Photonics

24 pages, 3261 KiB

Open AccessReview

by Kamel Aït-Ameur and Abdelkrim Hasnaoui

Photonics 2025, 12(6), 596; https://doi.org/10.3390/photonics12060596 - 10 Jun 2025

The research on high-order transverse modes in lasers was largely abandoned a few years after the invention of the laser in 1960. The main reason for this was that high-order beams are more divergent and less bright than the Gaussian beam. In the [...] Read more.

The research on high-order transverse modes in lasers was largely abandoned a few years after the invention of the laser in 1960. The main reason for this was that high-order beams are more divergent and less bright than the Gaussian beam. In the present paper, we showed that the behaviour of

L G_{p 0}

beams faced to the optical Kerr effect (OKE) varies considerably depending on the mode order (p = 0 or

p \geq 1

). We focused our attention on the properties of

L G_{00}

and

L G_{10}

beams when subject to OKE, and we found that the

L G_{10}

beam keeps its focusability much better than the

L G_{00}

beam. This property has at least two applications concerning first the conception of high-intensity laser chains not based on a Gaussian beam but on an

L G_{10}

beam and second, the use of an

L G_{10}

beam instead of the usual Gaussian beam which can reduce drastically the protection of optical limiters based on OKE; this constitutes a counter-measure against such limiters. Full article

(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)

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18 pages, 2909 KiB

Open AccessArticle

Characterization of a Supersonic Plasma Jet by Means of Optical Emission Spectroscopy

by Ruggero Barni, Hanaa Zaka, Dipak Pal, Irsa Amjad and Claudia Riccardi

Photonics 2025, 12(6), 595; https://doi.org/10.3390/photonics12060595 - 10 Jun 2025

Abstract

We discuss an innovative thin film deposition method, Plasma Assisted Supersonic Jet Deposition, which combines the chemistry richness of a reactive cold plasma environment and the assembly control of the film growth allowed by a supersonic jet directed at the substrate. Optical Emission [...] Read more.

We discuss an innovative thin film deposition method, Plasma Assisted Supersonic Jet Deposition, which combines the chemistry richness of a reactive cold plasma environment and the assembly control of the film growth allowed by a supersonic jet directed at the substrate. Optical Emission Spectroscopy was used to characterize the plasma state and the supersonic jet, together with its interaction with the substrate. We obtained several results in the deposition of silicon oxide thin films from Hexamethyldisiloxane, with different degrees of organic groups retention. In particular we exploited the features of emission spectra to measure the plasma dissociation and oxidation degree of the organic groups, as a function of the jet parameters. If controlled growth is achieved, such films are nanostructured materials suitable for applications like catalysis, photo catalysis, energy conversion and storage, besides their traditional uses as a barrier or protective coatings. Full article

(This article belongs to the Special Issue Steady-State and Ultrafast Time-Resolved Optical Spectroscopy and Laser Applications in Biology, Chemistry, Physics, Biomedical Optics and High-Resolution Imaging)

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9 pages, 1678 KiB

Open AccessCommunication

High-Brightness 1940 nm Gallium Antimonide Diode Lasers with External-Cavity Spectral and Polarization Beam Combining

by Rong Zhao, Yufei Zhao, Bo Meng and Cunzhu Tong

Photonics 2025, 12(6), 594; https://doi.org/10.3390/photonics12060594 - 10 Jun 2025

Abstract

In this paper, we present a beam-combining technique to boost GaSb-based 1940 nm diode laser output power through spectral beam combining (SBC), spatial beam combining, and polarization beam combining (PBC). Four spectral beam-combining (SBC) configurations were developed using commercially available standard bars. The [...] Read more.

In this paper, we present a beam-combining technique to boost GaSb-based 1940 nm diode laser output power through spectral beam combining (SBC), spatial beam combining, and polarization beam combining (PBC). Four spectral beam-combining (SBC) configurations were developed using commercially available standard bars. The four SBC configurations were paired to perform PBC after spatial beam combining. The total output power of the 1940 nm laser reached 23.4 W, with the beam qualities of the combined beam achieving 10.6 in the slow axis and 11 in the fast axis. The brightness of the combined laser reached 5.4 MW·cm⁻²·sr⁻¹. Full article

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29 pages, 819 KiB

Open AccessReview

Visible Light Communication for Underwater Applications: Principles, Challenges, and Future Prospects

by Vindula L. Jayaweera, Chamodi Peiris, Dhanushika Darshani, Sampath Edirisinghe, Nishan Dharmaweera and Uditha Wijewardhana

Photonics 2025, 12(6), 593; https://doi.org/10.3390/photonics12060593 - 10 Jun 2025

Abstract

Underwater wireless communications face significant challenges due to high attenuation, turbulence, and water turbidity. Traditional methods like acoustic and radio frequency (RF) communication suffer from low data rates (<100 kbps), high latency (>1 s), and limited transmission distances (<10 km).Visible Light Communication (VLC) [...] Read more.

Underwater wireless communications face significant challenges due to high attenuation, turbulence, and water turbidity. Traditional methods like acoustic and radio frequency (RF) communication suffer from low data rates (<100 kbps), high latency (>1 s), and limited transmission distances (<10 km).Visible Light Communication (VLC) emerges as a promising alternative, offering high-speed data transmission (up to 5 Gbps), low latency (<1 ms), and immunity to electromagnetic interference. This paper provides an in-depth review of underwater VLC, covering fundamental principles, environmental factors (scattering, absorption), and dynamic water properties. We analyze modulation techniques, including adaptive and hybrid schemes (QAM-OFDM achieving 4.92 Gbps over 1.5 m), and demonstrate their superiority over conventional methods. Practical applications—underwater exploration, autonomous vehicle control, and environmental monitoring—are discussed alongside security challenges. Key findings highlight UVLC’s ability to overcome traditional limitations, with experimental results showing 500 Mbps over 150 m using PAM4 modulation. Future research directions include integrating quantum communication and Reconfigurable Intelligent Surfaces (RISs) to further enhance performance, with simulations projecting 40% improved spectral efficiency in turbulent conditions. Full article

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19 pages, 4218 KiB

Open AccessArticle

A Multi-Deformable-Mirror 500 Hz Adaptive Optical System for Atmospheric Turbulence Simulation, Real-Time Reconstruction, and Wavefront Correction Using Bimorph and Tip-Tilt Correctors

by Ilya Galaktionov and Vladimir Toporovsky

Photonics 2025, 12(6), 592; https://doi.org/10.3390/photonics12060592 - 9 Jun 2025

Abstract

Atmospheric turbulence introduces distortions to the wavefront of propagating optical radiation. It causes image resolution degradation in astronomical telescopes and significantly reduces the power density of radiation on the target in focusing applications. The impact of turbulence fluctuations on the wavefront can be [...] Read more.

