Photonics

13 pages, 1888 KiB

Open AccessArticle

Femtosecond-Laser Direct Writing of Double-Line and Tubular Depressed-Cladding Waveguides in Ultra-Low-Expansion Glass

by Yuhao Wu, Sixuan Guo, Guanghua Cheng, Feiran Wang, Xu Wang and Yunjie Zhang

Photonics 2025, 12(8), 797; https://doi.org/10.3390/photonics12080797 - 8 Aug 2025

Addressing the stability requirements of photonic integrated devices operating over wide temperature ranges, this work achieves controlled fabrication of femtosecond-laser direct-written Type II double-line waveguides and Type III depressed-cladding tubular waveguides within ultra-low-expansion LAS glass-ceramics. The light-guiding mechanisms were elucidated through finite element [...] Read more.

Addressing the stability requirements of photonic integrated devices operating over wide temperature ranges, this work achieves controlled fabrication of femtosecond-laser direct-written Type II double-line waveguides and Type III depressed-cladding tubular waveguides within ultra-low-expansion LAS glass-ceramics. The light-guiding mechanisms were elucidated through finite element modeling. The influences of laser writing parameters and waveguide geometric structures on guiding performance were systematically investigated. Experimental results demonstrate that the double-line waveguides exhibit optimal single-mode guiding performance at 30 μm spacing and 120 mW writing power. For the tubular depressed-cladding waveguides, both single-mode and multi-mode fields are attainable across a broad processing parameter window. Large-mode-area characteristics manifested in the 50 μm core waveguide, exhibiting an edge-shifted intensity profile for higher-order modes that generated a hollow beam, enabling applications in atom guidance and particle trapping. Full article

(This article belongs to the Special Issue Direct Ultrafast Laser Writing in Photonics and Optoelectronics)

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18 pages, 5585 KiB

Open AccessArticle

A CNN-GS Hybrid Algorithm for Generating Pump Light Fields in Atomic Magnetometers

by Miaohui Song, Ying Liu, Feijie Lu, Qian Cao and Yueyang Zhai

Photonics 2025, 12(8), 796; https://doi.org/10.3390/photonics12080796 - 7 Aug 2025

Abstract

Atomic magnetometers (AMs), recognized for their ultra-high magnetic sensitivity, demand highly uniform pump light fields to maximize measurement accuracy. In this paper, a phase modulation-based method using convolutional neural networks (CNN) and the Gerchberg–Saxton (GS) algorithm is proposed to generate the pumping light [...] Read more.

Atomic magnetometers (AMs), recognized for their ultra-high magnetic sensitivity, demand highly uniform pump light fields to maximize measurement accuracy. In this paper, a phase modulation-based method using convolutional neural networks (CNN) and the Gerchberg–Saxton (GS) algorithm is proposed to generate the pumping light field, and the model was trained using a supervised learning approach with a custom dataset. The specific training settings are as follows: the backpropagation algorithm was adopted as the training algorithm, and the Adam optimization method was used for network training, with a learning rate of 0.001 and a total of 100 training epochs, utilizing a liquid crystal spatial light modulator (LCSLM) to regulate the light field phase distribution dynamically. By transforming Gaussian beams into flat-top beams, the method significantly enhances polarization uniformity within vapor cells, leading to improved magnetometric sensitivity. The proposed hybrid algorithm reduces the mean square error from 35% to 19% and peak non-uniformity from 21% to 7.6%. A reflective LCSLM-based optical setup is implemented to produce circular and square flat-top beams with a measured non-uniformity of 5.1%, resulting in an enhancement of magnetic sensitivity from 14.04 fT/Hz^1/2 to 7.80 fT/Hz^1/2. 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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13 pages, 1269 KiB

Open AccessArticle

Contrast-Enhancing Spatial–Frequency Deconvolution-Aided Interferometric Scattering Microscopy (iSCAT)

by Xiang Zhang and Hao He

Photonics 2025, 12(8), 795; https://doi.org/10.3390/photonics12080795 - 7 Aug 2025

Abstract

Interferometric scattering microscopy (iSCAT) is widely used for label-free tracking of nanoparticles and single molecules. However, its ability to identify small molecules is limited by low imaging contrast blurred with noise. Frame-averaging methods are widely used for reducing background noise but require hundreds [...] Read more.

