Research

11 pages, 2593 KiB

Open AccessArticle

Optical Design of a Novel Collimator System with a Variable Virtual-Object Distance for an Inspection Instrument of Mobile Phone Camera Optics

by Hojong Choi, Se-woon Choe and Jaemyung Ryu

Appl. Sci. 2021, 11(8), 3350; https://doi.org/10.3390/app11083350 - 08 Apr 2021

Cited by 7 | Viewed by 2466

Abstract

The resolution performance of mobile phone camera optics was previously checked only near an infinite point. However, near-field performance is required because of reduced camera pixel sizes. Traditional optics are measured using a resolution chart located at a hyperfocal distance, which can only [...] Read more.

The resolution performance of mobile phone camera optics was previously checked only near an infinite point. However, near-field performance is required because of reduced camera pixel sizes. Traditional optics are measured using a resolution chart located at a hyperfocal distance, which can only measure the resolution at a specific distance but not at close distances. We designed a new collimator system that can change the virtual image of the resolution chart from infinity to a short distance. Hence, some lenses inside the collimator systems must be moved. Currently, if the focusing lens is moved, chromatic aberration and field curvature occur. Additional lenses are required to correct this problem. However, the added lens must not change the characteristics of the proposed collimator. Therefore, an equivalent-lens conversion method was designed to maintain the first-order and Seidel aberrations. The collimator system proposed in this study does not move or change the resolution chart. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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13 pages, 4741 KiB

Open AccessArticle

Automatic Fabric Defect Detection Method Using PRAN-Net

by Peiran Peng, Ying Wang, Can Hao, Zhizhong Zhu, Tong Liu and Weihu Zhou

Appl. Sci. 2020, 10(23), 8434; https://doi.org/10.3390/app10238434 - 26 Nov 2020

Cited by 18 | Viewed by 3771

Abstract

Fabric defect detection is very important in the textile quality process. Current deep learning algorithms are not effective in detecting tiny and extreme aspect ratio fabric defects. In this paper, we proposed a strong detection method, Priori Anchor Convolutional Neural Network (PRAN-Net), for [...] Read more.

Fabric defect detection is very important in the textile quality process. Current deep learning algorithms are not effective in detecting tiny and extreme aspect ratio fabric defects. In this paper, we proposed a strong detection method, Priori Anchor Convolutional Neural Network (PRAN-Net), for fabric defect detection to improve the detection and location accuracy of fabric defects and decrease the inspection time. First, we used Feature Pyramid Network (FPN) by selected multi-scale feature maps to reserve more detailed information of tiny defects. Secondly, we proposed a trick to generate sparse priori anchors based on fabric defects ground truth boxes instead of fixed anchors to locate extreme defects more accurately and efficiently. Finally, a classification network is used to classify and refine the position of the fabric defects. The method was validated on two self-made fabric datasets. Experimental results indicate that our method significantly improved the accuracy and efficiency of detecting fabric defects and is more suitable to the automatic fabric defect detection. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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20 pages, 5971 KiB

Open AccessArticle

Process Parameter Optimization When Preparing Ti(C, N) Ceramic Coatings Using Laser Cladding Based on a Neural Network and Quantum-Behaved Particle Swarm Optimization Algorithm

by Zixin Deng, Tao Chen, Haojun Wang, Shengchen Li and Defu Liu

Appl. Sci. 2020, 10(18), 6331; https://doi.org/10.3390/app10186331 - 11 Sep 2020

Cited by 10 | Viewed by 2035

Abstract

The formation process of surface coatings fabricated with laser cladding is very complicated and coating quality is closely related to laser cladding process parameters. Generally, the optimization and control of process parameters play key roles when preparing high-quality ceramic coating. In this paper, [...] Read more.

