Photonics

15 pages, 1969 KiB

Open AccessArticle

A Conceptual Study of Rapidly Reconfigurable and Scalable Bidirectional Optical Neural Networks Leveraging a Smart Pixel Light Modulator

by Young-Gu Ju

Photonics 2025, 12(2), 132; https://doi.org/10.3390/photonics12020132 - 2 Feb 2025

Abstract

We explore the integration of smart pixel light modulators (SPLMs) into bidirectional optical neural networks (BONNs), highlighting their advantages over traditional spatial light modulators (SLMs). SPLMs enhance BONN performance by enabling faster light modulation in both directions, significantly increasing the refresh rate of [...] Read more.

We explore the integration of smart pixel light modulators (SPLMs) into bidirectional optical neural networks (BONNs), highlighting their advantages over traditional spatial light modulators (SLMs). SPLMs enhance BONN performance by enabling faster light modulation in both directions, significantly increasing the refresh rate of neural network weights to hundreds of megahertz, thus facilitating the practical implementation of the backpropagation algorithm and two-mirror-like BONN structures. The architecture of an SPLM-based BONN (SPBONN) features bidirectional modulation, simplifying hardware with electrical fan-in and fan-out. An SPBONN with an array size of 96 × 96 can achieve high throughput, up to 4.3 × 10¹⁶ MAC/s with 10 layers. Energy assessments showed that the SPLM array, despite its higher power consumption compared to the SLM array, is manageable via effective heat dissipation. Smart pixels with programmable memory in the SPBONN provide a cost-effective solution for expanding network node size and overcoming scalability limitations without the need for additional hardware. Full article

(This article belongs to the Special Issue Advances in Free-Space Optical Communications)

11 pages, 4045 KiB

Open AccessArticle

Sagnac Interference-Based Contact-Type Fiber-Optic Vibration Sensor

by Hongmei Li, Longhuang Tang, Lijie Zhang, Wenjuan Huang, Rong Cao, Cheng Huang, Xiaobo Hu, Yifei Sun and Jia Shi

Photonics 2025, 12(2), 131; https://doi.org/10.3390/photonics12020131 - 2 Feb 2025

Abstract

The observation and evaluation of vibration signals is crucial for enhancing engineering quality and ensuring the safe operation of equipment. This paper proposes a fiber-optic vibration sensor based on the Sagnac interference principle. The polarization-maintaining fiber (PMF) is spliced between two single mode [...] Read more.

The observation and evaluation of vibration signals is crucial for enhancing engineering quality and ensuring the safe operation of equipment. This paper proposes a fiber-optic vibration sensor based on the Sagnac interference principle. The polarization-maintaining fiber (PMF) is spliced between two single mode fibers (SMFs) to form the SMF-PMF-SMF (SPS) fiber structure. The Sagnac interferometer consists of an SPS fiber structure connected to a 3 dB coupler. Due to the principle of the elastic-optical effect, the interferometric spectrum of the PMF-based Sagnac interferometric structure changes when the PMF is subjected to stress, enabling vibration to be measured. The experimental results show that the relative measurement error of the fiber-optic vibration sensor for healthy and faulty bearings is less than 1.8%, which verifies the effectiveness and accuracy of the sensor. The sensor offers benefits of excellent anti-vibration fatigue characteristics, simple production, small size, light weight, and has a wide range of applications in mechanical engineering, fault detection, safety and security, and other fields. Full article

(This article belongs to the Special Issue Emerging Trends in Optical Fiber Sensors and Sensing Techniques)

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10 pages, 519 KiB

Open AccessArticle

High-Peak-Power Sub-Nanosecond Laser Pulse Sources Based on Hetero-Integrated “Heterothyristor–Laser Diode” Vertical Stack

by Sergey Slipchenko, Aleksander Podoskin, Ilia Shushkanov, Artem Rizaev, Matvey Kondratov, Viktor Shamakhov, Vladimir Kapitonov, Kirill Bakhvalov, Artem Grishin, Timur Bagaev, Maxim Ladugin, Aleksander Marmalyuk, Vladimir Simakov and Nikita Pikhtin

Photonics 2025, 12(2), 130; https://doi.org/10.3390/photonics12020130 - 1 Feb 2025

Abstract

Compact high-power sub-nanosecond laser pulse sources with a wavelength of 940 nm are developed and studied. A design for laser pulse sources based on a vertical stack is proposed, which includes a semiconductor laser chip and a current switch chip. To create a [...] Read more.