Interferometric scattering microscopy (iSCAT) is widely used for label-free tracking of nanoparticles and single molecules. However, its ability to identify small molecules is limited by low imaging contrast blurred with noise. Frame-averaging methods are widely used for reducing background noise but require hundreds of frames to produce a single frame as a trade-off. To address this, we applied a spatial–frequency domain deconvolution algorithm to suppress background noise and amplify the signal for each frame, achieving an improvement of ∼ 3-fold without hardware modification. This enhancement is achieved by compensating for missing information within the optical transfer function (OTF) boundary, while high-frequency components (noise) beyond this boundary are filtered. The resulting deconvolution process provides linear signal amplification, making it ideal for quantitative analysis in mass photometry. Additionally, the localization error is reduced by 20%. Comparisons with traditional denoising algorithms revealed that these methods often extract the side lobes. In contrast, our deconvolution approach preserves signal integrity while enhancing sensitivity. This work highlights the potential of image processing techniques to significantly improve the detection sensitivity of iSCAT for small molecule analysis. Full article

(This article belongs to the Special Issue Research, Development and Application of Raman Scattering Technology)

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15 pages, 4886 KiB

Open AccessArticle

Fabrication of Diffractive Optical Elements to Generate Square Focal Spots via Direct Laser Lithography and Machine Learning

by Hieu Tran Doan Trung, Young-Sik Ghim and Hyug-Gyo Rhee

Photonics 2025, 12(8), 794; https://doi.org/10.3390/photonics12080794 - 6 Aug 2025

Abstract

Recently, diffractive optics systems have garnered increasing attention due to their myriad benefits in various applications, such as creating vortex beams, Bessel beams, or optical traps, while refractive optics systems still exhibit some disadvantages related to materials, substrates, and intensity shapes. The manufacturing [...] Read more.

Recently, diffractive optics systems have garnered increasing attention due to their myriad benefits in various applications, such as creating vortex beams, Bessel beams, or optical traps, while refractive optics systems still exhibit some disadvantages related to materials, substrates, and intensity shapes. The manufacturing of diffractive optical elements has become easier due to the development of lithography techniques such as direct laser writing, photo lithography, and electron beam lithography. In this paper, we improve the results from previous research and propose a new methodology to design and fabricate advanced binary diffractive optical elements that achieve a square focal spot independently, reducing reliance on additional components. By integrating a binary square zone plate with an axicon zone plate of the same scale, we employ machine learning for laser path optimization and direct laser lithography for manufacturing. This streamlined approach enhances simplicity, accuracy, efficiency, and cost effectiveness. Our upgraded binary diffractive optical elements are ready for real-world applications, marking a significant improvement in optical capabilities. Full article

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

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12 pages, 1583 KiB

Open AccessArticle

Photothermal Performance Testing of Lithium Niobate After Ion Beam Radiation

by Junyi Liu, Daiyong Lin, Xing Peng, Yao Wu, Jian Li, Ziqiang Hu, Zhixuan He, Jiaqi Wang, Yuxia Tan, Xiaoshu Xu and Shuo Qiao

Photonics 2025, 12(8), 793; https://doi.org/10.3390/photonics12080793 - 6 Aug 2025

Abstract

To investigate the evolution of the optothermal properties of lithium niobate with ion beam irradiation parameters, the thermal effect theory was analyzed, and ion beam irradiation technology was used to modify lithium niobate samples. The transmittance of lithium niobate crystals after ion beam [...] Read more.

