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Harmonics-Assisted 50-Fold Optical Phase Amplification with a Self-Mixing Thin-Slice Nd:GdVO₄ Laser with Wide-Aperture Laser-Diode Pumping
High-Efficiency, High-Power Designs for ~10 μm-Emitting Quantum Cascade Lasers
Detection of Bisphenol a by a Chitosan-Coated Microstructured Optical Fiber Sensor
Genetic-Algorithm-Driven Intelligent Spatiotemporal Mode-Locking in All-Fiber Laser with Hysteresis

Journal Description

Photonics

Photonics is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
Journal Rank: CiteScore - Q2 (Instrumentation)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 15 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the second half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Lights.

Impact Factor: 1.9 (2024); 5-Year Impact Factor: 2.0 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

10 pages, 1304 KB

Open AccessArticle

Gain-Managed Nonlinear Fiber Source Enabled Line-Field Spectral-Domain OCT for High-Speed Imaging of Laser-Induced Tissue Ablation

by Ang Liu, Tao Ye, Shuyuan Zhu, Tong Xia, Shengli Pan, Chaowu Yan and Pu Wang

Photonics 2026, 13(3), 260; https://doi.org/10.3390/photonics13030260 - 6 Mar 2026

Line-field spectral-domain optical coherence tomography (LF-SD-OCT) offers high-speed parallel imaging, but lateral beam expansion limits the photon budget per spatial channel, compromising sensitivity. Here, we demonstrate a high-speed LF-SD-OCT system driven by a gain-managed nonlinear (GMN) all-fiber source operating at a central wavelength [...] Read more.

Line-field spectral-domain optical coherence tomography (LF-SD-OCT) offers high-speed parallel imaging, but lateral beam expansion limits the photon budget per spatial channel, compromising sensitivity. Here, we demonstrate a high-speed LF-SD-OCT system driven by a gain-managed nonlinear (GMN) all-fiber source operating at a central wavelength of 1063.2 nm. Delivering 269 mW of average power with a smooth 98 nm (3 dB) bandwidth, the GMN source effectively fulfills the stringent photon budget and stability requirements of parallel detection. The system achieves a 5.68 μm axial resolution and a ~1.2 mm effective imaging range. Ex vivo porcine myocardial tissue ablation experiments validate its capability for high-contrast cross-sectional visualization of ablation crater morphology, showing excellent agreement with optical microscopy. These results establish GMN-enabled LF-SD-OCT as a robust solution for the precise intraoperative monitoring of laser-induced tissue damage. Full article

(This article belongs to the Special Issue Advanced Photonic Technologies: From Light Sources and Nonlinear Optics to Sensing Applications)

15 pages, 1816 KB

Open AccessArticle

Photonic Crystal Fiber–Based Surface Plasmon Resonance Sensor for Precise Biochemical Refractive Index Sensing

by Lalit Garia, Rajeev Kumar, Chang-Won Yoon and Mangal Sain

Photonics 2026, 13(3), 259; https://doi.org/10.3390/photonics13030259 - 6 Mar 2026

In this work, a D-shaped Photonic Crystal Fiber (PCF) sensor with a detection range of 1.30–1.35 is proposed, including Gold (Au), Titanium Dioxide (TiO₂), graphene, and a functionalized sensing region. Instead of filling or coating inside the PCF’s air holes, the [...] Read more.

In this work, a D-shaped Photonic Crystal Fiber (PCF) sensor with a detection range of 1.30–1.35 is proposed, including Gold (Au), Titanium Dioxide (TiO₂), graphene, and a functionalized sensing region. Instead of filling or coating inside the PCF’s air holes, the Gold (Au) layer is applied to the polished surface. The effects of the larger air holes’ diameter and the thickness of the Au layer are examined. To achieve effective RI sensing, the proposed design leverages the strong coupling between the core mode and the Surface Plasmon (SP) excitation mode. Modal dispersion, confinement loss, and electric field distributions are analyzed for analyte RI values ranging from 1.30 to 1.35 using the Finite Element Method (FEM). The sensor demonstrates improved plasmonic excitation with a maximum Wavelength Sensitivity (WS) of 3000 nm/RIU (Au = 45 nm), strong confinement loss of more than 788.39 dB/cm (at Au = 40 nm), and a highest Figure of Merit (FoM) of 62.5/RIU (at Au = 40 nm with RI = 1.32). The TiO₂ layer enhances mode coupling and resonance sharpness, while the optimized Au thickness boosts sensitivity and spectral resolution. Additionally, the blood components reach the WS of 5000 nm/RIU for plasma and 3000 nm/RIU for Krypton. Because of its high tunability and repeatable performance, the PCF–SPR biosensor is a promising choice for precise biochemical and biomedical sensing applications. Full article

(This article belongs to the Special Issue Plasmonic Sensors: Advances and Applications)

