Applied Sciences

2024

Jump to: 2023, 2022, 2021, 2020, 2019

23 pages, 8425 KiB

Open AccessArticle

Optical Design Study with Uniform Field of View Regardless of Sensor Size for Terahertz System Applications

by Jungjin Park, Jaemyung Ryu and Hojong Choi

Appl. Sci. 2024, 14(19), 9097; https://doi.org/10.3390/app14199097 - 8 Oct 2024

Viewed by 571

Abstract

The focal length in a typical optical system changes with the angle of view, according to the size of the sensor. This study proposed an optical terahertz (THz) system application where the focal length changed while the angle of view was fixed; thus, [...] Read more.

The focal length in a typical optical system changes with the angle of view, according to the size of the sensor. This study proposed an optical terahertz (THz) system application where the focal length changed while the angle of view was fixed; thus, the image height was variable and responded to various sensor sizes. Therefore, it is possible to respond to various sensors with one optical system when the inspection distance is fixed. The fundamental optical system was designed by arranging the refractive power, which was determined according to the sensor size using the Gaussian bracketing method. A zoom optical system that changed the image height by fixing the angle of view and changed the focal length by moving the internal lens group was designed. THz waves exhibit minimal change in the refractive index depending on the wavelength. Moreover, their long-wavelength characteristics facilitate the development of millimeter-level pixel sizes. Therefore, the root mean square size of the maximum spot was 0.329 mm, which corrected the aberration to less than 1 mm (smaller than the pixel size). Further, a lighting analysis at 3 and 6 m locations confirmed the expansion of the lighting area by the magnification of the sensor size. After turning off certain light sources, we checked the contrast ratio via lighting analysis and confirmed that the size of one pixel was clearly distinguishable. Consequently, this newly designed optical system performed appropriately as an optical inspection system for THz system applications. Full article

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17 pages, 11172 KiB

Open AccessArticle

Light Beam Scattering from the Metal Surface with a Complex Mono- and Two-Periodic Microstructure Formed with Femtosecond Laser Radiation

by Sergey Dobrotvorskiy, Borys A. Aleksenko, Yevheniia Basova, Iaroslav M. Gnilitskyi, Mikołaj Kościński and José Machado

Appl. Sci. 2024, 14(19), 8662; https://doi.org/10.3390/app14198662 - 25 Sep 2024

Viewed by 883

Abstract

Currently, the technology of imparting the necessary reflective properties to a surface is becoming increasingly important. Darkening the surface and matting it helps to diffuse the reflected beam and prevent glare. The surface’s reflective properties are determined by its microstructure. Modern pico- and [...] Read more.

Currently, the technology of imparting the necessary reflective properties to a surface is becoming increasingly important. Darkening the surface and matting it helps to diffuse the reflected beam and prevent glare. The surface’s reflective properties are determined by its microstructure. Modern pico- and femtosecond lasers make it possible to obtain surfaces with high precision and create various LIPSS (laser-induced periodic surface structure) types. In this article, we describe the process of formation of a complex two-periodic microstructure on the surface of AISI 321 stainless steel under the influence of radiation from femtosecond lasers and describe the process of scattering of a light beam by the resulting surface. Modeling shows that the presence of an additional transparent coating on a flat surface does not improve its scattering properties and does not eliminate glare. In the event that a complex two-periodic structure is formed on the reflective surface and the coating surface, the nature of the reflection has a clearly defined scattered character, regardless of the angle of incidence of the light beam. This study shows the feasibility and effectiveness of forming a two-periodic structure in order to give it stealth characteristics and reduce visibility. Full article

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15 pages, 9797 KiB

Open AccessArticle

High-Precision Pointing and Tracking System Design for Near-Space Balloon-Based Optical Observation

by Lulu Qian, Min Huang, Wenhao Zhao, Yan Sun, Xiangning Lu, Zixuan Zhang, Guangming Wang, Yixin Zhao and Zhanchao Wang

Appl. Sci. 2024, 14(15), 6531; https://doi.org/10.3390/app14156531 - 26 Jul 2024

Viewed by 2081

Abstract

Near-space high-altitude balloon-based platforms have a series of advantages and provide superior conditions for optical observation. In order to ensure the stability of the optical axis of the optical detection load and stable tracking of the target, a near-space high-altitude balloon-based high-precision pointing [...] Read more.

Near-space high-altitude balloon-based platforms have a series of advantages and provide superior conditions for optical observation. In order to ensure the stability of the optical axis of the optical detection load and stable tracking of the target, a near-space high-altitude balloon-based high-precision pointing and tracking system was designed, which can compensate for changes in the pitch angle and azimuth angle of the platform during flight. The system includes a primary platform stable pointing system and a secondary precise tracking system. In the finished flight experiment, the primary platform pointing system and secondary precise tracking system on the balloon-based observation platform worked normally, providing a guarantee for the coronagraph’s stable tracking and detection of the sun. The primary platform pointing system can realize ±1° pointing accuracy, and the simulated accuracy of the secondary precise tracking system is 4″, which guaranteed that the coronagraph obtained more than 20,000 images. In subsequent works, we will upgrade and optimize the whole system and conduct our next flight experiment in the future. Full article

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16 pages, 8186 KiB

Open AccessArticle

Improved Adaptive Feedforward Controller Based on Internal Model Principle with Disturbance Observer for Laser-Beam Steering Systems

by Jung-Gon Kim

Appl. Sci. 2024, 14(13), 5631; https://doi.org/10.3390/app14135631 - 27 Jun 2024

Viewed by 633

Abstract

This study presents an effective control algorithm to improve the robustness of fast steering mirror (FSM)-based laser-beam steering systems against dynamic disturbances, such as repetitive disturbances resulting from operating conditions. A stable control system must be able to maintain the required high-precision control, [...] Read more.

This study presents an effective control algorithm to improve the robustness of fast steering mirror (FSM)-based laser-beam steering systems against dynamic disturbances, such as repetitive disturbances resulting from operating conditions. A stable control system must be able to maintain the required high-precision control, even when dynamic disturbances affect the FSM system. In this study, an improved control method is proposed using an internal model principle (IMP)-based nonlinear controller with a disturbance observer (DOB) for the FSM system. This IMP-based controller with DOB can attenuate the residual control-error signal under dynamic disturbance conditions. Full article

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14 pages, 5410 KiB

Open AccessArticle

Disturbance Observer-Based Anti-Shock Controller for Laser Beam Steering Systems

by Jung-Gon Kim

Appl. Sci. 2024, 14(11), 4774; https://doi.org/10.3390/app14114774 - 31 May 2024

Viewed by 600

Abstract

This paper presents an approach for improving the robustness of tip-tilt controllers for fast-steering mirror (FSM)-based laser beam steering (LBS) systems in the presence of dynamic disturbances such as external shocks. To this end, we propose the addition of a disturbance observer (DOB)-based [...] Read more.

This paper presents an approach for improving the robustness of tip-tilt controllers for fast-steering mirror (FSM)-based laser beam steering (LBS) systems in the presence of dynamic disturbances such as external shocks. To this end, we propose the addition of a disturbance observer (DOB)-based anti-shock controller in parallel to the original linear servo control loop to improve its control performance in the presence of external shocks. To increase the tip-tilt control performance against external shocks, the DOB-based control method, which is an improved control method for eliminating nonperiodic disturbances, is implemented in the original tip-tilt control system. The results indicate that the control error of the DOB-based anti-shock controller decreased, resulting in an efficient improvement in its disturbance-rejection performance. Full article

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14 pages, 3539 KiB

Open AccessArticle

Design of an Imaging Optical System for Large-Sized Stepped Shaft Diameter Detection

by Jie Duan, Jiyu Li, Yundong Zhu, Hongtao Zhang, Yuting Liu and Yanan Zhao

Appl. Sci. 2024, 14(8), 3423; https://doi.org/10.3390/app14083423 - 18 Apr 2024

Viewed by 1146

Abstract

Addressing the prevalent issues of low accuracy, low efficiency, and poor image quality in online diameter measurement of large-sized stepped shafts, this study introduces a novel method based on a symmetrical dual-telecentric optical path utilizing dual CCDs, specifically designed for step shafts with [...] Read more.

Addressing the prevalent issues of low accuracy, low efficiency, and poor image quality in online diameter measurement of large-sized stepped shafts, this study introduces a novel method based on a symmetrical dual-telecentric optical path utilizing dual CCDs, specifically designed for step shafts with diameters ranging from 600 mm to 800 mm. By developing and optimizing an imaging system grounded in the object-image dual-telecentric optical path principle and employing Zemax software for comprehensive analysis and optimization, this research achieves significant findings. The system’s Airy disk radius is calculated at 3.204 μm; the modulation transfer function (MTF) remains above 0.6 across various fields of view at a spatial cutoff frequency of 71.4 lp/mm, with smooth MTF curves; the field curvature is confined within 0.1 μm; and the distortion is maintained below 0.1%, fulfilling high-quality imaging requirements. Additionally, a tolerance analysis is conducted to ensure the system’s stability and reliability. Applied to an experimental setup for measuring the diameter of large-sized step shafts, the system demonstrates an improved measurement precision of 0.02 mm. This research offers a robust technical solution for the high-precision online measurement of large stepped shaft diameters, presenting significant practical implications for enhancing productivity and product quality. Full article

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19 pages, 4871 KiB

Open AccessArticle

Design of Parabolic Off-Axis Reflector Optical System for Large Aperture Single Star Simulators

by Tianyu Gao, Gaofei Sun, Guoyu Zhang, Zongyu Du, Qiang Liu, Qian Deng, Siwen Chen and Jierui Zhang

Appl. Sci. 2024, 14(5), 1926; https://doi.org/10.3390/app14051926 - 27 Feb 2024

Viewed by 1239

Abstract

This study proposes a parabolic off-axis reflective optical system design method to reduce the wave aberration of the optical system of a large aperture single star simulator and improve the optical system’s imaging quality. Firstly, we determined the design indexes of the optical [...] Read more.

This study proposes a parabolic off-axis reflective optical system design method to reduce the wave aberration of the optical system of a large aperture single star simulator and improve the optical system’s imaging quality. Firstly, we determined the design indexes of the optical system of the large aperture single star simulator by analyzing the technical indexes of the star sensitizer and the development status of the single star simulator; secondly, the initial structural parameters of the optical system were calculated based on the theory of primary aberration; then, we carried out the design optimization of the optical system, the image quality evaluation, and the tolerance analysis using Zemax software; finally, the study tested the wave aberration of the optical system by using the four-dimensional interferometer and the standard mirror together. The simulation results of the optical system are as follows: in the entire field of view, the aberration of the optical system is far less than 0.002%, the modulation transfer function (MTF) reaches the diffraction limit, and the maximum wave aberration is 0.0324 λ. The experimental results are as follows: the maximum wave aberration of the optical system is 0.0337 λ, which is less than 1/25 λ, and it meets the requirements of the index. The simulation and experimental results show that the optical system of the large aperture single star simulator designed by this method has good imaging quality and a simple system structure. Full article

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2023

Jump to: 2024, 2022, 2021, 2020, 2019

12 pages, 1627 KiB

Open AccessArticle

Problem of Measuring Absorption Using Time-Resolved Photothermal Common-Path Interferometry under Conditions of Developed Heat Diffusion

by Ksenia Vlasova, Alexandre Makarov and Nikolai Andreev

Appl. Sci. 2024, 14(1), 190; https://doi.org/10.3390/app14010190 - 25 Dec 2023

Cited by 1 | Viewed by 1025

Abstract

We present a study of the problem of measuring ultra-low absorption in quartz materials using the time-resolved photothermal common-path interferometry (TPCI) method, which we proposed and elaborated, with allowance for developed heat diffusion in the samples. This task is related to the implementation [...] Read more.

