Research

29 pages, 16188 KiB

Open AccessArticle

Single-Shot, Pixel-Encoded Strip Patterns for High-Resolution 3D Measurement

by Ahsan Elahi, Qidan Zhu, Jun Lu, Zahid Hammad, Muhammad Bilal and Yong Li

Photonics 2023, 10(11), 1212; https://doi.org/10.3390/photonics10111212 - 31 Oct 2023

Viewed by 1135

In this research, we combined two distinct, structured light methods, the single-shot pseudo-random sequence-based approach and the time-multiplexing stripe indexing method. As a result, the measurement resolution of the single-shot, spatially encoded, pseudo-random sequence-based method improved significantly. Since the time-multiplexed stripe-indexed-based techniques have [...] Read more.

In this research, we combined two distinct, structured light methods, the single-shot pseudo-random sequence-based approach and the time-multiplexing stripe indexing method. As a result, the measurement resolution of the single-shot, spatially encoded, pseudo-random sequence-based method improved significantly. Since the time-multiplexed stripe-indexed-based techniques have a higher measurement resolution, we used varying stripes to enhance the measurement resolution of the pseudo-random sequence-based approaches. We suggested a multi-resolution 3D measurement system that consisted of horizontal and vertical stripes with pixel sizes ranging from 8 × 8 to 16 × 16. We used robust pseudo-random sequences (M-arrays) to controllably distribute various stripes in a pattern. Since single-shape primitive characters only contribute one feature point to the projection pattern, we used multiple stripes instead of single-shape primitive symbols. However, numerous stripes will contribute multiple feature points. The single character-based design transforms into an increased featured size pattern when several stripes are employed. Hence, the projection pattern contains a much higher number of feature points. So, we obtained a high-resolution measurement. Each stripe in the captured image is located using adaptive grid adjustment and stripe indexing techniques. The triangulation principle is used to measure 3D. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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11 pages, 2715 KiB

Open AccessArticle

Wavelength-Tunable Pulsed Cylindrical Vector Beams in a 1.7-μm Mode-Locking Thulium-Doped All-Fiber Laser

by Xiaoliang Yang, Rufei Long, Yuhua Xie, Jiahao Wen, Hongwei Lv and Yu Chen

Photonics 2023, 10(10), 1163; https://doi.org/10.3390/photonics10101163 - 17 Oct 2023

Viewed by 1138

Abstract

Because of the special absorption peak, pulsed lasers at 1.7 μm have been rapidly developed in medical treatment, biological imaging and so on. Introducing the cylindrical vector beam (CVB) may further promote these special applications due to its unique intensity, phase and polarization [...] Read more.

Because of the special absorption peak, pulsed lasers at 1.7 μm have been rapidly developed in medical treatment, biological imaging and so on. Introducing the cylindrical vector beam (CVB) may further promote these special applications due to its unique intensity, phase and polarization characteristics. Herein, we have experimentally demonstrated the generation of wavelength-tunable pulsed CVBs at 1.7 μm based on a thulium-doped all-fiber laser. A bandpass filter with a wide bandwidth combined with nonlinear polarization rotation technology is used to obtain pulsed laser emission at 1.7 μm. By taking advantage of a home-made Lyot filter and mode selective coupler (MSC), pulsed CVBs can be obtained with a wavelength tuning range of 66 nm (1720–1786 nm). The development of wavelength-tunable pulsed CVBs at the 1.7 μm waveband has significant potential applications in deep bioimaging and laser processing. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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12 pages, 4493 KiB

Open AccessEditor’s ChoiceArticle

Structurally Stable Astigmatic Vortex Beams with Super-High Orbital Angular Momentum (ABCD Matrix Approach)

by Alexander Volyar, Mikhail Bretsko, Server Khalilov and Yana Akimova

Photonics 2023, 10(9), 1048; https://doi.org/10.3390/photonics10091048 - 15 Sep 2023

Cited by 1 | Viewed by 958

Abstract

We have demonstrated efficiency of employing the ABCD matrix approach to transform higher-order structured Laguerre–Gaussian (sLG) beams into structurally stable astigmatic sLG (asLG) beams, highlighting their dynamics at propagating. Radical transformations of the beam structure by a cylindrical lens form not only orbital [...] Read more.

