Photonics

16 pages, 3500 KB

Open AccessArticle

The Super Phase Sensitivity of an SU(1,1) Interferometer with a Two-Mode Squeezed Coherent State via Balanced Homodyne and Intensity Detection

by Changlan Xu, Lei Wang, Shaoqiu Ke, Jun Liu and Dongxu Chen

Photonics 2026, 13(3), 309; https://doi.org/10.3390/photonics13030309 - 23 Mar 2026

Viewed by 539

Abstract

We propose a novel scheme that is used for the enhancement of phase sensitivity. The SU(1,1) interferometer with a two-mode squeezed coherent state input, using balanced homodyne detection (BHD) and intensity detection (ID), is shown. Our results demonstrate that the phase sensitivity achieved [...] Read more.

We propose a novel scheme that is used for the enhancement of phase sensitivity. The SU(1,1) interferometer with a two-mode squeezed coherent state input, using balanced homodyne detection (BHD) and intensity detection (ID), is shown. Our results demonstrate that the phase sensitivity achieved via BHD outperforms that of ID. The optimal phase sensitivity via BHD surpasses the Heisenberg limit (HL) and approaches the quantum Cramér–Rao bound. A larger photon number and parameter strength can make the phase sensitivity better. Furthermore, we show the effects of internal and external losses on phase sensitivity in detail. When external loss reaches 10%, the phase sensitivity can reach the HL. Next, we have a detailed discussion on the impact of the squeezing parameter and photon number on phase sensitivity, which shows that our scheme has better phase sensitivity and enhanced robustness. This interferometer system thus holds significant potential for applications in quantum precision measurement. Full article

(This article belongs to the Section Quantum Photonics and Technologies)

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31 pages, 42010 KB

Open AccessArticle

SMS Fiber-Optic Sensing System for Real-Time Train Detection and Railway Monitoring

by Waleska Feitoza de Oliveira, Luana Samara Paulino Maia, João Isaac Silva Miranda, Alan Robson da Silva, Aedo Braga Silveira, Dayse Gonçalves Correia Bandeira, Antonio Sergio Bezerra Sombra and Glendo de Freitas Guimarães

Photonics 2026, 13(3), 308; https://doi.org/10.3390/photonics13030308 - 23 Mar 2026

Viewed by 588

Abstract

Railway traffic monitoring requires robust detection technologies capable of operating reliably under real-world vibration and environmental conditions. In this work, we present the design and validation of an optical vibration sensor based on a Single-mode–Multimode–Single-mode (SMS) fiber structure for Light Rail Vehicle (LRV) [...] Read more.

Railway traffic monitoring requires robust detection technologies capable of operating reliably under real-world vibration and environmental conditions. In this work, we present the design and validation of an optical vibration sensor based on a Single-mode–Multimode–Single-mode (SMS) fiber structure for Light Rail Vehicle (LRV) detection. The sensing mechanism relies on multimodal interference in the multimode fiber (MMF), where rail-induced vibrations modify the guided mode distribution and, consequently, the transmitted optical intensity. The optical signal is converted to voltage and processed through an embedded acquisition system. Additionally, we conducted tests with freight trains and maintenance trains in order to evaluate the applicability of the sensor in other types of trains besides the LRV. We conducted laboratory experiments to assess mechanical stability, sensibility, and packaging strategies, followed by supervised field tests on an operational LRV line. The recorded time-domain signal exhibited clear modulation during train passage, and first-derivative and sliding-window variance analyses were applied to reliably identify vibration events, even in the presence of slow baseline drift. In addition, frequency-domain analysis was performed by applying the Fast Fourier Transform (FFT) to the measured signal, enabling the identification of characteristic low-frequency spectral components induced by train passage. A quantitative sensitivity assessment was further carried out by correlating the integrated spectral energy (0–12 Hz) with vehicle weight, yielding a linear response with a sensitivity of 0.0017 a.u./t and coefficient of determination

R^{2} = 0.933

. The proposed solution demonstrated stable operation using commercially available low-cost components, confirming the feasibility of SMS-based optical sensing for railway monitoring. These results indicate strong potential for future deployment in traffic safety systems and distributed sensing networks. Full article

(This article belongs to the Special Issue Advances in Optical Fiber Sensing Technology: 2nd Edition)

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19 pages, 10695 KB

Open AccessArticle

Probabilistic Shaping-Assisted Bases Precoding in QAM Quantum Noise Stream Cipher

by Shuang Wei, Sheng Liu, Wei Wang, Chao Lei, Kongni Zhu, Mingrui Zhang, Yuang Li, Yunbo Li, Dong Wang, Dechao Zhang, Han Li, Yajie Li, Yongli Zhao and Jie Zhang

Photonics 2026, 13(3), 307; https://doi.org/10.3390/photonics13030307 - 23 Mar 2026

Viewed by 524

Abstract

We propose a probabilistic shaping-assisted base precoding quantum noise stream cipher (PSABP QNSC) scheme to effectively alleviate the encryption penalty in QAM QNSC systems. In contrast to the uniformly distributed bases adopted in traditional QNSC, Gaussian distributed bases can provide shaping gain. We [...] Read more.

We propose a probabilistic shaping-assisted base precoding quantum noise stream cipher (PSABP QNSC) scheme to effectively alleviate the encryption penalty in QAM QNSC systems. In contrast to the uniformly distributed bases adopted in traditional QNSC, Gaussian distributed bases can provide shaping gain. We theoretically analyze the underlying gain mechanism of Gaussian distributed bases in the PSABP QNSC scheme. Experimental results of 160 km reveal that the encryption penalties of QPSK and 16QAM are reduced by 0.44 dB and 0.27 dB, in terms of OSNR. Moreover, the security is quantified through the number of masked signals as a primary key metric. To mitigate the impact of base precoding, we propose the effective bases and effective ciphertext symbol points to refine the security evaluation. Moreover, the security is estimated in terms of mutual information leakage, with

2.2 \times 10^{- 4}

bits of QPSK and

1.85 \times 10^{- 4}

bits of 16QAM. The results indicate that the PSABP QNSC scheme provides effective protection against eavesdropping. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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8 pages, 2546 KB

Open AccessCommunication

A 6 mJ, 4 ns Pulse Generation at 2.09 µm from a Diode-Pumped Ho:YAG Thin-Disk Laser

by Yuya Koshiba, Jiří Mužík, Martin Smrž, Matyáš Dvořák, Sabina Kudělková, Antonín Fajstavr and Tomáš Mocek

Photonics 2026, 13(3), 306; https://doi.org/10.3390/photonics13030306 - 21 Mar 2026

Viewed by 571

Abstract

A holmium-doped yttrium aluminum garnet (Ho:YAG) thin disk was experimentally investigated under Q-switching and cavity-dumping operation schemes, pumped by a 1.9 µm laser diode (LD). The laser generated pulses at 2090 nm with energies more than 6 mJ and pulse duration down to [...] Read more.