We present a study of the problem of measuring ultra-low absorption in quartz materials using the time-resolved photothermal common-path interferometry (TPCI) method, which we proposed and elaborated, with allowance for developed heat diffusion in the samples. This task is related to the implementation of one of the ways of increasing the sensitivity of measurements, namely, increasing the energy of the heating pulse by increasing its duration. Analytical formulas for the time dependence of the power of the time-varying component of the probe radiation are obtained in the Gaussian approximation for the laser beams. A correction factor that takes into account the heat diffusion effect is calculated theoretically and used during calibration. The rate at which the power of the time-varying component decreases when the sample is cooled after the end of the heating pulse is calculated. When measuring in crystalline quartz, quartz glass, and also in air, the calculated rate coincided with the experimental one, which is additional evidence for the reliability of the calculations of the correction factor for calibrating the measurements. When the duration of the heating pulse is increased to 5 ms, the calculated sensitivity of the scheme for measuring absorption in quartz glasses is 2 × 10⁻⁹ cm⁻¹. Full article

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21 pages, 6743 KiB

Open AccessArticle

Dynamic Spectrum Assignment in Passive Optical Networks Based on Optical Integrated Microring Resonators Using Machine Learning and a Routing, Modulation Level, and Spectrum Assignment Method

by Andrés F. Calvo-Salcedo, Neil Guerrero González and Jose A. Jaramillo-Villegas

Appl. Sci. 2023, 13(24), 13294; https://doi.org/10.3390/app132413294 - 15 Dec 2023

Cited by 1 | Viewed by 1567

Abstract

The rising demand for bandwidth in optical communication networks has led to the need for more efficient solutions for spectrum allocation. This article presents a solution to enhance the capacity and efficiency of passive optical networks (PON) using optical microring resonators and dynamic [...] Read more.

The rising demand for bandwidth in optical communication networks has led to the need for more efficient solutions for spectrum allocation. This article presents a solution to enhance the capacity and efficiency of passive optical networks (PON) using optical microring resonators and dynamic spectrum allocation. The solution relies on wavelength division multiplexing (WDM). It proposes using a support vector machine (SVM) and a Routing, Modulation Level, and Spectrum Assignment (RMLSA) method to manage spectrum allocation based on the bandwidth and distance of multiple requests. The network employs a pulse shaper to physically allocate the spectrum, allowing for the separation of the spectrum generated by the microring resonators into different wavelengths or wavelength ranges (super-channel). Additionally, the SVM and RMLSA algorithms regulate the pulse shaper to execute the allocation. This photonic network achieves improved spectrum utilization and reduces the network blocking probability. Our proposal shows that we successfully addressed 1090 requests with a zero blocking probability, accounting for 81% of the total requests. These request scenarios can simultaneously accommodate up to 200 requests, with a maximum bandwidth of 31 THz. This highlights the efficacy of our approach in efficiently managing requests with substantial processing capacity. Full article

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12 pages, 5001 KiB

Open AccessArticle

Computational Imaging at the Infrared Beamline of the Australian Synchrotron Using the Lucy–Richardson–Rosen Algorithm

by Soon Hock Ng, Vijayakumar Anand, Molong Han, Daniel Smith, Jovan Maksimovic, Tomas Katkus, Annaleise Klein, Keith Bambery, Mark J. Tobin, Jitraporn Vongsvivut and Saulius Juodkazis

Appl. Sci. 2023, 13(23), 12948; https://doi.org/10.3390/app132312948 - 4 Dec 2023

Cited by 1 | Viewed by 1169

Abstract

The Fourier transform infrared microspectroscopy (FTIRm) system of the Australian Synchrotron has a unique optical configuration with a peculiar beam profile consisting of two parallel lines. The beam is tightly focused using a 36× Schwarzschild objective to a point on the sample and [...] Read more.

The Fourier transform infrared microspectroscopy (FTIRm) system of the Australian Synchrotron has a unique optical configuration with a peculiar beam profile consisting of two parallel lines. The beam is tightly focused using a 36× Schwarzschild objective to a point on the sample and the sample is scanned pixel by pixel to record an image of a single plane using a single pixel mercury cadmium telluride detector. A computational stitching procedure is used to obtain a 2D image of the sample. However, if the imaging condition is not satisfied, then the recorded object’s information is distorted. Unlike commonly observed blurring, the case with a Schwarzschild objective is unique, with a donut like intensity distribution with three distinct lobes. Consequently, commonly used deblurring methods are not efficient for image reconstruction. In this study, we have applied a recently developed computational reconstruction method called the Lucy–Richardson–Rosen algorithm (LRRA) in the online FTIRm system for the first time. The method involves two steps: training step and imaging step. In the training step, the point spread function (PSF) library is recorded by temporal summation of intensity patterns obtained by scanning the pinhole in the x-y directions across the path of the beam using the single pixel detector along the z direction. In the imaging step, the process is repeated for a complicated object along only a single plane. This new technique is named coded aperture scanning holography. Different types of samples, such as two pinholes; a number 3 USAF object; a cross shaped object on a barium fluoride substrate; and a silk sample are used for the demonstration of both image recovery and 3D imaging applications. Full article

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19 pages, 7129 KiB

Open AccessArticle

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

by Mianhui Weng, Yizhao Wang, Xuechang Ren and Qinghong Lu

Appl. Sci. 2023, 13(21), 11858; https://doi.org/10.3390/app132111858 - 30 Oct 2023

Cited by 2 | Viewed by 2013

Abstract

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development [...] Read more.

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications. Full article

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11 pages, 6341 KiB

Open AccessArticle

High-Power, High-Purity HG_0n Hermite–Gaussian Laser Beam Generation in Cascaded Large Aspect Ratio Slabs

by Tianli Yang, Jing Yang, Wangzhe Zhou, Xuepeng Li, Yinan Zhou, Zongzhe Zhang and Xiaojun Wang

Appl. Sci. 2023, 13(19), 11062; https://doi.org/10.3390/app131911062 - 8 Oct 2023

Cited by 1 | Viewed by 1031

Abstract

High-power, high-purity, nanosecond (ns) one-dimensional HG_0n laser beams are proposed and demonstrated by using Nd:YAG cascaded slabs with a large aspect ratio. The HG_0n laser beams are generated by adjusting the pump distribution, the intracavity apertures, and the tilt [...] Read more.

High-power, high-purity, nanosecond (ns) one-dimensional HG_0n laser beams are proposed and demonstrated by using Nd:YAG cascaded slabs with a large aspect ratio. The HG_0n laser beams are generated by adjusting the pump distribution, the intracavity apertures, and the tilt angle of the output coupler (OC). By controlling the gain and loss of HG_0n modes of different orders, the high-purity, one-dimensional, high-order HG_0n laser beams with orders 1 to 9 (HG₀₁ to HG₀₉) are produced, and their beam quality factors M² align well with the theoretical predictions. Meanwhile, the large aspect ratio slab provides an ideal amplifier for the strip-shaped HG_0n laser beams, and further power scaling is achieved by seeding the generated HG_0n laser beams into an amplifier with an identical slab module. For the HG₀₉ mode, the average power is amplified from 289 mW to 4.73 W with 294 ns pulse width, corresponding to a peak power of 32 kW. Moreover, above 5 W average power is achieved for all HG₀₁ to HG₀₈ modes. Hopefully, this scheme provides a solution for high-power and high-purity HG_0n laser beam generation based on the slab-shaped configuration. Full article

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16 pages, 5165 KiB

Open AccessArticle

Near-Infrared Spectral Analysis for Assessing Germination Rate of Rapeseed Seeds: An Applied Sciences Approach

by Shuaiyang Zhang, Chengxu Lv, Cheng Cui, Jizhong Wang, Jingzhu Wu and Wenhua Mao

Appl. Sci. 2023, 13(19), 11001; https://doi.org/10.3390/app131911001 - 6 Oct 2023

Cited by 1 | Viewed by 1502

Abstract

Brassica rapa, commonly known as the rapeseed plant, is globally recognized for its nutrient-rich composition and oil-packed seeds, earning its distinction as a substantial oil-seed crop. The seed quality, particularly the germination rate, is instrumental in guaranteeing a high-yield rapeseed crop. Given [...] Read more.

Brassica rapa, commonly known as the rapeseed plant, is globally recognized for its nutrient-rich composition and oil-packed seeds, earning its distinction as a substantial oil-seed crop. The seed quality, particularly the germination rate, is instrumental in guaranteeing a high-yield rapeseed crop. Given this, the accurate, quantitative determination and selection of germination rates in seed batches prior to sowing is of paramount importance. However, conventional germination tests, employed to determine the average germination rate of seed batches, are marred by substantial time and cost inefficiencies. This study proposes the use of near-infrared spectral analysis as a proficient, non-invasive approach for assessing germination rates in rapeseed seed batches. The research involved artificial aging of seeds procured from a variety of rapeseed strains, resulting in 228 batches with a broad germination rate spectrum of 15.73% to 99.13%. We recorded near-infrared diffuse reflectance spectra and applied a range of strategies for spectral data preprocessing and feature variable selection. Furthermore, we leveraged support vector regression (SVR) modeling to augment the detection methodology. SVR training and detection were conducted using MATLAB, with selected feature wavelengths undergoing rigorous scrutiny and discussion. The results indicated that employing Savitzky–Golay convolution smoothing for spectral preprocessing, along with Synergy interval Partial Least Squares (SiPLS) in conjunction with Random Frog (RF) for the selection of 50 feature wavelength points, yielded optimal germination rate prediction performance within the SVR model. The coefficients of determination (R²c) for the training set and (R²p) for the testing set were observed to be 0.8559 and 0.8386, respectively, while the Root Mean Square Errors of Calibration (RMSEC) and Prediction (RMSEP) were calculated to be 13.76% and 17.04%. The mechanism of detecting seed vigor through near-infrared spectroscopy was analyzed based on joint variable screening and sensitive variable traceability. Consequently, the SG–SiPLS–RF–SVR model demonstrates its effectiveness in predicting the average germination rate of seed batches, offering a rapid, non-invasive detection method that can be universally applied to various rapeseed strains, thus significantly improving seed production efficiency. Full article

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13 pages, 3981 KiB

Open AccessArticle

Spectra Prediction for WLEDs with High TLCI

by Haiyang Wang, Peipei Wang, Zhiliang Jin, Yang Song and Daxi Xiong

Appl. Sci. 2023, 13(14), 8487; https://doi.org/10.3390/app13148487 - 22 Jul 2023

Viewed by 1423

Abstract

White light-emitting diodes (WLEDs) with a high television lighting consistency index (TLCI) are becoming popular in stadium, studio, and stage lighting, but they are hard to empirically manufacture because they exploit the response of a camera rather than that of the human eye. [...] Read more.

White light-emitting diodes (WLEDs) with a high television lighting consistency index (TLCI) are becoming popular in stadium, studio, and stage lighting, but they are hard to empirically manufacture because they exploit the response of a camera rather than that of the human eye. In this study, blue chips with green and red phosphors were used to build high-TLCI WLEDs, and a spectral prediction model for WLEDs used for calculating the TLCI was established. The model considers the reabsorption and re-emission of phosphors and spectral shift. To validate the model, WLEDs with a TLCI greater than 90, from 3000 K to 7000 K, were predicted and packaged. The maximum difference in the TLCI between the measured and predicted model values is approximately 1.93%. The spectral prediction model proposed in this study is expected to provide a helpful guideline for building high-TLCI WLEDs. Full article

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13 pages, 10277 KiB

Open AccessArticle

Phase Mask Design Based on an Improved Particle Swarm Optimization Algorithm for Depth of Field Extension

by Zeyu Huang, Fei Li, Lina Zhu, Guo Ye and Tingyu Zhao

Appl. Sci. 2023, 13(13), 7899; https://doi.org/10.3390/app13137899 - 5 Jul 2023

Cited by 3 | Viewed by 1435

Abstract

Phase mask optimization is one of the critical steps in designing a wavefront coding system to extend the depth of field (DoF). As a classical phase mask, a cubic phase mask was taken as an example. An improved particle swarm optimization (PSO) algorithm [...] Read more.

