Photonics

18 pages, 3207 KB

Open AccessArticle

Meta-Learning-Based Multi-Task Framework for Joint Modulation Format Identification and ESNR Estimation in Coherent Optical Communication Systems

by Qifan Zhang, Shi Jia, Tianhao Zhang, Zhuangzhuang Zang, Shiqian Jia, Lianmeng Wu, Hao Luo and Jinlong Yu

Photonics 2026, 13(7), 607; https://doi.org/10.3390/photonics13070607 (registering DOI) - 24 Jun 2026

Abstract

Optical performance monitoring is essential for adaptive and intelligent coherent optical communication systems. In this paper, a Transformer-based multi-task meta-learning framework is proposed for joint modulation format identification and electrical signal-to-noise ratio (ESNR) estimation from original received waveforms. A simulated coherent optical communication [...] Read more.

Optical performance monitoring is essential for adaptive and intelligent coherent optical communication systems. In this paper, a Transformer-based multi-task meta-learning framework is proposed for joint modulation format identification and electrical signal-to-noise ratio (ESNR) estimation from original received waveforms. A simulated coherent optical communication system is established to generate QPSK, 16QAM, and 32QAM signals under different launch-power conditions. The received I/Q waveforms are directly used as model inputs, avoiding handcrafted feature extraction or constellation-image conversion. The proposed model employs a shared one-dimensional Transformer encoder to extract temporal waveform representations. A prototypical classification branch is used for few-shot modulation format identification, while an ESNR regression branch is introduced for continuous signal-quality estimation. The two tasks are jointly optimized under an episodic support-query training mechanism. Experimental results show that the proposed method achieves 99.99% modulation identification accuracy on the test episodes. For ESNR estimation, the model obtains an MAE of 0.1194 dB, an RMSE of 0.1738 dB, and an R² value of 99.83%. These results demonstrate that the proposed framework can simultaneously provide accurate modulation decisions and reliable ESNR estimation, showing its potential for waveform-based optical performance monitoring. Full article

(This article belongs to the Special Issue Microwave Photonics: Advances and Applications)

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12 pages, 2947 KB

Open AccessArticle

Broadband Source-Surrounded Cloak for On-Chip Antenna Radiation Pattern Protection

by Weifeng Han, Hanchuan Chen, Fei Sun, Yichao Liu and Shuai Zhang

Photonics 2026, 13(7), 606; https://doi.org/10.3390/photonics13070606 (registering DOI) - 24 Jun 2026

Abstract

With the expansion of electromagnetic wave communication frequency bands and the improvement of integrated circuit integration, electromagnetic waves emitted by on-chip antennas are easily scattered by electronic components, causing radiation pattern distortion, which limits the improvement of integration and communication stability. Traditional cloaks [...] Read more.

With the expansion of electromagnetic wave communication frequency bands and the improvement of integrated circuit integration, electromagnetic waves emitted by on-chip antennas are easily scattered by electronic components, causing radiation pattern distortion, which limits the improvement of integration and communication stability. Traditional cloaks can reduce electromagnetic scattering, but they cannot achieve broadband and omnidirectional performance simultaneously, and are mostly designed for external sources, making it difficult to protect on-chip antenna radiation patterns. In this work, a broadband air-impedance-matched metamaterial (AIMM) with characteristic impedance matched to free space is proposed in 2–8 GHz, with geometry-tunable phase delay and transmittance higher than 93%. Based on AIMM, a broadband source-surrounded cloak (SSC) is designed, which can guide electromagnetic waves from the surrounded source to bypass obstacles in any direction and restore the original wavefront outside the cloak, so as to protect the radiation pattern from scattering distortion. Numerical simulations show that the SSC works well in the whole bandwidth and remains effective when the source is offset. This work has important potential for improving the integration of integrated circuits and the stability of communication systems. Full article

(This article belongs to the Special Issue Invisibility Cloaking: Methods, Principles, Materials, and Extended Applications)

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17 pages, 958 KB

Open AccessArticle

Adaptive Time-Domain Simulation of Optical Cavities with Arbitrary Dynamics

by Andrea Svizzeretto, Julia Casanueva Diaz, Bas L. Swinkels and Mateusz Bawaj

Photonics 2026, 13(7), 605; https://doi.org/10.3390/photonics13070605 (registering DOI) - 23 Jun 2026

Abstract

We present a fast time-domain simulator for optical cavities capable of reproducing non-linear dynamical regimes arising from the ring-down effect during resonance crossings at high mirror velocities or from abrupt changes of the input field. The model is based on a recursive formulation [...] Read more.