The formation process of surface coatings fabricated with laser cladding is very complicated and coating quality is closely related to laser cladding process parameters. Generally, the optimization and control of process parameters play key roles when preparing high-quality ceramic coating. In this paper, three reasonable parameters were selected for each process parameter based on the preliminary experiment. The experiment of Ti(C, N) ceramic coating prepared with laser cladding was designed via the Taguchi method. The laser power, spot diameter, overlapping ratio, and scanning velocity were selected as the main process parameters, and their effects on coating micro-hardness were analyzed using the signal-to-noise (S/N) ratio and analysis of variance (ANOVA). Then, based on the back-propagation neural network (BPNN) and quantum-behaved particle swarm optimization (QPSO) algorithm, we created the prediction model of BPNN-QPSO neural network for laser cladding Ti(C, N) ceramic coating. The mapping of process parameters to the micro-hardness of the coating was obtained according to the model and we analyzed the influence of process parameters that interacted with the coating’s micro-hardness. The results showed that the interaction of laser cladding process parameters had a significant effect on the micro-hardness of the coating. The established BPNN-QPSO neural network model was able to map the relationship between laser cladding process parameters and coating micro-hardness. The process parameters optimized by this model had similar results with ANOVA. This research provides guidance for the selection and control of ceramic coating process parameters Ti(C, N) prepared via laser cladding. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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8 pages, 872 KiB

Open AccessArticle

Efficient Molecular Aggregation of Rhodamine 6G and Pseudoisocyanine by Light-Induced Force

by Masayuki Shirakawa, Takayoshi Kobayashi and Eiji Tokunaga

Appl. Sci. 2020, 10(10), 3563; https://doi.org/10.3390/app10103563 - 21 May 2020

Cited by 3 | Viewed by 2134

Abstract

A highly efficient light-induced aggregation of porphyrin molecules in solution was recently reported for 4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid (TPPS). Here, we demonstrate that rhodamine 6G (R6G) and pseudoisocyanine (PIC) also show efficient light-induced aggregation in unsaturated aqueous solution, being detected with a multichannel lock-in amplifier [...] Read more.

A highly efficient light-induced aggregation of porphyrin molecules in solution was recently reported for 4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid (TPPS). Here, we demonstrate that rhodamine 6G (R6G) and pseudoisocyanine (PIC) also show efficient light-induced aggregation in unsaturated aqueous solution, being detected with a multichannel lock-in amplifier as the absorbance decrease/increase in the monomers/aggregates, induced by a laser at 633 nm, which is non-resonant off their main monomer absorption wavelengths. The light-induced aggregation states are H-aggregates that are hardly formed in the thermal equilibrium. The similar absorbance changes are absent in the monomer molecules fixed in polyvinyl alcohol (PVA) films. The aggregation efficiency defined as

(Δ A / A) / (U_{t r a p} / k_{B} T)

, where

A

is the absorbance of the monomers,

Δ A

is the absorbance increase in the aggregates,

U_{t r a p}

is the optical gradient force potential, and

k_{B} T

is the thermal energy at room temperature, is approximately 100 for R6G and 500 for PIC, which are much smaller than that of TPPS. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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9 pages, 4215 KiB

Open AccessFeature PaperArticle

Unrepeatered 240-km 64-QAM Transmission Using Distributed Raman Amplification over SMF Fiber

by P. Rosa, G. Rizzelli, X. Pang, O. Ozolins, A. Udalcovs, M. Tan, M. Jaworski, M. Marciniak, S. Sergeyev, R. Schatz, G. Jacobsen, S. Popov and J. D. Ania-Castañón

Appl. Sci. 2020, 10(4), 1433; https://doi.org/10.3390/app10041433 - 20 Feb 2020

Cited by 6 | Viewed by 3727

Abstract

We present a theoretical and experimental investigation of unrepeatered transmission over standard single-mode fiber (SMF-28) using several schemes of distributed Raman amplification, including first, second, and dual order. In order to further extend the transmission distance, we utilize advanced bidirectional higher-order ultra-long Raman [...] Read more.