A holmium-doped yttrium aluminum garnet (Ho:YAG) thin disk was experimentally investigated under Q-switching and cavity-dumping operation schemes, pumped by a 1.9 µm laser diode (LD). The laser generated pulses at 2090 nm with energies more than 6 mJ and pulse duration down to 3.8 ns, corresponding to a peak power of 1.6 MW with near-diffraction-limited beam quality. The compact and robust system was used for laser-induced breakdown spectroscopy (LIBS) experiments, demonstrating its practical usability. These results represent, to the best of our knowledge, the first demonstration of a Ho:YAG thin-disk laser providing MW peak power in the nanosecond regime. Full article

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

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11 pages, 3141 KB

Open AccessCommunication

ZrGeTe₄ Nanoparticles as a Saturable Absorber for Mode-Locked Operations at 1 and 1.55 µm

by Xinxin Shang, Nannan Xu, Mengyu Zong, Weiyi Yu, Linguang Guo, Guanguang Gao, Ziqi Zhang, Huanian Zhang and Lianzheng Su

Photonics 2026, 13(3), 305; https://doi.org/10.3390/photonics13030305 - 20 Mar 2026

Cited by 4 | Viewed by 623

Abstract

In the current paper, the nonlinear absorption characteristics and laser modulation performance of the ternary anisotropic semiconductor material ZrGeTe₄ were successfully explored. The recovery time of the ZrGeTe₄-PVA thin film was measured to be 5.74 ps by the pump–probe technology. [...] Read more.

In the current paper, the nonlinear absorption characteristics and laser modulation performance of the ternary anisotropic semiconductor material ZrGeTe₄ were successfully explored. The recovery time of the ZrGeTe₄-PVA thin film was measured to be 5.74 ps by the pump–probe technology. By employing ZrGeTe₄ as a saturable absorber, a passive mode-locked Yb-doped fiber laser was demonstrated for the first time. In the 1 µm mode-locked operation, the central wavelength was 1031.29 nm, the pulse repetition rate was 24.85 MHz, and the pulse width was 786.3 ps. In an Er-doped fiber laser operating at a wavelength of 1561.10 nm, the pulse width was as short as 1.26 ps with a repetition rate of 4.38 MHz. The results show that ZrGeTe₄ has excellent broadband nonlinear optical characteristics. Full article

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

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16 pages, 7174 KB

Open AccessArticle

Aberration-Conditioned Attention-Driven Centroid Localization: From Simulation Mechanism to Double-Spot Experiment

by Zhonghao Zhao, Jia Hou, Yuanting Liu, Anwei Liu and Zhiping He

Photonics 2026, 13(3), 304; https://doi.org/10.3390/photonics13030304 - 20 Mar 2026

Viewed by 359

Abstract

In size, weight, and power (SWaP)-constrained optical systems, such as spaceborne LiDAR, high-precision centroid localization often relies on focal-plane measurements without dedicated wavefront sensors. Under such conditions, the nonlinear coupling between optical aberrations and sensor noise introduces systematic bias that is difficult to [...] Read more.

In size, weight, and power (SWaP)-constrained optical systems, such as spaceborne LiDAR, high-precision centroid localization often relies on focal-plane measurements without dedicated wavefront sensors. Under such conditions, the nonlinear coupling between optical aberrations and sensor noise introduces systematic bias that is difficult to mitigate using conventional centroiding methods. To address this issue, we propose a physics-conditioned feature correction framework based on an aberration-conditioned attention mechanism. A hybrid CNN–Transformer architecture is employed to predict and compensate for systematic centroid bias. Specifically, convolutional layers encode the degraded spot morphology, while a multi-head attention mechanism leverages Seidel aberration coefficients to adaptively modulate spatial features for precise regression. Given the unavailability of absolute ground-truth coordinates in empirical scenarios, a physics-consistent simulation framework based on scalar diffraction theory is constructed to generate synthetic data for supervised learning. Simulation results indicate that the proposed method objectively reduces anisotropic systematic bias, achieving a localization root-mean-square error (RMSE) of 0.011 to 0.021 pixels, and maintains stable sub-pixel accuracy even under a 10% empirical prior perturbation. To evaluate generalization performance and engineering reliability, a wedge-based double-spot platform is developed to verify physical consistency via geometric invariance. Experimental results demonstrate a measured spacing standard deviation (SD) of 0.015 to 0.039 pixels. This validates the framework’s transferability from theoretical simulation to controlled physical measurements, providing an algorithmic foundation for precision optical metrology in hardware-constrained environments. Full article

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

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21 pages, 2938 KB

Open AccessArticle

MAENet: A Multi-Scale Attention Efficient Network for Coherent Noise Suppression in Digital Holographic Microscopy

by Yifan Zhu, Jing Yu, Zihao Zhang, Ming Kong, Yushuo Feng, Feixue Hou, Zihan Tang and Wei Liu

Photonics 2026, 13(3), 303; https://doi.org/10.3390/photonics13030303 - 20 Mar 2026

Viewed by 434

Abstract

Coherent noise in digital holographic microscopy (DHM) seriously degrades the accuracy of quantitative phase imaging, limiting its applications in fields such as nondestructive testing. However, traditional numerical denoising methods struggle to achieve an ideal balance between noise suppression, detail preservation, and computational efficiency. [...] Read more.

Coherent noise in digital holographic microscopy (DHM) seriously degrades the accuracy of quantitative phase imaging, limiting its applications in fields such as nondestructive testing. However, traditional numerical denoising methods struggle to achieve an ideal balance between noise suppression, detail preservation, and computational efficiency. To address this challenge, we propose a multi-scale attention efficient network (MAENet). This network employs a dual-encoder architecture to achieve complementary extraction of multi-scale features. To efficiently integrate the features from these two branches, a dual-branch dense attention fusion (DDAF) module is designed. It performs a weighted fusion of features from the dual branches via an adaptive attention mechanism and enhances feature representation via dense residual connections, significantly boosting the model’s denoising performance. Furthermore, a hierarchical fusion strategy is adopted to preserve high-frequency details in the shallow layers of the network while performing feature fusion in the deeper layers, thereby maximizing protection of image textures while effectively suppressing noise. To address the lack of paired training data in real-world scenarios, a DHM simulation system capable of simulating the key physical characteristics of coherent noise was constructed. Extensive experiments on the simulated dataset show that MAENet achieves a PSNR of 33.25 dB and an SSIM of 0.93042, outperforming various mainstream denoising algorithms and demonstrating its excellent performance in suppressing coherent noise, providing an effective solution for denoising in coherent imaging systems. Full article

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16 pages, 2813 KB

Open AccessArticle

Compact EM Wave Trapping in Low-Index-Contrast Structures with Al₂O₃-Based Experimental Validation

by Irem O. Alp

Photonics 2026, 13(3), 302; https://doi.org/10.3390/photonics13030302 - 20 Mar 2026

Viewed by 444

Abstract

This study presents the design of a compact low-index-contrast structure capable of trapping electromagnetic waves within a highly confined region. The energy storage performance of the geometries was enhanced using a genetic algorithm that employed a binary (present/absent) assignment of insulating cylinders. Time-domain [...] Read more.

