Photonics

25 pages, 3121 KB

Open AccessArticle

Complex Dispersion of a Dielectric-Coated Cylindrical Conductor: A Spectral Study of the Sommerfeld–Goubau Line

by Eugen Smolkin and Yury Shestopalov

Photonics 2026, 13(9), 812; https://doi.org/10.3390/photonics13090812 - 25 Aug 2026

The complex dispersion and modal sensitivity of an axisymmetric transverse magnetic surface wave supported by a dielectric-coated perfectly conducting cylinder are investigated. Starting from Maxwell’s equations, the boundary-value problem is reduced to a nonlinear complex dispersion equation for the longitudinal propagation constant

β

[...] Read more.

The complex dispersion and modal sensitivity of an axisymmetric transverse magnetic surface wave supported by a dielectric-coated perfectly conducting cylinder are investigated. Starting from Maxwell’s equations, the boundary-value problem is reduced to a nonlinear complex dispersion equation for the longitudinal propagation constant

β

. A numerical framework combining zero-level localization of the real and imaginary parts of the dispersion function, nonlinear root refinement, numerical clustering, and adaptive continuation in the complex coating permittivity is used to identify and track a selected spectral branch. One- and two-parameter computations characterize the mapping

ε \mapsto β (ε)

over prescribed subsets of the complex-permittivity plane. At fixed

ℑ ε

, increasing

ℜ ε

increases

ℜ β

and decreases

ℑ β

, whereas at fixed

ℜ ε

, increasing

ℑ ε

increases both components of

β

in the investigated parameter range. The rectangular-grid, concentric-circle, and radial-beam experiments show that the spectral response is smooth on the considered parameter sets but non-affine, coupled, and direction-dependent. The corresponding longitudinal electric field is reconstructed, normalized, and phase-aligned along the tracked branch. Difference fields, radial localization measures, a global modal distance, and a normalized correlation coefficient show that the same qualitative radial TM mode is retained throughout the sampled parameter domain, while its propagation constant and spatial localization vary continuously with the complex coating permittivity. Full article

(This article belongs to the Special Issue Optical Waveguides: Numerical Methods, Mathematical Modeling, and AI Techniques)

18 pages, 5250 KB

Open AccessArticle

Switchable Triple-Mode Terahertz Polarization Control Based on a Hybrid Graphene-VO₂ Metasurface

by Yihao Wang, Yang Gao, Yuxin Fan, Maofu Gao and Jiabing Shen

Photonics 2026, 13(9), 811; https://doi.org/10.3390/photonics13090811 - 25 Aug 2026

Abstract

We propose a gold-graphene-vanadium dioxide (VO₂) hybrid metasurface capable of reversibly switching among three operational modes in the terahertz regime. The device achieves flexible polarization control by combining the insulator-to-metal phase transition of VO₂ with the electrical tunability of graphene. [...] Read more.

We propose a gold-graphene-vanadium dioxide (VO₂) hybrid metasurface capable of reversibly switching among three operational modes in the terahertz regime. The device achieves flexible polarization control by combining the insulator-to-metal phase transition of VO₂ with the electrical tunability of graphene. Simulation results reveal three distinct behaviors depending on the biasing conditions of the materials. With graphene held at a chemical potential of 0 eV and VO₂ in the insulating state, the metasurface acts as a linear-to-linear polarization converter. The polarization conversion ratio (PCR) exceeds 0.9 over the frequency range from 5.5 to 8.6 THz. When the graphene chemical potential is raised to 0.9 eV while VO₂ remains insulating, the metasurface switches to linear-to-circular conversion. Notably, the handedness of the outgoing wave depends on the polarization of the incoming signal. Over the 6.45–8.36 THz band, the axial ratio (AR) remains below 3 dB. A third functional state emerges when VO₂ switches to its metallic phase. In this state, the device simply operates as a broadband co-polarized reflector, covering the terahertz communication band from 0.1 to 10 THz. This switchable, multifunctional behavior should prove useful for terahertz communications, polarization imaging, and sensing applications. Full article

(This article belongs to the Special Issue Technologies and Applications of Terahertz Metamaterials)

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14 pages, 3930 KB

Open AccessArticle

Design of a Nanovoid Ring-Core Fiber for Ultra-Low-Bending-Loss Few-Mode Transmission

by Asma Mimouni, Younès Messaddeq and Bora Ung

Photonics 2026, 13(9), 810; https://doi.org/10.3390/photonics13090810 - 25 Aug 2026

Abstract

We present a nanovoid-assisted ring-core fiber designed for low-bending-loss few-mode transmission. We develop a 3D model that accounts for stress-induced perturbation in bending-loss evaluation. Our model yields closer agreement with published experimental data compared to conventional conformal mapping. The nanovoid ring-core fiber reduces [...] Read more.