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15 pages, 2544 KB

Open AccessArticle

Near-Infrared Radiation Tolerance of Anti-Resonant Hollow-Core Optical Fibers in a Nuclear Reactor Environment

by Shlomi Zilberman, Amy Van Newkirk, William Lo, Matthew Leoschke, Marcello Catellani, Daniel Beck, Jeffrey A. Geuther, Enrique Antonio Lopez, Rodrigo Amezcua Correa, Axel Schülzgen, Michael Reilly and Federico Scurti

Photonics 2026, 13(3), 258; https://doi.org/10.3390/photonics13030258 - 6 Mar 2026

This study investigates the radiation-induced attenuation (RIA) of an Anti-Resonant Hollow-Core Fiber (AR-HCF) exposed to neutron and gamma radiation in a nuclear reactor environment. The AR-HCF—with a revolver-style structure—was characterized for RIA and compared to a solid, pure-silica-core fiber. Experimental results demonstrate that [...] Read more.

This study investigates the radiation-induced attenuation (RIA) of an Anti-Resonant Hollow-Core Fiber (AR-HCF) exposed to neutron and gamma radiation in a nuclear reactor environment. The AR-HCF—with a revolver-style structure—was characterized for RIA and compared to a solid, pure-silica-core fiber. Experimental results demonstrate that the AR-HCF exhibits substantially higher radiation tolerance compared to pure-silica, solid-core fibers, by about a factor of six in terms of dB/m. Numerical modeling in COMSOL Multiphysics (Version 6.3) was performed to simulate potential contributors of RIA, including silica compaction due to neutron fluence and changes in light confinement. These simulations ruled out these effects as primary causes of the measured attenuation. We also show that our results are consistent with the radiolytic generation of nitric acid within the hollow core, an interpretation that aligns with findings from a prior study. The results included in this manuscript provide insight into the behavior of AR-HCFs in the radiation field of a nuclear reactor, a topic with very limited prior literature, and underscore their potential for use in high-radiation environments such as fission and fusion reactors, particle accelerators, and space applications. The findings also point to promising future directions, including spectral characterization and dosimetry applications that leverage the unique properties of these fibers. Full article

(This article belongs to the Special Issue Advanced Optical Fiber Sensors for Harsh Environment Applications)

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13 pages, 10463 KB

Open AccessArticle

Simulation Study of a Distributed Fiber Optic Vibration Sensing System Using Dual-Chirped Pulses and Frequency Division Multiplexing

by Huanyu Pu, Shuyang Hu, Jing Zhang and Yunxin Wang

Photonics 2026, 13(3), 257; https://doi.org/10.3390/photonics13030257 - 5 Mar 2026

This paper proposes a distributed vibration sensing system based on dual-chirped pulses and weak fiber Bragg gratings. Compared with conventional dual-pulse heterodyne detection techniques, the proposed approach utilizes the time-frequency characteristics of chirp signals, effectively relaxing the stringent requirements on the signal pulse [...] Read more.

This paper proposes a distributed vibration sensing system based on dual-chirped pulses and weak fiber Bragg gratings. Compared with conventional dual-pulse heterodyne detection techniques, the proposed approach utilizes the time-frequency characteristics of chirp signals, effectively relaxing the stringent requirements on the signal pulse width. In addition, when chirp signals with different chirp rates are adopted, frequency-division multiplexing technology can be realized to enhance the system’s response bandwidth. Last but not least, the sensing probe signal is generated in the optical domain using microwave photonic technology, which theoretically helps alleviate the dependence on arbitrary waveform generators. A simulation study on the system was conducted. Using a chirp signal of 200 MHz/μs and with a grating spacing of 50 m, the desired vibration signal is phased modulated onto a beat signal with a frequency of 100 MHz, and the allowable pulse width can be up to 500 ns. To verify frequency-division multiplexing capability further, an additional pair of chirped pulses with a chirp rate of 400 MHz/μs was introduced into the system, which was generated by frequency multiplication. The results demonstrate that the system response bandwidth is increased to twice the original bandwidth. The proposed scheme provides a new solution for performance enhancement in a distributed fiber optic vibration sensing system. Full article

(This article belongs to the Special Issue Advances and Applications of Fiber Grating)

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13 pages, 3486 KB

Open AccessArticle

Dual-Band Infrared Metasurface with High-Efficiency Focusing and Full-Stokes Polarization Analysis

by Lifeng Ma, Yi Huang, Yanhong Xie, Na Xie, Lu Zhang, Huilin Jiang and Jun Chang

Photonics 2026, 13(3), 256; https://doi.org/10.3390/photonics13030256 - 5 Mar 2026

This study proposes a dual-band, mid-wave infrared (MWIR) and long-wave infrared (LWIR) polarization-multiplexed optical system based on a metasurface. By employing matrix-based phase encoding technology, we pioneered the use of a dual-band polarization multiplexing architecture for parallel processing, achieving full-Stokes polarization detection. This [...] Read more.

