Photonics

13 pages, 1335 KB

Open AccessArticle

Charge-Asymmetric Dissociation of Iodine Bromide in an Intense Femtosecond Laser Field

by Botong Liu and Zhipeng Li

Photonics 2026, 13(2), 160; https://doi.org/10.3390/photonics13020160 - 6 Feb 2026

The mechanism of charge partitioning during Coulomb explosion, especially via charge-asymmetric dissociation (CAD) pathways, remains a key question in strong-field molecular dynamics. We present an experimental and theoretical study of CAD in the heteronuclear diatomic molecule iodine bromide (IBr) driven by 800 nm [...] Read more.

The mechanism of charge partitioning during Coulomb explosion, especially via charge-asymmetric dissociation (CAD) pathways, remains a key question in strong-field molecular dynamics. We present an experimental and theoretical study of CAD in the heteronuclear diatomic molecule iodine bromide (IBr) driven by 800 nm femtosecond laser pulses. Using dc-sliced ion velocity map imaging, we measured the kinetic energy releases of fragment ions I^p+ (p = 1–4) and Br^q+ (q = 1–3), observing both charge-symmetric (CSD) and charge-asymmetric (CAD) dissociation channels. A unified model combining charge-resonance-enhanced ionization (CREI) with a classical over-the-barrier (COB) picture is introduced, which accounts quantitatively for the observed channels. The findings reveal the correlated electron–nuclear dynamics in IBr during Coulomb explosion, advance the understanding of strong-field dissociation in heteronuclear systems, and contribute to the analysis of ultrafast charge transfer in molecules. Full article

(This article belongs to the Special Issue Femtosecond Lasers: Principles, Techniques and Applications)

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16 pages, 1217 KB

Open AccessArticle

A Multi-Scale Edge-Band-Preserving Phase Restoration Method Based on Fringe Projection Phase Profilometry

by Yuyang Yu, Pengfei Feng, Qin Zhang, Lei Qian and Yueqi Si

Photonics 2026, 13(2), 159; https://doi.org/10.3390/photonics13020159 - 6 Feb 2026

Abstract

Phase unwrapping is the decisive factor for achieving dimensional accuracy in phase-shifting profilometry, yet unavoidable phase jumps occur at discontinuities. Existing dual-frequency heterodyne techniques suffer from a narrow measurement range and overly coarse projected fringes due to grating superposition requirements, leading to large [...] Read more.

Phase unwrapping is the decisive factor for achieving dimensional accuracy in phase-shifting profilometry, yet unavoidable phase jumps occur at discontinuities. Existing dual-frequency heterodyne techniques suffer from a narrow measurement range and overly coarse projected fringes due to grating superposition requirements, leading to large errors when scanning objects with hole-like features. To address these issues, this paper proposes an edge-oriented phase-unwrapping error-compensation method based on fringe projection phase profilometry. First, the wrapped phase of the measured object is acquired via phase-shifting profiling. The wrapped phase map is then smoothed at multiple scales using Gaussian filters, and parallel Canny edge detection combined with phase gradient thresholding is applied to comprehensively capture both coarse and fine discontinuities. Morphological closing fills in breakpoints, followed by skeleton thinning and connectivity reconstruction to generate an edge band of defined width. Within this band, edge-preserving smoothing is performed using guided filtering or bilateral filtering, and the result is fused with the original phase through Gaussian weighting based on the distance to the skeleton. Finally, an ordered multi-frequency heterodyne unwrapping restores the absolute phase, maximally preserving true discontinuities while effectively correcting noise and detection errors. Experiments show that this method overcomes edge-induced phase jumps—with jump-error correction rates exceeding 96.7%—exhibits strong noise resilience under various conditions, and achieves measurement precision better than 0.06 mm. Full article

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

16 pages, 5384 KB

Open AccessArticle

In-Pixel Time-to-Digital Converter with 156 ps Accuracy in dToF Image Sensors

by Liying Chen, Bangtian Li and Chuantong Cheng

Photonics 2026, 13(2), 158; https://doi.org/10.3390/photonics13020158 - 6 Feb 2026

Abstract

As the mainstream technology solution for deep imaging LiDAR, dToF measurement has been widely applied in emerging fields such as environmental perception and obstacle recognition, 3D terrain reconstruction, real-time motion capture, and drone obstacle avoidance navigation due to its advantages of high resolution, [...] Read more.