We present a fast time-domain simulator for optical cavities capable of reproducing non-linear dynamical regimes arising from the ring-down effect during resonance crossings at high mirror velocities or from abrupt changes of the input field. The model is based on a recursive formulation of the intracavity electric field as a sum over round trips, preserving the cavity memory while maintaining high computational efficiency. The simulator is designed to achieve three main goals. First, the boundary conditions of the cavity can be modified at each simulation step, allowing arbitrary time-dependent variations of both mirror positions and input electric field during the simulation run. Second, the sampling frequency can be flexibly chosen by the user; however, it is internally adjusted before effectively executing the simulation to remain consistent with the cavity round-trip structure. Finally, high computational efficiency was obtained by avoiding the repeated evaluation of the full electric field history. The framework is validated through comparison with experimental data from the Virgo interferometer during a mechanical excitation experiment, showing good agreement in non-adiabatic regimes. Due to its efficiency and flexibility, the oreonspy simulator provides a versatile tool for time-domain studies of optical resonators and future applications in real-time control and reinforcement-learning-based lock acquisition. Full article

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20 pages, 23308 KB

Open AccessArticle

Simulation of Geometrical Scaling and Terahertz-Response Characteristics in Plasmonic Terahertz Photoconductive Antennas

by Mohammad Esmaeil Daraei, Mehdi Abedi-Varaki and Ignas Nevinskas

Photonics 2026, 13(7), 604; https://doi.org/10.3390/photonics13070604 (registering DOI) - 23 Jun 2026

Abstract

In this work, plasmonic photoconductive antenna (PCA) structures with different grating-width and gap configurations were numerically investigated to evaluate their influence on transient-current generation and terahertz (THz) emission performance. Two geometrical scaling strategies were considered: a fixed-gap configuration with a constant 100 nm [...] Read more.

In this work, plasmonic photoconductive antenna (PCA) structures with different grating-width and gap configurations were numerically investigated to evaluate their influence on transient-current generation and terahertz (THz) emission performance. Two geometrical scaling strategies were considered: a fixed-gap configuration with a constant 100 nm photoconductive gap and a proportional-gap configuration in which the gap size was equal to the grating width. Three-dimensional finite element method (FEM) simulations were performed to analyze transient carrier dynamics, THz pulse electric-field behavior, and frequency-domain spectral response under 800 nm optical excitation. The results demonstrate that reducing the inter-grating gap enhances plasmonic near-field confinement and carrier localization near the metal–semiconductor interface, leading to stronger transient-current responses and enhanced THz characteristics. Spatial field and carrier-distribution analyses further confirmed improved electric-field localization and carrier confinement for the fixed-gap structures. In addition, voltage-dependent investigations showed that increasing the applied bias voltage strengthens carrier acceleration and enhances the simulated THz response within the investigated operating range. The results further demonstrate that the observed enhancement is governed not only by grating periodicity but also by the grating-width/gap-size ratio, highlighting the importance of geometrical fill-factor optimization. Polarization-dependent simulations confirmed the plasmonic origin of the enhanced transient-current generation and THz emission. These findings demonstrate that optimal THz performance arises from a balanced interplay between plasmonic field localization, optical absorption, and carrier-transport dynamics, providing design guidelines for the optimization of plasmonic THz PCAs. Full article

(This article belongs to the Special Issue Advancements in Terahertz Metamaterial Optics, Devices, and Applications)

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37 pages, 3389 KB

Open AccessReview

Fiber Bragg Grating Accelerometers: A Review from Single-Axis to Multi-Dimensional Vector Sensing

by Jiahe Dai, Rui Zhou and Xueguang Qiao

Photonics 2026, 13(6), 602; https://doi.org/10.3390/photonics13060602 (registering DOI) - 22 Jun 2026

Abstract

Precise monitoring of vibration signals is crucial for early fault warning and localization in industrial applications. Traditional electromagnetic accelerometers are often unsuitable for harsh environments characterized by high temperatures, high pressures, and strong electromagnetic fields. Fiber Bragg grating (FBG) accelerometers have become a [...] Read more.

Precise monitoring of vibration signals is crucial for early fault warning and localization in industrial applications. Traditional electromagnetic accelerometers are often unsuitable for harsh environments characterized by high temperatures, high pressures, and strong electromagnetic fields. Fiber Bragg grating (FBG) accelerometers have become a major research topic in this field due to their unique advantages, including resistance to high temperature and pressure, immunity to electromagnetic interference, and ease of wavelength division multiplexing. This paper provides a systematic review of FBG accelerometers, covering their fundamental principles, classification, performance enhancement strategies, and applications. We focus on reviewing the research progress of FBG accelerometers from two main aspects, single-axis and multi-dimensional vector types, and offer an outlook on future development to provide a reference for the research and application of FBG accelerometers. Full article

(This article belongs to the Special Issue Emerging Technologies and Applications in Fiber Optic Sensing)

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18 pages, 12223 KB

Open AccessArticle

Integrated Design and Fabrication of Refractive–Diffractive Hybrid Lenses for Myopia Control

by Chuang Li, Chongxing Liu, Changxi Xue and Bo Dong

Photonics 2026, 13(6), 603; https://doi.org/10.3390/photonics13060603 (registering DOI) - 21 Jun 2026

Abstract

As the prevalence of myopia among adolescents continues to increase, the design and fabrication of myopia control lenses have become an important research direction in modern optics. Existing myopia control lenses mostly adopt purely refractive structures, which suffer from limited design freedom, insufficient [...] Read more.