Atmospheric turbulence introduces distortions to the wavefront of propagating optical radiation. It causes image resolution degradation in astronomical telescopes and significantly reduces the power density of radiation on the target in focusing applications. The impact of turbulence fluctuations on the wavefront can be investigated under laboratory conditions using either a fan heater (roughly tuned), a phase plate, or a deformable mirror (finely tuned) as a turbulence-generation device and a wavefront sensor as a wavefront-distortion measurement device. We designed and developed a software simulator and an experimental setup for the reconstruction of atmospheric turbulence-phase fluctuations as well as an adaptive optical system for the compensation of induced aberrations. Both systems use two 60 mm, 92-channel, bimorph deformable mirrors and two tip-tilt correctors. The wavefront is measured using a high-speed Shack–Hartmann wavefront sensor based on an industrial CMOS camera. The system was able to achieve a 500 Hz correction frame rate, and the amplitude of aberrations decreased from 2.6 μm to 0.3 μm during the correction procedure. The use of the tip-tilt corrector allowed a decrease in the focal spot centroid jitter range of 2–3 times from ±26.5 μm and ±24 μm up to ±11.5 μm and ±5.5 μm. Full article

(This article belongs to the Special Issue Optical Sensing Technologies, Devices and Their Data Applications)

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10 pages, 1533 KiB

Open AccessCommunication

Orthogonally Polarized Green Dual-Wavelength Pr³⁺:LiLuF₄ Laser at 523 and 538 nm with the Power Ratio of 1:1

by Haotian Huang, Yuzhao Li, Yanfei Lü, Nguyentuan Anh, Qian Zhang and Jing Xia

Photonics 2025, 12(6), 591; https://doi.org/10.3390/photonics12060591 - 9 Jun 2025

Abstract

An orthogonally polarized green dual-wavelength (OPGDW) laser output in a Pr³⁺:LiLuF₄ (Pr:LLF) crystal with the power ratio of 1:1 was realized for the first time. We calculated the condition for obtaining the identical power of the two output wavelengths and [...] Read more.

An orthogonally polarized green dual-wavelength (OPGDW) laser output in a Pr³⁺:LiLuF₄ (Pr:LLF) crystal with the power ratio of 1:1 was realized for the first time. We calculated the condition for obtaining the identical power of the two output wavelengths and achieved the OPGDW laser by adjusting the tilt angle of the intracavity etalon and optimizing the output coupling transmittance. Using a frequency-doubled (2ω) optically pumped semiconductor (OPS) laser of 10 W at 479 nm, a continuous wave (CW) OPGDW laser output at 523 nm (π-polarized) and 538 nm (σ-polarized) was achieved with a combined power of 1.83 W. In addition, by type-II critical phase-matched (CPM) β-BaB₂O₄ (BBO) nonlinear crystal, a 57 mW, 265 nm CW UV laser was also realized by sum-frequency generation (SFG) of 523 nm and 538 nm wavelengths. CW OPGDW lasers with identical power output were ideal for both medical detection and generating UV lasers. Full article

(This article belongs to the Special Issue Laser Technology and Applications)

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13 pages, 4604 KiB

Open AccessArticle

Research on the Detection of Middle Atmosphere Temperature by Pure Rotating Raman–Rayleigh Scattering LiDAR at Daytime and Nighttime

by Bangxin Wang, Cheng Li, Qian Deng, Decheng Wu, Zhenzhu Wang, Hao Yang, Kunming Xing and Yingjian Wang

Photonics 2025, 12(6), 590; https://doi.org/10.3390/photonics12060590 - 9 Jun 2025

Abstract

The temperature of the middle atmosphere is of great significance in the coupled study of the upper and lower layers. A pure rotational Raman–Rayleigh scattering LiDAR system was developed for profiling the middle atmospheric temperature at daytime and nighttime continuously by employing an [...] Read more.

The temperature of the middle atmosphere is of great significance in the coupled study of the upper and lower layers. A pure rotational Raman–Rayleigh scattering LiDAR system was developed for profiling the middle atmospheric temperature at daytime and nighttime continuously by employing an ultra-narrow band interferometer. The comparisons between LiDAR detections and radiosonde data show that the LiDAR system has temperature detection capabilities of 80 km and 60 km at night and during the day, respectively. The results demonstrate that our method can reliably detect the atmospheric temperature in the middle atmosphere. The significant non-uniformity in the horizontal distribution of temperature in the middle atmosphere and the vertical gradient of atmospheric temperature could be observed by using the developed LiDAR. Full article

(This article belongs to the Section New Applications Enabled by Photonics Technologies and Systems)

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11 pages, 1431 KiB

Open AccessArticle

Optimization of Output Characteristics in Figure-9 Mode-Locked Fiber Laser Based on Black Phosphorus Assistance

by Peiyuan Xiao, Lu Sui, Wanzhuo Ma, Renshun Pan and Huilin Jiang

Photonics 2025, 12(6), 589; https://doi.org/10.3390/photonics12060589 - 9 Jun 2025

Abstract

Utilizing the nonlinear effects of black phosphorus (BP), the self-starting threshold and noise performance were optimized in a figure-9 mode-locked fiber laser configuration. Experimental results demonstrate that a mode-locked pulse output with a spectral bandwidth of 8.2 nm, center wavelength of 1033.5 nm, [...] Read more.

Utilizing the nonlinear effects of black phosphorus (BP), the self-starting threshold and noise performance were optimized in a figure-9 mode-locked fiber laser configuration. Experimental results demonstrate that a mode-locked pulse output with a spectral bandwidth of 8.2 nm, center wavelength of 1033.5 nm, and repetition rate of 42 MHz is obtained. Compared with single-mechanism mode-locked lasers, the self-starting mode-locked threshold is reduced by 100 mW. Regarding noise characteristics, the signal-to-noise ratio (SNR) is enhanced to 68.4 dB and the phase noise is reduced to −115.6 dBc/Hz at 1 MHz to 10 MHz frequency offsets. The root mean square (RMS) of the output power is optimized to 0.9% and phase noise jitter is reduced to 1.9%. This work proves a novel approach to tackle the challenges of high self-starting thresholds and instability in mode-locked lasers. Full article

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

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21 pages, 17434 KiB

Open AccessArticle

Large Vessel Segmentation and Microvasculature Quantification Based on Dual-Stream Learning in Optic Disc OCTA Images

by Jingmin Luan, Zehao Wei, Qiyang Li, Jian Liu, Yao Yu, Dongni Yang, Jia Sun, Nan Lu, Xin Zhu and Zhenhe Ma

Photonics 2025, 12(6), 588; https://doi.org/10.3390/photonics12060588 - 9 Jun 2025

Abstract

Quantification of optic disc microvasculature is crucial for diagnosing various ocular diseases. However, accurate quantification of the microvasculature requires the exclusion of large vessels, such as the central artery and vein, when present. To address the challenge of ineffective learning of edge information, [...] Read more.