Compact high-power sub-nanosecond laser pulse sources with a wavelength of 940 nm are developed and studied. A design for laser pulse sources based on a vertical stack is proposed, which includes a semiconductor laser chip and a current switch chip. To create a compact high-speed current switch, a three-electrode heterothyristor is developed. It is found that the use of heterothyristor-based current switches allows the creation of a low-loss pump current circuit, generating short current pulses and operating the semiconductor laser in gain-switching mode. For the semiconductor laser chip, an asymmetric semiconductor heterostructure with a quantum-well active region is designed. The design of the emitting aperture of the laser chip is optimized to improve the operating characteristics of the laser beam when generating sub-ns optical pulses. It is shown that the transition to a monolithic emitting aperture design reduces the laser pulse turn-on spatial inhomogeneity, which is 90 ps over the entire range of optical powers studied. It is also demonstrated that by increasing the emitting aperture width to 400 μm, laser pulses with a peak power of 39.5 W and a pulse width at full width at half maximum (FWHM) of 120 ps can be generated. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

9 pages, 1179 KiB

Open AccessArticle

Continuous-Wave Room-Temperature External Cavity Quantum Cascade Lasers Operating at λ~8.5 μm

by Zixian Wang, Yuzhe Lin, Yuan Ma, Chenyang Wan, Fengxin Dong, Xuyan Zhou, Jinchuan Zhang, Fengqi Liu and Wanhua Zheng

Photonics 2025, 12(2), 129; https://doi.org/10.3390/photonics12020129 - 31 Jan 2025

Abstract

External cavity quantum cascade lasers (EC-QCLs) utilizing the Littrow configuration and operating at an approximate wavelength of 8.5 μm have been successfully demonstrated in continuous wave operations at room temperature. Our work provides ideas and experimental support for the optimization of the EC-QCL [...] Read more.

External cavity quantum cascade lasers (EC-QCLs) utilizing the Littrow configuration and operating at an approximate wavelength of 8.5 μm have been successfully demonstrated in continuous wave operations at room temperature. Our work provides ideas and experimental support for the optimization of the EC-QCL which indicate optimal EC-QCL performance with an external cavity length of 25 cm and investigates the impact of various parameters, including injection current and temperature on the performance of the EC-QCL. In the absence of anti-reflection (AR) coating, the tuning range at 25 °C extends up to 103.3 cm⁻¹, while the maximum side mode suppression ratio (SMSR) reaches 30.8 dB, accompanied by a full width half maximum linewidth (FWHM) of 0.76 nm. Full article

(This article belongs to the Special Issue The Three-Decade Journey of Quantum Cascade Lasers)

11 pages, 1534 KiB

Open AccessCommunication

SVM-Based Optical Detection of Retinal Ganglion Cell Apoptosis

by Mukhit Kulmaganbetov, Ryan Bevan, Andrew Want, Nantheera Anantrasirichai, Alin Achim, Julie Albon and James Morgan

Photonics 2025, 12(2), 128; https://doi.org/10.3390/photonics12020128 - 31 Jan 2025

Abstract

Background: Retinal ganglion cell (RGC) loss is crucial in eye diseases like glaucoma. Axon damage and dendritic degeneration precede cell death, detectable within optical coherence tomography (OCT) resolution, indicating their correlation with neuronal degeneration. The purpose of this study is to evaluate [...] Read more.