We present a nanovoid-assisted ring-core fiber designed for low-bending-loss few-mode transmission. We develop a 3D model that accounts for stress-induced perturbation in bending-loss evaluation. Our model yields closer agreement with published experimental data compared to conventional conformal mapping. The nanovoid ring-core fiber reduces the bending loss of higher-order modes by up to three orders of magnitude, and improves the degeneracy of the higher-order pair nearly ten-fold at tight bending radii. The proposed fiber maintains the same intermodal separation compared to the reference ring-core fiber across all investigated radii. Full article

(This article belongs to the Special Issue New Trends in Optical Sensing Techniques)

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16 pages, 15391 KB

Open AccessArticle

3D-Printed Biomimetic Sponge-Based Broadband and Highly Efficient Terahertz Absorber

by Pei-Di Yang

Photonics 2026, 13(9), 809; https://doi.org/10.3390/photonics13090809 - 24 Aug 2026

Abstract

With the rapid advancement of terahertz technology, electromagnetic interference has become a critical issue that compromises device performance, creating an urgent demand for high-performance terahertz absorbers. Three-dimensional (3D) printing, characterized by flexible structural design, monolithic fabrication, and mold-free processing, has emerged as a [...] Read more.

With the rapid advancement of terahertz technology, electromagnetic interference has become a critical issue that compromises device performance, creating an urgent demand for high-performance terahertz absorbers. Three-dimensional (3D) printing, characterized by flexible structural design, monolithic fabrication, and mold-free processing, has emerged as a promising technique for producing terahertz absorbers. In this work, inspired by the structural and functional characteristics of deep-sea sponges, we propose a bioinspired absorber design that integrates a porous topology with 3D printing. By optimizing the rotation angle and the hollowed array, the absorber establishes multiple internal reflection paths, which, combined with the structural matrix and the graphene conductive coating, enable highly efficient dissipation of electromagnetic energy. Experimental results show that the fabricated sample achieves an absorptivity exceeding 99% over the 0.5–2.0 THz frequency range, while also exhibiting wide-angle absorption and polarization-insensitive performance. The influence of pore size and graphene concentration on the absorption properties is systematically revealed. This work further enhances the performance of 3D-printed terahertz absorbers and provides a novel technical pathway for the design and fabrication of high-performance terahertz absorbers. Full article

(This article belongs to the Special Issue Novel Developments in Optoelectronic Materials and Devices)

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17 pages, 4628 KB

Open AccessProject Report

Investigation of a Dual-Wavelength Solid-State Laser Self-Mixing Vibration Measurement Method

by Jian Zhou, Bolin Li, Yicong Feng, Qi Wang and Xiaoming Nie

Photonics 2026, 13(9), 808; https://doi.org/10.3390/photonics13090808 - 24 Aug 2026

Abstract

To address the contradiction between high resolution and structural complexity in traditional laser self-mixing measurement systems, the co-axial dual-wavelength solid-state laser self-mixing technology was proposed and studied. An LD pumped the Nd:YVO4 crystal and doubled the frequency to generate two wavelengths laser at [...] Read more.

To address the contradiction between high resolution and structural complexity in traditional laser self-mixing measurement systems, the co-axial dual-wavelength solid-state laser self-mixing technology was proposed and studied. An LD pumped the Nd:YVO4 crystal and doubled the frequency to generate two wavelengths laser at 1064 nm and 532 nm, and a co-axial dual-wavelength laser self-mixing measurement system was constructed. A 90° phase difference between the two wavelengths was produced by adjusting the angle of incidence of the parallel glass plate. As a result, a set of orthogonal signals was built to distinguish the direction of the displacement for the target. The experiments showed that the measuring system can adapt to different vibration waveforms and that the frequency measurement upper limit can be reached at 7 kHz. The system exhibited high precision in displacement measurement, with an RMS displacement noise of 8.64 nm and a cumulative error of 33.66 nm at a peak-to-peak amplitude of 5000 nm, along with a short-term resolution better than 2 nm. Full article

(This article belongs to the Special Issue Advancements in Optics and Laser Measurement)

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13 pages, 3818 KB

Open AccessArticle

Hybrid THz/FSO Transmission System with a Shared Photonic Transmitter Enabled by PMMA-Based Beam Combining

by Qinyi Zhang, Jianjun Yu, Hanyu Zhang, Zhongxiao Pei, Jiali Chen, Xin Lu, Jianyu Long, Yifan Chen and Ye Zhou

Photonics 2026, 13(9), 807; https://doi.org/10.3390/photonics13090807 - 24 Aug 2026

Abstract

Hybrid terahertz (THz)/free-space optical (FSO) systems offer a promising paradigm for high-capacity, all-weather wireless communication, yet their deployment is often hindered by the bulky size and high complexity of discrete transceivers. This paper experimentally demonstrates a low-complexity hybrid THz/FSO transmission architecture featuring a [...] Read more.