Quantification of optic disc microvasculature is crucial for diagnosing various ocular diseases. However, accurate quantification of the microvasculature requires the exclusion of large vessels, such as the central artery and vein, when present. To address the challenge of ineffective learning of edge information, which arises from the adhesion and transposition of large vessels in the optic disc, we developed a segmentation model that generates high-quality edge information in optic disc slices. By integrating dual-stream learning with channel-spatial attention and multi-level attention mechanisms, our model effectively learns both the target’s primary structure and fine details. Compared to state-of-the-art methods, our proposed approach demonstrates superior performance in segmentation accuracy. Superior results were obtained when the model was tested on OCTA images of the optic disc from 10 clinical patients. This underscores the significant contribution of our method in achieving clearly defined multi-task learning while substantially enhancing inference speed. Full article

(This article belongs to the Section Biophotonics and Biomedical Optics)

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11 pages, 2558 KiB

Open AccessArticle

Highly Efficient Digitized Quasi-3D Photolithography Based on a Modified Golomb Coding via DMD Laser Direct Writing

by Hui Wang, Zhe Huang, Yanting Shen and Shangying Zhou

Photonics 2025, 12(6), 587; https://doi.org/10.3390/photonics12060587 - 9 Jun 2025

Abstract

Three-dimensional (3D) photolithography has found wide applications in microelectronics, optoelectronics, biomedicine, etc. Traditionally, it requires repetitive exposure and developing cycles. Meanwhile, a laser direct writing (LDW) system with a digital micromirror device (DMD) enables high-speed maskless lithography with programmable doses. In this paper, [...] Read more.

Three-dimensional (3D) photolithography has found wide applications in microelectronics, optoelectronics, biomedicine, etc. Traditionally, it requires repetitive exposure and developing cycles. Meanwhile, a laser direct writing (LDW) system with a digital micromirror device (DMD) enables high-speed maskless lithography with programmable doses. In this paper, we propose a quasi-3D digitized photolithography via LDW with a DMD to remove multiple developing cycles from the process. This approach quantizes the dose of the 3D geometry and stores it in a grayscale image. And the entire dose distribution can be formed by overlapping the exposures with sliced binary dose maps from the above grayscale dose map. In the image slicing algorithm, a modified Golomb coding is introduced to make full use of the highest available exposure intensity. Both 1D multi-step patterns and diffractive optical devices (DOEs) have been fabricated to verify its feasibility. This type of digitized quasi-3D photolithography can be applied to fabricating DOEs, microlens arrays (MLAs), micro-refractive optical elements (μROEs), etc., and 3D molds for micro-embossing/nano-imprinting. Full article

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10 pages, 977 KiB

Open AccessCommunication

Tailorable Brillouin Light Scattering in Air-Slit Suspended Waveguide

by Yanzhao Wang, Hongrun Ren and Yunjie Teng

Photonics 2025, 12(6), 586; https://doi.org/10.3390/photonics12060586 - 9 Jun 2025

Abstract

Silicon-based optical waveguides exhibit high Brillouin gain, enabling the realization of Brillouin lasers directly on silicon substrates. These lasers hold significant promise for applications such as tunable-frequency laser emission, ultrafast pulse generation via mode-locking techniques, and other advanced photonic functionalities. However, a key [...] Read more.

Silicon-based optical waveguides exhibit high Brillouin gain, enabling the realization of Brillouin lasers directly on silicon substrates. These lasers hold significant promise for applications such as tunable-frequency laser emission, ultrafast pulse generation via mode-locking techniques, and other advanced photonic functionalities. However, a key challenge in silicon-based Brillouin lasers is the requirement for long waveguide lengths to achieve sufficient optical feedback and reach the lasing threshold. This study proposes a novel floating waveguide architecture designed to significantly enhance the Brillouin gain in silicon-based systems. Furthermore, we introduce a breakthrough method for achieving wide-range phonon frequency tunability, enabling precise control over stimulated Brillouin scattering (SBS) dynamics. By strategically engineering the waveguide geometry (shape and dimensions), we demonstrate a tunable SBS phonon laser, offering a versatile platform for on-chip applications. Additionally, the proposed waveguide system features adjustable operating frequencies, unlocking new opportunities for compact Brillouin devices and integrated microwave photonic signal sources. Full article

(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)

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22 pages, 5040 KiB

Open AccessArticle

Multi-Partition Mapping Simulation Method for Stellar Spectral Information

by Yu Zhang, Da Xu, Bin Zhao, Songzhou Yang, Zhipeng Wei, Jian Zhang, Taiyang Ren, Junjie Yang and Yao Meng

Photonics 2025, 12(6), 585; https://doi.org/10.3390/photonics12060585 - 9 Jun 2025

Abstract

Stellar radiation simulation is critical in the space industry; however, with the current simulation methods, only a single color temperature and magnitude can be modulated at a time. Furthermore, star sensors rely on star observation tests for accurate calibration; this seriously restricts their [...] Read more.

Stellar radiation simulation is critical in the space industry; however, with the current simulation methods, only a single color temperature and magnitude can be modulated at a time. Furthermore, star sensors rely on star observation tests for accurate calibration; this seriously restricts their development. This paper presents a novel star spectral information multi-partition mapping simulation method to closely simulate real sky star map information, thus replacing non-scenario-specific field stargazing experiments. First, using the stellar spectral simulation principle, a multi-partition mapping principle based on a digital micro-mirror device is proposed, and the theoretical basis of sub-region division is provided. Second, multi-component mapping simulation of stellar spectral information is expounded, and a general architecture for the same based on a double-prism symmetry structure is presented. Next, the influence of peak spectral half-peak width and peak interval on spectral simulation accuracy is analyzed, and a pre-collimated beam expansion system, multi-dimensional slit, and spectral splitting system are designed accordingly. Finally, a test platform is set up, and single-region simulation results and multi-region consistency experiments are conducted to verify the feasibility of the proposed method. Our method can realize high-precision simulation and independently control the output of various color temperatures and magnitudes. It provides a theoretical and technical basis for the development of star sensor ground calibration tests and space target detection light environment simulation. Full article

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

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9 pages, 3584 KiB

Open AccessArticle

Parameter Study of 500 nm Thick Slot-Type Photonic Crystal Cavities for Cavity Optomechanical Sensing

by Zhe Li, Jun Liu, Yi Zhang, Chenguwei Xian, Yifan Wang, Kai Chen, Gen Qiu, Guangwei Deng, Yongjun Huang and Boyu Fan

Photonics 2025, 12(6), 584; https://doi.org/10.3390/photonics12060584 - 8 Jun 2025

Viewed by 71

Abstract

In recent years, research on light-matter interactions in silicon-based micro/nano cavity optomechanical systems demonstrates high-resolution sensing capabilities (e.g., sub-fm-level displacement sensitivity). Conventional 2D photonic crystal (PhC) cavity optomechanical sensors face inherent limitations: thin silicon layers (200–300 nm) restrict both the mass block (critical [...] Read more.