Background: Retinal ganglion cell (RGC) loss is crucial in eye diseases like glaucoma. Axon damage and dendritic degeneration precede cell death, detectable within optical coherence tomography (OCT) resolution, indicating their correlation with neuronal degeneration. The purpose of this study is to evaluate the optical changes of early retinal degeneration. Methods: The detection of optical changes in the axotomised retinal explants was completed in six C57BL/6J mice. OCT images were acquired up to 120 min from enucleation. A grey-level co-occurrence-based texture analysis was performed on the inner plexiform layer (IPL) to monitor changes in the optical speckles using a principal component analysis (PCA) and a support vector machine (SVM). In parallel tests, retinal transparency was confirmed by a comparison of the modulation transfer functions (MTFs) at 0 and 120 min. Results: Quantitative confirmation by analysis of the MTFs confirmed the non-degradation of optical transparency during the imaging period: MTF (fx) = 0.267 ± 0.02. Textural features in the IPL could discriminate between the optical signals of RGC degeneration. The mean accuracy of the SVM classification was 86.3%; discrimination was not enhanced by the combination of the SVM and PCA (81.9%). Conclusions: Optical changes in the IPL can be detected using OCT following RGC axotomy. High-resolution OCT can provide an index of retinal neuronal integrity and its degeneration. Full article

(This article belongs to the Special Issue Biomedical Optics：Imaging, Sensing and Therapy)

11 pages, 2273 KiB

Open AccessArticle

Demonstration of Quantum Polarized Microscopy Using an Entangled-Photon Source

by Mousume Samad, Maki Shimizu and Yasuto Hijikata

Photonics 2025, 12(2), 127; https://doi.org/10.3390/photonics12020127 - 31 Jan 2025

Abstract

With the advancement of non-classical light sources such as single-photon and entangled-photon sources, innovative microscopy based on quantum principles has been proposed for traditional microscopy. This paper introduces the experimental demonstration of a quantum polarization microscopic technique that incorporates a quantum-entangled photon source. [...] Read more.

With the advancement of non-classical light sources such as single-photon and entangled-photon sources, innovative microscopy based on quantum principles has been proposed for traditional microscopy. This paper introduces the experimental demonstration of a quantum polarization microscopic technique that incorporates a quantum-entangled photon source. Although the point that employs the variation in polarization angle due to reflection or transmission at the sample is similar to classical polarization microscopy, the method for constructing the image contrast is significantly different. The image contrast is constructed by the coincidence count of signal and idler photons. In the case that the coincidence count is recorded from both the signal and idler photons, the photon statistics resemble a thermal state, similar to the blackbody radiation, but with a significantly higher peak intensity in the second-order autocorrelation function at zero delay that is derived from the coincidence count, while, when the coincidence count is taken from either the signal or idler photon only, although the photon state exhibits a thermal state again, the photon statistics become more dispersive and result in a lower peak intensity of the autocorrelation function. These different thermal states can be switched by slightly changing the photon polarization, which is suddenly aroused within a narrow range of the analyzer angle. The autocorrelation function g²(0) at the thermal state exhibits a sensitivity that is three times higher compared to the classical coincidence count rate, and this concept can be effectively utilized to enhance the contrast of the image. One of the key achievements of our proposed method is ensuring a low power of illumination (in the order of Pico-joules) for constructing the image. In addition, the robustness without any precise setup is also favorable for practical use. This polarization microscopic technique can provide a superior imaging technique compared to the classical method, opening a new frontier for research in material sciences, biology, and other fields requiring high-resolution imaging. Full article

(This article belongs to the Special Issue Photonics: 10th Anniversary)

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7 pages, 1822 KiB

Open AccessCommunication

Grating Pair Wavepacket Shaper for Crafting Spatiotemporal Optical Vortices with Arbitrary Tilt Angles

by Jordan Adams and Andy Chong

Photonics 2025, 12(2), 126; https://doi.org/10.3390/photonics12020126 - 31 Jan 2025

Abstract

Spatiotemporal optical vortices with arbitrary tilt angles can be generated by adjusting spatial chirp and beam size at a phase modulation plane in a pulse shaper setup. A grating pair setup is proposed to generate variable spatial chirp independent of the beam profile. [...] Read more.