Hybrid terahertz (THz)/free-space optical (FSO) systems offer a promising paradigm for high-capacity, all-weather wireless communication, yet their deployment is often hindered by the bulky size and high complexity of discrete transceivers. This paper experimentally demonstrates a low-complexity hybrid THz/FSO transmission architecture featuring a unified photonic transmitter. By leveraging a polymethyl methacrylate (PMMA) plate serving as a dichroic beam combiner—which reflects the 1550 nm optical signal while transmitting the 300 GHz THz signal—we realize simultaneous signal propagation over a shared aperture and link. Photonics-aided techniques are employed to generate both carriers, ensuring system integration and coherence. The experimental results verify that both the THz and FSO links independently support 30-GBaud quadrature phase-shift keying (QPSK) transmission over a 10-m wireless distance, achieving a net data rate of 60 Gbps per link while satisfying the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10⁻³. This work validates the feasibility of shared-transmitter designs and provides a compact, cost-effective solution for future high-speed fronthaul/backhaul networks. Full article

(This article belongs to the Special Issue Microwave Photonics: Integrated Technologies, Advanced Sensing, and Communications for 6G Era)

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11 pages, 7390 KB

Open AccessArticle

Reversed Size Dependence of External Quantum Efficiency in GaN Micro-LEDs with an AlGaN-Interlayered QW–QD Composite Active Region

by Yi Gong, Ying Gu, Min Jiang, Shan Jin, Lifeng Bian and Shulong Lu

Photonics 2026, 13(9), 806; https://doi.org/10.3390/photonics13090806 - 24 Aug 2026

Abstract

Size-dependent efficiency degradation remains a major challenge for deeply scaled GaN-based micro-light-emitting diodes (micro-LEDs) because etched sidewalls increasingly influence carrier recombination. Here, square micro-LEDs with lateral dimensions of 5–50 μm were fabricated from the same plasma-assisted molecular-beam-epitaxy-grown wafer containing a five-period InGaN quantum-well/1 [...] Read more.

Size-dependent efficiency degradation remains a major challenge for deeply scaled GaN-based micro-light-emitting diodes (micro-LEDs) because etched sidewalls increasingly influence carrier recombination. Here, square micro-LEDs with lateral dimensions of 5–50 μm were fabricated from the same plasma-assisted molecular-beam-epitaxy-grown wafer containing a five-period InGaN quantum-well/1 nm Al_0.1Ga_0.9N interlayer/InGaN quantum-dot-like (QW–QD) composite active region. Contrary to the conventional size effect, the light output power density and external quantum efficiency (EQE) increased as the mesa size decreased. The peak EQEs were 3.66%, 4.53%, 5.63%, 7.04%, and 7.27% for the 50, 40, 30, 10, and 5 μm devices, respectively, corresponding to an approximately 98.6% increase from 50 to 5 μm. The favorable scaling is consistent with localization-mediated suppression of lateral carrier loss combined with size-dependent light extraction. The present measurements do not quantitatively separate injection, internal efficiency, and extraction contributions. These results demonstrate the potential of ultrathin-interlayer QW–QD active-region engineering for scaled GaN micro-LEDs. Full article

(This article belongs to the Special Issue Semiconductor Optoelectronic Devices: Characterizations, Design and Fabrication)

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25 pages, 1461 KB

Open AccessArticle

KAN-PINN-Based Simulation of DFB Lasers

by Guanliang Chen, Zhenyun Tang, Wanzhi Zhang, Yantong Wu, Li Xiang, Yinxian Luo, Sanjie Liu, Dongmei Li, Huiyun Wei, Mingzeng Peng, Zhigang Song and Xinhe Zheng

Photonics 2026, 13(9), 805; https://doi.org/10.3390/photonics13090805 - 23 Aug 2026

Abstract

To address the challenges encountered in the simulation and parameter extraction of distributed-feedback (DFB) lasers, this work starts from the rate equations of the DFB laser to derive its steady-state formulation and small-signal model, and constructs steady-state and transient KAN-based physics-informed neural-network (KAN-PINN) [...] Read more.

To address the challenges encountered in the simulation and parameter extraction of distributed-feedback (DFB) lasers, this work starts from the rate equations of the DFB laser to derive its steady-state formulation and small-signal model, and constructs steady-state and transient KAN-based physics-informed neural-network (KAN-PINN) architectures. In the steady state, accurate L-I/I–V curves and

- 3 dB

bandwidth results are obtained. In addition, the parameters of the DFB laser are systematically organized, and a KAN-PINN inverse mode, an adaptive moment estimation (Adam) optimizer-based physical inversion, and a hybrid strategy combining the two are proposed. The extracted parameters show small deviations from the true values, and the simulation results agree well with the actual data. The proposed methodology can be extended to other lasers and even to a broader class of optoelectronic devices for parameter extraction and simulation. Full article

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18 pages, 17687 KB

Open AccessArticle

Fast Non-Mechanical Beam Steering via Cascaded Stressed Polymer Network Liquid Crystal Optical Switch and Liquid Crystal Polarization Grating

by Jiahui Chen, Ziling Chen, Xitong Liang, Yuan Wang, Lin Xu and Chi Zhang

Photonics 2026, 13(9), 804; https://doi.org/10.3390/photonics13090804 - 23 Aug 2026

Abstract

Non-mechanical beam steering technology based on liquid crystal optical switches and liquid crystal polarization gratings holds significant application prospects in fields such as laser communication, radar detection, and optical information processing. Traditional nematic liquid crystal optical switches exhibit slow response speeds, whereas novel [...] Read more.