In recent years, research on light-matter interactions in silicon-based micro/nano cavity optomechanical systems demonstrates high-resolution sensing capabilities (e.g., sub-fm-level displacement sensitivity). Conventional 2D photonic crystal (PhC) cavity optomechanical sensors face inherent limitations: thin silicon layers (200–300 nm) restrict both the mass block (critical for thermal noise suppression) and optical Q-factor. Enlarging the detection mass in such thin layers exacerbates in-plane height nonuniformity, severely limiting high-precision sensing. This study proposes a 500 nm thick silicon-based 2D slot-type PhC cavity design for advanced sensing applications, fabricated on a silicon-on-insulator (SOI) substrate with optimized air slot structures. Systematic parameter optimization via finite element simulations defines structural parameters for the 1550 nm band, followed by 6 × 6 × 6 combinatorial experiments on lattice constant, air hole radius, and line-defect waveguide width. Experimental results demonstrate a loaded Q-factor of 57,000 at 510 nm lattice constant, 175 nm air hole radius, and 883 nm line-defect waveguide width (measured sidewall angle: 88.4°). The thickened silicon layer delivers dual advantages: enhanced mass block for thermal noise reduction and high Q-factor for optomechanical coupling efficiency, alongside improved ridge waveguide compatibility. This work advances the practical development of CMOS-compatible micro-opto-electromechanical systems (MOEMS). Full article

(This article belongs to the Section New Applications Enabled by Photonics Technologies and Systems)

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13 pages, 1744 KiB

Open AccessArticle

Numerical Optimization of Metamaterial-Enhanced Infrared Emitters for Ultra-Low Power Consumption

by Bui Xuan Khuyen, Pham Duy Tan, Bui Son Tung, Nguyen Phon Hai, Pham Dinh Tuan, Do Xuan Phong, Do Khanh Tung, Nguyen Hai Anh, Ho Truong Giang, Nguyen Phuc Vinh, Nguyen Thanh Tung, Vu Dinh Lam, Liangyao Chen and YoungPak Lee

Photonics 2025, 12(6), 583; https://doi.org/10.3390/photonics12060583 - 7 Jun 2025

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Abstract

This study addresses the challenges of high-power consumption and complexity in conventional infrared (IR) gas sensors by integrating metamaterials and gold coatings into IR radiation sources to reduce radiation loss. In addition, emitter design optimization and material selection were employed to minimize conduction [...] Read more.

This study addresses the challenges of high-power consumption and complexity in conventional infrared (IR) gas sensors by integrating metamaterials and gold coatings into IR radiation sources to reduce radiation loss. In addition, emitter design optimization and material selection were employed to minimize conduction loss. Our metasurface exhibited superior performance, achieving a narrower full width at half maximum at 4197 and 3950 nm, resulting in more confined emission spectral ranges. This focused emission reduced energy waste at unnecessary wavelengths, improving efficiency compared to traditional blackbody emitters. At 300 °C, the device consumed only 6.8 mW, while maintaining temperature uniformity and a fast response time. This enhancement is promising for the operation of such sensors in IoT networks with ultra-low power consumption and at suitably low costs for widespread demands in high-technology farming. Full article

(This article belongs to the Special Issue Emerging Trends in Metamaterials and Metasurfaces Research)

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11 pages, 1957 KiB

Open AccessArticle

Highly Efficient Upconversion Emission Platform Based on the MDM Cavity Effect in Aluminum Nanopillar Metasurface

by Xiaofeng Wu, Xiangyuan Mao, Shengbin Cheng, Haiou Li and Shiping Zhan

Photonics 2025, 12(6), 582; https://doi.org/10.3390/photonics12060582 - 7 Jun 2025

Viewed by 146

Abstract

Rare earth-doped upconversion nanoparticles (UCNPs) can convert low-energy photons (NIRs) into high-energy photons (visible light), offering advantages such as low background signal, good stability, and excellent biocompatibility. However, exploring a strategy to combine the advantages of high efficiency, low cost, and easy fabrication [...] Read more.

Rare earth-doped upconversion nanoparticles (UCNPs) can convert low-energy photons (NIRs) into high-energy photons (visible light), offering advantages such as low background signal, good stability, and excellent biocompatibility. However, exploring a strategy to combine the advantages of high efficiency, low cost, and easy fabrication of a plasmonics–UCNPs system is still a challenge. Here, we reported a metal–dielectric–metal (MDM)-type plasmonic platform based on the aluminum metasurface, which can efficiently enhance the luminescence intensity of magnetic and non-magnetic rare earth-doped UCNPs. Attributed to the strong local field effect of the nanocavities formed by the aluminum anti-transmission layer at the bottom, the fluorescence of the two types of UCNPs in such a platform can be enhanced by over 1000 folds compared with that in the conventional substrate. It is found that the deposited UCNPs amount and the aluminum pillar size can both impact the enhancement. We confirmed that the constructed MDM nanocavities could enhance and regulate the local field strength, and the optimum enhancement can be achieved by choosing proper parameters. All these findings provide an efficient way of exploring the plasmon-enhanced UCNPs luminescence system with low cost, high efficiency, and easy fabrication and can be promising in the fields of biosensing and photovoltaic devices. Full article

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11 pages, 2884 KiB

Open AccessArticle

The Design of a Circulator Based on Topological Photonic Crystals

by Yulin Zhao, Feng Liang, Jianfei Han, Jingsen Li, Haihua Hu, Weihao Zhang and Xiangjun Tan

Photonics 2025, 12(6), 581; https://doi.org/10.3390/photonics12060581 - 7 Jun 2025

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Abstract

Topological photonic crystals have garnered significant attention due to their fascinating topological edge states. These states are robust against sharp bends and defects and exhibit the novel property of unidirectional transmission. In this study, we analyze the topological edge states of gyromagnetic topological [...] Read more.