Spatiotemporal optical vortices with arbitrary tilt angles can be generated by adjusting spatial chirp and beam size at a phase modulation plane in a pulse shaper setup. A grating pair setup is proposed to generate variable spatial chirp independent of the beam profile. The initial dispersion of the pulse allows for the independent control of the vortex orientation. By adjusting the beam size, spatial chirp, and initial dispersion, arbitrary vortex orientation across all the possible angles can be achieved. The ability to achieve arbitrary vortex orientations at long propagation distances could offer significant advantages for long-distance communication applications. Full article

(This article belongs to the Special Issue Progress in OAM Beams: Recent Innovations and Future Perspectives)

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21 pages, 15250 KiB

Open AccessReview

Plasmonic Vortices: A Promising Tool Utilizing Plasmonic Orbital Angular Momentum

by Zhi Gao, Dmitri V. Voronine and Alexei V. Sokolov

Photonics 2025, 12(2), 125; https://doi.org/10.3390/photonics12020125 - 31 Jan 2025

Abstract

An optical vortex (OV) beam is an important type of spatially structured beam. However, the diffraction limit for light with orbital angular momentum (OAM) remains a challenge for certain applications. Surface plasmon polaritons (SPPs) can confine light to nanoscale dimensions and enhance light–matter [...] Read more.

An optical vortex (OV) beam is an important type of spatially structured beam. However, the diffraction limit for light with orbital angular momentum (OAM) remains a challenge for certain applications. Surface plasmon polaritons (SPPs) can confine light to nanoscale dimensions and enhance light–matter interactions. Over the past two decades, researchers have begun to explore the imparting of OAM onto SPPs to generate plasmonic vortices (PVs). Since the discovery of PVs, significant efforts have been made in this field, leading to considerable progress. This article reviews these studies in three key areas: (a) the generation and manipulation of PVs, (b) the characterization of PVs, and (c) the application of PVs. We believe that PVs represent a promising tool utilizing plasmonic OAM for both fundamental research and practical applications and hold great potential for the future with continued dedicated efforts. Full article

(This article belongs to the Special Issue Ultrafast Pulse Shaping Techniques: From Temporal to Spatiotemporal Control)

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8 pages, 2635 KiB

Open AccessArticle

Determination of the Effective Lifetime of a Spinor Bose–Einstein Condensate

by Xin Wang, Yong Qin, Jun Jian, Wenliang Liu, Jizhou Wu, Yuqing Li, Vladimir Sovkov and Jie Ma

Photonics 2025, 12(2), 124; https://doi.org/10.3390/photonics12020124 - 30 Jan 2025

Abstract

The effective lifetime of ultra-cold atoms in specific quantum states plays a crucial role in studying interaction parameters within quantum systems. Measuring the effective lifetime of various quantum states within ultra-cold atoms is a fundamental task in quantum operations. In this paper, the [...] Read more.

The effective lifetime of ultra-cold atoms in specific quantum states plays a crucial role in studying interaction parameters within quantum systems. Measuring the effective lifetime of various quantum states within ultra-cold atoms is a fundamental task in quantum operations. In this paper, the effective lifetimes of the excited electronic states

|F = 2, m_{F} = - 2⟩

,

|F = 2, m_{F} = - 1⟩

, and

|F = 2, m_{F} = 0⟩

for a sodium atomic Bose–Einstein condensate (BEC) are investigated in both the optical dipole trap (ODT) and one-dimensional optical lattice. Through the analysis of experimental data, we demonstrate the significant advantage of lattice loading over the optical dipole trap in terms of atomic lifetimes. The results provide crucial insights into the temporal scales relevant for investigating the evolution of boson gases in optical lattices, facilitating the realization of quantum simulations pertaining to unique quantum phases, and providing an important experimental basis for the research of non-equilibrium dynamics between different spin states. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

12 pages, 725 KiB

Open AccessArticle

Near-Field Enhancement in SPASER Nanostructures for High-Efficiency Energy Conversion

by Amine Jaouadi, Ahmed Mahjoub and Montacer Dridi

Photonics 2025, 12(2), 123; https://doi.org/10.3390/photonics12020123 - 29 Jan 2025

Abstract

We present in this study a theoretical investigation of the near-field enhancement phenomenon within nanostructures, which have garnered recent attention due to their potential applications in sensing, imaging, and energy harvesting. The analysis reveals a significant intensification of electromagnetic fields proximal to periodically [...] Read more.