To investigate the evolution of the optothermal properties of lithium niobate with ion beam irradiation parameters, the thermal effect theory was analyzed, and ion beam irradiation technology was used to modify lithium niobate samples. The transmittance of lithium niobate crystals after ion beam irradiation and the relationship between their optothermal properties and transmittance were studied. The results show that the average surface optothermal signal of lithium niobate exhibits a significant dependence on ion beam parameters. When the ion beam voltage is 800 V, the ion beam current is 30 mA, and the irradiation time is 60 s, a distinct absorption peak is observed on the surface of lithium niobate, with an average surface optothermal signal of 5377.34 ppm, demonstrating potential for all-optical modulation. Full article

(This article belongs to the Section Optical Interaction Science)

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16 pages, 2772 KiB

Open AccessArticle

Double Demodulation Incorporates Reciprocal Modulation and Residual Amplitude Modulation Feedback to Enhance the Bias Performance of RFOG

by Zhijie Yang, Xiaolong Yan, Guoguang Chen and Xiaoli Tian

Photonics 2025, 12(8), 792; https://doi.org/10.3390/photonics12080792 - 5 Aug 2025

Abstract

The suppression of Rayleigh backscattering noise in a resonant fiber optic gyro (RFOG) is accompanied by the emergence of residual amplitude modulation (RAM) effects, which impact the bias performance of the RFOG output. In this paper, we propose a double demodulation technique that [...] Read more.

The suppression of Rayleigh backscattering noise in a resonant fiber optic gyro (RFOG) is accompanied by the emergence of residual amplitude modulation (RAM) effects, which impact the bias performance of the RFOG output. In this paper, we propose a double demodulation technique that integrates reciprocal modulation and RAM feedback. By utilizing reciprocal modulation–demodulation along with a RAM feedback control method, we effectively suppress both RAM and laser frequency noise. Furthermore, the inherent suppression characteristics of the double modulation–demodulation scheme facilitate effective backscatter noise reduction. As a result, the gyro angular random walk of the RFOG has improved to

3^{°} / \sqrt{h}

, and the long-term bias instability has been enhanced to 0.1°/h over a test duration of 10 h. Full article

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

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13 pages, 3292 KiB

Open AccessArticle

Topological Large-Area Waveguide States Based on THz Photonic Crystals

by Yulin Zhao, Feng Liang, Jingsen Li, Jianfei Han, Jiangyu Chen, Haihua Hu, Ke Zhang and Yuanjie Yang

Photonics 2025, 12(8), 791; https://doi.org/10.3390/photonics12080791 - 5 Aug 2025

Abstract

Terahertz (THz) has attracted substantial attention owing to its unique advantages in high-speed communications. However, conventional THz waveguide systems are inherently constrained by high transmission losses, stringent fabrication precision requirements, and extreme sensitivity to structural defects. Topological edge states with topological protection have [...] Read more.

Terahertz (THz) has attracted substantial attention owing to its unique advantages in high-speed communications. However, conventional THz waveguide systems are inherently constrained by high transmission losses, stringent fabrication precision requirements, and extreme sensitivity to structural defects. Topological edge states with topological protection have driven significant advancements in THz wave manipulation. Nevertheless, the width of the topological waveguide based on edge states remains restricted. In this work, we put forward a type of spin photonic crystal with three-layer heterostructures, where large-area topological waveguide states are demonstrated. The results show that these topological waveguide states are localized within the region of Dirac photonic crystals. They also display spin-momentum-locking characteristics and maintain strong robustness against defects and sharp bends. Furthermore, a THz beam splitter and a topological beam modulator are implemented. The designed heterostructures expand the applications of multi-functional topological devices and provide a prospective pathway for overcoming the waveguide bottleneck in THz applications. Full article

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

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13 pages, 3882 KiB

Open AccessArticle

Thermal Damage Characterization of Detector Induced by Nanosecond Pulsed Laser Irradiation

by Zhilong Jian, Weijing Zhou, Hao Chang, Yingjie Ma, Xiaoyuan Quan and Zikang Wang

Photonics 2025, 12(8), 790; https://doi.org/10.3390/photonics12080790 - 5 Aug 2025

Abstract

Experimental and simulation analysis was conducted on the effects of 532 nm nanosecond laser-induced thermal damage on the front-side illuminated CMOS detector. The study examined CMOS detector output images at different stages of damage, including point damage, line damage, and complete failure, and [...] Read more.