Topological photonic crystals have garnered significant attention due to their fascinating topological edge states. These states are robust against sharp bends and defects and exhibit the novel property of unidirectional transmission. In this study, we analyze the topological edge states of gyromagnetic topological photonic crystals in analogy with the quantum Hall effect. Through expanding and shrinking six dielectric cylinders, the optical quantum spin Hall effect is achieved. And helical edge states with pseudo-spin are demonstrated. Owing to the novel topological properties of these edge states, robust waveguides are proposed. Furthermore, integrating these two distinct types of topological states, a novel circulator with topological characteristics is designed. These topologically protected photonic devices will be beneficial for developing integrated circuits. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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17 pages, 7356 KiB

Open AccessArticle

A Comprehensive Error Analysis of the Neutron Elliptical Cylindrical Mirror with High Gain

by Weichen Gu, Jun Yu, Pengfeng Sheng, Fengrui Tang, Qiya Zhang, Peng Chen, Qiaoyu Wu, Wentao Song, Zhangran Cao, Zhengxiang Shen, Zhong Zhang and Zhanshan Wang

Photonics 2025, 12(6), 580; https://doi.org/10.3390/photonics12060580 - 6 Jun 2025

Viewed by 110

Abstract

The elliptical cylindrical mirror has been utilized in neutron small-angle scattering and reflectometry to enhance the neutron intensity at the sample position. However, the performance of the elliptical cylindrical mirror can be impacted by surface slope errors, reflectivity, and misalignments. In this work, [...] Read more.

The elliptical cylindrical mirror has been utilized in neutron small-angle scattering and reflectometry to enhance the neutron intensity at the sample position. However, the performance of the elliptical cylindrical mirror can be impacted by surface slope errors, reflectivity, and misalignments. In this work, the performance of the elliptical cylindrical mirror under different error conditions has been analyzed comprehensively, and a 250-mm-long elliptical cylindrical mirror was designed and developed. The simulations show that a source size below 1 mm is required to achieve a peak gain above 6, with a theoretical peak gain of 16× with a 0.1 mm source. The rotational misalignment of 0.03° around the Y-axis can decrease gain from 16× to 6×. The designed mirror was fabricated with a surface figure error of 110 nm (RMS), and a roughness below 0.5 nm (RMS), and was coated with an m = 4 supermirror. The mirror was aligned and tested in the dedicated neutron beamline of the Chinese mianyang research reactor, and the results show a peak gain of 12.77 with a 0.1 mm slit source. Full article

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10 pages, 3701 KiB

Open AccessArticle

Mechanism of Impurity Content in Degradation and Damage Characteristics of Calcium Fluoride Crystals by X-Ray and Deep-Ultraviolet Laser Irradiation

by Ping Han, Dapeng Jiang, Huamin Kou, Rongrong Liu, Qinghui Wu, Zhonghan Zhang, Zhen Zhang, Chong Shan, Chongyun Shao, Yafei Lian, Yuanan Zhao, Xing Peng and Liangbi Su

Photonics 2025, 12(6), 579; https://doi.org/10.3390/photonics12060579 - 6 Jun 2025

Viewed by 127

Abstract

Calcium fluoride (CaF₂) crystals are widely utilized in deep-ultraviolet (DUV) lithography due to their excellent optical properties. The laser-induced degradation and damage of CaF₂ crystals is a critical concern that restricts its extended application. Impurities of CaF₂ crystal are [...] Read more.

Calcium fluoride (CaF₂) crystals are widely utilized in deep-ultraviolet (DUV) lithography due to their excellent optical properties. The laser-induced degradation and damage of CaF₂ crystals is a critical concern that restricts its extended application. Impurities of CaF₂ crystal are considered a key factor affecting its laser resistance. Establishing the quantitative relationship and mechanism of impurity content impacting the degradation and damage characteristics of CaF₂ crystal is essential. This study investigated the characteristics of different impurity contents affecting the degradation and laser-induced damage thresholds (LIDTs) of CaF₂ crystals under X-ray and 193 nm pulsed laser irradiations, and quantitatively analyzed the degradation process and mechanism. Our findings demonstrate that impurities at ppm levels significantly diminish the transmittance of CaF₂ crystals across various wavelengths following X-ray irradiation. In contrast, these impurities have a negligible effect on the LIDT test results, suggesting distinct damage mechanisms between X-ray and laser irradiation. This study provides valuable insights for optimizing the CaF₂ crystal fabrication process and enhancing irradiation resistance. Full article

(This article belongs to the Special Issue Innovative Optical Technologies in Advanced Manufacturing)

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15 pages, 4842 KiB

Open AccessArticle

Dynamic Spatial Small-Target Simulation System with Long-Exit Pupil Distance

by Yi Lu, Xiping Xu, Ning Zhang, Yaowen Lv and Hua Geng

Photonics 2025, 12(6), 578; https://doi.org/10.3390/photonics12060578 - 6 Jun 2025

Viewed by 116

Abstract

System architecture was developed to solve the issues of short pupil distance and mismatch between the simulated wavelength range and the sensor in the simulator of small targets in space. The system consists of Liquid Crystal on Silicon (LCOS), a Polarizing Beam Splitter [...] Read more.

System architecture was developed to solve the issues of short pupil distance and mismatch between the simulated wavelength range and the sensor in the simulator of small targets in space. The system consists of Liquid Crystal on Silicon (LCOS), a Polarizing Beam Splitter (PBS), a dual free-form surface-illumination system, and a long-exit-pupil-distance projection system. The innovatively designed long exit pupil distance projection system can achieve an exit pupil distance of 1250 mm, covering the visible and near-infrared bands from 400 to 950 nm. The dual free-form surface-illumination system reaches a divergence angle of ±4.3° and an illumination non-uniformity of 4.7%. Experimental validation shows that the system’s star position error is better than −3.94″, and the angular distance error between stars does not exceed −7.69″. The radiation simulation accuracy for stars ranging from magnitude 3 to 6 is between −0.049 and 0.085 magnitudes, demonstrating high-precision simulation capabilities for both geometric and radiation characteristics. The research results set a critical theoretical foundation for the development of high-fidelity space target simulators, and the proposed dual free-form surface-design method and wide-spectrum aberration compensation technology provide a new paradigm for precision optical system design. Full article

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14 pages, 5764 KiB

Open AccessArticle

First Real-Time 267.8 Tb/S 2 × 70.76 Km Integrated Communication and Sensing Field Trial over Deployed Seven-Core Fiber Cable Using 130 Gbaud PCS-64QAM 1.2 Tb/S OTN Transponders

by Jian Cui, Leimin Zhang, Yu Deng, Zhuo Liu, Chao Wu, Bin Hao, Ting Zhang, Yuxiao Wang, Bin Wu, Chengxing Zhang, Yong Chen, Lei Shen, Jie Luo, Yan Sun, Qi Wan, Cheng Chang, Bing Yan and Ninglun Gu

Photonics 2025, 12(6), 577; https://doi.org/10.3390/photonics12060577 - 6 Jun 2025

Viewed by 127

Abstract

Ultra-high-speed integrated communication and sensing (ICS) transmission techniques are highly desired for next-generation highly reliable optical transport networks (OTNs). The inherent multiple-channel advantage of uncoupled multi-core fibers (MCFs) empowers the evolution of ICS techniques. In this paper, we demonstrate an ultra-high-speed ICS OTN [...] Read more.