This study presents the design of a compact low-index-contrast structure capable of trapping electromagnetic waves within a highly confined region. The energy storage performance of the geometries was enhanced using a genetic algorithm that employed a binary (present/absent) assignment of insulating cylinders. Time-domain simulations performed with MEEP were experimentally validated using precisely positioned

θ

-phase alumina rods, resulting in a 13 dB increase in receiver-antenna power within the microwave regime. The measurements showed a correlation exceeding 99% with the computational results over a dielectric constant range of 4.5 to 5.0. A quality factor of Q

= 3.6 \times 10^{3}

was measured at 5.08 GHz in the experiment. Subsequently, machine learning techniques were applied, further increasing the Q value to approximately

10^{4}

, even within such a small configuration. Furthermore, the proposed structure does not require a complete photonic bandgap; instead, relatively high-Q factors were achieved by suppressing radiation losses through a pattern of low-index dielectric rods. Full article

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

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11 pages, 4228 KB

Open AccessArticle

Depth of Field Enhanced Integral Imaging Display System

by Xiao-Li Ma, Han-Le Zhang, Bo Hu, Meng-Ting Hao, Dao-Cheng Chen, Yuan-Yuan Chen, Shu-Bin Liu and Yan-Yan Wang

Photonics 2026, 13(3), 301; https://doi.org/10.3390/photonics13030301 - 20 Mar 2026

Viewed by 455

Abstract

Large depth of field (DOF) is a core pursuit in integral imaging (InIm). In this paper, we propose a DOF-enhanced InIm display system comprising a transmissive mirror device (TMD), a semi-transparent mirror (STM), two 2D displays, and a micro-lens array (MLA). The two [...] Read more.

Large depth of field (DOF) is a core pursuit in integral imaging (InIm). In this paper, we propose a DOF-enhanced InIm display system comprising a transmissive mirror device (TMD), a semi-transparent mirror (STM), two 2D displays, and a micro-lens array (MLA). The two 2D displays pre-render two sets of elemental image arrays (EIAs), each corresponding to a distinct depth plane. The STM spatially coaxializes the two EIAs emitted by the two 2D displays. At the same time, the TMD collaborates with the STM to adjust the effective projection distances of the coaxialized EIAs onto the MLA to different values. The MLA couples with the two EIAs projected at different effective distances, enabling the reconstruction of three-dimensional (3D) images at two separate central depth planes (CDPs). This system solves the narrow DOF issue in conventional InIm displays by reconstructing 3D images at two separate CDPs, thus enhancing the DOF. Notably, the proposed system achieves an approximate two-fold increase in DOF compared to a conventional one. A prototype of the DOF-enhanced InIm display system is constructed, and experimental results verify its feasibility. Full article

(This article belongs to the Special Issue Advanced Research in Computational Optical Imaging)

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11 pages, 1302 KB

Open AccessArticle

A Ring-Assisted Asymmetric Mach–Zehnder Interferometer for High-Sensitivity and Stable On-Chip Temperature Sensing

by Huan Guan, Zhuoting Wang, Shuhui Bo and Zhiyong Li

Photonics 2026, 13(3), 300; https://doi.org/10.3390/photonics13030300 - 20 Mar 2026

Viewed by 520

Abstract

A high-sensitivity and high-stability on-chip temperature sensor based on a silicon-on-insulator (SOI) platform is proposed and experimentally demonstrated in this work. The device employs a ring-assisted asymmetric Mach–Zehnder interferometer (RAMZI), enhancing both temperature sensitivity and measurement stability. Broadband, wavelength-insensitive components, including multimode interference [...] Read more.

A high-sensitivity and high-stability on-chip temperature sensor based on a silicon-on-insulator (SOI) platform is proposed and experimentally demonstrated in this work. The device employs a ring-assisted asymmetric Mach–Zehnder interferometer (RAMZI), enhancing both temperature sensitivity and measurement stability. Broadband, wavelength-insensitive components, including multimode interference couplers and adiabatic 3 dB splitters, reduce the influence of laser wavelength fluctuations and mitigate interference errors caused by environmental perturbations. The sensor achieves a temperature sensitivity of 108.74 pm/K, corresponding to an approximately 40% improvement over a conventional AMZI with the same footprint. Moreover, a wavelength drift of only 18 pm over 45 min demonstrates excellent stability and robustness. This work provides an effective solution for highly sensitive and stable on-chip temperature sensing in photonic integrated systems. Full article

(This article belongs to the Special Issue Advances in Optical Sensors and Applications)

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11 pages, 2885 KB

Open AccessArticle

Photoluminescence Enhancement from Semiconductor Quantum Dot/Polymer Composite Thin Films Using Ag Films

by Shogo Yoshioka, Tomohiko Niwa, Tatsuya Tanoue, Tetsuya Matsuyama, Kenji Wada and Koichi Okamoto

Photonics 2026, 13(3), 299; https://doi.org/10.3390/photonics13030299 - 19 Mar 2026

Viewed by 630

Abstract

Semiconductor quantum dots (QDs) are attractive materials for light-emitting devices, and the photoluminescence (PL) from QDs can be enhanced near a metal surface due to surface plasmon (SP) resonance. To integrate QDs into metal structures, QD/poly(methyl methacrylate) (PMMA) composite thin films are generally [...] Read more.

Semiconductor quantum dots (QDs) are attractive materials for light-emitting devices, and the photoluminescence (PL) from QDs can be enhanced near a metal surface due to surface plasmon (SP) resonance. To integrate QDs into metal structures, QD/poly(methyl methacrylate) (PMMA) composite thin films are generally used. However, it has been reported that QDs tend to aggregate in the PMMA matrix. In this study, we fabricated two types of QD/polymer composite thin films with different degrees of QD aggregation by additionally using poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MA), which is known to prevent QD aggregation. Furthermore, these two types of films were fabricated on Ag films, with the distance between the Ag films and the QDs controlled by Al₂O₃ spacer layers, and the PL enhancement was compared between the two film types. Finally, we reveal that QD aggregation in the polymer matrix significantly affects the PL enhancement. Although the aggregation trends differed between PMMA and PMMA-co-MA, the results suggest a possible increase in the internal quantum efficiency (IQE) in both film types. Full article

(This article belongs to the Special Issue Plasmonics for Advanced Photonic Applications)

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19 pages, 9543 KB

Open AccessArticle

Miniaturized Aiming/Tracking System and Control Model Analysis Based on Risley Gratings

by Xiaoming Li, Hao Wang, Lun Jiang, Tong Wang, Sheng Yang and Keyan Dong

Photonics 2026, 13(3), 298; https://doi.org/10.3390/photonics13030298 - 19 Mar 2026

Viewed by 367

Abstract

With the development of a photoelectric system in the aviation field, the requirements for airborne equipment have increased accordingly. The photoelectric aiming and tracking turntable as a crucial component in the photoelectric system has stringent requirements on weight and volume. A new type [...] Read more.