We present in this study a theoretical investigation of the near-field enhancement phenomenon within nanostructures, which have garnered recent attention due to their potential applications in sensing, imaging, and energy harvesting. The analysis reveals a significant intensification of electromagnetic fields proximal to periodically arranged arrays of gold nanoparticles sustaining a highly lossy mode. In addition to the existence of a localized surface plasmon (LSP) mode exhibiting suboptimal quality, our investigation unveils intricate aspects of near-field enhancement closely correlated to the dynamics of lasing mechanisms. Notably, our investigation is focused on elucidating the augmentation’s behavior across varying pumping energies. The achieved enhancement surpasses two orders of magnitude compared to the passive counterparts. We introduce a description of the energy conversion rate specific to the SPASER configuration. The conceptualized SPASER reveals a significant promise. It showcases energy conversion efficiency up to 80%, emphasizing the SPASER’s potential as a highly effective nano-scale energy source. Full article

(This article belongs to the Special Issue Optical Fiber Lasers and Laser Technology)

14 pages, 6634 KiB

Open AccessArticle

Method of Tissue Differentiation Based on Changes in Tissue Optical Properties Under Mechanical Stress Estimated with Optical Coherence Tomography

by Evgeny P. Sherstnev, Alexander A. Moiseev, Aleksander A. Sovetsky, Pavel A. Shilyagin, Sergey Y. Ksenofontov and Grigory V. Gelikonov

Photonics 2025, 12(2), 122; https://doi.org/10.3390/photonics12020122 - 29 Jan 2025

Abstract

This study highlights the possibility of contrasting the differences in tissues’ mechanical properties from Optical Coherence Tomography (OCT) data without maintaining phase stability during OCT data acquisition. The proposed method is based on the rate of attenuation coefficient changes under the mechanical pressure [...] Read more.

This study highlights the possibility of contrasting the differences in tissues’ mechanical properties from Optical Coherence Tomography (OCT) data without maintaining phase stability during OCT data acquisition. The proposed method is based on the rate of attenuation coefficient changes under the mechanical pressure evaluation of the OCT data. It was shown, both on the calibrated synthetic and ex vivo biological samples, that the rate of attenuation coefficient changes observed corresponds to the sample’s mechanical properties and could be used to characterize the sample and distinguish it from other samples even if their optical properties before the pressure application are similar. This opens up the possibility to use an in vivo OCT-based system that can contrast mechanical properties without ensuring phase stability. Full article

(This article belongs to the Special Issue Advanced Technologies in Biophotonics and Medical Physics)

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11 pages, 6125 KiB

Open AccessCommunication

Localized Effects in Graphene Oxide Systems: A Pathway to Hyperbolic Metamaterials

by Grazia Giuseppina Politano

Photonics 2025, 12(2), 121; https://doi.org/10.3390/photonics12020121 - 29 Jan 2025

Abstract

Graphene oxide (GO) has emerged as a carbon-based nanomaterial providing a different pathway to graphene. One of its most notable features is the ability to partially reduce it, resulting in graphene-like sheets through the elimination of oxygen-including functional groups. In this paper, the [...] Read more.

Graphene oxide (GO) has emerged as a carbon-based nanomaterial providing a different pathway to graphene. One of its most notable features is the ability to partially reduce it, resulting in graphene-like sheets through the elimination of oxygen-including functional groups. In this paper, the effect of localized interactions in an Ag/GO/Au multilayer system was studied to explore its potential for photonic applications. GO was dip-coated onto magnetron-sputtered silver, followed by the deposition of a thin gold film to form an Ag/GO/Au structure. Micro-Raman Spectroscopy, SEM and Variable Angle Ellipsometry (VASE) measurements were performed on the Ag/GO/Au structure. An interesting behavior of the GO deposited on magnetron-sputtered silver with the formation of Ag nanostructures on top of the GO layer is reported. In addition to typical GO bands, Micro-Raman analysis reveals peaks such as the 1478 cm⁻¹ band, indicating a transition from sp³ to sp² hybridization, confirming the partial reduction of GO. Additionally, calculations based on effective medium theory (EMT) highlight the potential of Ag/GO structures in hyperbolic metamaterials for photonics. The medium exhibits dielectric behavior up to 323 nm, transitions to type I HMM between 323 and 400 nm and undergoes an Epsilon Near Zero and Pole (ENZP) transition at 400 nm, followed by type II HMM behavior. Full article