Ultra-high-speed integrated communication and sensing (ICS) transmission techniques are highly desired for next-generation highly reliable optical transport networks (OTNs). The inherent multiple-channel advantage of uncoupled multi-core fibers (MCFs) empowers the evolution of ICS techniques. In this paper, we demonstrate an ultra-high-speed ICS OTN system utilizing 130 Gbaud probability constellation shaping 64-ary quadrature amplitude modulation (PCS-64QAM) 1.2 Tb/s OTN transponders and polarization-based sensing technique over a field-deployed seven-core MCF cable for the first time. A real-time 267.8 Tb/s 2 × 70.76 km transmission is achieved by only utilizing C-band signals thanks to the high-performance 1.2 Tb/s OTN transponders. Moreover, the ICS system can sense environmental impacts on the MCF cable such as shaking, striking, etc., in real time. The capacity of the transmission system can also be further enhanced by using signals in the L-band. Our work demonstrates the feasibility of simultaneously achieving ultra-high-speed data transmission and the real-time sensing of environmental disturbances over a field-deployed MCF cable, which we believe is a crucial milestone for next-generation ultra-high-speed highly reliable optical transmission networks. Full article

(This article belongs to the Special Issue Optical Networking Technologies for High-Speed Data Transmission)

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14 pages, 2006 KiB

Open AccessArticle

Design and Optimization of Optical NAND and NOR Gates Using Photonic Crystals and the ML-FOLD Algorithm

by Alireza Mohammadi, Fariborz Parandin, Pouya Karami and Saeed Olyaee

Photonics 2025, 12(6), 576; https://doi.org/10.3390/photonics12060576 - 6 Jun 2025

Viewed by 178

Abstract

The continuous demand for faster processing systems, driven by the rise of artificial intelligence, has exposed limitations in traditional transistor-based electronics, including quantum tunneling, heat dissipation, and switching delays due to challenges in further miniaturization. This study explores optical systems as a promising [...] Read more.

The continuous demand for faster processing systems, driven by the rise of artificial intelligence, has exposed limitations in traditional transistor-based electronics, including quantum tunneling, heat dissipation, and switching delays due to challenges in further miniaturization. This study explores optical systems as a promising alternative, leveraging the speed of photons over electrons. Specifically, we design and simulate optical NAND and NOR logic gates using a two-dimensional photonic crystal structure with a square lattice. Symmetrical waveguides are used for the input paths to make the structure relatively more straightforward to fabricate. A key innovation is the ability to realize both gates within a single structure by adjusting the phases of the input sources. To optimize the phase parameters efficiently, we employ the ML-FOLD (Meta-Learning and Formula Optimization for Logic Design) optimization formula, which outperforms traditional methods and machine learning approaches in terms of computational efficiency and data requirements. Through finite-difference time-domain (FDTD) simulations, the proposed optical structure demonstrates successful implementation of NAND and NOR gate logic, achieving high contrast ratios of 4.2 dB and 4.8 dB, respectively. The results validate the effectiveness of the ML-FOLD method in identifying optimal configurations, offering a streamlined approach for the design of all-optical logic devices. Full article

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13 pages, 2693 KiB

Open AccessCommunication

Prediction of Aluminum Alloy Surface Roughness Through Nanosecond Pulse Laser Assisted by Continuous Laser Paint Removal

by Jingyi Li, Rongfan Liang, Han Li, Junjie Liu and Jingdong Sun

Photonics 2025, 12(6), 575; https://doi.org/10.3390/photonics12060575 - 6 Jun 2025

Viewed by 99

Abstract

Reducing surface roughness can enhance the mechanical properties of processed materials. The variation law of the aluminum alloy surface roughness induced by continuous-nanosecond combined laser (CL) with different continuous laser power densities and laser delay is investigated experimentally. A back propagation neural network [...] Read more.

Reducing surface roughness can enhance the mechanical properties of processed materials. The variation law of the aluminum alloy surface roughness induced by continuous-nanosecond combined laser (CL) with different continuous laser power densities and laser delay is investigated experimentally. A back propagation neural network (BPNN) coupled with a sparrow search algorithm (SSA) is employed to predict surface roughness. The nanosecond laser energy density, continuous laser power density and laser delay are input parameters, while the surface roughness is output parameter. The lowest surface roughness is achieved with completely paint film removed by the CL while the nanosecond laser energy density is 1.99 J/cm², the continuous laser power density is 2118 W/cm² and the laser delay is 1 ms. Compared to the original target and the target irradiated by nanosecond pulse laser (ns laser), the reductions in the surface roughness are 20.62% and 12.00%, respectively. The SSA-BPNN model demonstrates high prediction accuracy, with a correlation coefficient (R²) of 0.98628, root mean square error (RMSE) of 0.024, mean absolute error (MAE) of 0.020 and mean absolute percentage error (MAPE) of 1.30% on the test set. These results indicate that the SSA-BPNN demonstrates higher-precision surface roughness prediction with limited experimental data than BPNN. Furthermore, the findings confirm that the CL can effectively reduce surface roughness. Full article

(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)

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11 pages, 2860 KiB

Open AccessCommunication

Threshold-Governed Inversion of Plasma Chronology at Air–Silicon Interfaces Under Tight Femtosecond Focusing

by Xian-An Dou, Xin Li, Qing Ye and Yuntao Xie

Photonics 2025, 12(6), 574; https://doi.org/10.3390/photonics12060574 - 6 Jun 2025

Viewed by 114

Abstract

The sequencing of laser-induced plasma formation in multi-material systems is fundamentally governed by the interplay between material ionization thresholds and laser temporal characteristics. This study uncovers a counterintuitive phenomenon where silicon plasma precedes air filamentation at air–silicon interfaces under tight femtosecond laser focusing, [...] Read more.