Phase mask optimization is one of the critical steps in designing a wavefront coding system to extend the depth of field (DoF). As a classical phase mask, a cubic phase mask was taken as an example. An improved particle swarm optimization (PSO) algorithm was applied to calculate the parameters of the cubic phase mask by introducing the modulation transfer function as the optimization criterion and a threshold as a constraint. The quality of the subsequent image restoration is guaranteed on the premise of the extended DoF. Finally, the improved PSO was proved to be faster, more efficient, and more accurate compared to the simulated annealing algorithm and the traditional PSO. The experimental results verify that the cubic phase mask optimized by the improved PSO can achieve DoF extension in the wavefront coding system. The improved PSO can also be applied to other phase masks of wavefront coding systems. Full article

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17 pages, 6731 KiB

Open AccessArticle

Breadboard of Microchip Laser and Avalanche Photodiode in Geiger and Linear Mode for LiDAR Applications

by Ana de Sousa, Rafael Pinto, Bruno Couto, Beltran Nadal, Hugo Onderwater, Paulo Gordo, Manuel Abreu, Rui Melicio and Patrick Michel

Appl. Sci. 2023, 13(9), 5631; https://doi.org/10.3390/app13095631 - 3 May 2023

Cited by 2 | Viewed by 2269

Abstract

This paper reports the implementation of two critical technologies used in light detection and ranging for space applications: (1) a microchip Q-switched laser breadboard; (2) a breadboard of an indium gallium arsenide avalanche photodiode working at 292 K with high reverse polarization voltages. [...] Read more.

This paper reports the implementation of two critical technologies used in light detection and ranging for space applications: (1) a microchip Q-switched laser breadboard; (2) a breadboard of an indium gallium arsenide avalanche photodiode working at 292 K with high reverse polarization voltages. Microchip Q-switched lasers are small solid-state back-pumped lasers that can generate high-energy short pulses. The implemented breadboard used an erbium and ytterbium co-doped phosphate glass, a Co:Spinel crystal with 98% initial transparency, and an output coupler with 98% reflectivity. For the sensor test, a system for simultaneous operation in vacuum and a wide range of temperatures was developed. Avalanche photodiodes are reverse-polarized photodiodes with high internal gain due to their multiple layer composition, capable of building up high values of photocurrent from small optical signals by exploiting the avalanche breakdown effects. The test avalanche photodetector was assembled to be operated in two modes: linear and Geiger mode. The produced photocurrent was measured by using: (1) a passive quenching circuit; (2) a transimpedance amplifier circuit. These two technologies are important for mobile light detection and ranging applications due to their low mass and high efficiencies. The paper describes the breadboard’s implementation methods and sensor characterization at low and room temperatures with high bias voltages (beyond breakdown voltage). Full article

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6 pages, 1666 KiB

Open AccessCommunication

A Compact Self-Injection-Locked Narrow-Linewidth Diode Laser with Narrowband Dielectric Filter

by Pengfei Fan, Peng Xu, Hua-Ying Liu, Minghao Shang, Zhenda Xie and Shining Zhu

Appl. Sci. 2023, 13(8), 4765; https://doi.org/10.3390/app13084765 - 10 Apr 2023

Viewed by 2059

Abstract

The self-injection-locked diode laser can significantly reduce the linewidth down to a sub-100 kHz level but requires optical filtering that is much narrower than the laser cavity linewidth. Such optical filtering is usually sophisticated and beyond the capability of the normal dielectric coating [...] Read more.

The self-injection-locked diode laser can significantly reduce the linewidth down to a sub-100 kHz level but requires optical filtering that is much narrower than the laser cavity linewidth. Such optical filtering is usually sophisticated and beyond the capability of the normal dielectric coating approach. Here we develop a 0.16 nm narrowband dielectric coating using a Fabry–Perot dielectric filter (HFFPF) for the narrow linewidth self-injection-locked laser demonstration using a cost-effective Fabry–Perot laser diode. Single-longitude-mode output is achieved, with beat linewidth down to ~66 kHz and a high side mode suppression ratio over 60 dB. This setup of self-injection-locked laser is cost-effective for mass production and thus is suitable for various applications such as laser ranging, LIDAR, optical communication, and holographic. Full article

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2022

Jump to: 2024, 2023, 2021, 2020, 2019

12 pages, 2860 KiB

Open AccessArticle

Geometric Method: A Novel, Fast and Accurate Solution for the Inverse Problem in Risley Prisms

by Juan Domingo Sandoval, Keyla Delgado, David Fariña, Fernando de la Puente, Roberto Esper-Chaín and Marrero Martín

Appl. Sci. 2022, 12(21), 11087; https://doi.org/10.3390/app122111087 - 1 Nov 2022

Cited by 3 | Viewed by 2391

Abstract

Today, mechanical tracking systems are becoming increasingly compact, enabling a new range of civil and military applications. These include aerial laser scanning, for which Risley prisms are used. In Risley systems, the so-called inverse problem, which focuses on obtaining the angles of the [...] Read more.

Today, mechanical tracking systems are becoming increasingly compact, enabling a new range of civil and military applications. These include aerial laser scanning, for which Risley prisms are used. In Risley systems, the so-called inverse problem, which focuses on obtaining the angles of the prisms for a given target coordinate, has not yet been solved mathematically. As a consequence, approximate approaches have been used, but the solutions obtained have significant errors and a lack of precision. To improve accuracy, iterative methods, which are computationally intensive, have also been implemented. In this paper, an analytical process which we call the geometric method is presented, and we verified that this strategy highly improves accuracy and computational speed. Using this method in an iterative process gives accuracies of up to 1 pm in only three iterations. This high accuracy would allow the geometric method to be applied in fields such as lithography, stereolithography, or 3D printing. Full article

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15 pages, 2814 KiB

Open AccessArticle

Wave Aberration Correction for an Unobscured Off-Axis Three-Mirror Astronomical Telescope Using an Aberration Field Compensation Mechanism

by Jinxin Wang, Xu He, Xiaohui Zhang, Mingze Ma and Zhirui Cao

Appl. Sci. 2022, 12(21), 10716; https://doi.org/10.3390/app122110716 - 22 Oct 2022

Cited by 1 | Viewed by 1848

Abstract

Studying how to use the coupling characteristics of net aberration fields induced by different perturbation parameters to realize the wave aberration compensation correction of perturbed telescopes is of great significance for the development of active optics. Based on nodal aberration theory, this paper [...] Read more.

Studying how to use the coupling characteristics of net aberration fields induced by different perturbation parameters to realize the wave aberration compensation correction of perturbed telescopes is of great significance for the development of active optics. Based on nodal aberration theory, this paper studies the wave aberration compensation correction method of an unobscured off-axis three-mirror telescope. Specifically, first of all, it theoretically analyzes the coupling effects and compensation relationships of net aberration fields induced by different perturbation parameters of the telescope. Furthermore, it establishes wave aberration correction models with the secondary mirror as the compensator and the third mirror as the compensator for the telescope, respectively. In the end, it verifies the two compensation correction models by simulations. The results show that the tolerance of the secondary mirror compensation correction mode (SMCM) to the perturbation parameter threshold is significantly better than that of the third mirror compensation correction model (TMCM). When the introduced perturbation parameter threshold is small, the correction accuracy of the two models for the wave aberrations is equivalent, and both reach the order of

10^{- 3}

λ (RMS, λ = 632.8 nm). When the perturbation parameter threshold is increased, the correction accuracy of SMCM can still be maintained at the order of

10^{- 3}

λ but the correction accuracy of TMCM would decrease by an order of magnitude. Full article

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15 pages, 8972 KiB

Open AccessArticle

Equivalent Modeling and Verification of a High-Steepness and Lightweight Elliptical Aluminum Mirror

by Shuanglong Tan, Xin Zhang, Lingjie Wang, Hongbo Wu, Qiang Fu, Lei Yan and Mingyu Hu

Appl. Sci. 2022, 12(18), 9091; https://doi.org/10.3390/app12189091 - 9 Sep 2022

Cited by 4 | Viewed by 1803

Abstract

In order to realize the compact layout of aerospace payloads, the design and manufacture of high-steepness lightweight aluminum alloy mirrors is a key technology to be explored. For high-steepness mirrors, the traditional method is to establish the initial thickness that satisfies the bending [...] Read more.

In order to realize the compact layout of aerospace payloads, the design and manufacture of high-steepness lightweight aluminum alloy mirrors is a key technology to be explored. For high-steepness mirrors, the traditional method is to establish the initial thickness that satisfies the bending stiffness through finite element optimization iteration, which cannot achieve fast modeling and performance estimation. In this paper, firstly, the equivalent modeling method of the mirror with high steepness is proposed to achieve the equivalent of the elliptic mirror with a diameter of 410 × 310 mm and F# less than 0.7. Based on the mathematical model, topology shape optimization was used to build a highly lightweight mirror structure that could be quickly assembled, and the equivalent area–mass density of the mirror is less than 34 kg/mm2. Next, the rationality of design feasibility was verified by simulation analysis. Finally, by using single point diamond turning combined with post polishing process, the high-precision manufacturing of conventional aluminum alloy mirror was realized. The results show that the mirror shape accuracy is 1/10 λ (λ = 632.8 nm), and the surface roughness Ra is 3.342 nm. This research provides strong theoretical support and application prospects for the low-cost and rapid manufacturing of high-steepness lightweight aluminum alloy mirrors. Full article

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18 pages, 3259 KiB

Open AccessArticle

Optimization Method for Low Tilt Sensitivity of Secondary Mirror Based on the Nodal Aberration Theory

by Jing Li, Yalin Ding, Yiming Cai, Guoqin Yuan and Mingqiang Zhang

Appl. Sci. 2022, 12(13), 6514; https://doi.org/10.3390/app12136514 - 27 Jun 2022

Cited by 1 | Viewed by 1641

Abstract

The optical system that combines imaging and image motion compensation is conducive to the miniaturization of aerial mapping cameras, but the movement of optical element for image motion compensation will cause a decrease in image quality. To solve this problem, reducing the sensitivity [...] Read more.

The optical system that combines imaging and image motion compensation is conducive to the miniaturization of aerial mapping cameras, but the movement of optical element for image motion compensation will cause a decrease in image quality. To solve this problem, reducing the sensitivity of moving optical element is one of the effective ways to ensure the imaging quality of aerial mapping cameras. Therefore, this paper proposes an optimization method for the low tilt sensitivity of the secondary mirror based on the Nodal aberration theory. In this method, the analytical expressions of the tilt sensitivity of the secondary mirror in different tilt directions are given in the form of zernike polynomial coefficients, and the influence of the field of view on the sensitivity is expressed in the mathematical model. The desensitization optimization function and desensitization optimization method are proposed. The catadioptric optical system with a focal length of 350 mm is used for desensitization optimization. The results show that the desensitization function proposed in this paper is linearly related to the decrease of sensitivity within a certain range, and the standard deviation of the system after desensitization is 0.020, which is 59% of the system without desensitization. Compared with the traditional method, the method in this paper widens the range of angle reduction sensitivity and has a better desensitization effect. The research results show that the optimization method for low tilt sensitivity of the secondary mirror based on the Nodal aberration theory proposed in this paper reduces the tilt sensitivity of the secondary mirror, revealing that the reduction of the sensitivity depends on the reduction of the aberration coefficient related to the misalignment in the field of view, which is critical for the development of an optical system for aerial mapping cameras that combines imaging and image motion compensation. Full article

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10 pages, 2460 KiB

Open AccessArticle

Development of Radiator with Thermoplastic Polymer and Insert-Molded Aluminum Alloy Parts for Light-Emitting Diode Headlights

by Yenlung Chen, Juikun Chang, Chun Huang, Changche Chiu, Wei Lai, Zhiting Ye and Pin Han

Appl. Sci. 2022, 12(11), 5385; https://doi.org/10.3390/app12115385 - 26 May 2022

Cited by 1 | Viewed by 2226

Abstract

The increasing popularity of electric vehicles has increased the demand for lightweight auto parts. However, the excessive weight of traditional metal heat sinks has remained a concern. Metal has excellent thermal conductivity but low radiation efficiency. Conversely, thermoplastic polymers have excellent heat radiation [...] Read more.