As the mainstream technology solution for deep imaging LiDAR, dToF measurement has been widely applied in emerging fields such as environmental perception and obstacle recognition, 3D terrain reconstruction, real-time motion capture, and drone obstacle avoidance navigation due to its advantages of high resolution, long-range detection capability, and high sensitivity. In order to adapt to functional applications in different scenarios, the resolution of TDC needs to be adjustable and can work normally in different environments. In view of this, this article studies the pixel array and TDC circuit in the chip and locks a voltage-controlled ring oscillator (VCRO) with the same structure as the pixel to a fixed frequency through a PLL structure. Then copy the control voltage of the locked VCRO to the control terminal of the TDC in each pixel. In an ideal situation, this control voltage can make the oscillation frequency of VCRO within the pixel consistent with the locking frequency of VCRO within the PLL, and insensitive to changes in PVT. This study developed a module expandable 16 × 16-pixel array dToF sensor chip based on TDC architecture using CMOS technology. Finally, six configurable 16 × 16-pixel subarrays were integrated and constructed into a 32 × 48 large-scale dToF sensor chip through modular splicing. The top-level layout design was completed using SMIC 180 nm technology, with a layout area of 5285 µm × 3669 µm. Post-simulation verification showed that, under the testing conditions of a 400 MHz system clock and a 33.3 kHz frame rate, the dToF chip system performance indicators were: time measurement resolution of 156 ps, DNL < 1 LSB, INL < 0.85 LSB, and absolute ranging accuracy better than 2.5 cm. Full article

(This article belongs to the Special Issue Laser as a Detection: From Spectral Imaging to LiDAR for Remote Sensing Applications (2nd Edition))

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15 pages, 3804 KB

Open AccessArticle

Design and Machine Learning Optimization of a Dynamically Tunable VO₂-Integrated Broadband Metamaterial Absorber for THz

by Nguyen Phuc Vinh, Ha Duy Toan, Bui Xuan Khuyen, Dam Quang Tuan, Nguyen Hai Anh, Nguyen Phon Hai, Bui Son Tung, Liyang Yue, Vu Dinh Lam, Liangyao Chen and YoungPak Lee

Photonics 2026, 13(2), 157; https://doi.org/10.3390/photonics13020157 - 6 Feb 2026

Abstract

This paper introduces a vanadium dioxide-integrated broadband metamaterial absorber designed for the terahertz frequency range. The simulation results for the proposed structure demonstrate a wide 90% absorption bandwidth of 8.23 THz, corresponding to a fractional bandwidth of 89.5%. By leveraging the phase-transition properties [...] Read more.

This paper introduces a vanadium dioxide-integrated broadband metamaterial absorber designed for the terahertz frequency range. The simulation results for the proposed structure demonstrate a wide 90% absorption bandwidth of 8.23 THz, corresponding to a fractional bandwidth of 89.5%. By leveraging the phase-transition properties of VO₂, the absorber demonstrated dynamic adjustability by modulating the absorption from 3% to 98.74%. The absorption mechanism was analyzed through the impedance matching theory and electromagnetic field distributions, confirming the role of magnetic resonance and interference. Furthermore, machine learning algorithms, specifically Linear Regression, Support Vector Regression, and Random Forest (RF), were applied to accelerate the design process and optimize the structural parameters. Among these, the RF model demonstrated superior prediction accuracy. The machine learning-assisted optimization successfully extended the effective absorption bandwidth to 9 THz, representing an improvement by 9.4% compared to the traditional optimization methods. These results validate the efficacy of combining electromagnetic simulation with data-driven techniques for advanced metamaterial design. Full article

(This article belongs to the Special Issue Photonic Metasurfaces: Advances and Applications)

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19 pages, 12003 KB

Open AccessArticle

Low Latency and Multi-Target Camera-Based Safety System for Optical Wireless Power Transmission

by Chen Zuo and Tomoyuki Miyamoto

Photonics 2026, 13(2), 156; https://doi.org/10.3390/photonics13020156 - 6 Feb 2026

Abstract

Optical Wireless Power Transmission (OWPT) holds a significant position for enabling cable-free energy delivery in long-distance, high-energy, and mobile scenarios. However, ensuring human and equipment safety under high-power laser exposure remains a critical challenge. This study reports a vision-based OWPT safety system that [...] Read more.