This study proposes a dual-band, mid-wave infrared (MWIR) and long-wave infrared (LWIR) polarization-multiplexed optical system based on a metasurface. By employing matrix-based phase encoding technology, we pioneered the use of a dual-band polarization multiplexing architecture for parallel processing, achieving full-Stokes polarization detection. This system realized wavelength and polarization multiplexing across six axial focal planes and the off-axis focal points on each focal plane. The system also achieved a high transmittance of 85%; the average transmittance of this system exceeded 70% in the 3–12 μm range. The focusing efficiency in the MWIR and LWIR is 71.1% and 62.5%, respectively, with polarization crosstalk below −25 dB. We used the inverse design method, shortening the design cycle by 80%. It provides a compact solution for infrared imaging, multispectral analysis, and biological tissue pathological detection. Full article

(This article belongs to the Special Issue Advanced Photonics Metamaterials and Metasurfaces: Science and Applications, 2nd Edition)

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10 pages, 1542 KB

Open AccessArticle

Laser Self-Mixing Sensor Based on Time–Frequency Spectrum for Material Damping Coefficient Measurement

by Xiulin Wang, Yiwei Jing, Yangtian Huang, Xuyue Zheng and Wencai Huang

Photonics 2026, 13(3), 255; https://doi.org/10.3390/photonics13030255 - 4 Mar 2026

A new method for measurement of the material damping coefficient based on the laser self-mixing interference (SMI) technique is proposed. The dominant frequency that varies over time is extracted by using the synchro-squeezed wavelet transform to obtain the time–frequency spectrum of a SMI [...] Read more.

A new method for measurement of the material damping coefficient based on the laser self-mixing interference (SMI) technique is proposed. The dominant frequency that varies over time is extracted by using the synchro-squeezed wavelet transform to obtain the time–frequency spectrum of a SMI signal. According to the linear relationship between the logarithm of the dominant frequency order and the damping coefficient, the damping coefficient of the material is obtained through linear fitting. The principle and process of the method are elaborated on and its performance is analyzed under different noise interferences and optical feedback factors. In tuning fork measurement, the root mean square error of the measured damping coefficient reaches 0.0133. With adaptive frequency resolution and window length, this method facilitates automated and high-precision damping coefficient measurement in materials. Full article

(This article belongs to the Special Issue Recent Research on Optical Sensing and Precision Measurement)

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17 pages, 3174 KB

Open AccessArticle

A Hybrid Model Integrating CNN–BiLSTM for Discriminating Strain and Temperature Effects on FBG-Based Sensors

by Chuanhao Wei, Qiang Liu, Dongdong Lin, Dan Zhu, Jingzhan Shi and Yiping Wang

Photonics 2026, 13(3), 254; https://doi.org/10.3390/photonics13030254 - 4 Mar 2026

A primary bottleneck in deploying Fiber Bragg Grating (FBG) sensors lies in their inherent dual sensitivity to thermal and mechanical variations, which mandates robust decoupling mechanisms for precise parameter extraction. To address this persistent cross-sensitivity issue, this study introduces a novel interrogation scheme [...] Read more.

A primary bottleneck in deploying Fiber Bragg Grating (FBG) sensors lies in their inherent dual sensitivity to thermal and mechanical variations, which mandates robust decoupling mechanisms for precise parameter extraction. To address this persistent cross-sensitivity issue, this study introduces a novel interrogation scheme that integrates a Convolutional Neural Network with a Bidirectional Long Short-Term Memory (CNN-BiLSTM) architecture. Instead of relying on conventional peak-tracking algorithms or isolated central wavelengths, our proposed data-driven strategy directly mines structural features from the full reflection spectra, thereby substantially mitigating cross-interference errors. The experimental results reveal that the coefficients of determination (R²) for strain and temperature prediction reach 99.37% and 99.75% each, while the root mean square errors (RMSEs) are 13.51 µε and 1.42 °C, respectively. The proposed method requires only a single FBG sensor, which reduces the sensor requirements, showing great potential in sensing applications requiring low costs and high adaptability. In addition, in some special environments, temperature information cannot be obtained, so we utilize another reference FBG to realize the temperature compensation. Meanwhile, we proposed a spectral differencing method (SDM) by differencing the spectra of the two FBGs to obtain the spectra containing only strain information and sent them as a dataset for model training, with a 4-times improvement in accuracy over traditional compensation methods. Finally, we also explored the application of the system for distributed FBGs, achieving an absolute peak wavelength interrogation precision of approximately ±0.02 nm. The system is expected to be applied in the field of structural health monitoring, which is promising even in harsh environments. Full article

(This article belongs to the Special Issue Fiber Optic Sensors: Advances, Technologies and Applications)

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16 pages, 3710 KB

Open AccessArticle

Cavity Length Demodulation of Optical Fiber FP Multi-Dimensional Accelerometer Based on Adaptive Filtering and Triple-Interferometric Information Complementarity

by Han Jiang, Dian Fan, Wenjia Chen, Ciming Zhou, Haoxiang Li, Ao Li and Mengfan Peng

Photonics 2026, 13(3), 253; https://doi.org/10.3390/photonics13030253 - 4 Mar 2026

In the optical fiber Fabry–Perot (FP) multi-dimensional acceleration sensing system, multi-dimensional acceleration measurement is realized based on a single optical path, resulting in the existence of multi-channel interference signals in the spectrum, and the traditional cavity length demodulation algorithm cannot achieve efficient separation [...] Read more.