The increasing popularity of electric vehicles has increased the demand for lightweight auto parts. However, the excessive weight of traditional metal heat sinks has remained a concern. Metal has excellent thermal conductivity but low radiation efficiency. Conversely, thermoplastic polymers have excellent heat radiation efficiency but poor thermal conductivity. In this study, we propose a radiator constructed using thermoplastic polymer and insert-molded aluminum alloy parts to maintain the low junction temperature of light-emitting diodes (LEDs); the radiator’s weight is reduced through a combination of aluminum alloy and a thermally conductive polymer designed for automotive headlights. At an LED thermal load of 11.48 W, the measured temperature on the LED pad is 60.8 °C. The weight of the proposed radiator is 23.37% lighter than that of a pure metal radiator. When the lightweight radiator is used in high-power LED headlights, it effectively dissipates heat within a limited space. Full article

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13 pages, 4208 KiB

Open AccessArticle

Calibration of Rotary Encoders Using a Shift-Angle Method

by Tsung-Han Hsieh, Tsukasa Watanabe and Po-Er Hsu

Appl. Sci. 2022, 12(10), 5008; https://doi.org/10.3390/app12105008 - 16 May 2022

Cited by 13 | Viewed by 4593

Abstract

Cross-calibration using an autocollimator and a polygon is the traditional method for calibrating a rotary encoder. These angles, which can be calibrated using this method, are limited by the pitch angle of the polygon, which is 15° for a 24-faced polygon. In this [...] Read more.

Cross-calibration using an autocollimator and a polygon is the traditional method for calibrating a rotary encoder. These angles, which can be calibrated using this method, are limited by the pitch angle of the polygon, which is 15° for a 24-faced polygon. In this work, we propose a new shift-angle method using the same setup as the traditional method. However, the new method can measure smaller than the pitch angle of the polygon, which is the measurement limitation of the traditional method. The proposed method can calibrate every angle of the rotary encoder. In the experiment, we use an autocollimator and a 24-faced polygon to calibrate the SelfA rotary encoder to verify the proposed shift-angle method. The SelfA rotary encoder, which comprises one rotary encoder and 12 read heads, is calibrated using self-calibration. The difference between the calibration results obtained by applying these two methods to the same SelfA rotary encoder is smaller than ±0.1″. Full article

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22 pages, 6244 KiB

Open AccessArticle

A Deconvolutional Deblurring Algorithm Based on Dual-Channel Images

by Yang Bai, Zheng Tan, Qunbo Lv, Peidong He and Min Huang

Appl. Sci. 2022, 12(10), 4864; https://doi.org/10.3390/app12104864 - 11 May 2022

Viewed by 1843

Abstract

Aiming at the motion blur restoration of large-scale dual-channel space-variant images, this paper proposes a dual-channel image deblurring method based on the idea of block aggregation, by studying imaging principles and existing algorithms. The study first analyzed the model of dual-channel space-variant imaging, [...] Read more.

Aiming at the motion blur restoration of large-scale dual-channel space-variant images, this paper proposes a dual-channel image deblurring method based on the idea of block aggregation, by studying imaging principles and existing algorithms. The study first analyzed the model of dual-channel space-variant imaging, reconstructed the kernel estimation process using the side prior information from the correlation of the two-channel images, and then used a clustering algorithm to classify kernels and restore the images. In the kernel estimation process, the study proposed two kinds of regularization terms. One is based on image correlation, and the other is based on the information from another channel input. In the image restoration process, the mean-shift clustering algorithm was used to calculate the block image kernel weights and reconstruct the final restored image according to the weights. As the experimental section shows, the restoration effect of this algorithm was better than that of the other compared algorithms. Full article

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9 pages, 1986 KiB

Open AccessArticle

Bound-State Soliton and Noise-like Pulse Generation in a Thulium-Doped Fiber Laser Based on a Nonlinear Optical Loop Mirror

by Maria Michalska, Jakub Michalski, Pawel Grzes and Jacek Swiderski

Appl. Sci. 2022, 12(3), 1664; https://doi.org/10.3390/app12031664 - 5 Feb 2022

Cited by 7 | Viewed by 2888

Abstract

We demonstrate a thulium-doped, mode-locked, all-fiber laser capable of operating in two generation regimes: dispersion-managed soliton and noise-like pulse (NLP). Employing a nonlinear optical loop mirror as an artificial saturable absorber, the oscillator generated optical pulses with a fundamental pulse repetition frequency of [...] Read more.

We demonstrate a thulium-doped, mode-locked, all-fiber laser capable of operating in two generation regimes: dispersion-managed soliton and noise-like pulse (NLP). Employing a nonlinear optical loop mirror as an artificial saturable absorber, the oscillator generated optical pulses with a fundamental pulse repetition frequency of ~15.795 MHz. The total net dispersion of the laser cavity had a slightly anomalous group delay dispersion value of −0.016 ps². After appropriate adjustment of a polarization controller, bound states of a dispersion-managed soliton composed of three pulses with fixed soliton separations were also observed. NLP generation, tunable over 35 nm from 1943.5 to 1978 nm, was also presented in the same laser setup. To our knowledge, this is the first report of the generation of tunable NLPs in a mode-locked thulium-doped fiber laser based on a nonlinear loop mirror saturable absorber. Full article

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15 pages, 3747 KiB

Open AccessArticle

Study on the Light Field Regulation of UVC-LED Disinfection for Cold Chain Transportation

by Zuwei Guan, Peng Liu, Tianfeng Zhou, Lin Zhou, Danmei Zhang, Qiuchen Xie, Qian Yu, Yupeng He, Sijiang Wang, Xibin Wang and Wenxiang Zhao

Appl. Sci. 2022, 12(3), 1285; https://doi.org/10.3390/app12031285 - 26 Jan 2022

Cited by 7 | Viewed by 3109

Abstract

In this paper, the pain point that cold chain transportation urgently needs for an efficient disinfection method is pointed out. Thus, this work aims at solving the problems and improving the disinfection efficiency in cold chain transportation. While Ultraviolet-C (UVC) irradiation is an [...] Read more.

In this paper, the pain point that cold chain transportation urgently needs for an efficient disinfection method is pointed out. Thus, this work aims at solving the problems and improving the disinfection efficiency in cold chain transportation. While Ultraviolet-C (UVC) irradiation is an effective method by which to kill viruses, it is difficult to apply the commonly used UVC-LED disinfection light source to ice-covered cold chain transportation due to its uneven light field distribution. Thus, the light field regulation of UVC-LED disinfection for cold chain transportation is studied. A UVC-LED chip with a wavelength of 275 nm was used as a light source, and parallel light was obtained by collimating lenses. Then, microlens array homogenization technology was used to shape the UVC light into a uniform light spot, with an energy space uniformity rate of 96.4%. Moreover, a simulation was conducted to compare the effects of the ice layer on the absorption of UVC light. Finally, an experiment was carried out to verify that the disinfection efficiency can be increased nearly by 30% with the proposed system by disinfecting E. coli (Escherichia coli), and the results indicate that the proposed system is an effective disinfection solution during cold chain transportation. Full article

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9 pages, 2516 KiB

Open AccessArticle

A Data Transmission Method with Spectral Switches via Electroabsorption

by Jyun-Ping Chang, Jun-Hong Weng, Hsun-Ching Hsu, Pei-Yuan Lee and Pin Han

Appl. Sci. 2022, 12(3), 979; https://doi.org/10.3390/app12030979 - 18 Jan 2022

Cited by 1 | Viewed by 1712

Abstract

In the past, the waveguide electroabsorption effect has generally been used as an intensity modulator for quasi-monochromatic light, such as lasers. Here, we study how this effect affects polychromatic light spectra. We find that for light with a Gaussian distribution spectrum, the spectral [...] Read more.

In the past, the waveguide electroabsorption effect has generally been used as an intensity modulator for quasi-monochromatic light, such as lasers. Here, we study how this effect affects polychromatic light spectra. We find that for light with a Gaussian distribution spectrum, the spectral peak shift (red shift or blue shift) can be controlled by the magnitude of the applied voltage, as long as the center wavelength and the spectral band are properly selected. This result can be used as a data transmission scheme at the integrated chip level or in free space. It may offer a good option for some other light sources, such as low-cost LED or ELED (edge emitting LED), with wider spectral bandwidths. Full article

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2021

Jump to: 2024, 2023, 2022, 2020, 2019

19 pages, 6277 KiB

Open AccessArticle

Assessment the Visual Clarity of the Projector in Classroom and Innovative Asymmetric Distribution LED Tube Applications

by Chun-Hsi Liu, Chun-Yu Hsiao, Jyh-Cherng Gu, Kuan-Yi Liu, Chih-Hung Chang, Chen-En Lee and Shu-Fen Yan

Appl. Sci. 2021, 11(23), 11153; https://doi.org/10.3390/app112311153 - 24 Nov 2021

Cited by 2 | Viewed by 3020

Abstract

The paper aims to explore the relationship between the vertical plane luminance on projection screens and human visual clarity in the classroom or meeting room. While controlling the lighting environment conditions of the classroom to create different luminous distributions and luminance on the [...] Read more.

The paper aims to explore the relationship between the vertical plane luminance on projection screens and human visual clarity in the classroom or meeting room. While controlling the lighting environment conditions of the classroom to create different luminous distributions and luminance on the projection screen, a survey is conducted to understand students’ visual experience about screen clarity during the field experiment. The luminance of each picture on the projection screen is measured under the specified lighting conditions of luminaires in the classroom, and the relationship is formulated between the average luminance on the projection screen and the visual satisfaction based on clarity of experience. This will be useful for further studying the acceptable threshold of luminance distribution in the classroom to provide a better visual clarity and lighting quality of projection screens while teaching. In this study, the measurement and performance evaluation on a projection screen were carried out at a classroom in the National Taiwan University of Science and Technology (NTUST). By using an image luminance meter and analyzing the research results, we propose an improvement strategy for asymmetric luminous distribution design of LED light tube and light switch control mechanism of luminaires to resolve the inadequate luminance of the vertical projection screen area to improve the lighting quality and visual clarity of the projection screen while teaching with the least cost. Full article

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11 pages, 5074 KiB

Open AccessArticle

Training and Inference of Optical Neural Networks with Noise and Low-Bits Control

by Danni Zhang, Yejin Zhang, Ye Zhang, Yanmei Su, Junkai Yi, Pengfei Wang, Ruiting Wang, Guangzhen Luo, Xuliang Zhou and Jiaoqing Pan

Appl. Sci. 2021, 11(8), 3692; https://doi.org/10.3390/app11083692 - 20 Apr 2021

Cited by 5 | Viewed by 2716

Abstract

Optical neural networks (ONNs) are getting more and more attention due to their advantages such as high-speed and low power consumption. However, in a non-ideal environment, the noise and low-bits control may heavily lead to a decrease in the accuracy of ONNs. Since [...] Read more.

