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Emerging Topics in Structured Light

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A special issue of Photonics (ISSN 2304-6732). This special issue belongs to the section "Lasers, Light Sources and Sensors".

Deadline for manuscript submissions: closed (31 March 2024) | Viewed by 9343

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Special Issue Editors

Dr. Yongjia Xu

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Guest Editor

EPSRC Future Metrology Hub, University of Huddersfield, Huddersfield, HD1 3DH, UK
Interests: structured light metrology; optical surface metrology; portable and in-situ metrology; optical system calibration; optical deflectometry; fringe projection profilometry

Prof. Dr. Jianfeng Zhong

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Guest Editor

Institute of Precision Instrument and Intelligent Measurement & Control, Fuzhou University, Fuzhou 350108, China
Interests: optical measurement; vision-based measurement; intelligent sensing and diagnosis; structural health/condition monitoring; fault diagnosis; optical coherence tomography and its applications; fringe-based dynamic measurement

Dr. Zhenqi Niu

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Guest Editor

Precision Optical Manufacturing and Testing Center, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Interests: optical freeform metrology; 3D structure‒light measuring; deflectometric measuring technology; computing optical imaging

Special Issue Information

Dear Colleagues,

Techniques based on structured light are essential optical methods with wide applications in many fields, including optical metrology, 3D imaging and sensing, non-destructive testing, microstructure fabrication, intelligent driving control, etc. Structured light technology integrates numerous techniques, such as structured-light generation, system calibration/alignment, feature matching, signal analysis, data fusion, phase shifting and unwrapping, reconstruction, system integration, and system control and programming, while crossing multiple disciplines in mathematics, control, computing science, signal processing, electronics, and mechanical engineering.

Technological breakthroughs in key fundamental science represented by photonic, material, and computing drive the future of structured light technology toward automation, smart, and miniaturization. For example, an artificial intelligence algorithm is introduced into the structured-light technique for speed improvement and intelligence. Metasurfaces can replace bulk optics made of natural materials using thin and flat elements, combining multiple functions in single optical elements, and realizing the novel optical components of structured-light system, e.g., metalenses and metasurface-based diffractive optical elements.

This Special Issue aims at presenting an overview of cutting-edge research vision, results, and applications of structured light techniques including Gray-coding structured light, fringe projection profilometry, 3D polarization imaging, deflectometry, etc. We welcome broad, visionary contributions of short research reports as well as collections of reviews of accomplishments. We are excited to invite researchers to submit their contributions to this Special Issue. Topics include but are not limited to:

Structured light in optical metrology;
Structured light in 3D imaging;
Structured-light-based sensing technique;
Structured light in fault diagnosis;
Structured light in intelligent driving control;
Structured-light-based fabrication technique;
Structured-light technique based on artificial intelligence;
Structured-light technology integrated with multi-modal data;
Structured-light-based extreme technology including super-fast, super-depth-of-field, super-dynamic-range, super-high-precision, super-large/small-size-measurement, and so on, features;
Metasurface-based structured-light technique;
Structured-light-based and fringe-based structural dynamic measurement;
New industry applications.

Dr. Yongjia Xu
Prof. Dr. Jianfeng Zhong
Dr. Zhenqi Niu
Guest Editors

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Keywords

structured light technique
optical metrology
optical imaging
optical sensing
non-destructive testing
computing optics

Published Papers (11 papers)

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Research

12 pages, 4734 KiB

Open AccessArticle

High Fidelity Full-Color Optical Sectioning Structured Illumination Microscopy by Fourier Domain Based Reconstruction

by Shipei Dang, Jia Qian, Wang Ma, Rui Ma, Xing Li, Siying Wang, Chen Bai, Dan Dan and Baoli Yao

Photonics 2024, 11(5), 405; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics11050405 - 26 Apr 2024

Viewed by 287

Abstract

The natural color of biological specimens plays a crucial role in body protection, signaling, physiological adaptations, etc. Full-color optical sectioning structured illumination microscopy (OS-SIM) color is a promising approach that can reconstruct biological specimens in three-dimension meanwhile maintaining their natural color. Full-color OS-SIM takes the advantages of rapid imaging speed, compatibility with fluorescence and non-fluorescence samples, compact configuration, and low cost. However, the commonly used HSV-RMS reconstruction algorithm for full-color OS-SIM faces two issues to be improved. One is the RMS (root-mean-square) OS reconstruction algorithm is prone to background noise, and the other is the reconstruction is bound in RGB and HSV color spaces, consuming more reconstructing time. In this paper, we propose a full-color Fourier-OS-SIM method that allows for the OS reconstruction using the high-frequency spectrum of the sample and thus is immune to the low-frequency background noise. The full-color Fourier-OS-SIM directly runs in the RGB color space, providing an easy way to restore the color information. Simulation and experiments with various samples (pollen grains and tiny animals) demonstrate that the full-color Fourier-OS-SIM method is superior to the HSV-RMS method regarding background noise suppression. Moreover, benefiting from the background noise suppression merit, the quantitative morphological height map analysis with the full-color Fourier-OS-SIM method is more accurate. The proposed full-color Fourier-OS-SIM method is expected to find broad applications in biological and industrial fields where the 3D morphology and the color information of objects both need to be recovered. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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15 pages, 8295 KiB