As the prevalence of myopia among adolescents continues to increase, the design and fabrication of myopia control lenses have become an important research direction in modern optics. Existing myopia control lenses mostly adopt purely refractive structures, which suffer from limited design freedom, insufficient chromatic aberration suppression, and relatively large lens thickness, thereby restricting further improvement of optical performance. This paper proposes a refractive–diffractive hybrid design and fabrication method for myopia control lenses. Centered on a harmonic diffractive optical element (HDOE), an optimization model is established to balance achromatization performance and fabrication feasibility. To address the challenges of small period width, tool shadow effect, and sensitivity to machining tolerances in diffractive lenses with large-aperture and high-additional-power, harmonic design is employed to increase the period width, thereby reducing fabrication difficulty and mitigating the influence of shadowing errors on diffraction efficiency. On this basis, two lenses with different phase structures are designed: one adopts a conventional diffractive correction phase to verify the role of HDOE in achromatization and edge-thickness reduction, while the other adopts a high-degree-of-freedom smooth phase to achieve a continuous multifocal visual effect. Both lenses are fabricated by single-point diamond turning (SPDT), and the effects of surface profile and machining parameters on performance are analyzed. Simulations and measurements show that the proposed method provides stable diffraction efficiency and effective chromatic aberration correction across the design band, while reducing the edge thickness by approximately 37.85% without additional thinning of the aspheric substrate. The results indicate that the refractive–diffractive hybrid design provides a feasible design and fabrication approach for functionally more complex myopia control lenses. Full article

(This article belongs to the Special Issue Recent Progress in Optical System Design)

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26 pages, 8518 KB

Open AccessArticle

CVA-Net: Multi-View 3D Reconstruction for Fringe Projection Profilometry via Cross-View Attention and Sim2Real Learning

by Zuqiong Chen, Xiaopin Zhong and Yibin Tian

Photonics 2026, 13(6), 601; https://doi.org/10.3390/photonics13060601 (registering DOI) - 21 Jun 2026

Abstract

Fringe projection profilometry (FPP) is widely used for 3D reconstruction, but conventional single-view FPP systems suffer from inherent occlusions and shadow regions, leading to incomplete surface recovery. In this study, we propose CVA-Net, an end-to-end deep learning framework with cross-view attention (CVA) that [...] Read more.

Fringe projection profilometry (FPP) is widely used for 3D reconstruction, but conventional single-view FPP systems suffer from inherent occlusions and shadow regions, leading to incomplete surface recovery. In this study, we propose CVA-Net, an end-to-end deep learning framework with cross-view attention (CVA) that directly reconstructs dense depth maps from multi-view fringe patterns. CVA-Net simultaneously processes four fringe images acquired from orthogonal projection directions and leverages a CVA module to explicitly model inter-view dependencies, enabling adaptive fusion of complementary information. A 3D U-Net backbone with attention gates, atrous spatial pyramid pooling (ASPP), and an auxiliary parameter estimation branch further enhances reconstruction accuracy and structural consistency via multitask learning. To support Sim2Real network training, we build a Blender-based digital twin of a multi-view FPP system and generate a large-scale synthetic dataset with perfect ground truth. Extensive experiments on both synthetic and real-world objects demonstrate that CVA-Net significantly outperforms state-of-the-art single-view methods. With a symmetric four-view configuration and fringe period of 8, CVA-Net achieves an MAE of 0.0359 mm, an MSE of 0.0379 mm² and an RMSE of 0.1947 mm, reducing the MAE, MSE, and RMSE by 32.8%, 54.1%, and 32.2%, respectively, compared to the best single-view competitor. Ablation studies validate the contribution of each architectural component, while real-system experiments demonstrate the feasibility of transferring a network trained purely on synthetic data to practical FPP measurements without domain adaptation. Although further improvements are required to enhance reconstruction accuracy under real imaging conditions, the proposed framework provides an effective initial step toward bridging the gap between digital-twin-based training and real-world multi-view FPP applications. CVA-Net provides a robust, occlusion-aware solution for multi-view FPP reconstruction. Full article

(This article belongs to the Special Issue Optical Imaging for 3D Surface and Phase Recovery: Techniques and Applications)

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16 pages, 1188 KB

Open AccessArticle

Multidimensional Optimization of Radio-over-Fiber Links Based on Tunable Carrier-to-Sideband Ratio

by Weile Zhai, Jinyuan Ye, Ruihao Wang, Zhong’ao Yang, Jiajun Tan, Xiaoyan Pang, Wanzhao Cui and Yongsheng Gao

Photonics 2026, 13(6), 600; https://doi.org/10.3390/photonics13060600 (registering DOI) - 21 Jun 2026

Abstract

In radio-over-fiber (RoF) links, optical single-sideband (OSSB) modulation is an effective method to mitigate power fading caused by chromatic dispersion. However, its low modulation efficiency leads to suboptimal link performance. To address this, we propose a tunable optical carrier-to-sideband ratio (OCSR) OSSB modulation [...] Read more.