Optical Wireless Power Transmission (OWPT) holds a significant position for enabling cable-free energy delivery in long-distance, high-energy, and mobile scenarios. However, ensuring human and equipment safety under high-power laser exposure remains a critical challenge. This study reports a vision-based OWPT safety system that implements the principle of automatic emission control (AEC)—dynamically modulating laser emission in real time to prevent hazardous exposure. While camera-based OWPT safety systems have been proposed in the concept, there are extremely limited working implementations to date. Moreover, existing systems struggle with response speed and single-object assumptions. To address these gaps, this research presents a low-latency safety architecture based on a customized deep learning-based object detection framework, a dedicated OWPT dataset, and a multi-threaded control stack. The research also introduces a real-time risk factor (RF) metric that evaluates proximity and velocity for each detected intrusion object (IO), enabling dynamic prioritization among multiple threats. The system achieves a minimum response latency of 14 ms (average 29 ms) and maintains reliable performance in complex multi-object scenarios. This work establishes a new benchmark for OWPT safety system and contributes a scalable reference for future development. Full article

(This article belongs to the Special Issue Latest Papers Related to OWPT 2026–2027 on the Topics of Devices, Components, and Systems)

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15 pages, 2423 KB

Open AccessArticle

Infrared Image Super Resolution Method Based on Stochastic Degradation Modeling

by Lihong Yang, Kai Hu, Hang Ge, Zhi Zeng and Shurui Ge

Photonics 2026, 13(2), 155; https://doi.org/10.3390/photonics13020155 - 5 Feb 2026

Abstract

Infrared images hold significant application value in fields such as military reconnaissance, security surveillance, and medical diagnosis. However, issues like low resolution, high noise, and complex degradation characteristics severely hinder their practical application effectiveness. This paper introduces an infrared super-resolution reconstruction algorithm based [...] Read more.

Infrared images hold significant application value in fields such as military reconnaissance, security surveillance, and medical diagnosis. However, issues like low resolution, high noise, and complex degradation characteristics severely hinder their practical application effectiveness. This paper introduces an infrared super-resolution reconstruction algorithm based on a random degradation model and Generative Adversarial Networks (GANs), addressing the diversity of infrared image degradation processes. The primary contribution lies in explicitly modeling key degradation parameters of infrared images (such as blur kernel and noise distribution) using a random degradation model, generating diverse low-resolution to high-resolution image pairs, and significantly enhancing the model’s generalization ability for complex degradations. Experiments on the Airo infrared dataset and a self-built infrared dataset demonstrate that when the resolution is increased by a factor of 2, 4, and 8, the 4× resolution reconstructed images exhibit notable advantages in terms of texture detail and noise suppression. Especially in 4× super-resolution reconstruction, compared to three typical deep learning algorithms, our algorithm improves the Peak Signal-to-Noise Ratio (PSNR) by 3.046 dB, 1.8489 dB, and 0.2108 dB, respectively, and the Structural Similarity Index (SSIM) by 0.0387 (4.76%), 0.0287 (3.48%), and 0.0131 (1.56%), respectively, with perceptual similarity decreasing by 0.2465, 0.13344, and 0.0514 (lower values indicate better perceptual quality). Subjective visual assessments further validate the algorithm’s significant advantages in noise reduction and weak texture restoration. This study proposes an infrared image super-resolution reconstruction method based on random degradation modeling, which holds significant theoretical and practical value in complex infrared degradation scenarios. Full article

(This article belongs to the Special Issue Next-Generation Optical Transmission Systems: Breakthroughs, Technologies, and Emerging Frontiers)

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14 pages, 5010 KB

Open AccessArticle

Tunable Broadband Terahertz Absorber Based on Triangular-Patterned Graphene with Sandwich Configuration

by Junqiang Zhang, Huijuan Niu, Mengyu Dong, Can Gu, Xiying Huang, Limei Qi, Jinhao Guo, Wenzheng Jia and Chenglin Bai

Photonics 2026, 13(2), 154; https://doi.org/10.3390/photonics13020154 - 4 Feb 2026

Abstract

A terahertz (THz) metamaterial broadband perfect absorber featuring a simple sandwich structure with a top layer composed of a triangular-patterned graphene film is presented. The graphene pattern is designed to exhibit a pronounced surface plasmon resonance (SPR) effect, which locally enhances the internal [...] Read more.