Open AccessArticle

Characterization of Orbital Angular Momentum Beams by Polar Mapping and Fourier Transform

by Ruediger Grunwald and Martin Bock

Photonics 2024, 11(4), 296; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics11040296 - 25 Mar 2024

Viewed by 583

Abstract

The recognition, decoding and tracking of vortex patterns is of increasing importance in many fields, ranging from the astronomical observations of distant galaxies to turbulence phenomena in liquids or gases. Currently, coherent light beams with orbital angular momentum (OAM) are of particular interest for optical communication, metrology, micro-machining or particle manipulation. One common task is to identify characteristic spiral patterns in pixelated intensity maps at real-world signal-to-noise ratios. A recently introduced combination of polar mapping and Fast Fourier Transform (FFT) was extended to novel sampling configurations and applied to the quantitative analysis of the spiral interference patterns of OAM beams. It is demonstrated that specific information on topological parameters in non-uniform arrays of OAM beams can be obtained from significantly distorted and noisy intensity maps by extracting one- or two-dimensional angular frequency spectra from single or concatenated circular cuts in either spatially fixed or scanning mode. The method also enables the evaluation of the quality of beam shaping and optical transmission. Results of proof-of-principle experiments are presented, resolution limits are discussed, and the potential for applications is addressed. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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15 pages, 7454 KiB

Open AccessArticle

Influence of Primary Coma on the Tightly Focusing Characteristics of Circular Basis Hybrid Order Poincaré Sphere Beams

by Sushanta Kumar Pal, Rakesh Kumar Singh and Paramasivam Senthilkumaran

Photonics 2024, 11(1), 98; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics11010098 - 22 Jan 2024

Viewed by 672

Abstract

Analogous to the Poincaré sphere, a hybrid order Poincaré sphere is used to represent the ellipse field singularities (C-points). We study the tight focusing properties of generic bright and dark hybrid order Poincaré sphere beams in the presence of primary coma. The role of the polarization singularity index and handedness of the polarization of the hybrid order Poincaré sphere beams on the focused structure has been discussed. Results have been presented for the total intensity, component intensities, and component phase distributions for left- and right-handed bright and dark star and lemon types singularities. The presence of primary coma distorted the focal plane intensity distributions for both positive and negative index generic C-points. Coma is known to disturb the circular symmetry of the focal plane intensity distribution. Similarly in tight focusing polarization is known to disturb the symmetry. Therefore, a beam with structured and inhomogeneous polarization distribution tightly focused under the influence of coma is a fit case to study. It is found that the presence of primary coma aberration in the focusing system produces a positional shift of the high-intensity peaks and a reduction of the intensity on one side of the center. As the strength of the primary coma increases, the focal plane intensity distributions shift more and more toward the right from the initial position. Unlike the scalar vortex case, in the case of hybrid order Poincaré sphere beams, the focal plane intensity distribution undergoes rotation, as the helicity of the hybrid order Poincaré sphere beams is inverted, in addition to shifting. All the component phase distributions are found to be embedded with phase vortices of charge

\pm 1

. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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13 pages, 9709 KiB

Open AccessCommunication

Improvement of Efficiency in 976 nm Fiber Amplifier by Spectral Filtering in Yb-Doped Fiber with Absorbing Rods Embedded in the Cladding

by Svetlana S. Aleshkina, Danila A. Davydov, Vladimir V. Velmiskin, Mikhail V. Yashkov, Andrey A. Umnikov, Sergey V. Alyshev, Liudmila D. Iskhakova, Mikhail M. Bubnov, Denis S. Lipatov and Mikhail E. Likhachev

Photonics 2024, 11(1), 89; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics11010089 - 17 Jan 2024

Viewed by 815

Abstract

A novel Yb-doped fiber design for improved lasing near 976 nm based on spectral filtering of the amplified spontaneous emission near 1030 nm was realized and investigated. A very sharp short-pass filter was implemented by adding appropriately chosen high-index absorbing rods into the silica cladding. In this case, the resonant interaction of the core mode with the high-index rod mode could be controlled by fiber bending, which allows for the precise adjustment of the stop-band position. It was shown that the utilization of Sm-doped absorbing rods allows one to achieve very high absorption of emission at unwanted wavelengths, but it also adds background losses for the pump near 915 nm and for the signal at 976 nm. Despite this fact, the improvement of efficiency in the 976 nm fiber amplifier, after shifting the stop-band to 1000 nm, was clearly demonstrated. Based on theoretical calculations, it was shown that, after optimizing the fiber parameters, a further twofold improvement in efficiency was possible despite the excess losses at the pump and signal wavelengths. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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13 pages, 1956 KiB