(This article belongs to the Special Issue Photonics Metamaterials: Processing and Applications)

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30 pages, 2229 KiB

Open AccessReview

Optoelectronic Oscillators: Progress from Classical Designs to Integrated Systems

by Qidi Liu, Jiuchang Peng and Juanjuan Yan

Photonics 2025, 12(2), 120; https://doi.org/10.3390/photonics12020120 - 29 Jan 2025

Abstract

Optoelectronic oscillators (OEOs) have emerged as indispensable tools for generating low-phase-noise microwave and millimeter-wave signals, which are critical for a variety of high-performance applications. These include radar systems, satellite links, electronic warfare, and advanced instrumentation. The ability of OEOs to produce signals with [...] Read more.

Optoelectronic oscillators (OEOs) have emerged as indispensable tools for generating low-phase-noise microwave and millimeter-wave signals, which are critical for a variety of high-performance applications. These include radar systems, satellite links, electronic warfare, and advanced instrumentation. The ability of OEOs to produce signals with exceptionally low phase noise makes them ideal for scenarios demanding high signal purity and stability. In radar systems, low-phase-noise signals enhance target detection accuracy and resolution, while, in communication networks, such signals enable higher data throughput and improved signal integrity over extended distances. Furthermore, OEOs play a pivotal role in precision instrumentation, where even minor noise can compromise the performance of sensitive equipment. This review examines the progress in OEO technology, transitioning from classical designs relying on long optical fiber delay lines to modern integrated systems that leverage photonic integration for compact, efficient, and tunable solutions. Key advancements, including classical setups, hybrid designs, and integrated configurations, are discussed, with a focus on their performance improvements in phase noise, side-mode suppression ratio (SMSR), and frequency tunability. A 20-GHz oscillation with an SMSR as high as 70 dB has been achieved using a classical dual-loop configuration. A 9.867-GHz frequency with a phase noise of −142.5 dBc/Hz @ 10 kHz offset has also been generated in a parity–time-symmetric OEO. Additionally, integrated OEOs based on silicon photonic microring resonators have achieved an ultra-wideband tunable frequency from 3 GHz to 42.5 GHz, with phase noise as low as −93 dBc/Hz at a 10 kHz offset. The challenges in achieving fully integrated OEOs, particularly concerning the stability and phase noise at higher frequencies, are also explored. This paper provides a comprehensive overview of the state of the art in OEO technology, highlighting future directions and potential applications. Full article

(This article belongs to the Special Issue Application and Development of Optoelectronic Oscillators (OEOs) in Microwave Photonics)

13 pages, 12684 KiB

Open AccessArticle

Creation of Bessel–Gaussian Beams from Necklace Beams via Second-Harmonic Generation

by Nikolay Dimitrov, Kiril Hristov, Maya Zhekova and Alexander Dreischuh

Photonics 2025, 12(2), 119; https://doi.org/10.3390/photonics12020119 - 28 Jan 2025

Abstract

The interest in (quasi-)nondiffracting beams is rooted in applications spanning from secure sharing cryptographic keys real-world free-space optical communications and high-order harmonic generation to high-aspect-ratio nanochannel machining, photopolymerization, and nanopatterning, just to mention a few. In this work, we explore the robustness of [...] Read more.

The interest in (quasi-)nondiffracting beams is rooted in applications spanning from secure sharing cryptographic keys real-world free-space optical communications and high-order harmonic generation to high-aspect-ratio nanochannel machining, photopolymerization, and nanopatterning, just to mention a few. In this work, we explore the robustness of the approach for generating Bessel–Gaussian beams by Fourier transforming ring-shaped beams and push the limits further. Here, instead of ring-shaped beams, we use strongly azimuthally modulated necklace beams. Necklace structures are generated by interference of OV beams that carry equal topological charges of opposite signs. In order to effectively account for the azimuthal

π

-phase jumps in the necklace beams, we first generate their second harmonic, thereafter focusing (i.e., Fourier transforming) them with a thin lens. In this way, we successfully create Bessel–Gaussian beams in the second harmonic of a pump beam with strong azimuthal modulation. The experimental data presented are in good agreement with the developed analytical model. Full article