A terahertz (THz) metamaterial broadband perfect absorber featuring a simple sandwich structure with a top layer composed of a triangular-patterned graphene film is presented. The graphene pattern is designed to exhibit a pronounced surface plasmon resonance (SPR) effect, which locally enhances the internal electric field’s intensity, leading to broadband absorption of 2.8 THz above 90% and a peak absorption rate of 99.99% at 6.05 THz. The broadband tunability of the absorber was further investigated by modulating the Fermi level of the graphene, demonstrating an adjustment in the absorption rate from 6.18% to 99.99% via an external voltage. This study shows that the absorber demonstrates excellent angular tolerance by maintaining an absorption rate above 90% across incident angles ranging from 0° to 50°. The absorber’s broadband perfect absorption properties were examined using relative impedance theory. Additionally, to reveal the fundamental physics behind this absorption, detailed analyses of the electric field distributions were carried out. Consequently, the origin of the absorption peaks is elucidated. This absorber enables noise suppression for optoelectronic integration and THz communications. Full article

(This article belongs to the Special Issue Advanced Photodetectors for Photonic and Hybrid Photonic–Electronic Systems and Applications)

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12 pages, 400 KB

Open AccessArticle

PHYSICAL SPACE AND ABSTRACT SPACES—Klein Space, Poincaré Space and the Stereographic Projection

by Tiberiu Tudor

Photonics 2026, 13(2), 153; https://doi.org/10.3390/photonics13020153 - 4 Feb 2026

Abstract

In this paper we compare the rotation of a rigid body in the real three-dimensional Euclidean space E³ and its representation in the complex plane (Klein space), on one hand, with the transformation of polarization states of light (SOPs) by the phase-shifters [...] Read more.

In this paper we compare the rotation of a rigid body in the real three-dimensional Euclidean space E³ and its representation in the complex plane (Klein space), on one hand, with the transformation of polarization states of light (SOPs) by the phase-shifters figured in the complex plane and on the Poincaré sphere, on the other hand. Both the Klein space, in classical mechanics, and the Poincaré sphere, in polarization theory, are abstract spaces, whose construction is based on the classical stereographical projection between Riemann sphere and the simple complex plane C¹. They are classical abstract spaces, even if they have been largely used for representing quantum spinorial physical realities too. At the interface of classical/quantum physics persist some misaperceptions about what is intrinsically of quantum origin and nature, and what is imported from the classical domain. In this context we examine some misunderstandings that take place in the field of these spaces. I shall focus on the double angle relationship between the rotation of representative points of the SOPs on the Poincaré sphere with respect to the corresponding rotations of the azimuthal and ellipticity angles of the “form of the SOPs”, at a transformation of state given by a phase shifter. This is a classical result, that is transferred on the sphere from the complex plane, on the basis of the stereographic bijective connection between the points on the sphere and those in the complex plane. In any textbook of quantum mechanics “the double angle/half angle problem” is presented as a pure quantum spinorial one, avoiding its classical face and origin. A quantum spinorial approach, obviously, recovers the classical results, together with the specific spinorial ones, but with regards to the double angle/half angle issue it is superfluous. We shall also briefly examine the classical and quantum spinorial content of what we know today under the global name of Pauli spin matrices. Often in papers or textbooks of physics the results are presented in a mélange in which it is difficult to establish from which point on one needs to appeal to spinorial or quantum aspects. Full article

17 pages, 9006 KB

Open AccessArticle

A Transmissive Metasurface Producing Wideband Higher-Order Vortex Modes to Increase the the Information-Carrying Capacity of Wireless Systems

by Muhammad Ishfaq, Weiqiang Tang, Abdul Aziz, Hafiz Muhammad Bilal, Zahid Iqbal and Md Aurongjeb

Photonics 2026, 13(2), 152; https://doi.org/10.3390/photonics13020152 - 4 Feb 2026

Abstract

High-order, broadband OAM-vortex beams have great potential to increase the information-carrying capacity of wireless systems, but their practical application is constrained by issues with low gain, limited bandwidth, and low mode purity in higher-order modes. To address these requirements, in this paper, we [...] Read more.