Open AccessArticle

A Multi-Objective Genetic Algorithm Approach for Silicon Photonics Design

by Hany Mahrous, Mostafa Fedawy, Mira Abboud, Ahmed Shaker, W. Fikry and Michael Gad

Photonics 2024, 11(1), 80; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics11010080 - 16 Jan 2024

Viewed by 1074

Abstract

A multi-objective genetic algorithm approach is formulated to optimize the design of silicon-photonics complex circuits with contradicting performance metrics and no closed-form expression for the circuit performance. A case study is the interleaver/deinterleaver circuit which mixes/separates optical signals into/from different physical channels while preserving the wavelength-division-multiplexing specifications. These specifications are given as channel spacing of 50 GHz, channel 3-dB bandwidth of at least 20 GHz, channel free spectral range of 100 GHz, crosstalk of −23 dB or less, and signal dispersion less than 30 ps/nm. The essence of the proposed approach lies in the formulation of the fitness functions and the selection criteria to optimize the values of the three coupling coefficients, which govern the circuit performance, in order to accommodate the contradicting performance metrics of the circuit. The proposed approach achieves the optimal design in an incomparably short period of time when contrasted with the previous tedious design method based on employing Z-transform and visual inspection of the transmission poles and zeros. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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13 pages, 2641 KiB

Open AccessArticle

Spin-Hall Effect of Cylindrical Vector Vortex Beams

by Xuyao Zhang, Shuo Wang, Jinhong Liu, Jinze Wu and Jinhong Li

Photonics 2023, 10(12), 1356; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10121356 - 08 Dec 2023

Cited by 1 | Viewed by 923

Abstract

Spin-Hall effect (SHE) of light is one of the main manifestations of the spin-orbit interaction of photons, and has been extensively studied for optical beams with homogeneous polarization. Here, we present a theoretical study of the SHE of cylindrical vector vortex beams (CVVBs) possessing inhomogeneous polarization. We derive the analytical expressions of the SHE of CVVBs reflected and refracted at a dielectric interface with radial and azimuthal polarization of incidence. The spin-dependent shifts of the SHE of light linearly depend on the topological charge of the CVVBs. In contrast to the conventional SHE of horizontally or vertically polarized beams, the SHE shifts of the CVVBs are asymmetrical when the topological charge is nonzero. This asymmetry results in the transverse Imbert–Fedorov (IF) shifts that are proportional to the topological charge. Furthermore, based on weak measurement, we propose an experimental scheme to enhance the SHE and related IF shifts with proper pre- and post-selection polarization states. Our results advance the study of the SHE of structured light and may find applications in SHE-based techniques such as precision measurement. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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23 pages, 7524 KiB

Open AccessArticle

The Flatness Error Evaluation of Metal Workpieces Based on Line Laser Scanning Digital Imaging Technology

by Zirui Mao, Chaolong Zhang, Benjun Guo, Yuanping Xu, Chao Kong, Yue Zhu, Zhijie Xu and Jin Jin

Photonics 2023, 10(12), 1333; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10121333 - 30 Nov 2023

Viewed by 868

Abstract

With the development of intelligent manufacturing, the production and assembly accuracy of components in factories is increasing in line with growing demand. However, the traditional manual quality inspection is inefficient, inaccurate, and costly. To this end, digital and optical imaging techniques are used to achieve intelligent quality inspection. However, during the reconstruction process, the high reflectivity of object materials affects the speed and accuracy of reconstruction results. To overcome these problems, this study investigated the three-dimensional (3D) digital imaging techniques based on line laser scanning. It advances a novel methodology for image segmentation, underpinned by deep learning algorithms, to augment the precision of the reconstruction results while simultaneously enhancing processing velocity. After the reconstruction phase, the research assesses flatness tolerance using point cloud registration technology. Finally, we constructed a measurement platform with a cost of less than CNY 100,000 (about USD 14,000) and obtained a measurement accuracy of 30 microns. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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14 pages, 7778 KiB

Open AccessArticle

Topological Edge States on Different Domain Walls of Two Opposed Helical Waveguide Arrays

by Junying Wang, Zhiwei Shi, Xifeng Ji, Yajing Zhang, Huagang Li, Yaohua Deng and Kang Xie

Photonics 2023, 10(11), 1220; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10111220 - 31 Oct 2023