Optical neural networks (ONNs) are getting more and more attention due to their advantages such as high-speed and low power consumption. However, in a non-ideal environment, the noise and low-bits control may heavily lead to a decrease in the accuracy of ONNs. Since there is AD/DA conversion in a simulated neural network, it needs to be quantified in the model. In this paper, we propose a quantitative method to adapt ONN to a non-ideal environment with fixed-point transmission, based on the new chip structure we designed previously. An MNIST hand-written data set was used to test and simulate the model we established. The experimental results showed that the quantization-noise model we established has a good performance, for which the accuracy was up to about 96%. Compared with the electrical method, the proposed quantization method can effectively solve the non-ideal ONN problem. Full article

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12 pages, 6023 KiB

Open AccessArticle

Two-Dimensional Digital Beam Steering Based on Liquid Crystal Phase Gratings

by Mario García de Blas, Morten Andreas Geday, Jose Manuel Otón and Xabier Quintana Arregui

Appl. Sci. 2021, 11(8), 3632; https://doi.org/10.3390/app11083632 - 17 Apr 2021

Cited by 9 | Viewed by 3739

Abstract

Electrically tunable phase gratings are able to steer an incoming light beam without employing movable parts. Here, we present the design and implementation of a 2D beam steering device by cascading two orthogonal 1D liquid crystal (LC) based phase gratings, each having an [...] Read more.

Electrically tunable phase gratings are able to steer an incoming light beam without employing movable parts. Here, we present the design and implementation of a 2D beam steering device by cascading two orthogonal 1D liquid crystal (LC) based phase gratings, each having an array of 72 rectangular individually controlled pixels and driven by a custom 12-bit Pulse-Width Modulation (PWM) electrical driver. High-resolution structures in glass wafers coated with transparent Indium-Tin Oxide (ITO) have been prepared using Direct Laser Writing (DLW) techniques. With DLW, a high number of pixels can easily be drawn with an interpixel space of less than 3 μm, leading to devices with a high fill factor. The active area of the cascaded device is 1.1 × 1.1 mm². We present a 72 × 72 point efficiency map corresponding to a maximum diagonal steering angle of 1.65°. Special attention has been paid to make the device compatible with space application by avoiding electronics in the active area. Full article

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11 pages, 5224 KiB

Open AccessArticle

Design of a Cell Phone Lens-Based Miniature Microscope with Configurable Magnification Ratio

by Xinjun Wan and Xuechen Tao

Appl. Sci. 2021, 11(8), 3392; https://doi.org/10.3390/app11083392 - 9 Apr 2021

Cited by 9 | Viewed by 5987

Abstract

Application of cell-phone-based microscopes has been hindered by limitations such as inferior image quality, fixed magnification and inconvenient operation. In this paper, we propose a reverse cell phone lens-based miniature microscope with a configurable magnification ratio. By switching the objectives of three camera [...] Read more.

Application of cell-phone-based microscopes has been hindered by limitations such as inferior image quality, fixed magnification and inconvenient operation. In this paper, we propose a reverse cell phone lens-based miniature microscope with a configurable magnification ratio. By switching the objectives of three camera lens and applying the digital zooming function of the cell phone, a cell phone microscope is built with the continuously configurable magnification ratio between 0.8×–11.5×. At the same time, the miniature microscope can capture high-quality microscopic images with a maximum resolution of up to 575 lp/mm and a maximum field of view (FOV) of up to 7213 × 5443 μm. Furthermore, by moving the tube lens module of the microscope out of the cell phone body, the built miniature microscope is as compact as a <20 mm side length cube, improving operational experience profoundly. The proposed scheme marks a big step forward in terms of the imaging performance and user operational convenience for cell phone microscopes. Full article

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14 pages, 3772 KiB

Open AccessArticle

Improvement for Convolutional Neural Networks in Image Classification Using Long Skip Connection

by Hong Hai Hoang and Hoang Hieu Trinh

Appl. Sci. 2021, 11(5), 2092; https://doi.org/10.3390/app11052092 - 26 Feb 2021

Cited by 11 | Viewed by 3702

Abstract

In this paper, we examine and research the effect of long skip connection on convolutional neural networks (CNNs) for the tasks of image (surface defect) classification. The standard popular models only apply short skip connection inside blocks (layers with the same size). We [...] Read more.

In this paper, we examine and research the effect of long skip connection on convolutional neural networks (CNNs) for the tasks of image (surface defect) classification. The standard popular models only apply short skip connection inside blocks (layers with the same size). We apply the long version of residual connection on several proposed models, which aims to reuse the lost spatial knowledge from the layers close to input. For some models, Depthwise Separable Convolution is used rather than traditional convolution in order to reduce both count of parameters and floating-point operations per second (FLOPs). Comparative experiments of the newly upgraded models and some popular models have been carried out on different datasets including Bamboo strips datasets and a reduced version of ImageNet. The modified version of DenseNet 121 (we call MDenseNet 121) achieves higher validation accuracy while it has about 75% of weights and FLOPs in comparison to the original DenseNet 121. Full article

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12 pages, 3860 KiB

Open AccessArticle

Fabrication and Optical Characterization of Polymeric Aspherical Microlens Array Using Hot Embossing Technology

by Yanlong Li, Kangsen Li and Feng Gong

Appl. Sci. 2021, 11(2), 882; https://doi.org/10.3390/app11020882 - 19 Jan 2021

Cited by 15 | Viewed by 4662

Abstract

Hot embossing has been widely used in fabricating microlens arrays because of its low cost, high efficiency, and high quality. The process parameters such as molding temperature, molding pressure, and holding temperature affect the microlens array’s replication quality. This work selected the stainless [...] Read more.

Hot embossing has been widely used in fabricating microlens arrays because of its low cost, high efficiency, and high quality. The process parameters such as molding temperature, molding pressure, and holding temperature affect the microlens array’s replication quality. This work selected the stainless steel S136H tool steel as the mold material to process an aspheric microlens array structure through ultra-precision milling. Polymethyl methacrylate (PMMA) microlens arrays with different surface replication were prepared by controlling the molding temperature, molding pressure, and holding temperature. By analyzing the surface quality, contour replication, and optical imaging of hot-embossed samples, the optimal molding temperature of PMMA for optimal replication of aspheric lens arrays was determined as 130 °C. Besides, the internal elastic recovery of PMMA affected the dimensional accuracy and optical performance of the lens. The results showed that, at the molding pressure of 400 N and the holding temperature of 60 °C, the surface defects were eliminated, and the aspheric lens array had perfect replication with a profile deviation of only 4 μm. The aspheric microlens array with good quality was eventually achieved by these optimal process parameters, which provides a foundation for producing aspheric microlens arrays in a low-cost and high-efficiency way. Full article

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2020

Jump to: 2024, 2023, 2022, 2021, 2019

11 pages, 1873 KiB

Open AccessArticle

Model-Based Design and Simulation of Paraxial Ray Optics Systems

by Eric Fujiwara and Cristiano M. B. Cordeiro

Appl. Sci. 2020, 10(22), 8278; https://doi.org/10.3390/app10228278 - 22 Nov 2020

Cited by 3 | Viewed by 3875

Abstract

A model-based design allows representing complex, multi-domain systems as interconnected functional blocks, yielding graphical, intuitive information about the overall project, besides simplifying simulation. This work proposes using the modular approach as an optical engineering design and educational tool for developing paraxial ray optics [...] Read more.

A model-based design allows representing complex, multi-domain systems as interconnected functional blocks, yielding graphical, intuitive information about the overall project, besides simplifying simulation. This work proposes using the modular approach as an optical engineering design and educational tool for developing paraxial ray optics setups, providing further integration with mechatronics subsystems and control loops. An expanded version of the ABCD transfer matrix modeling is implemented in MATLAB Simulink environment to simultaneously perform ray tracing and dynamic simulations. The methodology is validated for different problems, including paraxial cloaking, transmission through a multimode optical fiber, a Fabry–Perot interferometer, and an optical pickup with automatic focus, yielding reliable results with prospective applications in optical engineering design and for creating virtual labs devoted to multiphysics and mechatronics engineering courses. Full article

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13 pages, 24841 KiB

Open AccessArticle

Optimization Design of the Spaceborne Connecting Structure for a Lightweight Space Camera

by Mengqi Shao, Lei Zhang and Xuezhi Jia

Appl. Sci. 2020, 10(22), 8249; https://doi.org/10.3390/app10228249 - 20 Nov 2020

Cited by 2 | Viewed by 2183

Abstract

For a lightweight space camera installed vertically with a satellite platform, due to the different conditions between ground and orbit, the relative deformation between the camera and the satellite platform results in a drift of the camera line of sight (LOS), which affects [...] Read more.

For a lightweight space camera installed vertically with a satellite platform, due to the different conditions between ground and orbit, the relative deformation between the camera and the satellite platform results in a drift of the camera line of sight (LOS), which affects the imaging quality. This paper proposed an optimization method for the spaceborne connecting structure considering the camera LOS drift. By using a variable density topology optimization method, the configuration of the connecting structure was obtained. Based on the configuration, the sensitivity of its size parameters to the system’s performance was analyzed. Analysis data showed that the size parameters have an obvious influence on the camera LOS shift. In order to obtain the optimal combination of size parameters, a multi-objective parametric optimization model was established. Finally, engineering analysis of the optimized structure showed that the system performances meet the design requirements of the satellite, and the lightweight ratio of the connecting structure reaches 54%. This study provides a reference for the design of other similar structures for space cameras. Full article

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10 pages, 3576 KiB

Open AccessArticle

Tunable non-Hermiticity in Coupled Photonic Crystal Cavities with Asymmetric Optical Gain

by Kyoung-Ho Kim, Muhammad Sujak, Evan S. H. Kang and You-Shin No

Appl. Sci. 2020, 10(22), 8074; https://doi.org/10.3390/app10228074 - 14 Nov 2020

Cited by 1 | Viewed by 2331

Abstract

We report a rationally designed coupled photonic crystal (PhC) cavity system that comprises two identical linear defect nanocavities, and we numerically investigate the controllable non-Hermitian optical properties of the eigenmodes of the nanocavities. Three different coupling schemes, namely, the tuning of the sizes [...] Read more.

We report a rationally designed coupled photonic crystal (PhC) cavity system that comprises two identical linear defect nanocavities, and we numerically investigate the controllable non-Hermitian optical properties of the eigenmodes of the nanocavities. Three different coupling schemes, namely, the tuning of the sizes of shared airholes, vertical shifting of one of the nanocavities, and lateral shifting of one of the nanocavities, are proposed. We examined the ability of these schemes to control the coupling strength between component cavities, which is a key factor that determines the non-Hermiticity of the system. Moreover, we introduce controlled levels of spatially asymmetric optical gain to the coupled PhC cavity by employing the vertical shifting scheme and independently tuning the gain and loss of individual nanocavities. Consequently, we successfully achieve the correspondingly tuned non-Hermitian behaviors of complex eigenfrequencies, such as the controlled emergence of phase transitions at exceptional points and the asymmetric development of amplified and decayed eigenmodes. Full article

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15 pages, 3356 KiB

Open AccessArticle

Thermo-Optic Numerical Research on Segmented Circular LD Arrays Side-Pumping a Nd:YAG Laser Rod

by Wei Wang, Qin Zhao, Wenqing Gao, Zhenyue Hu, Qihang Zhao and Sen Yang

Appl. Sci. 2020, 10(20), 7316; https://doi.org/10.3390/app10207316 - 19 Oct 2020

Cited by 2 | Viewed by 2516

Abstract

The configuration designs of the laser diode (LD) side-pumping laser rods focus on how to solve the space conflict between the pump and heat-removal devices because both want to use the larger lateral surface of the laser rod. The conflict is better balanced [...] Read more.

The configuration designs of the laser diode (LD) side-pumping laser rods focus on how to solve the space conflict between the pump and heat-removal devices because both want to use the larger lateral surface of the laser rod. The conflict is better balanced in the three different side-pumping geometries: the segmented circular LD array side-pumping configuration, the annular liquid-cooling structure, and the compensated semicircular LD array side-pumping arrangement. The temperature distributions and thermo-optic effects of the laser rod in the segmented circular LD array side-pumping configuration are analyzed in contrast with those in the other arrangements. The numerical results indicate that the periodical segment-pumping scheme provides higher beam quality than the compensated semicircular side-pumping scheme, enabling removal of the complex liquid cooling system in medium-power applications, thus showing the potential to be used in compact and miniature laser systems. Full article

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10 pages, 3833 KiB

Open AccessArticle

Verification of an Accommodative Response for Depth Measurement of Floating Hologram Using a Holographic Optical Element

by Leehwan Hwang, Sungjae Ha, Philippe Gentet, Jaehyun Lee, Soonchul Kwon and Seunghyun Lee

Appl. Sci. 2020, 10(19), 6788; https://doi.org/10.3390/app10196788 - 28 Sep 2020

Cited by 3 | Viewed by 2998

Abstract

Floating holograms using holographic optical element screens differ from existing systems because they can float 2D images in the air and provide a sense of depth. Until now, the verification of such displays has been conducted only on the system implementation, and only [...] Read more.