With the development of a photoelectric system in the aviation field, the requirements for airborne equipment have increased accordingly. The photoelectric aiming and tracking turntable as a crucial component in the photoelectric system has stringent requirements on weight and volume. A new type of structure with the coaxial dual-axis turntable has been researched, it adopts a structural form with two rotating axes connected in series and rotating Risley gratings by two independent mechanical shaft axes to complete pointing, capturing and tracking functions. This type of structure features compactness, small moments of inertia and fast response speed; this miniaturized aiming and tracking system with Risley grating is more suitable for airborne equipment. The Risley grating aiming and tracking system adjusts the optical axis angle using two rotating Risley gratings; it realizes beam pointing within a conical range through polarization diffraction. The aiming and tracking system based on Risley grating has small moving parts so it is lighter; it has more advantages than the traditional turntable. Although the tracking range is relatively limited, it still offers significant lightweight effects for certain special applications and can effectively reduce weight and volume. In this paper, we research the system of aiming and tracking with Risley gratings, the influence of mechanical turntable parameters on the system’s tracking accuracy is analyzed based on its working principle; error analysis and allocation of turntable errors are carried out. Subsequently, the decoupling model of the system is analyzed and system errors are compensated; the miniaturized tracking and calibration system based on Risley gratings is developed. Then, the photoelectric testing method based on dual reference mirrors proposed by us is used to test the coaxiality and axis jitter accuracy of the turntable. The system has an effective aperture > Φ120 mm, weight < 10 kg and volume < Φ190 × 155 mm. Pointing accuracy and dynamic tracking test show that the system’s pointing accuracy is ≯10″ and tracking accuracy is ≯380 μrad. Finally, a field tracking test is carried out and verify the system’s capability and performance. Full article

(This article belongs to the Special Issue Stable Control Technology and Image Perception Technology in Optoelectronic Servo Systems)

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18 pages, 5492 KB

Open AccessArticle

Theoretical Model of Resonant Tunneling Diode Photodetector

by Guanliang Chen, Zhenyun Tang, Jin Yang, Zhongxian Wang, Sanjie Liu, Huiyun Wei, Mingzeng Peng, Zhigang Song and Xinhe Zheng

Photonics 2026, 13(3), 297; https://doi.org/10.3390/photonics13030297 - 19 Mar 2026

Viewed by 582

Abstract

RTD photodetectors have been widely applied in fields such as gas detection, weak signal detection, and single-photon detection. However, during further device design and optimization, it has been found that existing theoretical models cannot fully capture the diverse practical behaviors of RTD photodetectors. [...] Read more.

RTD photodetectors have been widely applied in fields such as gas detection, weak signal detection, and single-photon detection. However, during further device design and optimization, it has been found that existing theoretical models cannot fully capture the diverse practical behaviors of RTD photodetectors. In this work, we analyze the influence of optical illumination on the band structure of RTDs and, based on the model proposed by Schulman et al., develop a relatively comprehensive theoretical model for RTD photodetectors. By comparing the model predictions with experimental data reported in the literature, we demonstrate that the proposed model can accurately describe the various physical effects in RTD photodetectors and faithfully reproduce the actual evolution of the I-V characteristics. This model provides a solid foundation for the design and optimization of RTD photodetector devices. Full article

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14 pages, 2758 KB

Open AccessArticle

Dynamic Moiré Effect in Filled Volumetric Rectangular Objects with Refraction

by Vladimir Saveljev

Photonics 2026, 13(3), 296; https://doi.org/10.3390/photonics13030296 - 19 Mar 2026

Viewed by 344

Abstract

The moiré effect in refractive objects is rarely studied, especially in dynamics. We conducted a theoretical and experimental study of the dynamic moiré effect in rectangular containers with a refractive substance. We generalized the moiré magnification coefficient. The velocity was measured experimentally. Formulas [...] Read more.

The moiré effect in refractive objects is rarely studied, especially in dynamics. We conducted a theoretical and experimental study of the dynamic moiré effect in rectangular containers with a refractive substance. We generalized the moiré magnification coefficient. The velocity was measured experimentally. Formulas for the moiré magnification and the velocity of moiré patterns in rectangular containers with a refractive substance were obtained. The formulas were analyzed in detail, and numerous special cases were identified. The visual effect of the counter-movement of the moiré patterns was predicted theoretically and observed experimentally. This study is important for understanding the dynamic physical properties of the moiré effect with refraction. In practice, the results can be used to measure refractive indexes or levels, as well as in advertising. Full article

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19 pages, 5524 KB

Open AccessArticle

Design, Simulation, and Analysis of Novel Cross-Coupling-Based Self-Coupled Optical Waveguide (CC-SCOW) Circuit Under the Coupled Resonator-Induced Transparency (CRIT) Condition

by Charmaine Paglinawan, Benjamin Dingel, Arnold Paglinawan and Ramon Benedict Lapiña

Photonics 2026, 13(3), 295; https://doi.org/10.3390/photonics13030295 - 19 Mar 2026

Viewed by 490

Abstract

We introduce a novel cross-coupled self-coupled optical waveguide (CC-SCOW) architecture that leverages coupled-resonator-induced transparency (CRIT) via a cross-coupling mechanism. This design addresses key limitations of conventional self-coupled optical waveguides (SCOWs), particularly their restricted spectral tunability and fixed interference characteristics arising from direct coupling. [...] Read more.

We introduce a novel cross-coupled self-coupled optical waveguide (CC-SCOW) architecture that leverages coupled-resonator-induced transparency (CRIT) via a cross-coupling mechanism. This design addresses key limitations of conventional self-coupled optical waveguides (SCOWs), particularly their restricted spectral tunability and fixed interference characteristics arising from direct coupling. For the first time, we demonstrate and analyze the CRIT behavior of the CC-SCOW structure, showing that it offers enhanced design flexibility, compactness, and improved spectral performance. Through analytical modeling and finite-difference time-domain (FDTD) simulations, we show that CC-SCOWs enable tunable, narrowband filtering with improved free spectral range (FSR) and phase response. These features make the CC-SCOW architecture highly suitable for advanced photonic integrated circuits requiring high selectivity, tunability, and miniaturization. Full article

(This article belongs to the Special Issue Optical Sensors and Devices)

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15 pages, 1814 KB

Open AccessArticle

Physics-Prior-Guided Deep Learning for High-Precision Marker Localization Under Saturated Artifacts for Potential Surgical Navigation Applications

by Yan Xu, Shoubiao Zhang, Huanhuan Tian, Zhiyong Zou, Weilong Li, Anlan Huang, Nu Zhang and Xiang Ma

Photonics 2026, 13(3), 294; https://doi.org/10.3390/photonics13030294 - 18 Mar 2026

Viewed by 600

Abstract

Optical reflective markers are widely used in precision medicine, computer-assisted surgery, and robotic interventions. Nevertheless, intraoperative tracking still faces challenges such as sensor saturation, Point Spread Function (PSF) blooming, and flat-top artifacts, which affect localization precision and stability. Traditional deep learning detectors perform [...] Read more.