Experimental and simulation analysis was conducted on the effects of 532 nm nanosecond laser-induced thermal damage on the front-side illuminated CMOS detector. The study examined CMOS detector output images at different stages of damage, including point damage, line damage, and complete failure, and correlated these with microscopic structural changes observed through optical and scanning electron microscopy. A finite element model was used to study the thermal–mechanical coupling effect during laser irradiation. The results indicated that at a laser energy density of 78.9 mJ/cm², localized melting occurs within photosensitive units in the epitaxial layer, manifesting as an irreversible white bright spot appearing in the detector output image (point damage). When the energy density is further increased to 241.9 mJ/cm², metal routings across multiple pixel units melt, resulting in horizontal and vertical black lines in the output image (line damage). Upon reaching 2005.4 mJ/cm², the entire sensor area failed to output any valid image due to thermal stress-induced delamination of the silicon dioxide insulation layer, with cracks propagating to the metal routing and epitaxial layers, ultimately causing structural deformation and device failure (complete failure). Full article

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

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25 pages, 3310 KiB

Open AccessArticle

Real-Time Signal Quality Assessment and Power Adaptation of FSO Links Operating Under All-Weather Conditions Using Deep Learning Exploiting Eye Diagrams

by Somia A. Abd El-Mottaleb and Ahmad Atieh

Photonics 2025, 12(8), 789; https://doi.org/10.3390/photonics12080789 - 4 Aug 2025

Abstract

This paper proposes an intelligent power adaptation framework for Free-Space Optics (FSO) communication systems operating under different weather conditions exploiting a deep learning (DL) analysis of received eye diagram images. The system incorporates two Convolutional Neural Network (CNN) architectures, LeNet and Wide Residual [...] Read more.

This paper proposes an intelligent power adaptation framework for Free-Space Optics (FSO) communication systems operating under different weather conditions exploiting a deep learning (DL) analysis of received eye diagram images. The system incorporates two Convolutional Neural Network (CNN) architectures, LeNet and Wide Residual Network (Wide ResNet) algorithms to perform regression tasks that predict received signal quality metrics such as the Quality Factor (Q-factor) and Bit Error Rate (BER) from the received eye diagram. These models are evaluated using Mean Squared Error (MSE) and the coefficient of determination (

R^{2}

score) to assess prediction accuracy. Additionally, a custom CNN-based classifier is trained to determine whether the BER reading from the eye diagram exceeds a critical threshold of

10^{- 4}

; this classifier achieves an overall accuracy of 99%, correctly detecting 194/195 “acceptable” and 4/5 “unacceptable” instances. Based on the predicted signal quality, the framework activates a dual-amplifier configuration comprising a pre-channel amplifier with a maximum gain of 25 dB and a post-channel amplifier with a maximum gain of 10 dB. The total gain of the amplifiers is adjusted to support the operation of the FSO system under all-weather conditions. The FSO system uses a 15 dBm laser source at 1550 nm. The DL models are tested on both internal and external datasets to validate their generalization capability. The results show that the regression models achieve strong predictive performance, and the classifier reliably detects degraded signal conditions, enabling the real-time gain control of the amplifiers to achieve the quality of transmission. The proposed solution supports robust FSO communication under challenging atmospheric conditions including dry snow, making it suitable for deployment in regions like Northern Europe, Canada, and Northern Japan. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Optical Wireless Communication)

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17 pages, 4522 KiB

Open AccessArticle

A Blue LED Spectral Simulation Method Using Exponentially Modified Gaussian Functions with Superimposed Asymmetric Pseudo-Voigt Corrections

by Hongru Zhuang, Yanfei Wang, Caihong Dai, Ling Li, Zhifeng Wu and Jiang Pan

Photonics 2025, 12(8), 788; https://doi.org/10.3390/photonics12080788 - 4 Aug 2025

Abstract

Accurately simulating the asymmetric spectral profiles of blue LEDs is crucial for photobiological research, yet it remains a challenge for traditional symmetric models. This study proposes a novel spectral simulation model that effectively captures these asymmetries. The proposed model structure is partly motivated [...] Read more.