High-order, broadband OAM-vortex beams have great potential to increase the information-carrying capacity of wireless systems, but their practical application is constrained by issues with low gain, limited bandwidth, and low mode purity in higher-order modes. To address these requirements, in this paper, we propose a symmetric transmit unit cell that achieves full 360-degree phase coverage with acceptable transmission loss and a uniform configuration suitable for dual-polarized applications, which consists of four conductive layers interleaved with substrate layers. Experimental testing of higher-order modes on the manufactured transmissive prototype verifies broadband vortex-beam formation, which is consistent with the simulation results. Across the 26.5 to 40.5 GHz frequency span, the proposed design demonstrates a consistently high OAM-vortex mode purity exceeding 86% and covering 46.6% of the OAM bandwidth. It is also observed that the fabricated prototype achieves a peak realized gain of 21.7 dBi for the +2 mode, resulting in an aperture efficiency of 13.6%. With the implementation of the proposed transmitarray prototype, future wireless systems can attain significantly improved information-carrying capacity. Full article

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19 pages, 3560 KB

Open AccessReview

Perovskite Quantum Dots-Based Blue Light-Emitting Diodes: Advantages, Strategies, and Prospects

by Yuxian Shi, Jiayi Yang and Zhixuan Lu

Photonics 2026, 13(2), 151; https://doi.org/10.3390/photonics13020151 - 4 Feb 2026

Abstract

Perovskite quantum dots (PeQDs) are highly promising luminescent materials for next-generation displays owing to their excellent optoelectronic properties, such as narrow emission linewidth, high photoluminescence quantum yield, tunable bandgap, and solution processability. Blue-emitting PeQDs are particularly crucial for realizing full-color displays with high [...] Read more.

Perovskite quantum dots (PeQDs) are highly promising luminescent materials for next-generation displays owing to their excellent optoelectronic properties, such as narrow emission linewidth, high photoluminescence quantum yield, tunable bandgap, and solution processability. Blue-emitting PeQDs are particularly crucial for realizing full-color displays with high color purity. This review systematically summarizes synthesis strategies for blue-emitting PeQDs and their recent advances in perovskite light-emitting diodes (PeLEDs). We first introduce the working principles of PeLEDs and detail three primary approaches to achieving blue emission through mixed-halide engineering, quasi-two-dimensional structure construction via A-site cation substitution, and quantum size effect utilization. We then review mainstream synthesis methods, including hot-injection, ligand-assisted reprecipitation, and post-synthetic anion exchange, discussing their respective advantages and limitations. Key device optimization strategies are also outlined, covering surface passivation, core–shell structures, interface engineering, and light outcoupling enhancement. Finally, we address current challenges in material stability, efficiency roll-off, and charge imbalance and provide an overview of future research directions for high-performance blue PeLEDs based on PeQDs. Full article

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10 pages, 3088 KB

Open AccessArticle

256.5-W Chirped Amplitude-Modulated Fiber Laser for Single-Photon Differential Ranging

by Wenjuan Wu, Shuzhen Zou, Haijuan Yu, Chaojian He and Song Yang

Photonics 2026, 13(2), 150; https://doi.org/10.3390/photonics13020150 - 3 Feb 2026

Abstract

High-power chirped amplitude-modulated (CAM) lasers serve as essential sources for the promising high-precision single-photon differential ranging technique. However, the development of high-power CAM lasers is fundamentally constrained by the stimulated Brillouin scattering (SBS) effect and the degradation of the CAM waveform during amplification. [...] Read more.

High-power chirped amplitude-modulated (CAM) lasers serve as essential sources for the promising high-precision single-photon differential ranging technique. However, the development of high-power CAM lasers is fundamentally constrained by the stimulated Brillouin scattering (SBS) effect and the degradation of the CAM waveform during amplification. In this work, we propose a high-power CAM fiber laser system based on a dual linear frequency modulation (dual-LFM) architecture, wherein LFM signals are applied simultaneously to both the phase modulator and the intensity modulator. The experimental results demonstrate effective suppression of SBS, which enables an approximately eightfold enhancement in average output power—from 32.1 W to 256.5 W—while maintaining well-preserved CAM waveforms and a near-diffraction-limited beam quality (

M^{2}

= 1.073). To the best of our knowledge, this represents the highest output power reported to date for CAM lasers. Significantly, after amplification, the system exhibits a mere ~2% reduction in average modulation depth, attaining a final modulation depth of over 82%, a total harmonic distortion below 7%, and excellent CAM linearity across the 100 MHz to 1 GHz modulation frequency range. Furthermore, the proposed laser system enables single-photon differential ranging with millimeter-level precision over distances exceeding 100 km. This work represents a significant advancement in CAM laser power scaling, with potential applications in advanced precision ranging, quantum technology, and related emerging fields. Full article