We have demonstrated efficiency of employing the ABCD matrix approach to transform higher-order structured Laguerre–Gaussian (sLG) beams into structurally stable astigmatic sLG (asLG) beams, highlighting their dynamics at propagating. Radical transformations of the beam structure by a cylindrical lens form not only orbital angular momentum (OAM) fast oscillations and bursts, but also make the asLG beams structurally unstable in propagation through cylindrical and spherical lenses when focusing paraxially. But, if the spherical lens performs a Fourier transform of the asLG beam after a cylindrical lens, the symmetric beam emerges at the lens focal plane with a sharp OAM dip; then, the OAM restores its former astigmatism, becoming structurally stable at the far diffraction domain. By investigating the beam structure at the focal area, we have showed that the OAM sharp dip is associated with nothing less than the process of dividing the OAM into the vortex and astigmatic constitutes predicted by Anan’ev and Bekshaev. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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11 pages, 963 KiB

Open AccessArticle

Two-Dimensional Quasi-Periodic Diffraction Properties of the Scalar and Vector Optical Fields

by Yue Pan, Xue-Feng Sun, Guang-Bo Zhang, Qing-Lu Li, Ya-Ning Kong, Tian-Fei Zhao and Xu-Zhen Gao

Photonics 2023, 10(9), 1045; https://doi.org/10.3390/photonics10091045 - 14 Sep 2023

Viewed by 616

Abstract

As is known, quasi-periodicity attracts great attention in many scientific regions. For instance, the discovery of the quasicrystal was rewarded the Nobel Prize in 2011, leading to a series of its applications. However, in the area of manipulating optical fields, the two-dimensional quasi-periodicity [...] Read more.

As is known, quasi-periodicity attracts great attention in many scientific regions. For instance, the discovery of the quasicrystal was rewarded the Nobel Prize in 2011, leading to a series of its applications. However, in the area of manipulating optical fields, the two-dimensional quasi-periodicity is rarely considered. Here, we study the two-dimensional quasi-periodic diffraction properties of the scalar and vector optical fields based on the Penrose tiling, which is one of the most representative kinds of two-dimensional quasi-periodic patterns. We propose type-A and type-B Penrose tiling masks (PTMs) with phase modulation, and further show the diffraction properties of the optical fields passing through these masks. The intensity of the diffraction field holds a tenfold symmetry. It is proved that the iteration number n of the PTM shows the “weeding” function in the diffraction field, and this property is useful in filtering, shaping, and manipulating diffraction fields. Meanwhile, we also find that the diffraction patterns have the label of the Golden ratio, which can be applied in areas such as optical encryption and information transmission. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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11 pages, 7482 KiB

Open AccessCommunication

Airy Transform of the New Power-Exponent-Phase Vortex Beam

by Qidong Lin, Hao Zhang, Zhiquan Hu, Xiaotan Lu, Xingyuan Lu, Yangjian Cai and Chengliang Zhao

Photonics 2023, 10(9), 974; https://doi.org/10.3390/photonics10090974 - 25 Aug 2023

Viewed by 1081

Abstract

A new power-exponent-phase vortex beam with nonlinear phase winding has shown flexible control freedom compared with conventional vortex beams. In order to further enrich the modulation freedom and expand the ability of self-healing to meet current application requirements, we conducted a detailed study [...] Read more.