Accurately simulating the asymmetric spectral profiles of blue LEDs is crucial for photobiological research, yet it remains a challenge for traditional symmetric models. This study proposes a novel spectral simulation model that effectively captures these asymmetries. The proposed model structure is partly motivated by known broadening and dispersion mechanisms observed in real LED spectra; it employs a ‘base model + correction’ framework, where an Exponentially Modified Gaussian (EMG) function captures the primary spectral shape and falling edge and an Asymmetric Pseudo-Voigt (APV) function corrects the deviations on the rising edge. Requiring only the central wavelength and bandwidth as user inputs, the simulation results exhibit a high degree of agreement with the experimental data spectra. The model provides a rapid and robust tool for pre-evaluating light sources against regulatory criteria (e.g., >99% of the spectral intensity is in the 400–500 nm band), thereby enhancing the efficiency of experimental design in blue light protection studies. Full article

(This article belongs to the Special Issue Light-Emitting Diodes: Technology, Advances, Challenges and Applications)

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14 pages, 2905 KiB

Open AccessArticle

Optimal Design of a Lightweight Terahertz Absorber Featuring Ultra-Wideband Polarization-Insensitive Characteristics

by Yafeng Hao, Tengteng Li, Pu Zhu, Fupeng Ma, Huijia Wu, Cheng Lei, Meihong Liu, Ting Liang and Jianquan Yao

Photonics 2025, 12(8), 787; https://doi.org/10.3390/photonics12080787 - 4 Aug 2025

Abstract

Metamaterial absorbers in terahertz (THz) based bands have garnered significant attention for their potential applications in military stealth, terahertz imaging, and other fields. Nevertheless, the limited bandwidth, low absorption rate, and heavy weight greatly reduce the further development and wide application of terahertz [...] Read more.

Metamaterial absorbers in terahertz (THz) based bands have garnered significant attention for their potential applications in military stealth, terahertz imaging, and other fields. Nevertheless, the limited bandwidth, low absorption rate, and heavy weight greatly reduce the further development and wide application of terahertz absorbers. To solve these problems, we propose a polystyrene (PS)-based ultra-broadband metamaterial absorber integrated with a polyethylene terephthalate (PET) double-sided adhesive layer and a patterned indium tin oxide (ITO) film through the simulation method, which operates in the THz band. The electromagnetic wave absorption properties and underlying physical absorption mechanisms of the proposed metamaterial absorbers are comprehensively modeled and rigorously numerically simulated. The research demonstrates the metamaterial absorber can achieve absorption performance of over 90% for fully polarized incident waves in the ultra-wideband range of 1.2–10 THz, especially achieving perfect absorption characteristics of over 99.9% near 1.8–1.9 THz and 5.8–6.2 THz. The proposed absorber has a lightweight physical property of 0.7 kg/m² and polarization-insensitive characteristic, and it achieves a broad-angle that allows a range of incidence angles up to 60°. The simulation research results of this article provide theoretical support for the design of terahertz absorbers with ultra-wideband absorption characteristics. Full article

(This article belongs to the Special Issue Metamaterials and Nanophotonics: Fundamentals and Applications)

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13 pages, 2630 KiB

Open AccessArticle

Photodynamic Therapy in the Management of MDR Candida spp. Infection Associated with Palatal Expander: In Vitro Evaluation

by Cinzia Casu, Andrea Butera, Alessandra Scano, Andrea Scribante, Sara Fais, Luisa Ladu, Alessandra Siotto-Pintor and Germano Orrù

Photonics 2025, 12(8), 786; https://doi.org/10.3390/photonics12080786 - 4 Aug 2025

Abstract

The aim of this work is to evaluate the effectiveness of antimicrobial photodynamic therapy (aPDT) against oral MDR (multi-drug-resistant) Candida spp. infections related to orthodontic treatment with palatal expanders through in vitro study. Methods: PDT protocol: Curcumin + H₂O₂ was [...] Read more.