In radio-over-fiber (RoF) links, optical single-sideband (OSSB) modulation is an effective method to mitigate power fading caused by chromatic dispersion. However, its low modulation efficiency leads to suboptimal link performance. To address this, we propose a tunable optical carrier-to-sideband ratio (OCSR) OSSB modulation scheme based on a dual-electrode Mach–Zehnder modulator (DEMZM) in a Sagnac loop. Firstly, by adjusting the OCSR, higher radio-frequency (RF) transmission efficiency can be achieved. The experimental results demonstrate that the proposed link provides a 6 dB improvement in received RF power compared to conventional SSB modulation schemes. Furthermore, this approach effectively optimizes nonlinear distortions in the link, achieving a 12.14 dB enhancement in spurious-free dynamic range (SFDR). For tests conducted with a broadband signal featuring a 15 GHz carrier frequency and 500 MHz bandwidth, the optimal error vector magnitude (EVM) reaches 4.88%. Additionally, the link performance can be flexibly improved by adjusting the polarization controller configurations for each channel, making it suitable for multi-user application scenarios. Full article

(This article belongs to the Special Issue Optical Signal Processing for Advanced Communication Systems)

19 pages, 4732 KB

Open AccessArticle

YOLO-OBB and Two-Stage Geometric Correction for RGB-LED Array Optical Camera Communication

by Jiaqi Ju, Pan Qiu, Yipeng Tan and Zhengguang Shi

Photonics 2026, 13(6), 599; https://doi.org/10.3390/photonics13060599 (registering DOI) - 20 Jun 2026

Abstract

In Optical Camera Communication (OCC), precise localization of LED arrays under complex tilt conditions is a core challenge for reliable decoding. This paper proposes an OCC reception scheme for RGB-LED arrays that integrates YOLO-OBB rotated object detection with two-stage geometric correction. The system [...] Read more.

In Optical Camera Communication (OCC), precise localization of LED arrays under complex tilt conditions is a core challenge for reliable decoding. This paper proposes an OCC reception scheme for RGB-LED arrays that integrates YOLO-OBB rotated object detection with two-stage geometric correction. The system first employs a YOLOv8n-OBB model to extract a quadrilateral region of interest that tightly encloses the LED array boundary. This effectively suppresses background interference caused by superimposed perspective tilt and in-plane rotation. A coarse-to-fine two-stage correction framework is then applied. The first stage rapidly eliminates the dominant perspective distortion based on the detected bounding-box corners. The second stage performs a refined correction using the actual LED center positions. Two homography matrices are cascaded into a combined transformation, achieving two-stage correction accuracy through a single coordinate mapping. In the corrected image, K-Means clustering constructs a 16 × 16 LED topological grid. A locking strategy is adopted so that subsequent frames skip repeated LED detection and clustering. The steady-state per-frame processing time is reduced to approximately 78.9 ms. Experiments covered 16 cross-combinations of vertical tilt from 0° to 45° (0°, 15°, 30°, 45°) and in-plane rotation from 0° to 40° (0°, 15°, 30°, 40°). The uncorrected scheme and the horizontal-box scheme experienced severe bit errors or complete failure under complicated distortion. The proposed scheme maintained error-free transmission under all 16 tested conditions. The ratios of opposite sides of the corrected LED grid remained stable between 0.997 and 1.004. The system simultaneously achieves high reliability and low-latency real-time processing under complex geometric distortions. Full article

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

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37 pages, 2557 KB

Open AccessReview

Light-Emitting Diodes: Advances, Challenges and Applications in Musculoskeletal Pain

by Laura Marinela Ailioaie, Constantin Ailioaie, Georgiana Diana Ungureanu, Cristinel Ionel Stan, Anca Sava and Dragos Andrei Chiran

Photonics 2026, 13(6), 598; https://doi.org/10.3390/photonics13060598 (registering DOI) - 20 Jun 2026

Abstract

Musculoskeletal pain is a major cause of disability and long-term analgesic use, increasing interest in safe non-pharmacological interventions. This focused narrative review examines light-emitting diode (LED)-based photobiomodulation (PBM) for musculoskeletal pain, integrating molecular, mechanistic, clinical, and translational evidence. Red and near-infrared LED-PBM may [...] Read more.