Non-mechanical beam steering technology based on liquid crystal optical switches and liquid crystal polarization gratings holds significant application prospects in fields such as laser communication, radar detection, and optical information processing. Traditional nematic liquid crystal optical switches exhibit slow response speeds, whereas novel ferroelectric liquid crystal optical switches, despite their fast response, are hampered in engineering applications by complex fabrication processes, the large number of devices required for cascading, and substantial module thickness. To address these issues, this paper proposes and demonstrates a fast non-mechanical beam steering scheme by cascading a stressed polymer network liquid crystal (SPNLC) optical switch with a liquid crystal polarization grating. The SPNLC is fabricated by mechanically shearing a polymerized liquid crystal–polymer composite, enabling sub-millisecond response and continuous linear phase modulation without the need for an alignment layer. A 30-μm-thick SPNLC half-wave plate was prepared, which introduces a phase retardation of 3.6 μm under a driving voltage of 300 V, and the rise time and fall time are measured to be approximately 526 μs and 560 μs at a driving voltage of 20 V with a 1 kHz square wave, and 470 μs and 538 μs at 27 V under the same waveform conditions. Cascaded with a passive polarization grating, the waveplate enables fast electrical switching of the beam between the ±1st diffraction orders. Furthermore, a two-dimensional multi-angle beam deflector was constructed based on a supra-binary cascade scheme. Experimental results confirm that the system possesses sub-millisecond response, large phase retardation, continuous tunability, and an alignment-layer-free fabrication process, demonstrating its feasibility for large-range fast beam scanning. Full article

(This article belongs to the Special Issue Latest Advances in Optical Diffraction, Imaging and Display)

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20 pages, 7445 KB

Open AccessArticle

Ultraviolet Laser Texturing of PEEK: Finite Element Simulation and Surface Properties

by Xiaohui Wang, Enbing Qi, Yifan Wu, Xuan Sun, Xiuhua Men, Jianbin Wang and Junjie Zhang

Photonics 2026, 13(9), 803; https://doi.org/10.3390/photonics13090803 - 22 Aug 2026

Abstract

This paper comprehensively investigates the ultraviolet (UV) nanosecond laser fabrication of micro-groove textures on planar PEEK surfaces, as well as their surface performance in terms of wettability and frictional properties. Firstly, a three-dimensional finite element model, incorporating a moving Gaussian heat source, solid [...] Read more.

This paper comprehensively investigates the ultraviolet (UV) nanosecond laser fabrication of micro-groove textures on planar PEEK surfaces, as well as their surface performance in terms of wettability and frictional properties. Firstly, a three-dimensional finite element model, incorporating a moving Gaussian heat source, solid heat transfer and deformed geometry, was established to simulate the transient temperature field and ablation profile of PEEK during UV laser ablation. The predicted groove depth agreed with the experimental value with a low deviation of 11.19%. Based on the simulation and single-factor experiments, the optimized single-track laser parameters were determined as a laser power of 1.2 W, a scanning speed of 100 mm/s and a repetitive frequency of 100 kHz. Secondly, systematic single-factor and multi-pass laser ablation experiments of PEEK surfaces were conducted to fabricate micro-groove textures with precisely tailored geometric parameters. Furthermore, ablated surface characterization showed that the laser-textured surfaces exhibited increased roughness, apparent crystallinity up to 22.13%, and pronounced anisotropic wettability, with improved liquid spreading along the groove direction and restricted spreading across the grooves. Finally, fretting wear tests under simulated body fluid lubrication were carried out. The research findings reported in this paper provide a systematic theoretical and experimental basis for the application of UV nanosecond laser surface texturing in the fabrication of PEEK-based components. Full article

(This article belongs to the Special Issue Advanced Techniques for Laser Processing)

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22 pages, 3833 KB

Open AccessArticle

Structural Consistency-Aware LiDAR Super-Resolution Method

by Jun Zeng, Chunqiu Xia, Hongwei Zhang, Hongchao Gao, Ziyang Wang and Mingjun Li

Photonics 2026, 13(9), 802; https://doi.org/10.3390/photonics13090802 - 22 Aug 2026

Abstract

Existing LiDAR super-resolution methods primarily aim to increase point cloud density or improve coordinate reconstruction accuracy. However, they tend to introduce blurred edges and distorted planar surfaces during reconstruction, making it difficult to preserve the consistency of local scene geometry. To address this [...] Read more.