Floating holograms using holographic optical element screens differ from existing systems because they can float 2D images in the air and provide a sense of depth. Until now, the verification of such displays has been conducted only on the system implementation, and only the diffraction efficiency and angle of view of the hologram have been verified. Although such displays can be directly observed with the human eye, the eye’s control ability has not been quantitatively verified. In this study, we verified that the focus of the observer coincided with the appropriate depth value determined with experiments. This was achieved by measuring the amount of control reaction from the perspective of the observer on the image of the floating hologram using a holographic optical element (HOE). An autorefractor was used, and we confirmed that an image with a sense of depth can be observed from the interaction of the observer’s focus and convergence on the 2D floating image using a HOE. Thus, the realization of content with a sense of depth of 2D projected images using a HOE in terms of human factors was quantitatively verified. Full article

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25 pages, 12152 KiB

Open AccessArticle

Automatic Shadow Detection for Multispectral Satellite Remote Sensing Images in Invariant Color Spaces

by Hongyin Han, Chengshan Han, Taiji Lan, Liang Huang, Changhong Hu and Xucheng Xue

Appl. Sci. 2020, 10(18), 6467; https://doi.org/10.3390/app10186467 - 17 Sep 2020

Cited by 18 | Viewed by 3470

Abstract

Shadow often results in difficulties for subsequent image applications of multispectral satellite remote sensing images, like object recognition and change detection. With continuous improvement in both spatial and spectral resolutions of satellite remote sensing images, a more serious impact occurs on satellite remote [...] Read more.

Shadow often results in difficulties for subsequent image applications of multispectral satellite remote sensing images, like object recognition and change detection. With continuous improvement in both spatial and spectral resolutions of satellite remote sensing images, a more serious impact occurs on satellite remote sensing image interpretation due to the existence of shadow. Though various shadow detection methods have been developed, problems of both shadow omission and nonshadow misclassification still exist for detecting shadow well in high-resolution multispectral satellite remote sensing images. These shadow detection problems mainly include high small shadow omission and typical nonshadow misclassification (like bluish and greenish nonshadow misclassification, and large dark nonshadow misclassification). For further resolving these problems, a new shadow index is developed based on the analysis of the property difference between shadow and the corresponding nonshadow with several multispectral band components (i.e., near-infrared, red, green and blue components) and hue and intensity components in various invariant color spaces (i.e., HIS, HSV, CIELCh, YCbCr and YIQ), respectively. The shadow mask is further acquired by applying an optimal threshold determined automatically on the shadow index image. The final shadow image is further optimized with a definite morphological operation of opening and closing. The proposed algorithm is verified with many images from WorldView-3 and WorldView-2 acquired at different times and sites. The proposed algorithm performance is particularly evaluated by qualitative visual sense comparison and quantitative assessment of shadow detection results in comparative experiments with two WorldView-3 test images of Tripoli, Libya. Both the better visual sense and the higher overall accuracy (over 92% for the test image Tripoli-1 and approximately 91% for the test image Tripoli-2) of the experimental results together deliver the excellent performance and robustness of the proposed shadow detection approach for shadow detection of high-resolution multispectral satellite remote sensing images. The proposed shadow detection approach is promised to further alleviate typical shadow detection problems of high small shadow omission and typical nonshadow misclassification for high-resolution multispectral satellite remote sensing images. Full article

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17 pages, 8061 KiB

Open AccessArticle

A Design for a Manufacturing-Constrained Off-Axis Four-Mirror Reflective System

by Ruoxin Liu, Zexiao Li, Yiting Duan and Fengzhou Fang

Appl. Sci. 2020, 10(15), 5387; https://doi.org/10.3390/app10155387 - 4 Aug 2020

Cited by 5 | Viewed by 3811

Abstract

Off-axis reflective optical systems find wide applications in various industries, but the related manufacturing issues have not been well considered in the design process. This paper proposed a design method for cylindrical reflective systems considering manufacturing constraints to facilitate ultra-precision raster milling. An [...] Read more.

Off-axis reflective optical systems find wide applications in various industries, but the related manufacturing issues have not been well considered in the design process. This paper proposed a design method for cylindrical reflective systems considering manufacturing constraints to facilitate ultra-precision raster milling. An appropriate index to evaluate manufacturing constraints is established. The optimization solution is implemented for the objective function composed of primary aberration coefficients with weights and constraint conditions of the structural configuration by introducing the genetic algorithm. The four-mirror initial structure with a good imaging quality and a special structural configuration is then obtained. The method’s feasibility is validated by designing an off-axis four-mirror afocal system with an entrance pupil diameter of 170 mm, a field of view of 3° × 3° and a compression ratio of five times. All mirrors in the system are designed to be distributed along a cylinder. Full article

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10 pages, 2532 KiB

Open AccessArticle

Modulation and Control Technology for Generating Movable Super-Diffraction Optical Needle by Oblique Incidence

by Simo Wang, Siyang Yu, Fanxing Li, Fuping Peng, Jialin Du, Bo Qi, Lifang Shi and Wei Yan

Appl. Sci. 2020, 10(15), 5237; https://doi.org/10.3390/app10155237 - 29 Jul 2020

Cited by 3 | Viewed by 2358

Abstract

The movable super-diffraction optical needle (MSON) is a tightly focused beam like a “needle”, which can realize vector scanning on the focusing plane. Not only does it have a long focal depth, but its resolution also exceeds the diffraction limit. The modulation and [...] Read more.

The movable super-diffraction optical needle (MSON) is a tightly focused beam like a “needle”, which can realize vector scanning on the focusing plane. Not only does it have a long focal depth, but its resolution also exceeds the diffraction limit. The modulation and control technology required for generating MSON by oblique incidence is explored in this manuscript for the purpose of processing high-aspect-ratio, sub-wavelength structures. As the optical needle generated by traditional methods is static and sensitive to variation of the angle information of the incident beam, here we introduce a confocal scanning system by using a two-dimensional galvanometer system, a scan lens, and a tube lens to control the oblique incidence angle. The effects of the oblique incidence angle on the resolution, depth of focus, uniformity, and side lobes of the MSON were analyzed. Further, the voltage-controlled liquid crystal located between the scan lens and the 2D galvanometer system can be used to compensate for the additional phase difference caused by oblique incidence. The aspect ratio is defined as the ratio of depth of focus to resolution. By modulating and controlling the light field, the MSON with high aspect ratio (7.36), sub-diffractive beam size (0.42λ), and long depth of focus (3.09λ) has been obtained with homogeneous intensity, and suppressed side lobes. High speed, high axial positioning tolerance, and high-resolution laser processing can also be achieved, which removes the restrictions presented by traditional laser processing technology, for which high resolution and long depth of focus cannot be achieved simultaneously. Full article

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8 pages, 6068 KiB

Open AccessArticle

High-Power Broadband Frequency Chirped Intensity-Modulated Single-Frequency 1064-nm Laser

by Kun Li, Suhui Yang, Xin Wang and Zhuo Li

Appl. Sci. 2020, 10(13), 4450; https://doi.org/10.3390/app10134450 - 28 Jun 2020

Cited by 2 | Viewed by 2940

Abstract

Optical carried microwave radar (OCMR), combining the advantages of lidar and microwave radar, uses an intensity-modulated laser beam as the medium to detect the distance and velocity of objects. In order to achieve a high ranging resolution at long distance, a high-power frequency [...] Read more.

Optical carried microwave radar (OCMR), combining the advantages of lidar and microwave radar, uses an intensity-modulated laser beam as the medium to detect the distance and velocity of objects. In order to achieve a high ranging resolution at long distance, a high-power frequency chirped intensity-modulated light source at a 1064-nm wavelength was developed. A low-power narrow-linewidth 1064-nm laser beam was input to a Mach-Zehnder electro-optic modulator (EOM), and the frequency of the EOM was tuned from 10 MHz to 2.1 GHz. The output from the EOM was coupled to a laser-diode-pumped ytterbium-doped fiber amplifier (YDFA). A maximum output power of 29.5 W was achieved from the YDFA. We measured the frequency characteristics of the modulated laser beams before and after amplification, respectively. The amplification process did not bring any obvious degeneration of the modulation in terms of the bandwidth, frequency stability, chirping linearity, and modulation depth. Our research presents a new approach of obtaining a high-power broad-band intensity-modulated light source for OCMR. Full article

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13 pages, 6970 KiB

Open AccessArticle

Design and Evaluation of Uniform LED Illumination Based on Double Linear Fresnel Lenses

by Hoang Vu, Ngoc Minh Kieu, Do Thi Gam, Seoyong Shin, Tran Quoc Tien and Ngoc Hai Vu

Appl. Sci. 2020, 10(9), 3257; https://doi.org/10.3390/app10093257 - 7 May 2020

Cited by 11 | Viewed by 9143

Abstract

Redistribution of LED radiation in lighting is necessary in many applications. In this article, we propose a new optical component design for LED lighting to achieve a higher performance. The design consists of a commercial collimator and two linear Fresnel lenses. The LED [...] Read more.

Redistribution of LED radiation in lighting is necessary in many applications. In this article, we propose a new optical component design for LED lighting to achieve a higher performance. The design consists of a commercial collimator and two linear Fresnel lenses. The LED radiation is collimated by a collimator and redistributed by double linear Fresnel lenses to create a square-shaped, uniform distribution. The linear Fresnel lenses design is based on Snell’s law and the “edge-ray principle”. The optical devices are made from poly methyl methacrylate (PMMA) using a high-speed computer numerical control (CNC) machine. The LED prototypes with complementary optics were measured, and the optical intensity distribution was evaluated. The numerical results showed we obtained a free-form lens that produced an illumination uniformity of 78% with an efficiency of 77%. We used the developed LED light sources for field experiments in agricultural lighting. The figures of these tests showed positive effects with control flowering criteria and advantages of harvested products in comparison with the conventional LED sources. This allows our approach in this paper to be considered as an alternative candidate for highly efficient and energy-saving LED lighting applications. Full article

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11 pages, 3722 KiB

Open AccessArticle

A Displacement Measuring Interferometer Based on a Frequency-Locked Laser Diode with High Modulation Frequency

by Thanh Tung Vu, Hong Hai Hoang, Toan Thang Vu and Ngoc Tam Bui

Appl. Sci. 2020, 10(8), 2693; https://doi.org/10.3390/app10082693 - 13 Apr 2020

Cited by 4 | Viewed by 4169

Abstract

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, [...] Read more.

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I₂ hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I₂ hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I₂ absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I₂ hyperfine transition at a high modulation frequency. Full article

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12 pages, 4536 KiB

Open AccessArticle

Optical Design of a Miniaturized Airborne Push-Broom Spectrometer

by Yang Wang, Zhiyuan Gu, Xiangyue Meng, Lei Zhang and Yuegang Fu

Appl. Sci. 2020, 10(7), 2627; https://doi.org/10.3390/app10072627 - 10 Apr 2020

Cited by 6 | Viewed by 3565

Abstract

Combining the requirements of spectrometers for unmanned aerial vehicle platforms, a miniaturized airborne wide-angle push-broom imaging spectrometer with an Offner configuration is designed. The system comprises an objective lens and an Offner-type spectrometer with a spectral range of 400~1000 nm and a spectral [...] Read more.