Optical reflective markers are widely used in precision medicine, computer-assisted surgery, and robotic interventions. Nevertheless, intraoperative tracking still faces challenges such as sensor saturation, Point Spread Function (PSF) blooming, and flat-top artifacts, which affect localization precision and stability. Traditional deep learning detectors perform well in general object recognition but are limited in handling saturated infrared reflective markers due to their neglect of optical physics and inability to separate signal from blooming interference. This paper presents a physics-prior-guided network integrating a Brightness-Prior-Enhanced Spatial Attention (BPESA) mechanism for high-precision sub-pixel marker localization under saturation conditions. The method achieves a Root Mean Square (RMS) error of 0.52 pixels (approximately 0.11 mm) on a dataset of 8000 binocular images and reduces the localization error by approximately 54.4% compared with the baseline YOLOv8 model, while maintaining an inference speed of 134.6 FPS. The results demonstrate that optical blooming interference can be effectively mitigated by a learnable physics-prior branch, providing accurate marker coordinates that form a foundation for potential downstream tracking or navigation tasks. Full article

(This article belongs to the Special Issue Computational Optical Imaging: Theories, Algorithms, and Applications)

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12 pages, 912 KB

Open AccessArticle

Critical Cavities Design for High-Repetition-Frequency Self-Starting Kerr-Lens Mode-Locked Lasers

by Xinxin Wang, Xing Chen, Zhigang Zhang, Bin Luo and Song Yu

Photonics 2026, 13(3), 293; https://doi.org/10.3390/photonics13030293 - 18 Mar 2026

Viewed by 406

Abstract

The mode-locking mechanism of Kerr-lens mode-locked lasers is analyzed using the nonlinear ABCD matrix formalism. Our findings demonstrate that positioning the Kerr medium at the beam waist and operating the resonator near the stability boundary significantly enhances the nonlinear effect, thereby facilitating self-starting [...] Read more.

The mode-locking mechanism of Kerr-lens mode-locked lasers is analyzed using the nonlinear ABCD matrix formalism. Our findings demonstrate that positioning the Kerr medium at the beam waist and operating the resonator near the stability boundary significantly enhances the nonlinear effect, thereby facilitating self-starting mode-locking without requiring any external initiation mechanisms. Full article

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

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17 pages, 2806 KB

Open AccessArticle

Non-Destructive Sequence Determination of Seal Ink and Handwriting Using Structured Light and Deep Learning

by Hongyang Wang, Xin He, Zhonghui Wei, Zhuang Lv, Zhiya Mu, Lei Zhang, Jiawei He, Jun Wang and Yi Gao

Photonics 2026, 13(3), 292; https://doi.org/10.3390/photonics13030292 - 18 Mar 2026

Viewed by 544

Abstract

In the field of forensic document examination, accurately determining the chronological sequence of intersecting lines between seal ink and handwriting is a crucial technical step for verifying document authenticity, identifying contract tampering, and detecting forged signatures. This technique analyzes the physical superimposition relationship [...] Read more.

In the field of forensic document examination, accurately determining the chronological sequence of intersecting lines between seal ink and handwriting is a crucial technical step for verifying document authenticity, identifying contract tampering, and detecting forged signatures. This technique analyzes the physical superimposition relationship formed by the deposition of the two media on the paper substrate to provide objective scientific evidence for judicial practice. Although traditional methods such as microscopic imaging and mass spectrometry analysis have achieved some progress, they still suffer from common limitations including high equipment costs, complex operation, and potential damage to samples. This study proposes and validates an innovative non-destructive determination method that integrates structured light 3D reconstruction technology with deep learning algorithms. The research captures the microscopic 3D morphological features of the ink intersection area using a high-precision structured light scanning system and effectively eliminates noise interference caused by paper substrate undulation through Gaussian flattening technology. Subsequently, a multimodal fusion strategy combines 2D texture images with 3D depth information to construct a dataset rich in features. On this basis, a deep learning model based on an improved Residual Neural Network (ResNet) is designed, incorporating the ELU activation function and an EMA mechanism to enhance the model’s feature extraction capability and convergence stability. Experimental results demonstrate that the proposed method achieves a recognition accuracy of 94.39% on the test set, fully validating its effectiveness and application potential in the non-destructive determination of ink stroke sequencing. Full article

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11 pages, 2821 KB

Open AccessArticle

Sub-50 fs, 2.8 μm Pulse Generation Enabled by Nonlinear Pulse Stretching and Compression in a Chalcogenide–Fluoride Fiber-Integrated System

by Huiqi Xia, Lele Yu, Shuai Yin, Xuzhao Zhang, Kai Xia, Chao Chen, Biaoqi Wen, Chao Mei, Xing Luo, Peilong Yang and Shixun Dai

Photonics 2026, 13(3), 291; https://doi.org/10.3390/photonics13030291 - 18 Mar 2026

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Abstract

We report the generation of sub-50 fs mid-infrared (MIR) pulses using a fiber-integrated system comprising a several-centimeters-long chalcogenide (As₂S₃) fiber and a fluoride (ZBLAN) fiber. Initially, 127 fs pulses at 2.8 µm are generated via the soliton self-frequency shift [...] Read more.

We report the generation of sub-50 fs mid-infrared (MIR) pulses using a fiber-integrated system comprising a several-centimeters-long chalcogenide (As₂S₃) fiber and a fluoride (ZBLAN) fiber. Initially, 127 fs pulses at 2.8 µm are generated via the soliton self-frequency shift in the fluoride fiber. These pulses are then coupled into the As₂S₃ fiber, which provides substantial normal dispersion at this wavelength, enabling temporal stretching to achieve pulse durations of 1.02 ps (8 cm), 2.06 ps (15 cm), and 4.45 ps (24 cm), corresponding to a maximum stretch factor of approximately 35. Simultaneously, the pulses undergo significant spectral broadening via self-phase modulation during this process. Subsequent nonlinear compression within an optimized ZBLAN fiber yields compressed pulses as short as 46 fs, representing a compression ratio of approximately 63%. This work represents, for the first time, picosecond stretching and sub-50 fs nonlinear compression in a fiber-integrated architecture at 2.8 μm, establishing a critical component for future all-fiber MIR-chirped pulse amplification systems. Full article

(This article belongs to the Special Issue Nonlinear Optics and Optical Parametric Oscillators: From Fundamentals to Cutting-Edge Research)

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15 pages, 4211 KB

Open AccessArticle

Research on Laser Automatic Phase−Locking Technology for Atomic Interferometric Gravity Gradient Measurement

by Jipeng Wang, Bangcheng Han and Jinhai Bai

Photonics 2026, 13(3), 290; https://doi.org/10.3390/photonics13030290 - 18 Mar 2026

Viewed by 468

Abstract

Atomic interferometric gravity gradient measurement enables atomic interference by manipulating atoms with lasers of specific frequencies. Thus, the frequency and phase−locking performance of the laser system exerts a significant impact on key experimental parameters, including the loading rate and ultimate cooling temperature of [...] Read more.