In the optical fiber Fabry–Perot (FP) multi-dimensional acceleration sensing system, multi-dimensional acceleration measurement is realized based on a single optical path, resulting in the existence of multi-channel interference signals in the spectrum, and the traditional cavity length demodulation algorithm cannot achieve efficient separation of aliasing signals and high-precision demodulation of FP cavity length. To solve this problem, an adaptive filtering–multiple peaks–cooperative least squares algorithm (AF-MP-LS) is proposed for cavity length demodulation of optical fiber FP multi-dimensional accelerometer. The adaptive Gaussian filter is used to dynamically adjust the parameters according to the frequency difference in the aliasing optical signal, and the interference spectra of each channel are efficiently separated. The multiple peaks–least squares method is used to demodulate the separated signals, improve the demodulation resolution, and solve the problem of limited dynamic range of spectral signals. Furthermore, based on the multiplexing structure, a complementary correction method utilizing ‘triple-interferometric’ information—derived from the FP cavities and the auxiliary Michelson interference component—is proposed to improve the demodulation accuracy and stability of the system. The performance of the proposed method was verified through simulations, multi-angle vibration experiments and comparative algorithm analysis. The experimental results show that this algorithm can accurately demodulate multi-dimensional signals under different tilt angles of vibration excitation. Particularly, after compensating for the triple interference information, the mean square error (MSE) of the demodulated acceleration decreased by 0.0044 g, and the accuracy increased by 70.9% compared to before correction. Full article

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10 pages, 2899 KB

Open AccessArticle

A Deep Learning Framework for Multi-Plane Computer-Generated Holography

by Jiafeng Zeng, Yi Chen, Entong Kuang, Xinrui Li, Xiangsheng Xie and Qiang Wang

Photonics 2026, 13(3), 252; https://doi.org/10.3390/photonics13030252 - 4 Mar 2026

Multi-plane computer-generated holography is a key technology for enabling volumetric and near-eye displays. However, its widespread adoption remains constrained by the high computational cost of phase optimization and the persistent issue of axial crosstalk between depth planes. In this work, we propose a [...] Read more.

Multi-plane computer-generated holography is a key technology for enabling volumetric and near-eye displays. However, its widespread adoption remains constrained by the high computational cost of phase optimization and the persistent issue of axial crosstalk between depth planes. In this work, we propose a physics-informed deep learning framework that directly generates holograms for 3D multi-plane displays. Our approach implements a learnable mapping from spatial distributions to depth-dependent reconstructions and incorporates a trainable Fourier transform layer, enabling end-to-end optimization entirely in the physical domain (i.e., from the hologram plane to the multi-plane reconstruction). As a result, hologram generation time is decreased significantly, while effectively suppressing crosstalk across axial planes. Experimental validation demonstrates that the obtained phase hologram successfully reconstructs sparse multi-plane structured patterns with low visible crosstalk. These results highlight the potential of deep learning to advance practical applications in dynamic 3D display and holographic optical tweezer technologies. Full article

(This article belongs to the Special Issue Innovations in Structured Optical Field: From Fundamentals to Applications)

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13 pages, 2388 KB

Open AccessArticle

Bandgap Simulations in Randomized 3D Photonic Crystal Supercells

by Marcus Hall and Chris E. Finlayson

Photonics 2026, 13(3), 251; https://doi.org/10.3390/photonics13030251 - 4 Mar 2026

Periodic supercell lattice structures with elements of random polydispersity disorder were created to simulate the effect of randomization on photonic crystals using finite-difference time domain (FDTD) methods. As a key exemplar system, a three-dimensional “inverse opal” structure of a face-centered cubic lattice with [...] Read more.

Periodic supercell lattice structures with elements of random polydispersity disorder were created to simulate the effect of randomization on photonic crystals using finite-difference time domain (FDTD) methods. As a key exemplar system, a three-dimensional “inverse opal” structure of a face-centered cubic lattice with air spheres in a silicon dielectric was simulated, with sphere radii within supercells following a randomized Gaussian distribution, with characteristic standard deviation and mean. A corresponding ordered lattice with a bandgap with magnitude 3.5% of the normalized frequency range was used as a direct control, with sphere radius 0.34 times the lattice constant a. For a range of standard deviations, up to 5.9% of the 0.34a mean, a Monte Carlo-style approach was adopted, with photonic band properties analyzed over a large number of repeat simulations to ensure statistical significance. The corresponding Gaussian distribution in the resultant photonic bandgap magnitudes is broadened with increasing polydispersity such that an evolving fraction of simulations no longer exhibits a non-zero bandgap. A characteristic pseudo-transition occurs at a standard deviation of approximately 4.1% of the 0.34a mean, above where the frequency of simulations still returning a finite bandgap rapidly diminishes. Some isolated configurations, with a high degree of uniqueness, can exhibit enhanced bandgap properties (greater than the 3.5% benchmark) despite considerable polydisperse disordering; we envisage that these findings point towards the use of engineered randomness in supercell systems to create desired photonic crystal properties and functionality, such as localization and photonic bandgaps. Full article