Combining the requirements of spectrometers for unmanned aerial vehicle platforms, a miniaturized airborne wide-angle push-broom imaging spectrometer with an Offner configuration is designed. The system comprises an objective lens and an Offner-type spectrometer with a spectral range of 400~1000 nm and a spectral resolution of 15 nm. The objective lens and Offner spectrometer are designed in isolation before integration. The front objective lens is an inverted telephoto with a focal length of 13 mm, a relative aperture of 1/4.5, and a field of view of 54°. The frequency of the convex grating in the Offner configuration is 102 LP/mm, and the dispersion width is 2.6 mm. The modulation transfer function of the integrated system is greater than 0.4 at the Nyquist frequency in all spectral bands. To estimate the volume and weight of the system, a preliminary optical–mechanical design scheme is given in this paper. The entire spectrometer has a volume of 130 × 80 × 120 mm and is less than 3 kg, which realizes the miniaturization design of the imaging spectrometer with a wide field of view for unmanned aerial vehicle platforms. Full article

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13 pages, 4150 KiB

Open AccessArticle

Microscope 3D Point Spread Function Evaluation Method on a Confirmed Object Plane Perpendicular to the Optical Axis

by Shuai Mao, Zhenzhou Wang and Jinfeng Pan

Appl. Sci. 2020, 10(7), 2430; https://doi.org/10.3390/app10072430 - 2 Apr 2020

Cited by 2 | Viewed by 3499

Abstract

A point spread function evaluation method for a microscope on the object plane that is perpendicular to the optical axis is proposed. The measurement of the incident beam direction from the dual position-sensitive-detector (PSD)-based units, the determination of the object plane perpendicularity and [...] Read more.

A point spread function evaluation method for a microscope on the object plane that is perpendicular to the optical axis is proposed. The measurement of the incident beam direction from the dual position-sensitive-detector (PSD)-based units, the determination of the object plane perpendicularity and the paraxial region, and evaluation methods for the point spread function (PSF) are presented and integrated into the proposed method. The experimental verification demonstrates that the proposed method can achieve a 3D PSF on the perpendicular object plane, as well as magnification, paraxial region evaluation, and confirmation for any microscopic system. Full article

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14 pages, 3239 KiB

Open AccessArticle

Non-Rotationally Symmetric Field Mapping for Back-Scanned Step/Stare Imaging System

by Qiang Fu, Xin Zhang, Jianping Zhang, Guangwei Shi, Shangnan Zhao and Mingxin Liu

Appl. Sci. 2020, 10(7), 2399; https://doi.org/10.3390/app10072399 - 1 Apr 2020

Cited by 4 | Viewed by 2479

Abstract

Step/stare imaging with focal plane arrays (FPAs) has become the main approach to achieve wide area coverage and high resolution imaging for long range targets. A fast steering mirror (FSM) is usually utilized to provide back-scanned motion to compensate for the image motion. [...] Read more.

Step/stare imaging with focal plane arrays (FPAs) has become the main approach to achieve wide area coverage and high resolution imaging for long range targets. A fast steering mirror (FSM) is usually utilized to provide back-scanned motion to compensate for the image motion. However, the traditional optical design can just hold one field point relatively stable, typically the central or on-axis field point, on the FPA during back-scanning; all other field points may wander during the exposure due to imaging distortion characteristics of the optical system, which reduces the signal to noise ratio (SNR) of the target. Aiming toward this problem, this paper proposes a non-rotationally symmetric field mapping method for the back-scanned step/stare imaging system, which can make all field points stable on the FPA during back-scanning. First of all, the mathematical model of non-rotationally symmetric field mapping between object space and image space is established. Then, a back-scanned step/stare imaging system based on the model is designed, in which this non-rotationally symmetric mapping can be implemented with an afocal telescope including freeform lenses. Freeform lenses can produce an anamorphic aberration to adjust distortion characteristics of the optical system to control image wander on an FPA. Furthermore, the simulations verify the effectiveness of the method. Full article

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23 pages, 6053 KiB

Open AccessArticle

A Method for the Installation Measurement and Alignment of a Mirror Unit in the Solar Dish Concentrator

by Jian Yan, Youduo Peng and Duzhong Nie

Appl. Sci. 2020, 10(4), 1511; https://doi.org/10.3390/app10041511 - 23 Feb 2020

Cited by 3 | Viewed by 2928

Abstract

The mirror unit installation error of the solar parabolic dish concentrator can adversely affect its optical performance causing optical intercept losses and hot spots on the absorber surface, which in turn affect safety. Thus, minimizing mirror installation error is considered very important. In [...] Read more.

The mirror unit installation error of the solar parabolic dish concentrator can adversely affect its optical performance causing optical intercept losses and hot spots on the absorber surface, which in turn affect safety. Thus, minimizing mirror installation error is considered very important. In this paper, a new method for the facet installation measurement and facet alignment of the mirror unit in the dish concentrator is presented. Firstly, a “clean” facet installation error measurement method using photogrammetry is presented. The photogrammetry measures the spatial coordinates of three feature points to reverse the mirror facet alignment error parameters. Next, two novel methods, a three-rotation alignment method and two-rotation alignment method for aligning the mirror facet are presented and corresponding mathematical models. The advantage of these alignment methods is that the adjustment value and order for each support bolt can be determined before the mirror facet is aligned, which could provide quantitative adjustment information to operator and avoid repeated adjustments. Finally, validity of the installation measurement and facet alignment method was verified by a numerical simulation and an experiment using a metal facet alignment. The presented methods do not rely on the geometry of the reflector mirror and could therefore have extensive uses in applications such solar tower and trough concentrator. Full article

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18 pages, 5834 KiB

Open AccessArticle

Side-Scan Sonar Image Fusion Based on Sum-Modified Laplacian Energy Filtering and Improved Dual-Channel Impulse Neural Network

by Ping Zhou, Gang Chen, Mingwei Wang, Xianglin Liu, Song Chen and Runzhi Sun

Appl. Sci. 2020, 10(3), 1028; https://doi.org/10.3390/app10031028 - 4 Feb 2020

Cited by 9 | Viewed by 2729

Abstract

The operation mode of a single strip provides incomplete side-scan sonar image in a specific environment and range, resulting in the overlapping area between adjacent strips often with imperfect detection information or inaccurate target contour. In this paper, a sum-modified Laplacian energy filtering [...] Read more.

The operation mode of a single strip provides incomplete side-scan sonar image in a specific environment and range, resulting in the overlapping area between adjacent strips often with imperfect detection information or inaccurate target contour. In this paper, a sum-modified Laplacian energy filtering (SMLF) and improved dual-channel pulse coupled neural network (IDPCNN) are proposed for image fusion of side-scan sonar in the domain of nonsubsampled contourlet transform (NSCT). Among them, SMLF energy is applied to extract the fusion coefficients of the low frequency sub-band, which combines the characteristics of energy information, human visual contrast, and guided filtering to eliminate the pseudo contour effect of block flow. In addition, the IDPCNN model, which utilizes the average gradient, soft limit function, and novel sum-modified Laplacian (NSML) to adaptively represent the corresponding excitation parameters, is applied to improve the depth and activity of pulse ignition, so as to quickly and accurately select the image coefficients of the high frequency sub-band. The experimental results show that the proposed method displays fine geomorphic information and clear target contour in the overlapping area of adjacent strips. The objective index values are generally optimal, which reflect the information of image edge, clarity, and overall similarity. Full article

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13 pages, 2227 KiB

Open AccessArticle

Calibration of Large-Scale Spatial Positioning Systems Based on Photoelectric Scanning Angle Measurements and Spatial Resection in Conjunction with an External Receiver Array

by Chunbao Xiong and Hongzhi Bai

Appl. Sci. 2020, 10(3), 925; https://doi.org/10.3390/app10030925 - 31 Jan 2020

Cited by 5 | Viewed by 3000

Abstract

Positioning systems providing high-precision real-time measurements over very large spatial scales are urgently required for large-scale industrial manufacturing applications. While large-scale positioning systems (LSPSs) employing laser transmitter stations have been employed in engineering practice, the introduction of an LSPS into an existing industrial [...] Read more.

Positioning systems providing high-precision real-time measurements over very large spatial scales are urgently required for large-scale industrial manufacturing applications. While large-scale positioning systems (LSPSs) employing laser transmitter stations have been employed in engineering practice, the introduction of an LSPS into an existing industrial manufacturing setting must first solve the problems of docking with existing control points and external parameter calibration. However, calibrating the external parameters of a measurement system is very difficult under extreme and complicated working conditions due to the limited visibility of transmitter stations and the measurement distances involved. This problem is addressed in this paper by proposing a single transmitter station calibration method based on a photoelectric scanning multi-angle resection positioning model that combines photoelectric scanning angle measurements and spatial resection in conjunction with an external receiver array. Positioning information is obtained by solving the unknown parameters of the model according to a nonlinear optimization approach using the Levenberg–Marquardt least-squares fitting algorithm. The feasibility and spatial positioning accuracy of the proposed method are verified experimentally. The experimental results demonstrate that the principles of the proposed method are correct, and the method can achieve millimeter measurement accuracy, which meets the requirements of measurement tasks in engineering applications. Full article

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2019

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15 pages, 5472 KiB

Open AccessArticle

Design of Wide Angle and Large Aperture Optical System with Inner Focus for Compact System Camera Applications

by Hojong Choi and Jaemyung Ryu

Appl. Sci. 2020, 10(1), 179; https://doi.org/10.3390/app10010179 - 25 Dec 2019

Cited by 16 | Viewed by 4575

Abstract

Conventionally, a bright, very wide-angle optical system is designed as a floating type optical system that moves two or more lens groups composed of multiple lens in order to focus accurately. These have been widely used as phase detection auto focus (AF) methods [...] Read more.

Conventionally, a bright, very wide-angle optical system is designed as a floating type optical system that moves two or more lens groups composed of multiple lens in order to focus accurately. These have been widely used as phase detection auto focus (AF) methods within conventional digital single-lens reflex (DSLR) cameras. However, a phase detection AF optical system cannot be used when recording motion pictures. In contrast, a compact system camera (CSC) performs AF by the contrast method, where a stepper motor is used as the driving source for moving the optical lens. Nonetheless, to ensure that the focusing lens is lighter, these stepper motors should not have high torque and AF must be possible by moving only one lens. Yet, when focusing is performed with only one lens, aberration change due to focusing lens movement is magnified. Therefore, a very wide-angle optical system comprised of a half-angle of view more than 40 degrees and F of 1/4 has not been developed. Here, a very wide-angle optical system was designed with high resolving power that enables high speed AF, even in contrast mode, by moving only one lens while minimizing aberration change. Full article

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13 pages, 3055 KiB

Open AccessArticle

A Three-Dimensional Tracking Method with the Self-Calibration Functions of Coaxiality and Magnification for Single Fluorescent Nanoparticles

by Shuai Mao, Jin Shen, Yajing Wang, Wei Liu and Jinfeng Pan

Appl. Sci. 2020, 10(1), 131; https://doi.org/10.3390/app10010131 - 23 Dec 2019

Viewed by 2570

Abstract

A self-calibrating variable magnification three-dimensional (3D) tracking system for single fluorescent nanoparticles is proposed. The system was based on astigmatic micro-imaging and has a simple configuration incorporating a dual-spot position detection unit ray transfer matrix. By analyzing this matrix and utilizing the beam [...] Read more.