A new power-exponent-phase vortex beam with nonlinear phase winding has shown flexible control freedom compared with conventional vortex beams. In order to further enrich the modulation freedom and expand the ability of self-healing to meet current application requirements, we conducted a detailed study on the characteristics of the Airy transform of the new power-exponent-phase vortex beam. The influences of the Airy function, the power exponent, and the topological charge on normalized intensity and phase distributions are investigated theoretically and experimentally. More importantly, the self-healing properties of the new power-exponent-phase vortex beam with and without the Airy transform are compared. This shows that the new power-exponent-phase vortex beam with the Airy transform exhibits better self-healing ability when obstructed by obstacles. This study has potential applications in optical trapping and free-space optical communication. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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14 pages, 10543 KiB

Open AccessArticle

Topological Charge of Propagation-Invariant Laser Beams

by Victor V. Kotlyar, Alexey A. Kovalev and Eugeny G. Abramochkin

Photonics 2023, 10(8), 915; https://doi.org/10.3390/photonics10080915 - 09 Aug 2023

Cited by 1 | Viewed by 759

Abstract

If a vortex propagation-invariant beam is given by all its intensity nulls, then its topological charge (TC) can be defined easily: its TC is equal to the sum of topological charges of all optical vortices in these intensity nulls. If, however, a propagation-invariant [...] Read more.

If a vortex propagation-invariant beam is given by all its intensity nulls, then its topological charge (TC) can be defined easily: its TC is equal to the sum of topological charges of all optical vortices in these intensity nulls. If, however, a propagation-invariant beam is given as a superposition of several light fields, then determining its TC is a complicated task. Here, we derive the topological charges of four different types of propagation-invariant beams, represented as axial superpositions of Hermite–Gaussian beams with different amplitudes and different phase delays. In particular, topological charges are obtained for such beam families as the Hermite–Laguerre–Gaussian (HLG) beams and two-parametric vortex Hermite beams. We show that the TC is a quantity resistant to changing certain beam parameters. For instance, when the parameters θ and α of the HLG beams are altered, the beam intensity also changes significantly, but the TC remains unchanged. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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18 pages, 1248 KiB

Open AccessArticle

Partially Coherent Cylindrical Vector Sources

by Massimo Santarsiero, Juan Carlos González de Sande, Olga Korotkova, Rosario Martínez-Herrero, Gemma Piquero and Franco Gori

Photonics 2023, 10(7), 831; https://doi.org/10.3390/photonics10070831 - 17 Jul 2023

Viewed by 703

Abstract

A new class of stationary electromagnetic sources radiating outward from the surface of an infinitely long cylinder is introduced via vectorial coherent mode representation. First, two particular types of such sources are discussed: with either an electric or magnetic field aligned with the [...] Read more.

A new class of stationary electromagnetic sources radiating outward from the surface of an infinitely long cylinder is introduced via vectorial coherent mode representation. First, two particular types of such sources are discussed: with either an electric or magnetic field aligned with the cylinder’s axis. The former case represents a scalar scenario, while the latter leads to the two-component electric field. The combination of these two types of sources is then considered by forming the three-component electric field vector. An extension to the stationary case is then made in which the electric field correlations are shown to be described by the intrinsically

3 \times 3

cross-spectral density matrix. Several known theories of electromagnetic coherence and polarization are then invoked for the analysis of radiation, on and off the source surface. The results for the spectral density, degree of coherence, and degree of polarization are then discussed in detail. The effects of mutual correlation of modes are also outlined. The new family of sources is of importance for any application involving cylindrical sources with controllable radiation. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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13 pages, 6033 KiB

Open AccessArticle

Trapping of Rayleigh Spheroidal Particles Using Tightly Focused Higher-Order Vector Vortex Beams

by Dong Li, Hongxu Zhang, Chengquan Wei, Yundi Zhang, Xize Gao, Dandan Wen, Peng Li and Jianlin Zhao

Photonics 2023, 10(7), 785; https://doi.org/10.3390/photonics10070785 - 06 Jul 2023

Cited by 1 | Viewed by 902

Abstract

Considering the advantages of higher-order vector vortex beams (HOVVBs) with their diverse intensity distribution of the focal field and adjustable longitudinal field component, we investigated the optical forces and torques on Rayleigh spheroidal particles induced by tightly focused HOVVBs based on the Rayleigh [...] Read more.