Atomic interferometric gravity gradient measurement enables atomic interference by manipulating atoms with lasers of specific frequencies. Thus, the frequency and phase−locking performance of the laser system exerts a significant impact on key experimental parameters, including the loading rate and ultimate cooling temperature of atomic clouds, the state selection efficiency of Raman transitions, the contrast of atomic interference fringes, and the level of detection noise. As atomic interferometric gravity gradient measurement transitions from static laboratory measurements to mobile field operations, conventional laser frequency and phase−locking methods struggle to meet the demand for rapid re−locking after device movement and cannot achieve timely system recovery in the event of laser unlocks. This work proposes an automatic laser frequency and phase−locking system that can detect real−time deviations in laser frequency and phase and implement rapid and precise corrections. Meanwhile, by utilizing the reference signal source in the optical phase−locked loop, the system realizes laser frequency hopping to satisfy the diverse laser frequency requirements across all stages of atomic interferometric gravity gradient measurement. Full article

(This article belongs to the Special Issue Quantum Optics: Advances and Applications)

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13 pages, 2292 KB

Open AccessArticle

Investigation on Wavelength-Dependent Light Extraction Efficiency of InGaN-Based Micro-LED Structures Using Numerical Simulations

by Chibuzo Onwukaeme and Han-Youl Ryu

Photonics 2026, 13(3), 289; https://doi.org/10.3390/photonics13030289 - 17 Mar 2026

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Abstract

The external quantum efficiency (EQE) of InGaN-based LEDs typically decreases as wavelength shifts from blue to green to red. While this trend has often been attributed to the internal quantum efficiency of InGaN quantum wells (QWs), the influence of light extraction efficiency (LEE) [...] Read more.

The external quantum efficiency (EQE) of InGaN-based LEDs typically decreases as wavelength shifts from blue to green to red. While this trend has often been attributed to the internal quantum efficiency of InGaN quantum wells (QWs), the influence of light extraction efficiency (LEE) on the wavelength-dependent EQE has received less attention. In this study, we numerically investigated the LEE of blue, green, and red InGaN micro-LED structures using finite-difference time-domain simulations, including the dispersion of composite materials. We first optimized the distance between the QW and the Ag reflector for each color, then evaluated the total LEE and the LEE within a 20° collection angle as the micro-LED structure diameter varied. For diameters ranging from 2 to 6 μm, green and red micro-LEDs exhibited average LEE values that were over 10% and 20% higher than those of blue micro-LEDs, respectively. This is attributed to the decreasing refractive index of GaN and increasing reflectance of the Ag reflector as the wavelength increases. Such substantial variations in LEE among blue, green, and red InGaN micro-LEDs highlight the importance of considering wavelength-dependent LEE when interpreting measured EQE results. Full article

(This article belongs to the Special Issue Light Emitting Devices: Science and Applications)

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27 pages, 4520 KB

Open AccessReview

Damping–Positioning Mechanisms in Segmented Mirror Systems: Principle, Integrated Design and Control Methods

by Wuyang Wang, Qichang An and Xiaoxia Wu

Photonics 2026, 13(3), 288; https://doi.org/10.3390/photonics13030288 - 17 Mar 2026

Viewed by 795

Abstract

Segmented telescopes face significant challenges in achieving high segment positioning accuracy under complex disturbances, which directly impact observational sensitivity and resolution. Conventional rigid actuators with limited bandwidth (e.g., Keck ~20 Hz) struggle to maintain control stability. Novel dual-stage actuators combining coarse and fine [...] Read more.

Segmented telescopes face significant challenges in achieving high segment positioning accuracy under complex disturbances, which directly impact observational sensitivity and resolution. Conventional rigid actuators with limited bandwidth (e.g., Keck ~20 Hz) struggle to maintain control stability. Novel dual-stage actuators combining coarse and fine adjustment (e.g., voice coil motors) now achieve <8 nm precision over millimeter-level strokes. Moreover, their higher closed-loop bandwidth (e.g., TMT ~60 Hz) can ensure rapid settling without overshoot and robust suppression of high-frequency disturbances (e.g., pulsating wind and mechanical vibration). In parallel, system-level control strategies have been updated accordingly. Ground-based systems focus on real-time multimodal decoupling, while space-based systems emphasize non-contact vibration isolation and nested multi-loop control to achieve sub-arcsecond pointing stability. This review surveys the design and control strategies of damping–positioning mechanisms for segmented telescopes and discusses the key trade-offs among critical performance metrics, including resolution, stroke, and load capacity. Particular attention is given to the disturbance-sensitivity analysis and active damping techniques (up to ~50% vibration reduction) implemented in the ELT “hard” actuator approach. Future directions include cross-scale collaborative control, smart material applications, and AI-based adaptive parameter optimization, which together provide a technical pathway toward high-precision imaging in next-generation highly segmented telescopes. Full article

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

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17 pages, 1628 KB

Open AccessArticle

Interplay of Aspect Ratio and Emission Dipole Orientation for Light Extraction in Corrugated Red, Green and Blue OLEDs

by Milan Kovačič, Janez Krč and Marko Topič

Photonics 2026, 13(3), 287; https://doi.org/10.3390/photonics13030287 - 17 Mar 2026

Viewed by 615

Abstract

Using advanced optical modelling, we quantify how sinusoidal corrugation and emitter dipole orientation jointly govern light extraction from OLED thin-film stacks into a glass substrate for red, green, and blue emission. Irrespective of emission colour, the corrugation aspect ratio (AR = height/period) [...] Read more.

Using advanced optical modelling, we quantify how sinusoidal corrugation and emitter dipole orientation jointly govern light extraction from OLED thin-film stacks into a glass substrate for red, green, and blue emission. Irrespective of emission colour, the corrugation aspect ratio (AR = height/period) is the dominant geometric parameter controlling extraction, with absolute period and height playing secondary roles, as periods of 600–1000 nm deliver similar gains across all colours. Extraction peaks at AR ≈ 0.2 for predominantly horizontal dipoles, AR ≈ 0.5 for vertical dipoles, and AR ≈ 0.3 for isotropic orientations. For the isotropic case, extraction improves by up to 40%, 34%, and 20% relative to flat red, green, and blue devices, respectively. Absorption analysis attributes the principal gains to suppression of surface-plasmon-polariton losses of vertical dipoles, supported by local dipole reorientation, waveguide disruption, and scattering. Because practical texturing can alter dipole orientation, optimum conditions must be re-evaluated; if orientations follow the sinusoidal profile, an AR of approximately 0.2–0.3 is favoured for isotropic to moderately horizontal orientations, whereas higher ARs benefit strongly vertical orientations. The results provide guidelines for co-optimising corrugation geometry and dipole orientation for high-efficiency OLEDs. Full article

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

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19 pages, 2330 KB

Open AccessArticle

Mercury: Accelerating 3D Parallel Training with an AWGR-WSS-Based All-Optical Reconfigurable Network

by Shi Feng, Jiawei Zhang, Huitao Zhou, Xingde Li and Yuefeng Ji

Photonics 2026, 13(3), 286; https://doi.org/10.3390/photonics13030286 - 16 Mar 2026

Viewed by 543

Abstract

The network traffic of 3D parallel training in large-scale deep learning, featuring burstiness, hot-spots, and periodic large-bandwidth patterns, severely challenges network efficiency, necessitating a high-performance and flexible optical network solution. To address this, this paper proposes Mercury, a hybrid optical network based on [...] Read more.