(This article belongs to the Special Issue Advances in Structured Light: Propagation, Scattering, and Applications)

17 pages, 3014 KiB

Open AccessArticle

Design and Application of Laser Polarization Underwater Detection Equipment

by Yong Zhu, Fangxing Zong, Chao Dong, Qiang Fu, Xiansong Gu, Qingyi He, Jianhua Liu, Li Zheng, Geng Dong, Haili Zhao and Jin Duan

Photonics 2025, 12(2), 118; https://doi.org/10.3390/photonics12020118 - 28 Jan 2025

Abstract

With the increasing demand for precise identification of underwater targets, the development of advanced underwater detection technologies has become a pivotal area of research. This study presents the design and implementation of a laser-based underwater detection system that leverages polarization characteristics to significantly [...] Read more.

With the increasing demand for precise identification of underwater targets, the development of advanced underwater detection technologies has become a pivotal area of research. This study presents the design and implementation of a laser-based underwater detection system that leverages polarization characteristics to significantly enhance detection accuracy and target identification capabilities in complex aquatic environments. A key innovation of this research lies in the application of a dual-frequency modulation technology using a 532 nm pulsed laser. By modulating the high-frequency characteristics of the laser, this technique effectively suppresses backscattering interference within the water medium, improves the efficiency of target signal extraction, and exhibits exceptional performance, particularly in long-range detection and highly turbid water conditions. This paper elucidates the principles of underwater laser detection and polarization measurement, outlines the design of an integrated optical and mechanical system for laser transmission and reception, and introduces an optimized signal processing methodology. Experimental results demonstrate that the proposed system can reliably distinguish targets composed of different materials while maintaining high detection accuracy across a range of challenging environmental conditions. A comparative analysis further highlights the system’s significant advantages over traditional technologies, including enhanced noise suppression and greater detection depth. These findings establish a solid foundation for advancing underwater detection technologies and broadening their practical applications. Full article

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9 pages, 2820 KiB

Open AccessArticle

A Fast Rearrangement Method for Defect-Free Atom Arrays

by Yuqing Zhang, Zeyan Zhang, Guoqing Zhang, Zhehua Zhang, Yanpu Chen, Yuqing Li, Wenliang Liu, Jizhou Wu, Vladimir Sovkov and Jie Ma

Photonics 2025, 12(2), 117; https://doi.org/10.3390/photonics12020117 - 28 Jan 2025

Abstract

Defect-free atom arrays provide new possibilities for exploring exotic quantum phenomena and realizing quantum computing. However, quickly and efficiently preparing defect-free atom arrays poses challenges. This paper proposes an innovative parallel rearrangement method, namely the parallel compression filling algorithm (PCFA), wherein multiple movable [...] Read more.

Defect-free atom arrays provide new possibilities for exploring exotic quantum phenomena and realizing quantum computing. However, quickly and efficiently preparing defect-free atom arrays poses challenges. This paper proposes an innovative parallel rearrangement method, namely the parallel compression filling algorithm (PCFA), wherein multiple movable optical tweezers operate simultaneously. By limiting the shape of the initial loading, the method reduces movement complexity. The simulation comparisons show that this algorithm is more efficient in preparing defect-free atom arrays and can also be applied to the generation of other periodic structure arrays. The simulation results show that, in most cases, preparing a defect-free array of 400 atoms requires no more than 30 steps. Full article

18 pages, 14990 KiB

Open AccessArticle

Design of a Freeform Surface Optical Detection System with a Square Aperture

by Hongkai Zhao and Xianglong Mao

Photonics 2025, 12(2), 116; https://doi.org/10.3390/photonics12020116 - 28 Jan 2025

Abstract

To meet the demands for heightened detection sensitivity in satellite-based space target detection systems, we introduce an innovative square aperture diaphragm system utilizing freeform surfaces for detecting targets in the visible light spectrum. Characterized by a 40 mm × 40 mm square entrance [...] Read more.