We present a theoretical and experimental investigation of unrepeatered transmission over standard single-mode fiber (SMF-28) using several schemes of distributed Raman amplification, including first, second, and dual order. In order to further extend the transmission distance, we utilize advanced bidirectional higher-order ultra-long Raman fiber laser-based amplification, where we use fiber Bragg gratings (FBGs) to reflect Stokes-shifted light from the secondary pumps. Our work demonstrates the possibility of transmission up to 240-km span length with a total span loss of 52.7 dB. Here, we use a 28-Gbaud signal using a 64-quadrature amplitude modulation (QAM) modulation format. Our results highlight the contribution of nonlinear compensation using digital back propagation in a digital signal processor (DSP) code at the receiver. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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11 pages, 775 KiB

Open AccessArticle

Deep Learning for Computational Mode Decomposition in Optical Fibers

by Stefan Rothe, Qian Zhang, Nektarios Koukourakis and Jürgen W. Czarske

Appl. Sci. 2020, 10(4), 1367; https://doi.org/10.3390/app10041367 - 18 Feb 2020

Cited by 17 | Viewed by 3875

Abstract

Multimode fibers are regarded as the key technology for the steady increase in data rates in optical communication. However, light propagation in multimode fibers is complex and can lead to distortions in the transmission of information. Therefore, strategies to control the propagation of [...] Read more.

Multimode fibers are regarded as the key technology for the steady increase in data rates in optical communication. However, light propagation in multimode fibers is complex and can lead to distortions in the transmission of information. Therefore, strategies to control the propagation of light should be developed. These strategies include the measurement of the amplitude and phase of the light field after propagation through the fiber. This is usually done with holographic approaches. In this paper, we discuss the use of a deep neural network to determine the amplitude and phase information from simple intensity-only camera images. A new type of training was developed, which is much more robust and precise than conventional training data designs. We show that the performance of the deep neural network is comparable to digital holography, but requires significantly smaller efforts. The fast characterization of multimode fibers is particularly suitable for high-performance applications like cyberphysical systems in the internet of things. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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9 pages, 1641 KiB

Open AccessFeature PaperArticle

Circular Dichroism in Low-Cost Plasmonics: 2D Arrays of Nanoholes in Silver

by Emilija Petronijevic, Alessandro Belardini, Grigore Leahu, Tiziana Cesca, Carlo Scian, Giovanni Mattei and Concita Sibilia

Appl. Sci. 2020, 10(4), 1316; https://doi.org/10.3390/app10041316 - 15 Feb 2020

Cited by 24 | Viewed by 2726

Abstract

Arrays of nanoholes in metal are important plasmonic devices, proposed for applications spanning from biosensing to communications. In this work, we show that in such arrays the symmetry can be broken by means of the elliptical shape of the nanoholes, combined with the [...] Read more.

Arrays of nanoholes in metal are important plasmonic devices, proposed for applications spanning from biosensing to communications. In this work, we show that in such arrays the symmetry can be broken by means of the elliptical shape of the nanoholes, combined with the in-plane tilt of the ellipse axes away from the array symmetry lines. The array then differently interacts with circular polarizations of opposite handedness at normal incidence, i.e., it becomes intrinsically chiral. The measure of this difference is called circular dichroism (CD). The nanosphere lithography combined with tilted silver evaporation was employed as a low-cost fabrication technique. In this paper, we demonstrate intrinsic chirality and CD by measuring the extinction in the near-infrared range. We further employ numerical analysis to visualize the circular polarization coupling with the nanostructure. We find a good agreement between simulations and the experiment, meaning that the optimization can be used to further increase CD. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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8 pages, 1015 KiB

Open AccessArticle

An Assemble Based on Clustering and Monte Carlo for the Wavelengths Selection of Excitation Emission Fluorescence Spectra

by Can Hao, Ying Wang, Guoming Wang and Zhizhong Zhu

Appl. Sci. 2020, 10(3), 1134; https://doi.org/10.3390/app10031134 - 07 Feb 2020

Cited by 1 | Viewed by 1941

Abstract

Excitation-emission fluorescence spectra is very effective to predict the concentration of organics in samples. However, redundant information and noises in the excitation-emission matrix (EEM) decrease the accuracy of the prediction concentration. Here we proposed a method to select more useful excitation and emission [...] Read more.