(This article belongs to the Special Issue Advances in Micro and Nano-Photonics: Emerging Materials and Applications)

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14 pages, 3511 KB

Open AccessArticle

Comparison of Imaging Properties of Bangerter Foils and Myopia Control Spectacle Lens

by Susanna Pearline Clement, Augusto Arias and Siegfried Wahl

Photonics 2026, 13(3), 250; https://doi.org/10.3390/photonics13030250 - 4 Mar 2026

To evaluate whether Bangerter foils (BFs) could serve as a low-cost myopia control intervention, we measured and compared the imaging properties of fifteen BFs from two manufacturers, four myopia control spectacles, and a single-vision lens. Image quality metrics related to light-signaling theories of [...] Read more.

To evaluate whether Bangerter foils (BFs) could serve as a low-cost myopia control intervention, we measured and compared the imaging properties of fifteen BFs from two manufacturers, four myopia control spectacles, and a single-vision lens. Image quality metrics related to light-signaling theories of myopia onset and progression were evaluated in three tests: i. the assessment of the focusing properties through the maximum of the point spread function (MaxPSF), modulation transfer function (MTF), and area under the MTF (AUMTF); ii. the quantification of the scattered light (s) using the optical integration method; and iii. the calculation of the Michelson contrast (MiC) on a binary grating imaged under dark and bright illumination. BFs exhibited lower MaxPSF, AUMTF, and MTF values than the myopia control lenses. Except for one 0.6-graded BF, none of the other BFs mimicked the scattering behavior of the diffusion optics technology lenses. Moreover, BFs showed lower MiC values than with myopia control lenses under both lighting conditions. Although the BFs did not replicate the imaging properties of myopia control lenses, they still demonstrated effective contrast reduction across the lighting conditions. Whether they may help to slow myopia progression remains uncertain, perhaps even unlikely, given the fundamental imaging differences. Full article

(This article belongs to the Special Issue Advances in Visual Optics)

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16 pages, 19250 KB

Open AccessArticle

Variable Bit-Width All-Optical Content-Addressable Memory Enabled by Sb₂Se₃ for Similarity Search

by Yi Guo, Xinmeng Hao, Yibo Zhang, Guangsong Yuan, Hongxiang Guo, Bing Song, Jian Wu and Qingjiang Li

Photonics 2026, 13(3), 249; https://doi.org/10.3390/photonics13030249 - 3 Mar 2026

In the big-data-driven artificial intelligence era, similarity search, as a core operation in machine learning and data mining, demands high speed, energy efficiency, and scenario adaptability. Conventional electronic content-addressable memory (ECAMs) suffer from inherent RC delay bottlenecks, whereas existing optical content-addressable memory (OCAMs) [...] Read more.

In the big-data-driven artificial intelligence era, similarity search, as a core operation in machine learning and data mining, demands high speed, energy efficiency, and scenario adaptability. Conventional electronic content-addressable memory (ECAMs) suffer from inherent RC delay bottlenecks, whereas existing optical content-addressable memory (OCAMs) are restricted by fixed bit-widths and limited distance metrics. In this work, we propose a variable bit-width all-optical CAM leveraging multi-segment modulators and phase-change material (PCM) Sb₂Se₃. The multi-segment memory unit (MSMU) therein compresses N-bit binary data into a single analog photonic unit, supporting direct data writing/loading without digital-to-analog converters (DACs) and flexible trade-offs between precision, storage capacity, noise immunity, and energy while enabling Hamming and nonlinear distance metrics. A six-element three-bit OCAM prototype was fabricated on a silicon nitride silicon-on-insulator (SiN-SOI) platform. Despite the absence of integrated high-speed phase shifters, the device still achieves reliable optical data storage and retrieval. K-nearest neighbor (kNN) simulations based on experimentally derived statistical data—validated on the iris, wine, and breast cancer datasets—show that the three-bit operating mode achieves classification accuracy comparable to Manhattan/Euclidean distances at high signal-to-noise ratios (SNRs), while the one-bit mode exhibits strong noise robustness. Energy consumption is 364 fJ/bit (3-bit) and 890 fJ/bit (1-bit). This work provides a high-speed, energy-efficient, and reconfigurable all-optical similarity search solution with experimentally verified device performance and dataset-validated applicability, showing great potential for widespread deployment in data-intensive machine learning and data-mining applications. Full article

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15 pages, 5074 KB

Open AccessArticle

Joint Nonlinear Trellis-Coded Precoding and Noise-Weighted Viterbi Decoding for Robust High-Speed MISO Underwater Visible Light Communication

by Yunlong Pan, Jiabin Ye, Yunkai Wang, Zhe Feng, Xinyi Liu, Zengyi Xu, Fujie Li, Chao Shen and Nan Chi

Photonics 2026, 13(3), 248; https://doi.org/10.3390/photonics13030248 - 3 Mar 2026

In this paper, we propose a robust multi-input single-output (MISO) underwater visible light communication (UVLC) system. By integrating NLTCP and NW-Viterbi decoding, the system effectively alleviates nonlinear distortions and stochastic power fluctuations. NLTCP is employed to achieve probabilistic shaping by generating a non-uniformly [...] Read more.