To meet the demands for heightened detection sensitivity in satellite-based space target detection systems, we introduce an innovative square aperture diaphragm system utilizing freeform surfaces for detecting targets in the visible light spectrum. Characterized by a 40 mm × 40 mm square entrance pupil, a 4° × 4° field of view (FOV), and a 150 mm focal length, this system achieves a spot size of 2 × 2 pixels with 85% energy concentration within 18.4 μm, showcasing exceptional performance. Our design, compared to a circular aperture system of similar specifications, increases the entrance pupil area by 27% while having a smaller volume, resulting in a 0.24 magnitude improvement in the detection of space targets. This advancement significantly enhances our ability to detect fainter space targets with high sensitivity. The findings of this study pave the way for advancements in satellite-based space target detection technology. Full article

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12 pages, 28322 KiB

Open AccessArticle

Optimization of Erbium-Doped Fiber to Improve Temperature Stability and Efficiency of ASE Sources

by Jia Guo, Hao Zhang, Wenbin Lin and Wei Xu

Photonics 2025, 12(2), 115; https://doi.org/10.3390/photonics12020115 - 27 Jan 2025

Abstract

The ASE (Amplified Spontaneous Emission) light source, based on erbium-doped fiber (EDF), is a broadband light source with advantages such as high power, excellent temperature stability, and low coherent light generation. It is widely used in the field of fiber optic sensing. However, [...] Read more.

The ASE (Amplified Spontaneous Emission) light source, based on erbium-doped fiber (EDF), is a broadband light source with advantages such as high power, excellent temperature stability, and low coherent light generation. It is widely used in the field of fiber optic sensing. However, traditional ASE sources suffer from temperature sensitivity and low efficiency, which can compromise the accuracy and stability of the output light’s average wavelength. This study focuses on optimizing the erbium-doped fiber (EDF) to improve the temperature stability and efficiency of the ASE light source. Through simulations, we found that the appropriate doping concentration and length of the EDF are key factors in enhancing the stability and efficiency of the ASE source. Inorganic metal chloride vapor-phase doping combined with an improved chemical vapor deposition process was used to fabricate the erbium-doped fiber, ensuring low background loss, minimal OH⁻ absorption, and uniform distribution of the erbium ions in the core of the fiber. The optimized EDFs were integrated into the ASE source, achieving a power conversion efficiency of 53.6% and a temperature stability of 0.118 ppm/°C within the temperature range of −50 °C to 70 °C. This study offers a practical approach for improving the performance of ASE light sources and advancing the development of high-precision fiber optic sensing technologies. Full article

(This article belongs to the Special Issue Novel Two-Dimensional Materials Based on Nonlinear Photonics)

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12 pages, 1458 KiB

Open AccessArticle

Correlated Photon Lidar Based on Time-Division Multiplexing

by Yun Jiang, Bo Liu, Zixun Wang, Fengyun Huang, Taibei Liu, Lan Luo, Feifan He, Yongqi Yang and Bin Zhao

Photonics 2025, 12(2), 114; https://doi.org/10.3390/photonics12020114 - 27 Jan 2025

Abstract

Single-photon lidar (SPL) exhibits high sensitivity, making it particularly suitable for detecting weak echoes over long distances. However, its susceptibility to background noise necessitates the implementation of advanced filtering techniques and complex algorithms, which can significantly increase system cost and complexity. To address [...] Read more.

Single-photon lidar (SPL) exhibits high sensitivity, making it particularly suitable for detecting weak echoes over long distances. However, its susceptibility to background noise necessitates the implementation of advanced filtering techniques and complex algorithms, which can significantly increase system cost and complexity. To address these challenges, we propose a time-division-multiplexing-based correlated photon lidar system that employs a narrowband pulsed laser with stable time delays and variable pulse intensities, thereby establishing temporal and intensity correlations. This all-fiber solution not only simplifies the system architecture but also enhances operational efficiency. An adaptive cross-correlation method incorporating time slicing has been developed to extract histogram signals, enabling successful 1.5 km distance measurements under intense daytime noise conditions, using a 1 s accumulation time and a 20 mm receiving aperture. The experimental results demonstrate a 38% (from 1.11 to 1.52) improvement in the signal-to-noise ratio (SNR), thereby enhancing the system’s anti-noise capability, facilitating rapid detection, and reducing overall system costs. Full article

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