Excitation-emission fluorescence spectra is very effective to predict the concentration of organics in samples. However, redundant information and noises in the excitation-emission matrix (EEM) decrease the accuracy of the prediction concentration. Here we proposed a method to select more useful excitation and emission spectra from the EEM to increase the accuracy of prediction concentration and reduce the processing time. First, the excitation wavelengths were selected based on the clustering method to limit the redundant information in the EEM. Then the emission wavelengths were selected based on the Monte-Carlo method. To validate this method, we established the concentration prediction model with the spectra corresponding to the selected wavelengths by partial least square regression and predicted the multi component concentrations in the test samples. Our studies indicate that incorporation of this method increases the accuracy of the prediction concentration of organics and reduces the processing time. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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13 pages, 2420 KiB

Open AccessArticle

Thermal Relaxation Spectra for Evaluating Luminescence Quantum Efficiency of CASN:Eu²⁺ Measured by Balanced-Detection Sagnac-Interferometer Photothermal Deflection Spectroscopy

by Hiromichi Chima, Naoyuki Shiokawa, Keisuke Seto, Kohsei Takahashi, Naoto Hirosaki, Takayoshi Kobayashi and Eiji Tokunaga

Appl. Sci. 2020, 10(3), 1008; https://doi.org/10.3390/app10031008 - 04 Feb 2020

Cited by 3 | Viewed by 2924

Abstract

Highly sensitive broadband photothermal spectroscopy with a white-light lamp as the excitation source was developed by combining a Sagnac interferometer and balanced detection with a photothermal deflection method. A probe beam was split by a birefringent crystal CaCO₃ into signal and reference [...] Read more.

Highly sensitive broadband photothermal spectroscopy with a white-light lamp as the excitation source was developed by combining a Sagnac interferometer and balanced detection with a photothermal deflection method. A probe beam was split by a birefringent crystal CaCO₃ into signal and reference beams with a balanced intensity. This balanced detection enabled the measurement of photoexcited thermal relaxation spectra of materials in the air over the whole visible range in the weak excitation limit 50 µW/cm². The photothermal excitation spectrum of Eu²⁺-doped CaAlSiN₃ phosphors (CASN:Eu²⁺) with a high luminescent quantum efficiency was measured to be distinctly different from the photoluminescence excitation spectrum which reflects the absorption spectrum, revealing the thermal relaxation mechanism of the phosphor. Assuming a typical non-radiative relaxation from the higher excited states to the lowest excited state and successively to the ground state, it is demonstrated that the photoluminescence efficiency of the phosphors is readily evaluated simply by comparing the photothermal and photoluminescence excitation spectra. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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9 pages, 1761 KiB

Open AccessArticle

Tri- and Tetrahyperbolic Isofrequency Topologies Complete Classification of Bianisotropic Materials

by Maxim Durach, Robert Williamson, Morgan Laballe and Thomas Mulkey

Appl. Sci. 2020, 10(3), 763; https://doi.org/10.3390/app10030763 - 21 Jan 2020

Cited by 10 | Viewed by 2156

Abstract

We describe novel topological phases of isofrequency k-space surfaces in bianisotropic optical materials—tri- and tetrahyperbolic materials—which are induced by the introduction of chirality. This completes the classification of isofrequency topologies for bianisotropic materials, as we showed that all optical materials belong to one [...] Read more.

We describe novel topological phases of isofrequency k-space surfaces in bianisotropic optical materials—tri- and tetrahyperbolic materials—which are induced by the introduction of chirality. This completes the classification of isofrequency topologies for bianisotropic materials, as we showed that all optical materials belong to one of the following topological classes—tetra-, tri-, bi-, mono-, or nonhyperbolic. We showed that phase transitions between these classes occur in the k-space directions with zero group velocity at high k-vectors. This classification is based on the sets of high-k polaritons (HKPs), supported by materials. We obtained the equation describing these sets and characterized the longitudinal polarization-impedance of HKPs. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in "Optics and Lasers" Section)

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