Considering the advantages of higher-order vector vortex beams (HOVVBs) with their diverse intensity distribution of the focal field and adjustable longitudinal field component, we investigated the optical forces and torques on Rayleigh spheroidal particles induced by tightly focused HOVVBs based on the Rayleigh scattering model and dipole approximation. It was found that the maximal optical forces were obtained when the major axis of the Rayleigh spheroidal particles was parallel to the x–y plane. We achieved the three-dimensional stable trapping of Rayleigh spheroidal particles at the focus by using an HOVVB. Further analysis showed that the optical torque caused the major axis of the spheroidal particle to rotate towards the x–y plane, which is conducive to the large-scale stable trapping of Rayleigh spheroidal particles in the two-dimensional plane. Moreover, the optical torque Γ_x could achieve a maximum of 0.869 pN·nm at φ₀ = 90° and 270°, while Γ_y could achieve a maximum of 0.869 pN·nm at φ₀ = 0° and 180° for the case of θ₀ = 30°. Our findings provide a clear strategy for extending the degrees of freedom in the control of the beam. We envision a significant role for these results in optical micro-manipulation. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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15 pages, 5222 KiB

Open AccessArticle

Atmospheric Turbulence Effects on the Performance of Orbital Angular Momentum Multiplexed Free-Space Optical Links Using Coherent Beam Combining

by Pei Ju, Wenhui Fan, Wei Gao, Zhe Li, Qi Gao, Xiaoqiang Jiang and Tongyi Zhang

Photonics 2023, 10(6), 634; https://doi.org/10.3390/photonics10060634 - 31 May 2023

Cited by 3 | Viewed by 1317

Abstract

Atmospheric effects including absorption and scattering, and turbulence could introduce signal power loss and severe mode crosstalk for the orbital angular momentum (OAM)-based free-space optical communication (FSOC). Therefore, it is of great significance to simultaneously increase signal power and mitigate mode crosstalk. In [...] Read more.

Atmospheric effects including absorption and scattering, and turbulence could introduce signal power loss and severe mode crosstalk for the orbital angular momentum (OAM)-based free-space optical communication (FSOC). Therefore, it is of great significance to simultaneously increase signal power and mitigate mode crosstalk. In this paper, for the OAM beam from a coherent laser array with a discrete vortex (CLA-DV) based on coherent beam combining, we investigate its propagation characteristics by employing theoretical derivation and the random phase screens simulation in atmospheric propagation, respectively. The probability density and OAM spectrum are given and compared for CLA-DV and Gaussian vortex beam. The results demonstrate that the Gaussian vortex beam exhibits smaller mode crosstalk under weak atmospheric turbulence conditions, while CLA-DV shows a good performance on crosstalk mitigation for strong atmospheric turbulence conditions in long-distance links. Furthermore, with a specially designed radial phase-locked Gaussian laser array composed of two orthogonal polarized coherent laser arrays carrying different OAM states, a scheme of optical communication system possessing simultaneously polarization-division multiplexing and OAM multiplexing is proposed. The normalized energy weight matrices of all 16 non-zeroth-order OAM modes are numerically calculated. To verify the feasibility of the proposed scheme, the performance of an eight-bit grayscale Lena image facing various atmosphere turbulences is evaluated. The quality of transmitted images becomes worse with the turbulence strength and transmission distance increase, which is confirmed by the trend of average optical signal error rates. This work will provide theoretical insight for improving the performance of OAM-based FSOC under scattering conditions. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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8 pages, 5932 KiB

Open AccessCommunication

Intra-Cavity Cascaded Pumped 946/1030 nm Dual-Wavelength Vortex Laser Using a Spot-Defect Mirror

by Yashuai Yang, Yongliang Li, Xinyi Zhu, Chi Wang and Chao Yang

Photonics 2023, 10(5), 554; https://doi.org/10.3390/photonics10050554 - 10 May 2023

Viewed by 1023

Abstract

Due to their unique properties, vortex lasers have high application value in frontier fields such as optical micromanipulation, super-resolution imaging, quantum entanglement, and optical communication. In this study, we demonstrated a 946/1030 nm Laguerre-Gaussian (LG₀₁) mode dual-wavelength vortex laser by using [...] Read more.