In this paper, we propose a robust multi-input single-output (MISO) underwater visible light communication (UVLC) system. By integrating NLTCP and NW-Viterbi decoding, the system effectively alleviates nonlinear distortions and stochastic power fluctuations. NLTCP is employed to achieve probabilistic shaping by generating a non-uniformly distributed constellation, which effectively suppresses the occurrence of high-amplitude symbols to mitigate device nonlinearity. To further optimize power allocation, a MISO architecture is utilized to distribute the signal load and reduce the power burden on individual devices. Moreover, the NW-Viterbi decoder incorporates a noise-aware weighting mechanism to optimize the decision metric, thereby enhancing decoding reliability in response to signal-dependent power fluctuations and noise variations in the underwater channel. Experimental results confirm that at an aggregate data rate of 5.8 Gbps, the proposed scheme achieves a significant Q-factor gain of 0.92 dB compared to the traditional PAM4 scheme, alongside a 90.76% enlargement in the effective operating dynamic range. This approach offers a computationally efficient yet effective solution to nonlinearity and power jitter, demonstrating significant potential for practical underwater deployments. Full article

(This article belongs to the Special Issue Progress and Prospects in Visible Light Communications)

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14 pages, 3808 KB

Open AccessArticle

A Multichannel Vortex Beam Generator via Spatially Structured Bidirectional Two-Color-Pump Four-Wave Mixing in a Single ¹³³Cs Vapor Cell

by Dan Wang, Meng-Yu Bian, Zi-Yi Gao, Liang-Hui Huang, Hai-Tao Zhou and Jun-Xiang Zhang

Photonics 2026, 13(3), 247; https://doi.org/10.3390/photonics13030247 - 3 Mar 2026

Multichannel vortex beams serve as an essential physical source for enabling multi-spot laser processing and high-dimensional spatial multiplexing communications. We demonstrate a compact, flexibly tunable multichannel vortex beam generator using spatially structured bidirectional two-color pump vortex four-wave mixing in a single ¹³³Cs [...] Read more.

Multichannel vortex beams serve as an essential physical source for enabling multi-spot laser processing and high-dimensional spatial multiplexing communications. We demonstrate a compact, flexibly tunable multichannel vortex beam generator using spatially structured bidirectional two-color pump vortex four-wave mixing in a single ¹³³Cs vapor cell. To enhance spatial multiplexing, both sides of the cell are utilized. By engineering the propagation directions and frequencies of five input beams, we establish a nonlinear interaction region that supports 16 concurrent phase-matching conditions, thereby enabling the parallel generation of up to eight vortex channels. The orbital angular momentum of the output beams follows deterministic algebraic rules, allowing for programmable control via tailored input orbital angular momentum combinations. Moreover, the channel count can be linearly tuned by selectively deactivating pumps—each switched-off pump reduces the number of output channels by two. This flexible control over orbital angular momentum states, together with channel count and spatial arrangement, establishes a highly integrated platform for on-demand vortex generation. This work highlights the potential of spatially bidirectional structured pumping in atomic vapor to expand optical dimensionality and enhance multiplexing capacity, paving the way toward multidimensional communications, quantum networks, and integrated photonics. Full article

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17 pages, 1853 KB

Open AccessArticle

65% Efficient Multijunction Photovoltaic Laser Power Converters Operating over 150 W/cm²

by Simon Fafard and Denis Masson

Photonics 2026, 13(3), 246; https://doi.org/10.3390/photonics13030246 - 3 Mar 2026

Multijunction laser power converters are demonstrated for the first time with high efficiencies for average optical irradiances exceeding 150 W/cm². The GaAs-based photovoltaic power converting III-V heterostructures are designed with six GaAs subcells having an area of 0.14 cm², [...] Read more.