Musculoskeletal pain is a major cause of disability and long-term analgesic use, increasing interest in safe non-pharmacological interventions. This focused narrative review examines light-emitting diode (LED)-based photobiomodulation (PBM) for musculoskeletal pain, integrating molecular, mechanistic, clinical, and translational evidence. Red and near-infrared LED-PBM may act through mitochondrial and non-mitochondrial photoacceptors, modulation of ATP production, reactive oxygen species, nitric oxide, calcium signaling, inflammatory pathways, oxidative stress responses, and extracellular matrix repair. Clinical evidence suggests a potential benefit in selected conditions, particularly temporomandibular disorders, fibromyalgia, cervical and myofascial pain, tendon and plantar fascia disorders, knee osteoarthritis, and mild-to-moderate peripheral nerve compression, while findings for non-specific low back pain remain inconsistent. The reviewed literature indicates that therapeutic response depends less on emitter identity alone than on wavelength, irradiance, radiant exposure, treatment geometry, target depth, timing, disease phenotype, and protocol quality. LED-based PBM appears generally well tolerated and clinically promising as an adjunct to rehabilitation, but current evidence is limited by heterogeneous devices, incomplete dosimetry, variable comparators, and short follow-up. Future studies should prioritize standardized reporting, depth-aware dosing, phenotype-based recruitment, biomarker-linked outcomes, and direct laser–LED comparisons under dosimetrically matched conditions. Full article

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

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9 pages, 2178 KB

Open AccessArticle

Switchable Multi-Wavelength Nd:Lu₂SiO₅ Laser Based on a Wedge Birefringent Filter for the ⁴F_3/2 → ⁴I_13/2 Transition

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

Photonics 2026, 13(6), 597; https://doi.org/10.3390/photonics13060597 (registering DOI) - 19 Jun 2026

Abstract

We report, for the first time, a continuous-wave (CW) switchable multi-wavelength Nd:Lu₂SiO₅ (Nd:LSO) laser using two wedge birefringent filters (WBFs) operating on the ⁴F_3/2 → ⁴I_13/2 transition. The threshold equivalence condition was calculated via the two [...] Read more.

We report, for the first time, a continuous-wave (CW) switchable multi-wavelength Nd:Lu₂SiO₅ (Nd:LSO) laser using two wedge birefringent filters (WBFs) operating on the ⁴F_3/2 → ⁴I_13/2 transition. The threshold equivalence condition was calculated via the two intracavity WBFs to achieve the simultaneous multiple-wavelength operation. Three dual-wavelength pairs (1332/1344 nm, 1344/1359 nm, and 1359/1363 nm), two triple-wavelength combinations (1332/1344/1359 nm and 1344/1359/1363 nm), and a four-wavelength set (1332/1344/1359/1363 nm) were further experimentally demonstrated. These wavelength combinations are mutually switchable via tuning of the WBF. Under an incident pump power of 20 W at 808 nm, the total output powers for the dual-wavelength pairs (1332/1344 nm, 1344/1359 nm, and 1359/1363 nm) were measured to be 1.55 W, 2.17 W, and 3.40 W, respectively. The triple-wavelength outputs at 1332/1344/1359 nm and 1344/1359/1363 nm delivered 1.57 W and 1.91 W, respectively. The four-wavelength emission at 1332/1344/1359/1363 nm reached 913 mW. Full article

(This article belongs to the Special Issue Advanced Lasers and Their Applications, 3rd Edition)

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11 pages, 5541 KB

Open AccessArticle

Aperiodic Frequency-Agile Optoelectronic Hybrid Oscillator

by Tong Yang, Tengfei Hao, Yiwen Lu, Feifei Yin, Kun Xu, Ming Li and Yitang Dai

Photonics 2026, 13(6), 596; https://doi.org/10.3390/photonics13060596 (registering DOI) - 19 Jun 2026

Abstract

In modern radar and electronic countermeasure systems, frequency-agile (FA) signal generators with low phase noise are of vital importance. The optoelectronic oscillator (OEO) is restricted by the periodic boundary condition (PBC), despite its superior performance in phase noise and frequency tunability. This paper [...] Read more.

In modern radar and electronic countermeasure systems, frequency-agile (FA) signal generators with low phase noise are of vital importance. The optoelectronic oscillator (OEO) is restricted by the periodic boundary condition (PBC), despite its superior performance in phase noise and frequency tunability. This paper proposes a new FA optoelectronic hybrid oscillator scheme, which employs a reconfigurable aperiodic FA filter and a dynamic frequency compensation module to collaboratively break the PBC limitation. It achieves fast switching and fine-grained frequency hopping at the 100 kHz level while maintaining low phase noise. Theoretical and experimental verification show that the system can generate arbitrary FA radio frequency (RF) signals from 1.95 GHz to 2.05 GHz with a tuning range of 10³ times the free spectral range (FSR), and the phase noise reaches −120 dBc/Hz at 10 kHz offset. This study provides a novel technical route for generating narrow-step frequency-agile signals and effectively improves target detection accuracy and anti-jamming performance in electronic warfare applications. Full article

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

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21 pages, 570 KB

Open AccessArticle

Interpretable Microwave Sensing Using E-Band Commercial Links: Physics-Aware Deep Learning for Rainfall Detection

by Lukasz Pawlik and Jacek Lukasz Wilk-Jakubowski

Photonics 2026, 13(6), 595; https://doi.org/10.3390/photonics13060595 (registering DOI) - 18 Jun 2026

Abstract

Accurate rainfall monitoring is vital for hydrology and environmental sensing. This study presents a physics-aware deep learning framework using E-band (71–86 GHz) commercial microwave links (CMLs). Using the extensive urban CML dataset and methodology, a bi-directional Long Short-Term Memory (Bi-LSTM) model is developed [...] Read more.