The network traffic of 3D parallel training in large-scale deep learning, featuring burstiness, hot-spots, and periodic large-bandwidth patterns, severely challenges network efficiency, necessitating a high-performance and flexible optical network solution. To address this, this paper proposes Mercury, a hybrid optical network based on physical optical components: its optical timeslot switching (OTS) subnet uses an arrayed waveguide grating router (AWGR) and tunable lasers for dynamic traffic, while the optical circuit switching (OCS) subnet relies on wavelength selective switches (WSSs) for low-latency high-bandwidth transmission, which is coordinated by selective valiant load balancing (S-VLB) and most efficient path configuration (MEPC) mechanisms. Validated via simulations and FPGA-based testbed experiments, Mercury outperforms the Sirius network by reducing epoch training time (e.g., 179s with five jobs) and relieving OTS congestion through offloading large flows to OCS. This work demonstrates that Mercury provides a flexible, high-performance physical optical solution for 3D parallel training of large-scale deep learning models. Full article

(This article belongs to the Special Issue Neural Networks in Optical Communications and Optical Computing: Implementation, Applications, and Prospects)

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16 pages, 3261 KB

Open AccessArticle

Design Method of a Stepped Integrated Natural Lighting System

by Jing Xu, Shilong Xu, Yuying Han, Xuqing Zheng, Borui Zhang, Sirui Du, Yueyang Ma, Jingcheng Shi, Yue Yu, Shuhang Li, Boran Li and Peng Yin

Photonics 2026, 13(3), 285; https://doi.org/10.3390/photonics13030285 - 16 Mar 2026

Viewed by 357

Abstract

To address the problems of insufficient light energy utilization and light leakage in existing concentrator lighting systems, this paper proposes a novel Stepped Integrated No-Leakage Concentrator Lighting System. This system adopts a design that combines a concentrator module array with a stepped light [...] Read more.

To address the problems of insufficient light energy utilization and light leakage in existing concentrator lighting systems, this paper proposes a novel Stepped Integrated No-Leakage Concentrator Lighting System. This system adopts a design that combines a concentrator module array with a stepped light guide plate. By constructing a stepped integrated concentrator structure and a composite parabolic coupling configuration, the system enables efficient solar energy collection and delivery, significantly improving concentration efficiency and energy utilization. First, based on the principles of geometric optics, theoretical modeling of the concentrator modules and light guide plate was conducted. The relationships among the paraboloid coefficient, step height of the light guide plate, and the number of concentrator modules were analyzed to clarify their influence on the geometric concentration ratio and concentration efficiency of the system. Subsequently, optical performance simulations under varying structural parameters were performed using a joint simulation platform based on SolidWorks Premium 2024 SP5.0 and LightTools(64) 8.6.0 Copyright (c) 1994-2018 Synopsys, Inc. The results indicate that the proposed structure achieves excellent light-guiding performance and high optical efficiency, with a maximum concentration efficiency of 94% and a geometric concentration ratio of 50. On this basis, a physical prototype was fabricated, and experimental testing was carried out. The results validated the accuracy of the simulation, with the system reaching a concentration efficiency of 54.6% at noon, further confirming the feasibility and superior performance of the proposed design. This study demonstrates that the Stepped Integrated No-Leakage Concentrator Lighting System offers significant advantages in enhancing light energy utilization and reducing leakage losses, providing an efficient solution for natural daylighting and interior illumination in green buildings. Full article

(This article belongs to the Special Issue Innovation in Optical Design)

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10 pages, 3337 KB

Open AccessArticle

Study on Side-Pumping and Electro-Optical Q-Switched Laser Performance of a Novel Near-Infrared Laser Crystal Nd:GYSAG

by Jianling Gu, Haiyue Wang, Lei Huang, Qingli Zhang and Guihua Sun

Photonics 2026, 13(3), 284; https://doi.org/10.3390/photonics13030284 - 16 Mar 2026

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Abstract

The Nd:GYSAG crystal enables multi-wavelength near-infrared laser output, with adjustable wavelengths tailored for specific application requirements, making it highly valuable for space-borne water vapor detection. This study reports, for the first time, the side-pumping characteristics and electro-optical Q-switching performance of this crystal. Using [...] Read more.

The Nd:GYSAG crystal enables multi-wavelength near-infrared laser output, with adjustable wavelengths tailored for specific application requirements, making it highly valuable for space-borne water vapor detection. This study reports, for the first time, the side-pumping characteristics and electro-optical Q-switching performance of this crystal. Using Ø3 × 73 mm and Ø4 × 73 mm crystal rods doped with 1.21 at.% Nd:GYSAG (chemical formula Nd_0.033Gd_0.93Y_1.79Sc_0.70Al_4.54O_11.99), 1060.4 nm laser output was achieved under 808 nm laser diode (LD) side-pumping at a repetition rate of 100 Hz and a pump pulse width of 250 μs. The experimental results show that the Ø4 × 73 mm rod had a higher laser threshold but exhibited significantly superior slope efficiency and maximum output power compared to the Ø3 × 73 mm rod. Using a flat–flat resonator, optimal laser performance was obtained with an output coupler transmission of 35%, yielding a slope efficiency of 37.2%. A maximum output energy of 179.4 mJ was achieved at a pump energy of 646 mJ. Thermal lensing effects were compensated using a flat–convex cavity, leading to improved laser performance and beam quality. Electro-optical Q-switching experiments were conducted using a KD*P crystal. A comparison between voltage-applied and voltage-removed Q-switching techniques revealed superior performance for the voltage-applied method. High-performance laser output was realized, achieving a maximum pulse energy of 59.6 mJ, a pulse width of 14.93 ns, and a peak power of 3.99 MW. This study provides an important foundation for the development of near-infrared laser devices based on Nd:GYSAG. Full article

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

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22 pages, 6652 KB

Open AccessArticle

Multi-Objective Optimization of Space Camera Primary Mirror Structure Based on Dynamic Constraint SHAMODE Algorithm

by Jiaheng Tan, Wei Xu, Shuangtong Zhu, Lin Chang and Qiang Yong

Photonics 2026, 13(3), 283; https://doi.org/10.3390/photonics13030283 - 16 Mar 2026

Viewed by 409

Abstract

Aiming at the structural lightweight design of a 700 mm aperture primary mirror for a space camera, a novel success history-based adaptive multi-objective differential evolution algorithm with dynamic constraint handling is proposed to solve the multi-objective optimization problem of simultaneously minimizing mass and [...] Read more.