Cited by 1 | Viewed by 849

Abstract

Floquet topological insulators (FTIs) have richer topological properties than static systems. In this work, we designed different domain wall (DW) structures consisting of a Floquet photonic lattice with opposite helical directions. We investigated the existence and types of edge states in three shared coupling structures and the impact of these shared coupling structures on edge states. When two opposite helical lattices share a straight waveguide array coupling, the edge states are localized on the straight waveguide. When two opposite helical lattices share a clockwise (or anticlockwise) helical waveguide array coupling, the DWs consist of zigzag and bearded edges, but the positions of the zigzag and bearded edges of the shared clockwise waveguide array are different from those of the shared anticlockwise waveguide array. The slope and transmission rate of the edge states both vary with the degree of coupling between the shared waveguides. The characteristics of these edge states, such as transmission speed and band gap width, are also affected by the incidence angle, modulation phase factor, and helical radii, and the methods for controlling the edge states in different shared coupling structures are provided. This will help deepen our understanding of how topological structures influence the electronic and photonic properties of materials. This could also lead to combining topology with metasurface-based structured light, which would highlight many novel properties with great application potential for various fields, such as imaging, metrology, communication, quantum information processing, and light–matter interaction. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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14 pages, 6286 KiB

Open AccessArticle

The Mechanism of the Formation of the Spin Hall Effect in a Sharp Focus

by Victor V. Kotlyar, Sergey S. Stafeev, Alexey M. Telegin and Elena S. Kozlova

Photonics 2023, 10(10), 1093; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10101093 - 29 Sep 2023

Cited by 1 | Viewed by 686

Abstract

We have shown how the spin Hall effect is formed in a tight focus for two light fields with initial linear polarization. We have demonstrated that an even number of local subwavelength regions appear in which the sign of the longitudinal projection of the spin angular momentum (the third Stokes component) alternates. When an optical vortex with topological charge n and linear polarization passes through an ideal spherical lens, additional optical vortices with topological charges n + 2, n − 2, n + 1, and n − 1 with different amplitudes are formed in the converged beam. The first two of these vortices have left and right circular polarizations and the last two vortices have linear polarization. Since circularly polarized vortices have different amplitudes, their superposition will have elliptical polarization. The sign of this elliptical polarization (left or right) will change over the beam cross section with the change in the sign of the difference in the amplitudes of optical vortices with circular polarization. We also have shown that optical vortices with topological charges n + 2, n − 2 propagate in the opposite direction near the focal plane, and together with optical vortices with charges n + 1, n − 1, they form an azimuthal energy flow at the focus. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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16 pages, 8364 KiB

Open AccessArticle

An Optimized Error Compensation Method for Phase Measurement Profilometry

by Benjun Guo, Yuanping Xu, Chaolong Zhang, Jianfeng Tang, Dan Tang, Chao Kong and Jin Jin

Photonics 2023, 10(9), 1036; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10091036 - 11 Sep 2023

Cited by 1 | Viewed by 723

Abstract

Phase measurement profilometry (PMP) is primarily employed to analyze the morphology of a functional surface with precision. Historically, one of the most complex and persistent challenges in PMP has been reducing errors stemming from inconsistent indicators at the edges of a surface. In response to this challenge, we propose an optimized error compensation methodology specifically designed to handle edge artefacts. This methodology introduces the Hilbert transform and object surface albedo as tools to detect the edges of the artefact region that need to be compensated. Moreover, we analyze the characteristics of the sinusoidal fringe waveform propagation direction and investigate the reconstruction results of the fringe vertical to the current directions to compensate for edge artefacts. The experimental results for various objects show that the optimized approach can compensate for edge artefacts by projecting in two directions and reducing the projection by half. The compensated root mean square error (RMSE) for planar objects can be reduced by over 45%. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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12 pages, 5818 KiB

Open AccessArticle

Local Energy Velocity of the Air-Core Modes in Hollow-Core Fibers

by Andrey Pryamikov

Photonics 2023, 10(9), 1035; https://0-doi-org.brum.beds.ac.uk/10.3390/photonics10091035 - 10 Sep 2023

Cited by 1 | Viewed by 748

Abstract

In this paper, we consider the behavior of the local energy flow velocity of the fundamental air-core mode at the core-cladding boundary in two types of hollow-core fibers: hollow-core fibers with a negative curvature of the core boundary and single-capillary fibers with similar geometrical parameters. It is demonstrated that the behavior of both axial and radial components of the local energy velocity of the fundamental air-core mode is completely different for these two types of hollow-core fibers. The negative curvature of the core boundary leads to an alternating behavior of the radial projection of the local energy velocity and a decrease of two orders of magnitude compared to the values of this projection for a single capillary. In our opinion, this behavior of the local energy velocity of the fundamental air-core mode is caused by a periodic set of Poynting vector vortices that appear in the cladding capillary walls. Full article

(This article belongs to the Special Issue Emerging Topics in Structured Light)

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