Accurate rainfall monitoring is vital for hydrology and environmental sensing. This study presents a physics-aware deep learning framework using E-band (71–86 GHz) commercial microwave links (CMLs). Using the extensive urban CML dataset and methodology, a bi-directional Long Short-Term Memory (Bi-LSTM) model is developed to classify wet and dry periods under a temporal generalization framework across heterogeneous link configurations. The approach integrates physical signal decomposition, including baseline estimation, gaseous attenuation correction, and wet antenna attenuation (WAA) modeling, with sequence-based learning. Results demonstrate that the temporal deep learning model outperforms classical threshold-based and physical k–R approaches when evaluated over independent temporal validation blocks, effectively reducing sensitivity to path-length-related variability on heterogeneous paths. The model maintains stable performance (loss < 3%) under moderate signal-level noise. SHapley Additive exPlanations (SHAP) confirm the model relies on physical features, such as signal volatility and temporal trends, to reliably differentiate rainfall from WAA. This framework highlights the potential of E-band infrastructure as a distributed sensing network for integrated sensing and communication (ISAC) architectures. Full article

(This article belongs to the Special Issue Microwave Photonics: Devices, Systems and Emerging Applications)

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20 pages, 8064 KB

Open AccessArticle

Centroid Extraction Method Based on Multi-Scale Gaussian Fitting and Subpixel Edge Reconstruction

by Bing Han, Yuanzhang Song, Zhijing Fang, Hangyu Yue, Hongtao Ma, Yuegang Fu and Jian Song

Photonics 2026, 13(6), 594; https://doi.org/10.3390/photonics13060594 (registering DOI) - 18 Jun 2026

Abstract

Accurate spot-centroid localization is fundamental for determining optical metrics such as modulation transfer function (MTF) and effective focal length (EFL). Conventional methods struggle under non-ideal conditions—asymmetric spots, high noise, and vibration—and mid-wave infrared (MWIR) vibration has received little attention. To address these gaps, [...] Read more.

Accurate spot-centroid localization is fundamental for determining optical metrics such as modulation transfer function (MTF) and effective focal length (EFL). Conventional methods struggle under non-ideal conditions—asymmetric spots, high noise, and vibration—and mid-wave infrared (MWIR) vibration has received little attention. To address these gaps, we propose multi-scale Gaussian fitting with subpixel edge reconstruction (MSGF-SER), combining image pyramid fitting, Zernike-moment edge extraction, and adaptive eccentricity-weighted fusion. Validated on simulated spots with varying SNRs and experimental sequences (visible off-axis aberration, long-wave infrared (LWIR) high-noise, MWIR micro-vibration), MSGF-SER achieved a noise-free RMSE of 0.03 pixel and 0.84 pixel at 5 dB SNR. On real MWIR vibration sequences, the Y-direction standard deviation (STD) dropped to 0.098 pixel, and the trajectory displacement variance was more than an order of magnitude lower than that of conventional methods. MTF deviations remained within 0.01, and the deviation of the measured mean EFL from the nominal focal length was better than 0.05 mm, and the STD was below 0.02 mm. These results demonstrate that MSGF-SER substantially improves centroid localization accuracy, repeatability, and smoothness under challenging conditions, providing reliable support for high-precision optical system parameter measurement. Full article

(This article belongs to the Special Issue Precision Measurement and Perception: Enabled by Advanced Optical Sensing, Imaging, and LiDAR Technologies)

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15 pages, 4372 KB

Open AccessArticle

High-Resolution Broadband Ptychography with an EUV Continuum

by Nicholas W. Jenkins, Wilhelm Eschen, Will Hettel, John Gallagher, Benjamin Shearer, Gabriella Seifert, Yunzhe Shao, Clay Klein, Drew Morrill, Grzegorz Golba, Michaël Hemmer, Henry Kapteyn and Margaret Murnane

Photonics 2026, 13(6), 593; https://doi.org/10.3390/photonics13060593 (registering DOI) - 18 Jun 2026

Abstract

Ptychography implemented with coherent high-harmonic (HHG) sources enables high-resolution, high-fidelity imaging of nanostructures and biosystems. However, when driven by mid-infrared lasers to generate light at higher photon energies, HHG inherently produces a broadband quasi-continuum, which is less suited for coherent imaging compared with [...] Read more.