The aim of this work is to evaluate the effectiveness of antimicrobial photodynamic therapy (aPDT) against oral MDR (multi-drug-resistant) Candida spp. infections related to orthodontic treatment with palatal expanders through in vitro study. Methods: PDT protocol: Curcumin + H₂O₂ was used as a photosensitizer activated by a 460 nm diode LED lamp, with an 8 mm blunt tip for 2 min in each spot of interest. In vitro simulation: A palatal expander sterile device was inserted into a custom-designed orthodontic bioreactor, realized with 10 mL of Sabouraud dextrose broth plus 10% human saliva and infected with an MDR C. albicans clinical isolate CA95 strain to reproduce an oral palatal expander infection. After 48 h of incubation at 37 °C, the device was treated with the PDT protocol. Two samples before and 5 min after the PDT process were taken and used to contaminate a Petri dish with a Sabouraud field to evaluate Candida spp. CFUs (colony-forming units). Results: A nearly 99% reduction in C. albicans colonies in the palatal expander biofilm was found after PDT. Conclusion: The data showed the effectiveness of using aPDT to treat palatal infection; however, specific patient oral micro-environment reproduction (Ph values, salivary flow, mucosal adhesion of photosensitizer) must be further analyzed. Full article

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

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11 pages, 2306 KiB

Open AccessArticle

Optical Path Design of an Integrated Cavity Optomechanical Accelerometer with Strip Waveguides

by Chengwei Xian, Pengju Kuang, Zhe Li, Yi Zhang, Changsong Wang, Rudi Zhou, Guangjun Wen, Yongjun Huang and Boyu Fan

Photonics 2025, 12(8), 785; https://doi.org/10.3390/photonics12080785 - 4 Aug 2025

Abstract

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element [...] Read more.

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element Analysis (FEA) and Finite-Difference Time-Domain (FDTD) methods are employed to systematically investigate the performance of key optical structures, including the resonant modes and bandgap characteristics of photonic crystal (PhC) microcavities, transmission loss of strip waveguides, coupling efficiency of tapered-lensed fiber-to-waveguide end-faces, coupling characteristics between strip waveguides and PhC waveguides, and the coupling mechanism between PhC waveguides and microcavities. Simulation results demonstrate that the designed PhC microcavity achieves a quality factor (Q-factor) of 2.26 × 10⁵ at a 1550 nm wavelength while the optimized strip waveguide exhibits a low loss of merely 0.2 dB over a 5000 μm transmission length. The strip waveguide to PhC waveguide coupling achieves 92% transmittance at the resonant frequency, corresponding to a loss below 0.4 dB. The optimized edge coupling structure exhibits a transmittance of 75.8% (loss < 1.2 dB), with a 30 μm coupling length scheme (60% transmittance, ~2.2 dB loss) ultimately selected based on process feasibility trade-offs. The total optical path system loss (input to output) is 5.4 dB. The paper confirms that the PhC waveguide–microcavity evanescent coupling method can effectively excite the target cavity mode, ensuring optomechanical coupling efficiency for the accelerometer. This research provides theoretical foundations and design guidelines for the fabrication of high-precision monolithic integrated cavity optomechanical accelerometers. Full article

(This article belongs to the Special Issue Emerging Trends in Spectral Analysis with Optical Sensors: Modern Approaches and Applications)

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11 pages, 1709 KiB

Open AccessArticle

Beam Profile Prediction of High-Repetition-Rate SBS Pulse Compression Using Convolutional Neural Networks

by Hongli Wang, Chaoshuai Liu, Panpan Yan and Qinglin Niu

Photonics 2025, 12(8), 784; https://doi.org/10.3390/photonics12080784 - 4 Aug 2025

Abstract

Fast prediction of beam quality in SBS pulse compression for high-repetition-rate operation is urgently important for SBS experimental parameter acquisition. In this study, a fast computational prediction model for SBS beam profiles is developed using a convolutional neural network (CNN) method, which is [...] Read more.