Existing LiDAR super-resolution methods primarily aim to increase point cloud density or improve coordinate reconstruction accuracy. However, they tend to introduce blurred edges and distorted planar surfaces during reconstruction, making it difficult to preserve the consistency of local scene geometry. To address this issue, this paper proposes a structural consistency-aware LiDAR super-resolution method that aims to preserve the local geometric relationships of the reconstructed point cloud with respect to the ground-truth point cloud in edge and planar regions. Specifically, complementary observations from adjacent frames are first fused using multi-scale dilated convolutions. An anisotropic Swin Transformer and a Coordinate-Aware Structure Enhancement (CASE) module are then employed to accommodate the horizontally dense and vertically sparse sampling pattern of LiDAR, strengthen long-range geometric modeling, and reduce the loss of critical structural information. During training, a local curvature-based structural consistency loss is designed to separately constrain edge sharpness and planar smoothness. During inference, prediction uncertainty and point cloud height are combined to adaptively remove low-confidence points, further improving the geometric reliability of the reconstructed point cloud. Experiments on the KITTI dataset show that the proposed method achieves an MAE of 0.4916 and an IoU of 0.4633, outperforming the representative comparison methods on both metrics. When the reconstructed point clouds are applied to A-LOAM, the average RTE and RRE values are reduced by 34.6% and 31.2%, respectively. In addition, experiments on the self-collected CSU-SLAM dataset provide preliminary evidence of the applicability of the proposed method to indoor and outdoor scenes under a different LiDAR configuration. Full article

(This article belongs to the Special Issue Computational Imaging)

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24 pages, 706 KB

Open AccessArticle

Signal-Feature-Matched Non-Uniform Photonic Sampling and Broadband Waveform Reconstruction

by Zhaoyu Li

Photonics 2026, 13(9), 801; https://doi.org/10.3390/photonics13090801 - 22 Aug 2026

Abstract

This paper proposes Non-Uniform Adaptive Acquisition (NUAA), a signal-feature-matched non-uniform adaptive photonic sampling framework that recovers broadband radio-frequency (RF) waveforms from highly sparse programmable non-uniform photonic sampling points. A 200 MHz mode-locked laser together with five electrical optical delay lines (EDLs; motor-actuated optical [...] Read more.

This paper proposes Non-Uniform Adaptive Acquisition (NUAA), a signal-feature-matched non-uniform adaptive photonic sampling framework that recovers broadband radio-frequency (RF) waveforms from highly sparse programmable non-uniform photonic sampling points. A 200 MHz mode-locked laser together with five electrical optical delay lines (EDLs; motor-actuated optical delay units) arranges the non-uniform sampling instants. Benefiting from the joint design of the photodetector/track-and-hold amplifier (PD/THA) response model and programmable non-uniform optical pulse spacing, a low-bandwidth PD infers neighboring pulse amplitudes from their deterministic superposition at the readout. In numerical simulations of this physical forward operator, that construction corresponds to a 1 THz equivalent sampling rate on the 1 ps EDL grid, while the electrical front end operates at a 1 GHz average sampling rate (cascaded PD–THA analog 3 dB bandwidth

\approx 0.676

GHz). Under severe blocking interference and low signal-to-noise ratio (SNR), the numerical simulations show that the strongest broadband chirplet result uses a scene prior with support locking: with the NUAA–MU (Mamba–Unfolding) reconstructor at 0.1% multi-coset sparsity, all

N_{trial} = 50

Monte Carlo trials succeed within 200 ms (Wilson 95% CI

[93, 100] %

; cumulative-best NMSE

- 28.0

dB), whereas the configuration without a scene prior is substantially weaker in the same window. A scene prior may come from known radar or communication waveform families, coarse occupancy reported by a companion sensor, or accumulation across related tasks. Full article

(This article belongs to the Special Issue AI for Photonics: Intelligent Imaging, Learning-Driven Optics, and Photonic Computing)

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16 pages, 2369 KB

Open AccessArticle

Effect of Graphene Oxide on the Structural and Optical Properties of FTO Layers Obtained by Spray Pyrolysis

by Pavel Parchinsky, Abdumanap A. Nasirov, Shavkat U. Yuldashev, Azamat Arslanov, Rafael A. Nusretov, Natalia A. Kulagina, Sultan Kh. Suleymanov, Peng Li, Sergei A. Khakhomov, Alina V. Semchenko, Vitali V. Sidski, Vladimir E. Gaishun and Konstantin D. Danilchenko

Photonics 2026, 13(9), 800; https://doi.org/10.3390/photonics13090800 - 22 Aug 2026

Abstract

This study examines the effect of graphene oxide nanoparticle (NGO) doping (0.12–0.24 mol%) on the properties of FTO layers obtained by spray pyrolysis. The results show that nanographene promotes phase separation within the FTO bulk. The resulting inhomogeneities are fluorine-depleted relative to the [...] Read more.