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

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12 pages, 13187 KB

Open AccessArticle

Electro-Thermo-Optical Modulation of Silicon Nitride Integrated Photonic Filters for Analog Applications

by Clement Deleau, Han Cheng Seat, Olivier Bernal and Frederic Surre

Photonics 2026, 13(2), 149; https://doi.org/10.3390/photonics13020149 - 3 Feb 2026

Abstract

High-quality spectral filters with versatile tuning mechanisms are essential for applications in photonic integrated circuits, including sensing, laser stabilization, and spectral signal processing. We report the implementation of thermo-optic (TO) and electro-optic (EO) spectral tuning in silicon nitride Mach–Zehnder interferometers (MZIs) and micro-ring [...] Read more.

High-quality spectral filters with versatile tuning mechanisms are essential for applications in photonic integrated circuits, including sensing, laser stabilization, and spectral signal processing. We report the implementation of thermo-optic (TO) and electro-optic (EO) spectral tuning in silicon nitride Mach–Zehnder interferometers (MZIs) and micro-ring resonators (MRRs) by functionalizing the devices with a PMMA:JRD1 polymer cladding and integrating titanium tracks as heaters and electrodes. The fabricated MZIs and MRRs exhibit narrow linewidths of 25–30 pm and achieved TO tuning efficiencies of 1.7 and 13 pm/mW and EO tuning efficiencies of 0.33 and 1.6 pm/V, respectively. Closed-loop regulation using TO and EO effects enables stable half-fringe locking under environmental perturbations. This simple, broadly compatible hybrid platform demonstrates a practical approach to dual-mode spectral tuning and modulation in integrated photonic filters, providing a flexible route toward compact, reconfigurable, and environmentally robust photonic circuits. Full article

(This article belongs to the Special Issue Photonic Integrated Circuits: Emerging Spectra and Technologies)

11 pages, 3340 KB

Open AccessArticle

An Adaptive Optical Limiter Based on a VO₂/GaN Thin Film for Infrared Lasers

by Yafan Li, Changqi Zhou, Yunsong Feng, Jinglin Zhu, Wei Jin, Siyu Wang, Shanguang Zhao, Jiahao Huang, Yuanxin Shang and Congwen Zou

Photonics 2026, 13(2), 148; https://doi.org/10.3390/photonics13020148 - 3 Feb 2026

Abstract

Vanadium dioxide (VO₂) is a highly promising material for infrared laser protection due to the pronounced optical switching effect during its metal–insulator transition (MIT). However, due to the relatively high MIT temperature of VO₂ and the low transmittance contrast before [...] Read more.

Vanadium dioxide (VO₂) is a highly promising material for infrared laser protection due to the pronounced optical switching effect during its metal–insulator transition (MIT). However, due to the relatively high MIT temperature of VO₂ and the low transmittance contrast before and after the MIT, practical applications face challenges in modulation depth and response time. In this study, we address these issues using a wafer-scale VO₂/GaN/Al₂O₃ heterostructure fabricated by oxide molecular beam epitaxy. The conductive GaN interlayer enables local Joule heating of the VO₂ film, permitting direct control of the MIT via an external bias with a threshold of 4.7 V. This structure exhibits a substantial resistance change of four orders of magnitude and enables adaptive limiting of a 3.7 μm laser, reducing transmittance from 60% to 10%. Our work demonstrates a practical, wafer-scale laser-protection device and introduces a pre-excitation strategy via external biasing to enhance response performance. Full article

(This article belongs to the Special Issue Emerging Trends in Photodetector Technologies)

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17 pages, 1345 KB

Open AccessArticle

Design and Numerical Analysis of an Ultra-Sensitive π-Configuration Fibre Optic-Based SPR Sensor: Dual Plasmonic Enhancement for Low-Refractive-Index Biomolecular Detection

by John Ehiabhili, Radhakrishna Prabhu and Somasundar Kannan

Photonics 2026, 13(2), 147; https://doi.org/10.3390/photonics13020147 - 3 Feb 2026

Abstract

Surface plasmon resonance (SPR)-based optical fibre sensors have transformed label-free biosensing; however, single-interface evanescent field interactions continue to limit their sensitivity. This study presents a novel π-configuration optical fibre-based surface plasmon resonance sensor that greatly increases sensitivity by enabling dual plasmonic excitation on [...] Read more.