Fast prediction of beam quality in SBS pulse compression for high-repetition-rate operation is urgently important for SBS experimental parameter acquisition. In this study, a fast computational prediction model for SBS beam profiles is developed using a convolutional neural network (CNN) method, which is trained and validated using experimental data from SBS pulse compression experiments. The CNN method can predict beam spot images for experimental conditions in the range of 100–500 Hz repetition rates and 5–40 mJ injection energy. The proposed CNN-based SBS beam profile prediction model has a fast convergence of the loss function and an average error of 15% with respect to the experimental results, indicating a high accuracy of the model. The CNN-based prediction model achieves an average error of 11.8% for beam profile prediction across various experimental conditions, demonstrating its potential for SBS beam profile characterization. The CNN method could provide a fast means for predicting the characteristic law of the beam intensity distribution in high-repetition-rate SBS pulse compression systems. 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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7 pages, 183 KiB

Open AccessEditorial

Editorial Board Members’ Collection Series: Nonlinear Photonics

by Luigi Sirleto

Photonics 2025, 12(8), 783; https://doi.org/10.3390/photonics12080783 - 4 Aug 2025

Abstract

Photonics has often been defined as the key technology of the 21st century [...] Full article

(This article belongs to the Special Issue Editorial Board Members' Collection Series: Nonlinear Photonics)

17 pages, 7323 KiB

Open AccessArticle

Line Laser 3D Measurement Method and Experiments of Gears

by Yanqiang Sun, Zhaoyao Shi, Bo Yu and Meichuan Li

Photonics 2025, 12(8), 782; https://doi.org/10.3390/photonics12080782 - 4 Aug 2025

Abstract

Line laser measurement, as a typical method of laser triangulation, makes the acquisition of 3D tooth-surface data more accurate, efficient, and informative. Thus, a line laser 3D measurement model of gears is established, and a specialized polyhedral artifact with specific geometric features is [...] Read more.

Line laser measurement, as a typical method of laser triangulation, makes the acquisition of 3D tooth-surface data more accurate, efficient, and informative. Thus, a line laser 3D measurement model of gears is established, and a specialized polyhedral artifact with specific geometric features is invented to determine the pose parameters of the line laser sensor in measuring space. Based on this, a single-spindle gear-measuring instrument is developed and a series of experimental studies are conducted for gears with different module and flank directions in this instrument, including profile deviation, helix deviation, pitch deviation, topological deviation, etc. A comparative experiment with traditional contact measurement methods validates the correctness of the methods mentioned in this paper for the accurate evaluation of tested gears. In further research, the mining and utilization of big data obtained from the line laser 3D measurement of gears will be an important topic. Full article

(This article belongs to the Special Issue Advancements in Optical Metrology and Imaging)

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11 pages, 4858 KiB

Open AccessCommunication

Customized Chirality of an Optical Vortex Pair: Helical Dichroism and Enantioselective Force

by Xingxing Han, Haibo Niu, Jing Shi, Weili Dong and Jiajie Wang

Photonics 2025, 12(8), 781; https://doi.org/10.3390/photonics12080781 - 4 Aug 2025

Abstract

Tailoring the chirality of an optical vortex is crucial for advancing helical chiroptical spectroscopy techniques in various scenarios and attracts great attention. In contrast to the single vortex, the optical vortex pair exhibits richer, fantastic chirality properties due to its additional adjustment parameters. [...] Read more.