This study examines the effect of graphene oxide nanoparticle (NGO) doping (0.12–0.24 mol%) on the properties of FTO layers obtained by spray pyrolysis. The results show that nanographene promotes phase separation within the FTO bulk. The resulting inhomogeneities are fluorine-depleted relative to the surrounding film. NGO doping also modifies the position and intensity of peaks in the absorption spectra, indicating a change in the nature of the absorbing centers. The optical bandgap of the FTO layers decreases with the increase in NGO from 4.4 eV (undoped samples) to 3.95 eV (samples with the highest NGO concentration). Furthermore, NGO doping reduces the sheet resistance of the FTO layers. This reduction is attributed to increased charge carrier mobility resulting from passivation of nanocrystallite interfaces by graphene oxide nanoparticles. However, the sheet resistance depends non-monotonically on NGO content, with the lowest value observed at 0.16 mol% NGO. The increase in resistance at higher NGO concentrations is due to enhanced carrier scattering caused by the growing size and number of the phase inhomogeneities within the FTO layer. Full article

(This article belongs to the Special Issue Optical Materials: Novel Properties and Engineering for Future Photonic Devices)

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15 pages, 8063 KB

Open AccessArticle

Synthesis, Crystal Structure, and Properties of New Layered Rare-Earth Selenites Ln(HSeO₃)(SeO₃)·2H₂O (Ln = Yb, Dy, Eu)

by Lingli Li, Lianzheng Su, Bingxing Zhang, Kaiyue Xie, Xuyang Feng, Meihua Yan, Xueling Yang, Zhimei Wang, Jun Ma, Hang Zhao, Tianyu Mao, Xinxin Shang and Bingying Pan

Photonics 2026, 13(8), 799; https://doi.org/10.3390/photonics13080799 - 21 Aug 2026

Abstract

Three layered rare-earth hydrogenselenite–selenite hydrates, Ln(HSeO₃)(SeO₃)·2H₂O (Ln = Yb, Dy, Eu), were synthesized under hydrothermal conditions and systematically characterized. Single-crystal and powder X-ray diffraction show that the compounds are isostructural and crystallize in the non-centrosymmetric orthorhombic Sohncke [...] Read more.

Three layered rare-earth hydrogenselenite–selenite hydrates, Ln(HSeO₃)(SeO₃)·2H₂O (Ln = Yb, Dy, Eu), were synthesized under hydrothermal conditions and systematically characterized. Single-crystal and powder X-ray diffraction show that the compounds are isostructural and crystallize in the non-centrosymmetric orthorhombic Sohncke space group P2₁2₁2₁, featuring LnO₈ polyhedra and SeO₃/HSeO₃ units assembled into hydrogen-bonded layered frameworks. Two-component inversion-twin refinements gave Flack x values of 0.06(4), 0.27(3), and 0.22(3) for the Yb-, Dy-, and Eu-containing crystals, respectively; the Yb crystal is dominated by one inversion domain, whereas the Dy and Eu crystals contain appreciable inverted-domain fractions. Because L/D/DL descriptors conventionally refer to the absolute configuration of chiral molecular entities, they are not assigned to these extended inorganic frameworks. Under the present achiral synthesis conditions, crystals dominated by the opposite, inversion-related framework hand cannot be excluded. Photoluminescence measurements reveal characteristic Dy³⁺ and Eu³⁺ emissions, while the Yb analogue exhibits a broad visible band tentatively related to host-framework states. Magnetic measurements show no long-range ordering above 2 K; the Yb and Dy phases display dominant antiferromagnetic correlations, whereas the Eu phase is governed mainly by Van Vleck paramagnetism. These results identify Ln(HSeO₃)(SeO₃)·2H₂O as a layered Sohncke-symmetry platform with lanthanide-dependent optical and magnetic behavior. The observed lanthanide emissions and non-centrosymmetric framework suggest prospective photonic and nonlinear-optical applications, although device-level performance remains to be established. Full article

(This article belongs to the Special Issue Advancements in Ultrafast Laser Science and Technology)

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25 pages, 53996 KB

Open AccessArticle

Versatile Spectral Tunability in One-Dimensional Graphene-Based Photonic Crystals via Thue–Morse Quasi-Periodic Chemical Potential Modulation

by Jianing Yu, Luwei Li and Yichong Liu

Photonics 2026, 13(8), 798; https://doi.org/10.3390/photonics13080798 - 21 Aug 2026

Abstract

A one-dimensional Thue–Morse graphene photonic crystal (1D TMGPC) composed of alternating identical dielectric layers and graphene sheets is proposed, in which two distinct graphene chemical potentials are arranged according to a Thue–Morse quasi-periodic sequence. Using the transfer matrix method, we demonstrate that this [...] Read more.