Surface plasmon resonance (SPR)-based optical fibre sensors have transformed label-free biosensing; however, single-interface evanescent field interactions continue to limit their sensitivity. This study presents a novel π-configuration optical fibre-based surface plasmon resonance sensor that greatly increases sensitivity by enabling dual plasmonic excitation on two symmetrically polished surfaces coated with optimized metallic thin films (Ag, Au, or Cu). We show, using finite element method simulations in COMSOL Multiphysics v6.3, that the π-configuration increases the interaction volume between the analyte and guided light, resulting in an enhanced sensitivity of 3300 nm/RIU for silver at refractive index (RI) 1.37–1.38, which is a 120% improvement over traditional D-shaped sensors (1500 nm/RIU). The maximum field norm for the π-configuration sensor is approximately 1.4 times greater than the maximum observed for the D-shaped SPR sensor at an analyte RI of 1.38. The sensor’s performance is evaluated using full-width half-maximum, wavelength sensitivity, and wavelength interrogation metrics. For the π-configuration sensor at an analyte RI of 1.38, the values of the FWHM, figure of merit, detection accuracy, and confinement loss were 36 nm, 94.29 RIU⁻¹, 0.94, and 38.5 dB/cm, respectively. The results obtained are purely simulated using COMSOL. With the support of electric field confinement analysis, a thorough theoretical framework describes the crucial coupling regime that causes ultra-high sensitivity at low RI. This design provides new opportunities for environmental monitoring, low-abundance biomarker screening, and early-stage virus detection, where it is necessary to resolve minute RI changes with high precision. Full article

(This article belongs to the Special Issue Science and Applications of Optical Fiber Sensors: Recent Advances and Future Trends)

10 pages, 1548 KB

Open AccessCommunication

Deep-Subwavelength Negative Refraction of Hyperbolic Plasmon Polariton at Visible Frequencies

by Shuxin Qi, Xuanbin Chen, Haoran Lv, Yuqi Wang, Jihong Zhu, Jiadian Yan and Qing Zhang

Photonics 2026, 13(2), 146; https://doi.org/10.3390/photonics13020146 - 3 Feb 2026

Abstract

Negative refraction of nanolight (e.g., polaritons, hybrid light, and matter excitation) provides a promising building block for nanophotonics, as it paves the way for developing cutting-edge nanoscale applications, such as super-resolution and subwavelength imaging. In the visible regime, negative refraction of surface plasmon [...] Read more.

Negative refraction of nanolight (e.g., polaritons, hybrid light, and matter excitation) provides a promising building block for nanophotonics, as it paves the way for developing cutting-edge nanoscale applications, such as super-resolution and subwavelength imaging. In the visible regime, negative refraction of surface plasmon polaritons has been extensively studied in conventional plasmonic and metamaterial systems; however, the inherent metallic losses remain a challenge that hinders their practical applications. Herein, we demonstrate negative refraction of low-loss and highly confined hyperbolic plasmon polaritons (HPPs) in a lateral heterojunction of a natural hyperbolic van der Waals material, molybdenum dioxide chloride (MoOCl₂). Owing to the exotic and ray-like propagating properties of HPPs, the negative refraction-inspired superlens can easily reach into the deep subwavelength scale, with spatial confinement of 800 nm near-infrared light wavelengths to below 150 nm focal spots. By elaborately adjusting the orientation directions of two-sided MoOCl₂, the mirror-symmetric superlensing effect can be tilted, and therefore, the focal spots are tuned and steered to deviate from the vertical interfacial lines. Our results applying the concepts of in-plane negative refraction with vdW materials achieve deep subwavelength light confinement and manipulation, offering new possibilities for constructing efficient and compact nanophotonic and opto-electronic devices. Full article

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15 pages, 1176 KB

Open AccessArticle

Optical Multi-Frequency Discrimination and Phase Identification System Based on On-Chip Dual MZM

by Xiang Li, Hanyu Wang, Xiang Zheng, Mingxuan Li, Jianguo Liu and Zeping Zhao

Photonics 2026, 13(2), 145; https://doi.org/10.3390/photonics13020145 - 2 Feb 2026

Abstract

A photonic frequency discrimination and phase identification system based on an on-chip dual Mach–Zehnder modulator (MZM) is proposed. By utilizing the power cancellation (PCD) condition, the system achieves high-precision frequency discrimination and phase identification of multi-frequency radio frequency (RF) signals. The system adopts [...] Read more.