The sequencing of laser-induced plasma formation in multi-material systems is fundamentally governed by the interplay between material ionization thresholds and laser temporal characteristics. This study uncovers a counterintuitive phenomenon where silicon plasma precedes air filamentation at air–silicon interfaces under tight femtosecond laser focusing, which can be attributed to the significant difference in their ionization thresholds. Through time-resolved shadowgraphy with 550 fs resolution, we demonstrate that silicon plasma precedes air filamentation by approximately 3 ps, a temporal discrepancy that can be quantitatively attributed to the 137.5-fold lower ionization threshold of silicon compared to air. The combined influence of the laser temporal contrast and tight focusing geometry modulates this lead time from femtosecond to picosecond scales. This threshold-governed plasma chronology mechanism provides a new paradigm for controlling laser–material interactions, with direct implications for precision manufacturing of layered composites, depth-resolved optical diagnostics, phase-change material characterization, and 3D material architectures. Full article

(This article belongs to the Special Issue Advances in Nonlinear Optics: From Fundamentals to Applications)

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14 pages, 7312 KiB

Open AccessArticle

Application and Performance Improvement of an Optical Power Stabilization System Based on MEMS-LCVR in a SERF Atomic Magnetometer

by Yitong Li, Wenfei Zhang, Jianqi Yang, Ying Liu and Yueyang Zhai

Photonics 2025, 12(6), 573; https://doi.org/10.3390/photonics12060573 - 6 Jun 2025

Viewed by 126

Abstract

A stabilization method utilizing MEMS technology combined with a liquid crystal variable retarder (LCVR) was developed to enhance fiber laser output power stability and was applied to a spin-exchange relaxation-free (SERF) atomic magnetometer. Comparative experiments demonstrated that the unstabilized laser output exhibited [...] Read more.

A stabilization method utilizing MEMS technology combined with a liquid crystal variable retarder (LCVR) was developed to enhance fiber laser output power stability and was applied to a spin-exchange relaxation-free (SERF) atomic magnetometer. Comparative experiments demonstrated that the unstabilized laser output exhibited

2.8 %

power fluctuations over a 500 s period, while the stabilized laser reduced this to

0.2 %

. Spectral density analysis confirmed suppressed frequency-domain fluctuations, indicating improved robustness against disturbances. Furthermore, the stabilized laser also reduced optical noise in SERF magnetometry, achieving a sensitivity of

19.2 fT / {Hz}^{1 / 2}

. These results validate that the method optimizes both time- and frequency-domain performance, thereby advancing high-precision SERF magnetometry. Full article

(This article belongs to the Special Issue Advancements in Optical Techniques for Enhancing the Sensitivity and Precision of Atomic Magnetometers)

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20 pages, 1195 KiB

Open AccessArticle

Inverse Design of Plasmonic Nanostructures Using Machine Learning for Optimized Prediction of Physical Parameters

by Luana S. P. Maia, Darlan A. Barroso, Aêdo B. Silveira, Waleska F. Oliveira, André Galembeck, Carlos Alexandre R. Fernandes, Dayse G. C. Bandeira, Benoit Cluzel, Auzuir R. Alexandria and Glendo F. Guimarães

Photonics 2025, 12(6), 572; https://doi.org/10.3390/photonics12060572 - 6 Jun 2025

Viewed by 148

Abstract

Plasmonic nanostructures have been widely studied for their unique optical properties, which are useful in sensing, photonics, and energy. However, the efficient design of these structures, considering the complex relationship between geometry, material, and optical response, remains a challenge. In this study, we [...] Read more.

Plasmonic nanostructures have been widely studied for their unique optical properties, which are useful in sensing, photonics, and energy. However, the efficient design of these structures, considering the complex relationship between geometry, material, and optical response, remains a challenge. In this study, we propose a machine learning-based approach to address the inverse design problem in nanostructures, using data generated by numerical simulations via the Finite Element Method (FEM). We used a dataset of over 140,000 entries to train the regression models CatBoost, Random Forest, and Extra Trees, capable of predicting physical parameters, such as the radius of the nanocylinder, based on the simulated optical response. The CatBoost model achieved the best performance, with a Mean Absolute Error below 0.3 nm on unseen data. In parallel, we applied a direct design approach to experimental data of metallic nanoparticles, focusing on the optical absorption prediction from particle size. In this case, Random Forest presented the best performance, with a lower risk of overfitting. The results indicate that machine learning models are promising tools for optimizing the design and characterization of plasmonic nanostructures, thus reducing the need for costly experimental techniques. Full article

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26 pages, 6803 KiB

Open AccessArticle

Capacity Enhancement in Free-Space Optics Networks via Optimized Optical Code Division Multiple Access Image Transmission

by Somia A. Abd El-Mottaleb, Mehtab Singh, Hassan Yousif Ahmed, Median Zeghid and Maisara Mohyeldin Gasim Mohamed

Photonics 2025, 12(6), 571; https://doi.org/10.3390/photonics12060571 - 5 Jun 2025

Viewed by 168

Abstract

This paper presents a new high-speed RGB image transmission system over Free-Space Optics (FSO) channel employing Optical Code Division Multiple Access (OCDMA) with Permutation Vector (PV) codes. Four RGB images are transmitted simultaneously at 10 Gbps per image, achieving a total capacity of [...] Read more.

This paper presents a new high-speed RGB image transmission system over Free-Space Optics (FSO) channel employing Optical Code Division Multiple Access (OCDMA) with Permutation Vector (PV) codes. Four RGB images are transmitted simultaneously at 10 Gbps per image, achieving a total capacity of 40 Gbps. The system’s performance is evaluated under various atmospheric conditions, including three fog levels and real-world visibility data from Alexandria city, Egypt. Image Quality Assessment (IQA) metrics, including Signal-to-Noise Ratio (SNR), Root Mean Square Error (RMSE), Peak Signal-to-Noise Ratio (PSNR), correlation coefficients, and Structural Similarity Index Measure (SSIM), are evaluated for both unfiltered and median-filtered images. The results show significant degradation in image quality due to transmission distance and atmospheric attenuation. In Alexandria’s clear atmospheric conditions, the system achieves a maximum transmission range of 15 km with acceptable visual quality, while the range is reduced to 2.6 km, 1.6 km, and 1 km for Low Fog (LF), Medium Fog (MF), and Heavy Fog (HF), respectively. At these distances, the RGB images achieve minimum SNR, RMSE, and SSIM values of 7.27 dB, 47.66, and 0.20, respectively, with further improvements when applying median filtering. Full article

(This article belongs to the Special Issue Optical Wireless Communication in 5G and Beyond)

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14 pages, 3205 KiB

Open AccessArticle

Research on Gas Detection Algorithm Based on Reconstruction of Background Infrared Radiation

by Li Chen and Zhen Yang

Photonics 2025, 12(6), 570; https://doi.org/10.3390/photonics12060570 - 5 Jun 2025

Viewed by 174

Abstract

In response to the pressing need for long-range, non-contact detection in hazardous gas leakage monitoring within chemical industrial parks, this study proposes a gas detection algorithm based on an infrared radiation physical model that utilizes dual-band infrared radiation background reconstruction. The proposed method [...] Read more.

