method for acquiring low-light true-color images using a large-aperture, low-distortion optical lens combined with an RGB filter wheel capable of multi-line sequential exposure. The optical field segmentation is achieved using a four-panel optical reflective prism, and the images from four high-sensitivity SCOMS detectors are stitched together to form a composite image. The working principle of the system is explained, and the low-light imaging capability is thoroughly evaluated. The dimensions and rotation speed of the filter wheel are then calculated in detail, ensuring accurate synchronization of the filter wheel’s speed and exposure time. The calculation method for the parameters of the four-panel reflective prism structure is investigated, mathematical expressions for the geometric parameters of the prism assembly are provided, and a prism assembly suitable for four-way spectral separation is designed. Based on the research and design results, a large-swath-width, low-light true-color imaging system is developed that is suitable for an environmental illuminance of 0.01 lux. The system achieves a ground pixel resolution of 0.5 m (at an altitude of 5 km) and an effective image resolution of 4 K × 4 K, and is capable of accurately reproducing target color information. Laboratory and field flight tests verified that the large-swath-width images obtained by the imaging system are clear, with high contrast and resolution. After image fusion and spectral registration, the color images exhibit full saturation and high fidelity, meeting the requirements of low-light true-color imaging under airborne conditions. The design methodology of this low-light imaging system can serve as a reference for the development of airborne low-light imaging equipment. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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8 pages, 1118 KiB

Open AccessCommunication

High-Sensitivity Quantum-Enhanced Interferometers

by Juan Yu, Yinhua Wu, Liang Nie and Xiaojie Zuo

Photonics 2023, 10(7), 749; https://doi.org/10.3390/photonics10070749 - 29 Jun 2023

Viewed by 930

Abstract

High-sensitivity interferometers are one of the basic tools for precision measurement, and their sensitivity is limited by their shot noise limit (SNL), which is determined by vacuum fluctuations of the probe field. The quantum interferometer with novel structures can break the SNL and [...] Read more.

High-sensitivity interferometers are one of the basic tools for precision measurement, and their sensitivity is limited by their shot noise limit (SNL), which is determined by vacuum fluctuations of the probe field. The quantum interferometer with novel structures can break the SNL and measure the weak signals, such as the direct observation of gravity wave signal. Combining classical interferometers and the optical parametric amplifier (OPA) can enhance the signal; meanwhile, the quantum noise is kept at the vacuum level, so that the sensitivity of the nonlinear interferometer beyond the SNL can be achieved. By analyzing in detail the influence of system parameters on the precision of quantum metrology, including the intensity of optical fields for phase sensing, the gain factor of OPA, and the losses inside and outside the interferometers, the application conditions of high-sensitivity nonlinear quantum interferometers are obtained. Quantum interferometer-based OPAs provide the direct references for the practical development of quantum precise measurement. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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16 pages, 9976 KiB

Open AccessArticle

A Polarized Structured Light Method for the 3D Measurement of High-Reflective Surfaces

by Jixin Liang, Yuping Ye, Feifei Gu, Jiankai Zhang, Juan Zhao and Zhan Song

Photonics 2023, 10(6), 695; https://doi.org/10.3390/photonics10060695 - 19 Jun 2023

Cited by 4 | Viewed by 1667

Abstract

The reflection phenomenon exhibited by highly reflective surfaces considerably affects the quality of captured images, thereby rendering the task of structured light (SL) 3D reconstruction. In this paper, a polarized SL method is proposed to address the reconstruction issues on high-reflectance surfaces. The [...] Read more.

The reflection phenomenon exhibited by highly reflective surfaces considerably affects the quality of captured images, thereby rendering the task of structured light (SL) 3D reconstruction. In this paper, a polarized SL method is proposed to address the reconstruction issues on high-reflectance surfaces. The SL system we build in this paper involves a four-channel polarizing camera and a digital light processing (DLP) projector equipped with a polarizer in the lens. The built system enables the simultaneous acquisition of four groups of fringe images, each with different brightness differences. Then, a binary time-multiplexing SL method is adopted to obtain four distinct point clouds. Additionally, a fusion algorithm is proposed to merge the four point clouds into a single, precise, and complete point cloud. Several experiments have been conducted to demonstrate that the proposed method is capable of achieving excellent reconstruction outcomes on highly reflective surfaces. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements)

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