Aiming at the structural lightweight design of a 700 mm aperture primary mirror for a space camera, a novel success history-based adaptive multi-objective differential evolution algorithm with dynamic constraint handling is proposed to solve the multi-objective optimization problem of simultaneously minimizing mass and compliance under strict constraints for surface error and first-order modal frequency. Firstly, a surrogate model for the mirror was constructed using the Kriging algorithm based on Optimal Latin Hypercube Sampling, establishing a mapping relationship between input design variables and output responses, thereby replacing computationally expensive finite element simulations. Subsequently, a dynamic constraint adjustment mechanism was introduced into the Success History-based Adaptive Multi-Object Differential Evolution algorithm for the surrogate model, dynamically relaxing and tightening constraint violation requirements during iteration. This allows for utilizing promising yet infeasible solutions for rapid convergence while ensuring the feasibility of the final solutions. Comparisons with 13 advanced constrained multi-objective optimization algorithms demonstrate that the proposed algorithm exhibits excellent convergence, diversity, and consistency. Finally, the optimal solution was selected from the Pareto front obtained by the proposed algorithm, and the design variable values were adjusted according to manufacturing constraints to yield the final optimization result, which was then verified by finite element simulation. The simulation results show that the final mirror structure meets all performance constraints, demonstrating the effectiveness and engineering applicability of the proposed algorithm for the structural lightweight design of space camera mirrors. Full article

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20 pages, 21808 KB

Open AccessArticle

Long-Wave Infrared Multispectral Imager for Lunar Remote Sensing: Optical Design and Performance Evaluation

by Haoyang Hu, Jianan Xie, Shiyi Qian, Liyin Yuan and Zhiping He

Photonics 2026, 13(3), 282; https://doi.org/10.3390/photonics13030282 - 15 Mar 2026

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Abstract

High-resolution long-wave infrared imaging is critical for lunar mineralogy. However, it must balance a large FOV, a small F-number, chromatic aberration correction, optical efficiency, and system compactness. We introduce a push-broom multispectral imager employing a collaborative integrated filter array and an off-axis two-mirror [...] Read more.

High-resolution long-wave infrared imaging is critical for lunar mineralogy. However, it must balance a large FOV, a small F-number, chromatic aberration correction, optical efficiency, and system compactness. We introduce a push-broom multispectral imager employing a collaborative integrated filter array and an off-axis two-mirror Gregorian telescope. The system, utilizing an uncooled Vanadium Oxide detector, has an F-number of 1.0, an IFOV of 0.04943 mrad, and a 2.90° × 2.83° FOV that covers eight bands ranging between 7.38 and 14.3 μm. Optical simulation confirms that the modulation transfer function exceeds 0.25 at the Nyquist frequency of 42 lp/mm, with a maximum RMS spot radius of less than 12 μm. The system has remarkable versatility within an operating temperature range of 0 °C to 40 °C. Thermal background radiation analysis, stray light analysis, and detection sensitivity were conducted, which indicated that the system has good compliance with indicators and engineering feasibility. This high-throughput optical design meets the rigorous criteria for lunar remote sensing and provides a reliable device for site evaluation in future manned lunar missions. Full article

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

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15 pages, 7599 KB

Open AccessArticle

Measurement of the Surface Spacing of Optical Components Based on Low-Coherence Four-Quadrant Envelope Detection

by Xiaoqin Shan, Zhigang Han and Rihong Zhu

Photonics 2026, 13(3), 281; https://doi.org/10.3390/photonics13030281 - 15 Mar 2026

Viewed by 510

Abstract

A four-quadrant low-coherence envelope detection method was proposed for measuring the surface spacing of optical components, eliminating the requirement for precise control of the delay line scanning step to generate a π/2 phase shift. The method employs an orthogonal polarization Mach–Zehnder (MZ) fiber [...] Read more.

A four-quadrant low-coherence envelope detection method was proposed for measuring the surface spacing of optical components, eliminating the requirement for precise control of the delay line scanning step to generate a π/2 phase shift. The method employs an orthogonal polarization Mach–Zehnder (MZ) fiber interferometer, illuminated by a broadband superluminescent diode (SLD), and a four-quadrant polarization-resolved detector to simultaneously acquire spatially phase-shifted interference signals carrying surface spacing information. The interference envelope is directly demodulated to extract surface spacing, thereby decoupling measurement accuracy from mechanical stepping constraints. To enable real-time, high-precision calibration of the delay line, two complementary schemes were implemented: wavelength division multiplexing (WDM)-based calibration and dual optical path calibration. Experimental results confirm that the dual-path scheme exhibits weak dependence on scanning velocity and remains stable across a wide speed range. Repeat measurements of the surface spacing of a 1 mm thick sapphire plate yielded a standard deviation (STD) of 1.3 μm. By relaxing the strict π/2 phase shift condition traditionally imposed on scanning step size, this method improves operational efficiency while maintaining measurement reliability—providing a robust and broadly applicable solution for metrology, including lens surface spacing and transparent plate thickness characterization. Full article

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

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16 pages, 4714 KB

Open AccessArticle

Metasurface-Enabled Dual-Channel Optical Image Authentication Based on Polarization Multiplexing

by Yanfeng Su, Biao Zhu, Wenming Chen, Ruijie Xue, Zijing Li, Zhijian Cai, Qibin Feng and Guoqiang Lv

Photonics 2026, 13(3), 280; https://doi.org/10.3390/photonics13030280 - 15 Mar 2026

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Abstract

In this paper, a metasurface-enabled dual-channel optical image authentication based on polarization multiplexing is proposed. During encryption, authentication phases corresponding to dual-channel plaintext images are firstly calculated by using a sparse-constraint-driven authentication-holography (SCDAH) algorithm. Then, target transmission phase and geometric phase of metasurface [...] Read more.

In this paper, a metasurface-enabled dual-channel optical image authentication based on polarization multiplexing is proposed. During encryption, authentication phases corresponding to dual-channel plaintext images are firstly calculated by using a sparse-constraint-driven authentication-holography (SCDAH) algorithm. Then, target transmission phase and geometric phase of metasurface to be designed are obtained accordingly by the composite phase modulation (CPM) principle. Next, the nanopillar-type metasurface unit is performed with parameter scanning to establish the transmission and geometric phase databases. Finally, the structural parameters of each nanopillar are determined on a pixel-by-pixel basis to complete the construction of polarization-multiplexing authentication metasurface (PMAM). During authentication, the PMAM are respectively illuminated by the left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light to obtain pseudo-random images produced by far-field diffraction, and then the nonlinear correlation distribution between diffraction image and corresponding channel plaintext image is calculated, and the final authentication result of each channel is determined based on whether the signal-to-noise ratio of the nonlinear correlation distribution meets the standard. In fact, a new physical-characteristic-driven dual-channel optical image authentication technology is formed, where double identities of the user holding this PMAM can be simultaneously verified, breaking through the rigid constraint of conventional single metasurface-to-single image, meanwhile improving the capacity and efficiency for authentication metasurface from the perspective of physical mechanism. Numerical simulations are performed to demonstrate the feasibility of the proposed method, and the simulation results prove that the proposed method exhibits high feasibility and security as well as strong robustness against cropping attack, showing a promising application potential in the field of identity recognition and authentication. Full article

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