Ptychography implemented with coherent high-harmonic (HHG) sources enables high-resolution, high-fidelity imaging of nanostructures and biosystems. However, when driven by mid-infrared lasers to generate light at higher photon energies, HHG inherently produces a broadband quasi-continuum, which is less suited for coherent imaging compared with a single harmonic order. Consequently, experiments typically select a narrow bandwidth of ≈1%, leaving most of the HHG photons unused, increasing exposure times. In this work, we demonstrate broadband ptychography utilizing an extreme UV (EUV) continuum centered at 92 eV, with a bandwidth of up to 7.9 eV (a relative bandwidth of ~9%). By focusing the HHG beam to a sub-micrometer spot size to relax the temporal coherence constraints, and utilizing a multi-wavelength ptychographic reconstruction algorithm, we achieve a spatial resolution of 42 nm, which is near the diffraction limit of ~30 nm for our setup. To the best of our knowledge, this represents the broadest spectral bandwidth successfully employed to date for EUV ptychography, with the potential to increase the usable photon flux by up to an order of magnitude relative to previous approaches. In the future, broadband soft X-ray ptychography can be used to image hydrated samples around the carbon K-edge and magnetic textures at the L-edges of transition metals. Full article

(This article belongs to the Special Issue Computational Imaging for Semiconductor Devices Metrology Applications)

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15 pages, 1655 KB

Open AccessArticle

Time-Delay Signature Suppressed Broadband Chaos for Dual-Polarization Bidirectional Chaotic Communication with Synchronized VCSELs

by Xingyu Huang, Zhuqiang Zhong, Jianjun Chen, Yipeng Zhu, Jinzhi Xu, Haiyang Yang, Chuanyi Tao and Yanhua Hong

Photonics 2026, 13(6), 592; https://doi.org/10.3390/photonics13060592 - 18 Jun 2026

Abstract

We propose a time-delay signature suppressed broadband chaotic (TSBC) carrier generation scheme and theoretically investigate its performance in a dual-polarization bidirectional chaotic communication system based on synchronized vertical-cavity surface-emitting lasers (VCSELs). The TSBC scheme is implemented by combining fiber Bragg grating (FBG) feedback [...] Read more.

We propose a time-delay signature suppressed broadband chaotic (TSBC) carrier generation scheme and theoretically investigate its performance in a dual-polarization bidirectional chaotic communication system based on synchronized vertical-cavity surface-emitting lasers (VCSELs). The TSBC scheme is implemented by combining fiber Bragg grating (FBG) feedback with an external electro-optic (EO) phase modulation loop to introduce synergistic nonlinear perturbations. The results demonstrate that the proposed TSBC scheme effectively suppresses the time-delay signature (TDS) to less than 0.03 while significantly enhancing the chaotic carrier bandwidth to over 23 GHz for each polarization channel. Meanwhile, high-quality chaotic synchronization can be achieved with laser parameter mismatches of approximately 30%. Finally, an aggregated 46 Gbit/s dual-polarization bidirectional chaotic transmission is demonstrated, which confirms the effectiveness and the potential of the TSBC dual-polarization bidirectional scheme for secure optical communication applications. Full article

(This article belongs to the Special Issue Recent Advances in Optical Communication and Networks)

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11 pages, 2313 KB

Open AccessArticle

LiNbO₃:RE³⁺ (RE = Yb, Ho) Crystals as Radiation-Balanced Laser Materials in Infrared Region

by Gagik Demirkhanyan, Narine Babajanyan, Ninel Kokanyan, Marco Bazzan and Edvard Kokanyan

Photonics 2026, 13(6), 591; https://doi.org/10.3390/photonics13060591 - 18 Jun 2026

Abstract

Based on the analysis of the emission spectra of LiNbO₃:Ho³⁺ and LiNbO₃:Yb³⁺ crystals in the infrared region, the feasibility of radiation-balanced (RB) lasing in the infrared region at room temperature has been investigated. The parameters of RB [...] Read more.

Based on the analysis of the emission spectra of LiNbO₃:Ho³⁺ and LiNbO₃:Yb³⁺ crystals in the infrared region, the feasibility of radiation-balanced (RB) lasing in the infrared region at room temperature has been investigated. The parameters of RB lasing were calculated, and the optimal pump and laser wavelengths were determined as follows: λ_OP = 2015.2 nm and λ_OL = 2072.3 nm for LiNbO₃:Ho³⁺ crystals, and λ_OP = 1004.7 nm and λ_OL = 1060.8 nm for LiNbO₃:Yb³⁺ crystals. The dependence of RB lasing intensity on pump intensity, ensuring radiation balance, was established. For representative values of intracavity losses (γ_i = 0.1%, 0.4%, 0.8%) and output coupler transmission losses (T₂ = 2%), the expected output powers of RB lasing were estimated. Full article