A self-calibrating variable magnification three-dimensional (3D) tracking system for single fluorescent nanoparticles is proposed. The system was based on astigmatic micro-imaging and has a simple configuration incorporating a dual-spot position detection unit ray transfer matrix. By analyzing this matrix and utilizing the beam vector measurement of a dual-spot position detection unit, it was demonstrated that the proposed tracking system had the self-calibration functions of coaxiality and magnification; thus, it could accurately track the adopted fluorescent nanoparticles through zoom microscopical measurements in 3D. The available measurements of the proposed system and accuracy were experimentally validated. Full article

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13 pages, 3714 KiB

Open AccessArticle

Double-Sided Freeform Lens for Light Collimation of Light Emitting Diodes

by Yong-Sin Syu, Chun-Ying Wu and Yung-Chun Lee

Appl. Sci. 2019, 9(24), 5452; https://doi.org/10.3390/app9245452 - 12 Dec 2019

Cited by 8 | Viewed by 5229

Abstract

A double-sided freeform lens is proposed for collimating light emitted from light emitting diodes (LEDs). The surface profiles of the lens are mathematically characterized and precisely determined based on a point-source assumption and differential geometry theory. The proposed lens design method is straightforward, [...] Read more.

A double-sided freeform lens is proposed for collimating light emitted from light emitting diodes (LEDs). The surface profiles of the lens are mathematically characterized and precisely determined based on a point-source assumption and differential geometry theory. The proposed lens design method is straightforward, flexible, and effective. Moreover, the optical performance of the lens can be intuitively adjusted by tuning just a small number of design parameters. The simulation results showed that the proposed lens achieved an excellent collimating effect for a commercial ultraviolet (UV) LED. A prototype lens is fabricated in UV-grade poly(methyl methacrylate) material using a standard injection molding process. The light collimating effect of the lens/UV-LED assembly was measured experimentally and was shown to be in good agreement with the simulation results. The collimating angle at the half-energy level was equal to 1.88°. The performance of the UV-LED is thus comparable to that of conventional lithography UV light sources based on mercury arc lamps. Consequently, the proposed double freeform lens showed significant potential for photolithography applications within the industry. Full article

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15 pages, 2833 KiB

Open AccessArticle

Analysis of Dynamic Modulation Transfer Function for Complex Image Motion

by Lizhi Xu, Changxiang Yan, Zhiyuan Gu, Mengyang Li and Chenghao Li

Appl. Sci. 2019, 9(23), 5142; https://doi.org/10.3390/app9235142 - 27 Nov 2019

Cited by 8 | Viewed by 3896

Abstract

In remote-sensing imaging, the modulation transfer function (MTF) for image motion relevant to the mixing of multiple forms of motions is hard to calculate because of the complicated image motion expression. In this paper, a new method for calculating the MTF for complex [...] Read more.

In remote-sensing imaging, the modulation transfer function (MTF) for image motion relevant to the mixing of multiple forms of motions is hard to calculate because of the complicated image motion expression. In this paper, a new method for calculating the MTF for complex image motion is proposed. The presented method makes it possible to obtain an analytical MTF expression derived from the mixing of linear motion and sinusoidal motion at an arbitrary frequency. On this basis, we used the summation of infinitely many terms involving the Bessel function to simplify the MTF expression. The truncation error obtained by the use of finite order sum approximations instead of infinite sums is investigated in detail. In order to verify the MTF calculation method, we proposed a simulation method to calculate the variation of MTF in an actual optical system caused by image motion. The mean value of the relative error between the calculation method and the simulation method is less than 5%. The experimental results are consistent with the MTF curve calculated by our method. Full article

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9 pages, 6611 KiB

Open AccessArticle

Silica-Based Sol-Gel Coating with High Transmission at 1053 and 527 nm and Absorption at 351 nm for Frequency-Converting Crystals in High-Power Laser System

by Xue-Ran Deng, Wei Yang, Hao-Hao Hui, Qing-Hua Zhang, Qiao Xu, Jin-Ju Chen, Ji-Liang Zhu and Xiang-Yang Lei

Appl. Sci. 2019, 9(23), 5038; https://doi.org/10.3390/app9235038 - 22 Nov 2019

Cited by 4 | Viewed by 2487

Abstract

A high-power laser system is employed to drive the fusion ignition to realize sustainable supply of green energy according to the inertial confinement fusion theory, in which frequency-converting crystals are sealed in the terminal vacuum chamber and utilized to turn the incident laser [...] Read more.

A high-power laser system is employed to drive the fusion ignition to realize sustainable supply of green energy according to the inertial confinement fusion theory, in which frequency-converting crystals are sealed in the terminal vacuum chamber and utilized to turn the incident laser (1053 nm) to the desired one (351 nm). However, the reflected 351 nm laser from the pellet hohlraum that goes back through the frequency-converting crystal is found to be harmful for the upstream elements that are located before the terminal chamber. In this study, a specialized coating system for the frequency-converting crystals was designed and fabricated to both ensure high output power for the fusion and reduce the reflected 351 nm laser energy by absorption. Furthermore, the structural, mechanical, and laser-damage resistant properties of this coating were investigated as well. Full article

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7 pages, 2246 KiB

Open AccessArticle

Self-Injection Locking of a Distributed Feedback Laser Diode Using a High-Finesse Fabry-Perot Microcavity

by Xing Wei, ZhenDa Xie and Shi-Ning Zhu

Appl. Sci. 2019, 9(21), 4616; https://doi.org/10.3390/app9214616 - 30 Oct 2019

Cited by 8 | Viewed by 3923

Abstract

Optical microcavities have been widely used in nonlinear optics, quantum optics, and laser technologies. Here we demonstrate the self-injection locking of a distributed feedback diode laser using home-made high-finesse Fabry-Perot microcavity. The Fabry-Perot microcavity is fabricated from an x-cut lithium niobate crystal with [...] Read more.

Optical microcavities have been widely used in nonlinear optics, quantum optics, and laser technologies. Here we demonstrate the self-injection locking of a distributed feedback diode laser using home-made high-finesse Fabry-Perot microcavity. The Fabry-Perot microcavity is fabricated from an x-cut lithium niobate crystal with highly reflective coatings. Frequency pulling effect can be observed for a successful locking, and results in a single-longitudinal mode lasing with narrow linewidth. The lasing wavelength and output power are found robust to the laser-diode current and temperature variations, in comparison to the free-running case. We further characterize the laser linewidth with beat note measurement with a high-performance external cavity diode laser, with beat-note linewidth of 601.85 kHz. This results shows a new method for laser frequency stabilization in a simple setup, and may find applications in telecommunication and spectroscopy. Full article

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14 pages, 7329 KiB

Open AccessArticle

Optical Design of an LED Lighting Source for Fluorescence Microscopes

by Tai-Chih Kuo, Ting-Jou Ding, Jui-Hui Lin and Shih-Hsin Ma

Appl. Sci. 2019, 9(21), 4574; https://doi.org/10.3390/app9214574 - 28 Oct 2019

Cited by 7 | Viewed by 6040

Abstract

In this study, we reveal an LED light source model applied in fluorescence microscopes. This optical model is composed of a confocal total internal reflection lens array system (CTLAS) with a nine-LED array. The CTLAS optical system that we designed consists of a [...] Read more.

In this study, we reveal an LED light source model applied in fluorescence microscopes. This optical model is composed of a confocal total internal reflection lens array system (CTLAS) with a nine-LED array. The CTLAS optical system that we designed consists of a total internal reflection (TIR) lens array and a confocal system. The electrical power of the nine-LED array is 7.9 watts, which is lower than traditional light sources, such as the original 120-watt halogen lamps used in fluorescence microscopes (Zeiss, Axio Imager 2). We have successfully applied the CTLAS system to an Axio Imager 2 fluorescence microscope to observe the vascular bundle organization, modified with Cy3 fluorescence molecules, and have found that in the process of system assembly, the fabrication errors of optical lenses could have a critical effect on the CTLAS system. The results of our experiment show that, in order to achieve the same illuminance as that of the halogen lamp, the displacement error tolerances of the lateral x-axis and the longitudinal z-axis must be controlled within 1.3 mm and 1.7 mm, respectively. Full article

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18 pages, 7005 KiB

Open AccessArticle

Imaging Correlography Using Ptychography

by Zhixin Li, Desheng Wen, Zongxi Song, Tuochi Jiang, Weikang Zhang, Gang Liu and Xin Wei

Appl. Sci. 2019, 9(20), 4377; https://doi.org/10.3390/app9204377 - 16 Oct 2019

Cited by 7 | Viewed by 3737

Abstract

Imaging correlography, an effective method for long-distance imaging, recovers an object using only the knowledge of the Fourier modulus, without needing phase information. It is not sensitive to atmospheric turbulence or optical imperfections. However, the unreliability of traditional phase retrieval algorithms in imaging [...] Read more.

Imaging correlography, an effective method for long-distance imaging, recovers an object using only the knowledge of the Fourier modulus, without needing phase information. It is not sensitive to atmospheric turbulence or optical imperfections. However, the unreliability of traditional phase retrieval algorithms in imaging correlography has hindered their development. In this work, we join imaging correlography and ptychography together to overcome such obstacles. Instead of detecting the whole object, the object is measured part-by-part with a probe moving in a ptychographic way. A flexible optimization framework is proposed to reconstruct the object rapidly and reliably within a few iterations. In addition, novel image space denoising regularization is plugged into the loss function to reduce the effects of input noise and improve the perceptual quality of the recovered image. Experiments demonstrate that four-fold resolution gains are achievable for the proposed imaging method. We can obtain satisfactory results for both visual and quantitative metrics with one-sixth of the measurements in the conventional imaging correlography. Therefore, the proposed imaging technique is more suitable for long-range practical applications. Full article

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12 pages, 2663 KiB

Open AccessArticle

Research on Polarization and Phase Fading Compensation in Michelson Interferometer Based on 3 × 3 Coupler and Novel Probe with Built-in Faraday Rotator

by Shuaiqi Jing, Jian Rong and Jiayan Tian

Appl. Sci. 2019, 9(19), 4173; https://doi.org/10.3390/app9194173 - 5 Oct 2019

Cited by 2 | Viewed by 3344

Abstract

A self-designed probe and a feedback control scheme based on the Michelson interferometer with a 3 × 3 fiber coupler are proposed. A 45° Faraday rotator is built into the self-designed probe, and a feedback control scheme is used to judge the direction [...] Read more.

A self-designed probe and a feedback control scheme based on the Michelson interferometer with a 3 × 3 fiber coupler are proposed. A 45° Faraday rotator is built into the self-designed probe, and a feedback control scheme is used to judge the direction of increase or decrease for the phase compensation, so as to solve the problems of polarization and phase fading. In addition, a result-normalized method is applied in a micro-vibration measurement experiment. The experimental interferometer system achieves a high frequency of 1 MHz micro-vibration. The normalized results keep stable with a maximum deviation from the mean of 1.9% when the power of light reflected back into the self-designed probe is altered. Applied research is carried out by detecting the displacement due to a photoacoustic wave. Therefore, the experimental interferometer system is available for the practical application of micro-displacement measurements, noncontact high-frequency detection, and point-by-point image scanning in biological tissue. Full article

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9 pages, 2326 KiB

Open AccessArticle

Method to Remove Tilt-to-Length Coupling Caused by Interference of Flat-Top Beam and Gaussian Beam

by Ya Zhao, Zhi Wang, Yupeng Li, Chao Fang, Heshan Liu and Huilong Gao

Appl. Sci. 2019, 9(19), 4112; https://doi.org/10.3390/app9194112 - 1 Oct 2019

Cited by 11 | Viewed by 3824

Abstract

We discuss the tilt-to-length (TTL) coupling noise caused by interference between a flat-top beam and a Gaussian beam. Several physical models are presented to research the effects of non-diffracted and diffracted beams on TTL noise. A special case that can remove TTL coupling [...] Read more.

We discuss the tilt-to-length (TTL) coupling noise caused by interference between a flat-top beam and a Gaussian beam. Several physical models are presented to research the effects of non-diffracted and diffracted beams on TTL noise. A special case that can remove TTL coupling noise is discovered and is verified via both theoretical analysis and numerical simulations. The proposed case could provide desirable suggestions for the construction of high-precision interferometers such as the Laser Interferometer Space Antenna (LISA), Taiji program, or other interferometry systems. Full article

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