A one-dimensional Thue–Morse graphene photonic crystal (1D TMGPC) composed of alternating identical dielectric layers and graphene sheets is proposed, in which two distinct graphene chemical potentials are arranged according to a Thue–Morse quasi-periodic sequence. Using the transfer matrix method, we demonstrate that this structure effectively modulates terahertz waves and generates multiple abundant photonic bandgaps at both 20 K and 300 K. Notably, a novel splitting of low-frequency bandgaps produces two additional omnidirectional and polarization-insensitive bandgaps centered at approximately 1.45 THz and 1.95 THz. By analyzing the dispersion relations, reflection phase, photonic density of states, and electric field distributions, the boundary-driven modulation mechanism associated with the quasi-periodic chemical potential is elucidated. Furthermore, the proposed structure exhibits excellent multi-dimensional tunability. The bandgap properties can be dynamically tuned via the electrical control of graphene chemical potentials without altering the physical geometry. Structural tailoring provides an additional degree of freedom, as increasing the Thue–Morse sequence order induces passband splitting. Additionally, increasing the number of repeating periods yields comb-like multi-channel narrowband filtering responses. At a cryogenic temperature of 20 K, two distinct multi-channel narrowband comb filtering responses appear in the frequency ranges of 1.20–1.33 THz and 4.10–4.80 THz, with a minimum full width at half maximum (FWHM) of 1.10 GHz. At a room temperature of 300 K, the higher-frequency comb filtering response remains in the range of 4.10–4.80 THz, with a minimum FWHM of 5.70 GHz. Moreover, we evaluate the performance and stability of the structure when employed as filters and electro-optic switches, thereby providing useful insights for terahertz applications. With its simple geometry, abundant bandgaps, and flexible electro-structural tunability, the proposed 1D TMGPC is highly promising for broadband and electrically tunable terahertz devices. Full article

(This article belongs to the Special Issue Advancements in Photonic Crystals: Materials, Design, and Applications)

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14 pages, 8723 KB

Open AccessArticle

SD-GS: Gradient-Semantic Analysis Based on Multi-State Scene 3D Gaussian Splatting

by Yiting Li, Jun Chang, Xuehui Zhao, Yue Zhong and Xianzhu Liu

Photonics 2026, 13(8), 797; https://doi.org/10.3390/photonics13080797 - 21 Aug 2026

Abstract

By analyzing the semantic information of Direct Current (DC, the zeroth-order spherical harmonic coefficient) gradients during 3D Gaussian Splatting (3DGS) optimization, this paper achieves unsupervised state classification in scenes with discrete appearance states under the proposed State-Discovery Gaussian Splatting (SD-GS) framework via SVD [...] Read more.

By analyzing the semantic information of Direct Current (DC, the zeroth-order spherical harmonic coefficient) gradients during 3D Gaussian Splatting (3DGS) optimization, this paper achieves unsupervised state classification in scenes with discrete appearance states under the proposed State-Discovery Gaussian Splatting (SD-GS) framework via SVD dimensionality reduction and K-means clustering. To improve the stability of the clustering results, an appearance-difference-weighted refinement mechanism is further proposed to confirm high-confidence labels. To address the difficulty of distinguishing similar states when the number of states exceeds two, a sequential peeling strategy is proposed that decomposes a multi-class partition into several two-class separations. On four real-world scene datasets, SD-GS achieves 100% classification accuracy with reconstruction quality of 31.98–38.83 dB PSNR. Ablation studies validate the effectiveness of the gradient direction mode and the SVD dimensionality reduction strategy. Full article

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

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11 pages, 1218 KB

Open AccessArticle

Fabrication and Characterization of a 37 × 1 Fiber Pump Combiner for Multi-Kilowatt Semiconductor-Laser Power Combining

by Yong Wang, Li Pei, Zhenyu Gu, Wei Jiang, Wensheng Wang, Jing Li, Jingjing Zheng and Tigang Ning

Photonics 2026, 13(8), 796; https://doi.org/10.3390/photonics13080796 - 21 Aug 2026

Abstract

High-port-count fiber pump combiners are important passive components for scalable laser diode (LD) power combining in high-power fiber-laser systems. However, increasing the number of input ports from 19 to 37 narrows the fabrication window because fiber bundle packing, taper uniformity, splice matching, thermal [...] Read more.

High-port-count fiber pump combiners are important passive components for scalable laser diode (LD) power combining in high-power fiber-laser systems. However, increasing the number of input ports from 19 to 37 narrows the fabrication window because fiber bundle packing, taper uniformity, splice matching, thermal management, and backward-light tolerance must be controlled simultaneously. In this work, a 37 × 1 tapered fiber bundle pump combiner was fabricated by a tubing-based method using thirty-seven 135/155 µm multimode input fibers and an 800/880 µm output fiber. The input fibers were weakly etched to improve bundle compactness, and the glass-tube-assisted fiber bundle was tapered, cleaved, and fusion-spliced with a tapered output fiber. The fabricated combiner was characterized using thirty-seven 915 nm fiber-coupled LDs. At a total injected power of 4.89 kW, the combiner delivered 4.80 kW output power, corresponding to an overall transmission efficiency of 98.16%. The single-port transmission efficiencies were approximately in the range of 97.3–98.1%, indicating good port-to-port uniformity for the dense 37-fiber bundle. During full-power operation, the highest temperature appeared in the tapered fiber bundle region and reached 103.8 °C, while the fusion-splice region reached 76.2 °C. In addition, the device withstood 500 W backward-propagating light without observable damage, indicating its practical tolerance to reverse-power loading. These results show that the proposed 37 × 1 fiber pump combiner provides an effective all-fiber solution for multi-kilowatt LD power combining. Full article