Due to their unique properties, vortex lasers have high application value in frontier fields such as optical micromanipulation, super-resolution imaging, quantum entanglement, and optical communication. In this study, we demonstrated a 946/1030 nm Laguerre-Gaussian (LG₀₁) mode dual-wavelength vortex laser by using an intracavity cascade pumped structure and a spot-defect output mirror. Using a coaxial linear cavity structure, the 808 nm laser diode (LD) was used to end-pump the Nd:YAG crystal to generate a 946 nm laser and then use it to directly pump the Yb:YAG crystal in the cavity to generate a 1030 nm laser, and finally a 946/1030 nm dual-wavelength laser came out. By making a spot defect in the center of the output mirror to suppress the oscillation of the fundamental Gaussian mode laser and carefully adjusting the position of the laser crystals, the LG₀₁ mode dual-wavelength vortex laser was output in single handedness. When the pump power was 40 W, the total output was 664 mW (356 and 308 mW at 946 and 1030 nm LG₀₁ mode vortex lasers), and the total optical-optical conversion efficiency was 1.7%; the output power fluctuations of 946 and 1030 nm LG₀₁ mode vortex lasers within 1 h were 3.43% and 3.13%, respectively; the beam quality factors M² of 946 and 1030 nm LG₀₁ mode vortex lasers were 2.35 and 2.40, respectively. It was proved that the generated dual-wavelength vortex laser had the wavefront phase

\exp (i ϕ)

by the self-interference method. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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12 pages, 3850 KiB

Open AccessCommunication

Topological Charge Measurement of a Partially Coherent Vortex Beam Using Dual Cylindrical Lenses with an Arbitrary Angle

by Xiaotan Lu, Zhuoyi Wang, Xingyuan Lu, Chengliang Zhao and Yangjian Cai

Photonics 2023, 10(4), 444; https://doi.org/10.3390/photonics10040444 - 13 Apr 2023

Cited by 2 | Viewed by 978

Abstract

For a partially coherent Laguerre–Gaussian (PCLG) vortex beam, information regarding the topological charge (TC) is concealed in the cross-spectral density (CSD) function phase. Herein, a flexible method for the simultaneous determination of the sign and magnitude of the TC for a PCLG vortex [...] Read more.

For a partially coherent Laguerre–Gaussian (PCLG) vortex beam, information regarding the topological charge (TC) is concealed in the cross-spectral density (CSD) function phase. Herein, a flexible method for the simultaneous determination of the sign and magnitude of the TC for a PCLG vortex beam is proposed based on the measured CSD amplitude and phase after the beam propagates through a dual cylindrical lens with adjustable angles. Both the stripes in the CSD amplitude and phase exhibit quantitative relationships with the value of TC, that is,

N = 2 |l| + 1

. Meanwhile, the angle adjustability of cylindrical lenses allows flexible measurements, thus rendering the scheme effective for both high and extreme coherences. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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14 pages, 4517 KiB

Open AccessArticle

Generation, Topological Charge, and Orbital Angular Momentum of Off-Axis Double Vortex Beams

by Mingxian Guo, Wei Le, Chao Wang, Guanghao Rui, Zhuqing Zhu, Jun He and Bing Gu

Photonics 2023, 10(4), 368; https://doi.org/10.3390/photonics10040368 - 25 Mar 2023

Cited by 8 | Viewed by 1731

Abstract

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital [...] Read more.

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital angular momentum (OAM) of off-axis double vortex beams. It is demonstrated that the tilted lens method can detect not only the magnitudes and signs of two TCs of the off-axis double vortex beam but also the spatial distribution of the TCs. Moreover, the average OAM value of the off-axis double vortex beam decreases nonlinearly as the off-axis distance increases, although its TC is independent of the off-axis distance of phase singularities. The results indicate that the average OAM of the off-axis double vortex beam can be easily controlled by changing the relative position of two-phase singularities, thereby realizing the applications of multi-degrees of freedom particle manipulation, optical communication, and material processing. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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