Multijunction laser power converters are demonstrated for the first time with high efficiencies for average optical irradiances exceeding 150 W/cm². The GaAs-based photovoltaic power converting III-V heterostructures are designed with six GaAs subcells having an area of 0.14 cm², receiving up to 22 W of input power at ~811 nm, delivering over 14 W of output power. The maximum efficiencies are obtained in the range of 30 to 75 W/cm², and efficiencies > 64% are still obtained at 160 W/cm². The efficiency reduction for higher irradiance values originates predominantly from residual heat generated in the active layers. For example, in 100% duty factor measurements, the bandgap voltage offset saturates to W_oc ~ 170 mV. However, in pulsed mode, W_oc values as low as 150 mV have been obtained for a device base temperature of 20 °C. For smaller 0.029 cm² devices, W_oc values around 137 mV are obtained at 240 W/cm². Full article

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

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11 pages, 2679 KB

Open AccessArticle

Power-Scaled Mode-Locked Femtosecond Pulses from an All-Polarization-Maintaining Tm-Doped Figure-9 Fiber Laser

by Mingrui Jiang, Ting Wen, Yuhang Wei, Liang Zhao, Senyu Wang, Jinlong Wan, Hongyu Luo and Jianfeng Li

Photonics 2026, 13(3), 245; https://doi.org/10.3390/photonics13030245 - 2 Mar 2026

We demonstrate an all-polarization-maintaining (PM) mode-locked thulium-doped fiber laser operating in the net-normal-dispersion regime based on a figure-9 nonlinear amplifying loop mirror (NALM) configuration. A chirped fiber Bragg grating (CFBG) and a commercial PM dispersion-compensating fiber (PM-DCF) are incorporated into the figure-9 cavity, [...] Read more.

We demonstrate an all-polarization-maintaining (PM) mode-locked thulium-doped fiber laser operating in the net-normal-dispersion regime based on a figure-9 nonlinear amplifying loop mirror (NALM) configuration. A chirped fiber Bragg grating (CFBG) and a commercial PM dispersion-compensating fiber (PM-DCF) are incorporated into the figure-9 cavity, providing a large normal net dispersion and enabling stable dissipative-soliton mode-locking. Under stable dissipative-soliton operation, the laser delivers a maximum output power of 53.6 mW at a repetition rate of 12.31 MHz, corresponding to a pulse energy of 4.3 nJ. The output spectrum has a central wavelength of ~1952 nm with a 3 dB bandwidth of ~11 nm. The all-PM laser oscillator directly generates a fs pulse without extra-cavity compression, achieving a pulse duration of 545 fs at the CFBG arm. Moreover, stable fundamental mode-locking is verified by a high radio-frequency signal-to-noise ratio (SNR) exceeding 82 dB and a long-term root-mean-square (RMS) power fluctuation of 0.45% over two hours. To the best of our knowledge, this represents the highest output power generated from an all-PM-fiber figure-9 laser oscillator in the 2 μm band, alongside fs-pulse operation. This high-power, compact, stable and environment-insensitive fs-pulsed laser source shows great potential as an ideal seed for biomedical imaging and mid-infrared frequency combs. Full article

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

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20 pages, 1882 KB

Open AccessArticle

Quantum-Enhanced Imaging Model Based on Squeezed States

by Chunrong Peng, Yanxiang Xie and Kui Liu

Photonics 2026, 13(3), 244; https://doi.org/10.3390/photonics13030244 - 2 Mar 2026

Aided by quantum sources, quantum metrology helps enhance measurement precision. Here, we construct a theoretical model for quantum imaging based on squeezed states and present the corresponding numerical results. Through discretization and quantum Fisher information theory, we investigate the two-point resolution and spatial [...] Read more.

Aided by quantum sources, quantum metrology helps enhance measurement precision. Here, we construct a theoretical model for quantum imaging based on squeezed states and present the corresponding numerical results. Through discretization and quantum Fisher information theory, we investigate the two-point resolution and spatial multi-parameter estimation of optical fields with unknown spatial distributions. We calculate and compare imaging results based on squeezed vacuum states, coherent states, and squeezed coherent states; our results show that squeezed coherent states yield greater quantum Fisher information, which can effectively improve imaging quality. In addition, we analyze the influence of imaging basis functions, degree of squeezing, quantum correlations, and other factors on imaging performance. The proposed quantum imaging model and computational method can be extended to more complex scenarios, such as multi-mode squeezed-state imaging schemes and incoherent imaging systems. In the future, this approach is expected to find applications in practical imaging systems, including Raman microscopy and stimulated Brillouin scattering imaging. Full article

(This article belongs to the Special Issue Advanced Research in Quantum Optics)

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16 pages, 3216 KB

Open AccessArticle

Chaotic Fiber Laser-Based Distributed Fiber Sensing for Weak Vibration Detection Using Machine Learning

by Weicheng Zheng, Yiwei Chen, Haoran Pan, Xiangkun Ma, Jiahua Xu, Junmin Liu and Chunxiang Zhang

Photonics 2026, 13(3), 243; https://doi.org/10.3390/photonics13030243 - 2 Mar 2026

To address the challenge of weak vibration signal detection, we propose a chaotic fiber laser-based distributed sensing system integrated with machine learning-assisted signal extraction. The system combines a chaotic fiber laser with a linear non-balanced Sagnac interferometer, enabling high sensitivity to external perturbations [...] Read more.