Tailoring the chirality of an optical vortex is crucial for advancing helical chiroptical spectroscopy techniques in various scenarios and attracts great attention. In contrast to the single vortex, the optical vortex pair exhibits richer, fantastic chirality properties due to its additional adjustment parameters. Here, a comprehensive investigation of the chirality for linearly polarized optical vortex pairs based on the vector angular spectrum decomposition method is conducted. The numerical results show that the magnitudes and distributions of local chirality density, helical dichroism, and enantioselective force of the optical vortex pair can be flexibly customized by the position as well as sign combination of vortices, and can vary during free space propagation. The underlying physical mechanism behind these phenomena is ascribed to the interplay of two vortices. Our work can deepen the understanding of the chirality for multiple vortices and open-up the prospect for relevant applications in chiral recognition and manipulation. Full article

(This article belongs to the Special Issue Realization and Application of Vortex Laser)

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14 pages, 10145 KiB

Open AccessArticle

Wavefront-Corrected Algorithm for Vortex Optical Transmedia Wavefront-Sensorless Sensing Based on U-Net Network

by Shangjun Yang, Yanmin Zhao, Binkun Liu, Shuguang Zou and Chenghu Ke

Photonics 2025, 12(8), 780; https://doi.org/10.3390/photonics12080780 - 1 Aug 2025

Abstract

Atmospheric and oceanic turbulence can severely degrade the orbital angular momentum (OAM) mode purity of vortex beams in cross-media optical links. Here, we propose a hybrid correction framework that fuses multiscale phase-screen modeling with a lightweight U-Net predictor for phase-distortion—driven solely by measured [...] Read more.

Atmospheric and oceanic turbulence can severely degrade the orbital angular momentum (OAM) mode purity of vortex beams in cross-media optical links. Here, we propose a hybrid correction framework that fuses multiscale phase-screen modeling with a lightweight U-Net predictor for phase-distortion—driven solely by measured optical intensity—and augments it with a feed-forward, Gaussian-reference subtraction scheme for iterative compensation. In our experiments, this approach boosts the l = 3 mode purity from 38.4% to 98.1%. Compared to the Gerchberg–Saxton algorithm, the Gaussian-reference feed-forward method achieves far lower computational complexity and greater robustness, making real-time phase recovery feasible for OAM-based communications over heterogeneous channels. Full article

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11 pages, 1758 KiB

Open AccessArticle

Nonlinear Absorption Properties of Phthalocyanine-like Squaraine Dyes

by Fan Zhang, Wuyang Shi, Xixiao Li, Yigang Wang, Leilei Si, Wentao Gao, Meng Qi, Minjie Zhou, Jiajun Ma, Ao Li, Zhiqiang Li, Hongming Wang and Bing Jin

Photonics 2025, 12(8), 779; https://doi.org/10.3390/photonics12080779 - 1 Aug 2025

Abstract

This study synthesizes and comparatively investigates two squaric acid-based phthalocyanine-like dyes, SNF and its long-chain alkylated derivative LNF, to systematically elucidate the influence of peripheral hydrophobic groups on their third-order nonlinear optical (NLO) properties. The NLO characteristics were comprehensively characterized using femtosecond Z-scan [...] Read more.

This study synthesizes and comparatively investigates two squaric acid-based phthalocyanine-like dyes, SNF and its long-chain alkylated derivative LNF, to systematically elucidate the influence of peripheral hydrophobic groups on their third-order nonlinear optical (NLO) properties. The NLO characteristics were comprehensively characterized using femtosecond Z-scan and I-scan techniques at both 800 nm and 900 nm. Both dyes exhibited strong saturable absorption (SA), confirming their potential as saturable absorbers. Critically, the comparative analysis revealed that SNF exhibits a significantly greater nonlinear absorption coefficient (β) compared to LNF under identical conditions. For instance, at 800 nm, the β of SNF was approximately 3–5 times larger than that of LNF. This result conclusively demonstrates that the introduction of long hydrophobic alkyl chains attenuates the NLO response. Furthermore, I-scan measurements revealed excellent SA performance, with high modulation depths (e.g., LNF: 43.0% at 900 nm) and low saturation intensities. This work not only clarifies the structure–property relationship in these D-A-D dyes but also presents a clear strategy for modulating the NLO properties of organic chromophores for applications in near-infrared pulsed lasers. Full article

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

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