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21 pages, 3094 KB

Open AccessArticle

Neural-Network-Assisted Compensation for Enhanced High-Temperature Pressure Measurement Accuracy Using a Silica-Diaphragm Fiber-Optic Fabry–Perot Sensor

by Zhaoyi Li, Shanmin Gao, Rui Liang, Zhengyang Zhong, Hongtian Zhu, Enbo Wang, Qi Zhang, Zhichun Liu, Zhenyin Hai and Chenyang Xue

Photonics 2026, 13(6), 590; https://doi.org/10.3390/photonics13060590 - 17 Jun 2026

Abstract

Accurate pressure measurement under high-temperature conditions is challenging for silica-diaphragm-based fiber-optic Fabry–Perot (F-P) sensors because temperature causes both optical cavity length (OCL) baseline drift and pressure-sensitivity variation. In this work, a structurally simple and readily fabricated silica-diaphragm-based fiber-optic F-P pressure sensor was developed, [...] Read more.

Accurate pressure measurement under high-temperature conditions is challenging for silica-diaphragm-based fiber-optic Fabry–Perot (F-P) sensors because temperature causes both optical cavity length (OCL) baseline drift and pressure-sensitivity variation. In this work, a structurally simple and readily fabricated silica-diaphragm-based fiber-optic F-P pressure sensor was developed, and a neural-network-assisted compensation strategy was proposed to suppress the residual errors of conventional analytical compensation. A temperature-dependent response model was established to describe OCL drift and sensitivity variation. The OCL was demodulated from reflection spectra using an FFT-assisted dual-peak and MMSE refinement method, and static pressure measurements were performed over 25–400 °C and 0–2.4 MPa. Based on the experimentally verified response characteristics, a fitting-based compensation method considering both OCL drift and sensitivity variation was first implemented. A lightweight neural network was then constructed using the OCL variation,

Δ O C L

, and ambient temperature as physically meaningful input features. Compared with fixed-sensitivity compensation and drift-and-sensitivity fitting compensation, whose maximum full-scale errors were 7.10% F.S. and 2.74% F.S., respectively, the proposed method reduced the maximum error to 0.90% F.S. with an RMSE of 0.0045 MPa. Additional validation at the independent intermediate temperatures of 150, 250, and 350 °C further confirmed the generalization capability of the proposed NNC model between calibrated temperature gradients, achieving an overall RMSE of 0.0055 MPa and a maximum full-scale error below 0.77% F.S. The proposed approach provides a high-accuracy and practical solution for high-temperature pressure monitoring using simple fabricated silica-diaphragm F-P sensors. Full article

(This article belongs to the Special Issue Recent Advances in Precision Optical Measurement)

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40 pages, 742 KB

Open AccessReview

Cross-Platform Neuromorphic Photodetectors: From Organic and Oxide to Perovskite, Wide-Bandgap, and Si-CMOS

by Martin Weis

Photonics 2026, 13(6), 589; https://doi.org/10.3390/photonics13060589 - 17 Jun 2026

Abstract

Conventional photodetectors and image sensors deliver high-fidelity digital outputs but face a growing data-movement bottleneck: the energy and latency cost of transferring raw pixel streams to off-chip memory and processors increasingly dominates over both sensing and computation in modern machine-vision pipelines. An emerging [...] Read more.

Conventional photodetectors and image sensors deliver high-fidelity digital outputs but face a growing data-movement bottleneck: the energy and latency cost of transferring raw pixel streams to off-chip memory and processors increasingly dominates over both sensing and computation in modern machine-vision pipelines. An emerging response is the neuromorphic photodetector, a class of optoelectronic device that converts incident light into an electrical signal while simultaneously storing, modulating, and pre-processing that signal in a manner inspired by biological synapses and retinas. Over the past decade, demonstrations have spanned at least eight material platforms—organic semiconductors, organic–carbon-nanotube hybrids, perovskite and perovskite hybrids, metal oxides (including ultra-wide-bandgap and printable variants), wide-bandgap III-nitrides and 4H-SiC, two-dimensional materials, photo-memristors, and silicon CMOS in-sensor compute architectures—and have been realised through four distinct architectural families: phototransistor synapses, photo-memristors, heterojunction in-sensor compute, and linear photovoltaic neural networks. Here, we provide a quantitative cross-platform benchmark across forty in-scope articles, identify persistent photoconductivity as a near-universal device-physical substrate underlying synaptic functionality, characterise the responsivity–speed–energy trade-off structure observed across platforms, and present a critical assessment of energy-reporting practice in the field. We further identify three best-practice exemplars from three independent material platforms that converge on operating biases of 0.01–0.1 V and energies of 0.07–0.8 fJ per event, and we propose a unified reporting framework to enable meaningful cross-platform benchmarking of next-generation neuromorphic photodetectors. Full article

(This article belongs to the Special Issue New Perspectives in Photodetectors)

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