(This article belongs to the Special Issue High Power Fiber Lasers: Advances and Applications)

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32 pages, 3266 KB

Open AccessArticle

Chance-Constrained Receiver–Scheduler Co-Design via Probabilistic Decodability Graphs for Reliable SIC in Overlapping Multi-Cell NOMA VLC Networks

by Tingting Qin and Yang Tu

Photonics 2026, 13(8), 795; https://doi.org/10.3390/photonics13080795 - 21 Aug 2026

Abstract

Overlapping optical cells create geometry-dependent inter-cell interference, while receiver-geometry and channel-estimation errors can reverse the effective non-orthogonal multiple access (NOMA) decoding order and increase successive interference cancelation (SIC) failures. This paper develops a chance-constrained receiver–scheduler co-design framework for a multi-cell NOMA visible-light communication [...] Read more.

Overlapping optical cells create geometry-dependent inter-cell interference, while receiver-geometry and channel-estimation errors can reverse the effective non-orthogonal multiple access (NOMA) decoding order and increase successive interference cancelation (SIC) failures. This paper develops a chance-constrained receiver–scheduler co-design framework for a multi-cell NOMA visible-light communication network with an asymmetrically clipped DC-biased optical orthogonal frequency-division multiplexing physical layer. Correlated position, photodetector-orientation, and channel-estimation errors are propagated through nonlinear geometry-based scenarios. For each SIC direction, a joint three-SINR event defines a layer-, resource-, and direction-labeled probabilistic decodability graph. Candidate NOMA and orthogonal modes are screened on optimization scenarios, admitted by independent one-sided confidence bounds, and selected through resource-constrained mixed-integer linear programming. With the matching fixed, hierarchical powers are adapted under empirical conditional-value-at-risk constraints using trust-region sequential quadratic programming. Because candidate-edge certificates need not remain valid after global matching and power redistribution, the frozen complete assignment is independently recertified before held-out testing. Under the specified uncertainty generator, the proposed method maintains selected-pair outage probabilities of approximately

2.7 \times 10^{- 3}

–

3.3 \times 10^{- 3}

over the half-power-angle sweep, compared with

0.027

–

0.060

for nominal-CSI allocation. Additional experiments quantify network-wide outage, model misspecification, unbalanced deployments, feasibility, and computational cost. The results support reliable slow-timescale scheduling under the adopted link and uncertainty models, without implying distribution-free, waveform-level, or real-time guarantees. Full article

(This article belongs to the Section Optical Communication and Network)

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19 pages, 4368 KB

Open AccessArticle

Comparative Investigation of LG and HG Modes for a QKD-Assisted High-Capacity and Secure LiFi/MDM System

by Meet Kumari, Satyendra K. Mishra and Jyoteesh Malhotra

Photonics 2026, 13(8), 794; https://doi.org/10.3390/photonics13080794 - 21 Aug 2026

Abstract

Light fidelity (LiFi) is progressively evolving as a highly promising communication technology because of its unique benefits, available spectrum, low implementation costs, and adaptive beamforming capabilities. Despite their advantages, existing LiFi networks remain constrained by limited data rates, coverage area, and information security [...] Read more.

Light fidelity (LiFi) is progressively evolving as a highly promising communication technology because of its unique benefits, available spectrum, low implementation costs, and adaptive beamforming capabilities. Despite their advantages, existing LiFi networks remain constrained by limited data rates, coverage area, and information security in practical environments. Therefore, a high-speed, high-capacity, and secure quantum key distribution (QKD)-assisted integrated multi-wavelengths (450/532/620 nm) LiFi system using mode division multiplexing (MDM) is proposed. The results demonstrate that the proposed system achieves maximum transmission distances of 20.5–22 m and 19–22 m using different Laguerre–Gaussian (LG) and Hermite–Gaussian (HG) mode indices {[0,0], [0,10], [0,20], [0,30]}, at an aggregate data rate of 40 Gbps. Furthermore, the minimum acceptable transmitter angles of 30–90° for irradiance angles of 20–80° are required to maintain the target bit error rate (BER) of 10⁻⁹. The minimum photodetector detection areas required at transmission distances of 20–30 m are 1–2 cm² at the minimum BER limit. Moreover, the proposed system exhibits optimum performance, achieving an optical loss of −39.47 dB, −49.03 dBm received power, and 45.39 dB signal-to-noise ratio for 1–10 photons/pulse. Compared with existing studies, the proposed system demonstrates enhanced overall performance across various communication metrics. Full article

(This article belongs to the Special Issue Recent Progress in Optical Quantum Information and Communication)

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