To address the challenge of weak vibration signal detection, we propose a chaotic fiber laser-based distributed sensing system integrated with machine learning-assisted signal extraction. The system combines a chaotic fiber laser with a linear non-balanced Sagnac interferometer, enabling high sensitivity to external perturbations while effectively suppressing reciprocal effects of traditional ring interferometer systems. A convolutional neural network (CNN) is employed to directly learn and extract discriminative vibration features from the chaotic sensing signals, facilitated by phase space reconstruction (PSR), which preserves the system’s intrinsic dynamics under extreme noise. By jointly exploiting the broadband, noise-like characteristics of chaotic laser sensing, and the nonlinear feature extraction capability of CNNs, the proposed system enables reliable detection of weak vibration signals under ultra-low signal-to-noise ratio (SNR) conditions, down to −22 dB. Experimental results demonstrate a weak frequency detection ranging from 0.1 Hz to 10 kHz, with significantly enhanced sensitivity and bandwidth compared with conventional signal processing-based methods. Full article

(This article belongs to the Special Issue Fiber Optics and Fiber Lasers)

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18 pages, 8322 KB

Open AccessArticle

Validation of a Single-Image Inverse Rendering Setup for Optical Property Estimation in Turbid Materials

by Philipp Nguyen, David Hevisov, Markus Wagner, Joachim Jelken, Florian Foschum and Alwin Kienle

Photonics 2026, 13(3), 242; https://doi.org/10.3390/photonics13030242 - 28 Feb 2026

This work presents an experimental validation of a physics-based inverse rendering method for determining the reduced scattering and absorption coefficients of turbid materials in arbitrary shape from a single image per wavelength. Based on our previously published theoretical inverse rendering framework, we constructed [...] Read more.

This work presents an experimental validation of a physics-based inverse rendering method for determining the reduced scattering and absorption coefficients of turbid materials in arbitrary shape from a single image per wavelength. Based on our previously published theoretical inverse rendering framework, we constructed and experimentally characterised a wavelength-selective measurement setup to realise and validate the method under real acquisition conditions. By accurately modelling the spectral behaviour and angle-dependent transmission of the employed bandpass filters, we ensured a close correspondence between captured and simulated reflectance. The method was evaluated on three silicone materials, beginning with simple cube geometries and later extending to a complex Einstein bust. Relative to integrating-sphere reference data, the recovered optical properties exhibit maximum absolute errors of approximately 4–10% for reduced scattering and 5–10% for absorption for the cubes, and 16–19% and 16–22%, respectively, for the bust. Forward renderings based on the recovered coefficients achieve CIE

Δ E_{2000}

values below 1 for the cube and below 2 for the complex geometry when compared with photographs. Additionally, we demonstrated that the approach can be applied using a common commercially available RGB camera, recovering optical parameters from each RGB channel, albeit with increased errors due to the camera’s broad spectral channels. Overall, our method enables the recovery of optical properties and the creation of accurate digital twins for objects of arbitrary shape using comparatively simple hardware, including common commercially available RGB cameras. This broadens its applicability to practical scenarios such as process monitoring and digital twinning when appearance, rather than precise material parameters, is the primary focus. Full article

(This article belongs to the Special Issue Computational Optical Imaging: Progress and Future Prospects)

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20 pages, 2605 KB

Open AccessArticle

Interference-Aware User Grouping and Power Allocation for Overlapping Multi-LED ADO-OFDM NOMA VLC Networks

by Yang Tu, Chuan Li and Cu Van Pham

Photonics 2026, 13(3), 241; https://doi.org/10.3390/photonics13030241 - 28 Feb 2026

Overlapping illumination in multi-LED visible light communication (VLC) networks introduces cross-LED coupling that reshapes the received-signal composition and may trigger error propagation in successive interference cancellation (SIC) for layered ADO-OFDM NOMA. This work employs an overlap factor [...] Read more.

Overlapping illumination in multi-LED visible light communication (VLC) networks introduces cross-LED coupling that reshapes the received-signal composition and may trigger error propagation in successive interference cancellation (SIC) for layered ADO-OFDM NOMA. This work employs an overlap factor

β \in [0, 1]

to quantify the severity of overlap-induced cross-LED coupling and develops a

β

-aware resource-allocation framework for a dual-LED indoor downlink. The proposed design integrates channel-aware MCGAD user grouping with three-level coefficient adaptation, including the inter-LED power split

η

, the inter-layer ACO/DCO split

ρ

, and the intra-layer two-user NOMA coefficients

α

. Monte Carlo evaluations over

β \in {0, 0.2, 0.5}

show that stronger coupling drives the system into an interference-limited regime with a pronounced high-SNR BER floor for strong users after SIC; the proposed

β

-aware design consistently reduces this floor relative to a

β

-blind fixed-coefficient baseline. Meanwhile, the spectral-efficiency curves remain close to the baseline, with only a minor gap at moderate-to-high SNR, and the Shannon-rate energy-efficiency trends remain comparable across coupling scenarios. The grouping-and-allocation procedure is dominated by sorting and deterministic pairing, exhibiting

O (U log U)

complexity and avoiding the combinatorial growth of exhaustive grouping. Full article

(This article belongs to the Special Issue Advanced Technologies in Optical Wireless Communications—2nd Edition)

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