In response to the pressing need for long-range, non-contact detection in hazardous gas leakage monitoring within chemical industrial parks, this study proposes a gas detection algorithm based on an infrared radiation physical model that utilizes dual-band infrared radiation background reconstruction. The proposed method addresses the issues of the existing detection methods’ lack of physical model support. First, appropriate filter wavelength ranges are selected based on the absorption spectral characteristics of the target gas. Subsequently, a physical model incorporating atmospheric attenuation, background radiation, and gas absorption properties is established based on gas radiative transfer theory. The non-absorption band data are then employed to reconstruct the theoretical background radiation of the absorption band. Furthermore, leveraging the synergistic observation advantages of a dual-band infrared imaging system, gas morphology identification is achieved by inverting the difference between the theoretical background and the actual measured values in the absorption band. Experimental results demonstrate that this method enables gas morphology detection through background reconstruction without requiring pre-collected gas-free background images. By implementing dual-band infrared radiation background reconstruction, this study achieves effective gas detection, providing a reliable technical approach for real-time monitoring and early warning of industrial gas leaks. The proposed algorithm enhances detection capabilities, offering significant potential for applications in industrial safety and environmental monitoring. Full article

(This article belongs to the Special Issue Adaptive Optics Imaging: Science and Applications)

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11 pages, 2032 KiB

Open AccessCommunication

Super-Resolution Reconstruction of LiDAR Images Based on an Adaptive Contour Closure Algorithm over 10 km

by Liang Shi, Xinyuan Zhang, Fei Han, Yicheng Wang, Shilong Xu, Xing Yang and Yihua Hu

Photonics 2025, 12(6), 569; https://doi.org/10.3390/photonics12060569 - 5 Jun 2025

Viewed by 179

Abstract

Reflective Tomography LiDAR (RTL) imaging, an innovative LiDAR technology, offers the significant advantage of an imaging resolution independent of detection distance and receiving optical aperture, evolving from Computed Tomography (CT) principles. However, distinct from transmissive imaging, RTL requires precise alignment of multi-angle echo [...] Read more.

Reflective Tomography LiDAR (RTL) imaging, an innovative LiDAR technology, offers the significant advantage of an imaging resolution independent of detection distance and receiving optical aperture, evolving from Computed Tomography (CT) principles. However, distinct from transmissive imaging, RTL requires precise alignment of multi-angle echo data around the target’s rotation center before image reconstruction. This paper presents an adaptive contour closure algorithm for automated multi-angle echo data registration in RTL. A 10.38 km remote RTL imaging experiment validates the algorithm’s efficacy, showing that it improves the quality factor of reconstructed images by over 23% and effectively suppresses interference from target/detector jitter, laser pulse transmission/reception fluctuations, and atmospheric turbulence. These results support the development of advanced space target perception capabilities and drive the transition of space-based LiDAR from “point” measurements to “volumetric” perception, marking a crucial advancement in space exploration and surveillance. Full article

(This article belongs to the Special Issue Technologies and Applications of Optical Imaging)

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19 pages, 7350 KiB

Open AccessArticle

Hybrid Self-Attention Transformer U-Net for Fourier Single-Pixel Imaging Reconstruction at Low Sampling Rates

by Haozhen Chen, Hancui Zhang, Bo Zou and Long Wu

Photonics 2025, 12(6), 568; https://doi.org/10.3390/photonics12060568 - 5 Jun 2025

Viewed by 200

Abstract

Fourier Single-Pixel Imaging exhibits significant advantages over conventional imaging techniques, including high interference resistance, broad spectral adaptability, nonlocal imaging capability, and long-range detection. However, in practical applications, FSPI relies on undersampling reconstruction, which inevitably leads to ringing artifacts that degrade image quality. To [...] Read more.

Fourier Single-Pixel Imaging exhibits significant advantages over conventional imaging techniques, including high interference resistance, broad spectral adaptability, nonlocal imaging capability, and long-range detection. However, in practical applications, FSPI relies on undersampling reconstruction, which inevitably leads to ringing artifacts that degrade image quality. To enhance reconstruction performance, a Transformer-based FSPI reconstruction network is proposed. The network adopts a U-shaped architecture, composed of multiple Hybrid Self-Attention Transformer Modules and Feature Fusion Modules. The experimental results demonstrate that the proposed network achieves high-quality reconstruction at low sampling rates and outperforms traditional reconstruction methods and convolutional network-based approaches in terms of both visual appearance and image quality metrics. This method holds significant potential for high-speed single-pixel imaging applications, enabling the reconstruction of high-quality images at extremely low sampling rates. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

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13 pages, 2686 KiB

Open AccessArticle

Research on Wavelength-Shifting Fiber Scintillator for Detecting Low-Intensity X-Ray Backscattered Photons

by Baolu Yang, Zhe Yang, Xin Wang, Baozhong Mu, Jie Xu, Cheng Yang and Hong Li

Photonics 2025, 12(6), 567; https://doi.org/10.3390/photonics12060567 - 4 Jun 2025

Viewed by 163

Abstract

High-sensitivity fiber scintillator detectors are the key to achieving high signal-to-noise ratio and high contrast imaging in X-ray Compton backscattering technology. We established a simulation model of wavelength-shifting fiber (WSF) scintillator detectors based on Geant4. The influences of ray source energy, detection area, [...] Read more.

High-sensitivity fiber scintillator detectors are the key to achieving high signal-to-noise ratio and high contrast imaging in X-ray Compton backscattering technology. We established a simulation model of wavelength-shifting fiber (WSF) scintillator detectors based on Geant4. The influences of ray source energy, detection area, number of WSFs, and coupling mechanism on detection efficiency were simulated. By using the epoxy resin coupling method, the transmission efficiency between the WSF and scintillator was increased from 4.56% to 19.79%. Based on the simulation data, we developed an X-ray WSFs scintillator detector, built an X-ray backscattering imaging experimental system, obtained high-contrast backscattering images, and verified the performance of the detector. Full article

(This article belongs to the Special Issue Optical Technologies for Measurement and Metrology)

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