A photonic frequency discrimination and phase identification system based on an on-chip dual Mach–Zehnder modulator (MZM) is proposed. By utilizing the power cancellation (PCD) condition, the system achieves high-precision frequency discrimination and phase identification of multi-frequency radio frequency (RF) signals. The system adopts an on-chip dual-MZM architecture, effectively reducing phase interference in signal transmission caused by environmental factors. This is achieved through precise bias control and the adjustment of the local oscillator (LO) signal’s optical path delay using a tunable optical delay line (TODL), ensuring that the dual MZM operates in the phase inversion condition. When the LO frequency matches that of an RF signal, a significant power attenuation is observed at the system output. The phase of the RF signal is extracted from the corresponding PCD. Experimental results demonstrate that the system achieves a bandwidth of 30 GHz, a frequency resolution of 700 kHz, and a frequency resolution error of less than 498 kHz, with a phase identification range from 0° to 65°. With high integration, the system demonstrates excellent accuracy in multi-frequency signal measurement and phase identification, offering a reliable solution for complex RF scenarios. Full article

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

17 pages, 3661 KB

Open AccessArticle

Wavefront Prediction for Adaptive Optics Without Wavefront Sensing Based on EfficientNetV2-S

by Zhiguang Zhang, Zelu Huang, Jiawei Wu, Zhaojun Yan, Xin Li, Chang Liu and Huizhen Yang

Photonics 2026, 13(2), 144; https://doi.org/10.3390/photonics13020144 - 2 Feb 2026

Abstract

Adaptive optics (AO) aims to counteract wavefront distortions caused by atmospheric turbulence and inherent system errors. Aberration recovery accuracy and computational speed play crucial roles in its correction capability. To address the issues of slow wavefront aberration detection speed and low measurement accuracy [...] Read more.

Adaptive optics (AO) aims to counteract wavefront distortions caused by atmospheric turbulence and inherent system errors. Aberration recovery accuracy and computational speed play crucial roles in its correction capability. To address the issues of slow wavefront aberration detection speed and low measurement accuracy in current wavefront sensorless adaptive optics, this paper proposes a wavefront correction method based on the EfficientNetV2-S model. The method utilizes paired focal plane and defocused plane intensity images to directly extract intensity features and reconstruct phase information in a non-iterative manner. This approach enables the direct prediction of wavefront Zernike coefficients from the measured intensity images, specifically for orders 3 to 35, significantly enhancing the real-time correction capability of the AO system. Simulation results show that the root mean square error (RMSE) of the predicted Zernike coefficients for D/r₀ values of 5, 10, and 15 are 0.038λ, 0.071λ, and 0.111λ, respectively, outperforming conventional convolutional neural network (CNN), ResNet50/101 and ConvNeXt-T models. The experimental results demonstrate that the EfficientNetV2-S model maintains good wavefront reconstruction and prediction capabilities at D/r₀ = 5 and 10, highlighting its high precision and robust wavefront prediction ability. Compared to traditional iterative algorithms, the proposed method offers advantages such as high precision, fast computation, no need for iteration, and avoidance of local minima in processing wavefront aberrations. Full article

(This article belongs to the Special Issue Adaptive Optics: Recent Technological Breakthroughs and Applications)

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29 pages, 8631 KB

Open AccessArticle

From PSNR to Frequency Evidence: Evaluating Super-Resolution Reliability on Low-SNR Fluorescence Channels

by Haoxuan Huang and Hasan Abbas

Photonics 2026, 13(2), 143; https://doi.org/10.3390/photonics13020143 - 31 Jan 2026

Abstract

Existing super-resolution evaluation systems for fluorescence microscopy images struggle to effectively detect potential artifacts in weak signal reconstruction. This study aims to establish a multi-dimensional evaluation framework that integrates frequency-domain evidence to verify the reliability of super-resolution techniques under low signal-to-noise ratio (SNR) [...] Read more.

Existing super-resolution evaluation systems for fluorescence microscopy images struggle to effectively detect potential artifacts in weak signal reconstruction. This study aims to establish a multi-dimensional evaluation framework that integrates frequency-domain evidence to verify the reliability of super-resolution techniques under low signal-to-noise ratio (SNR) conditions. All ground-truth (HR) images used in this study are experimentally acquired fluorescence microscopy data; the corresponding low-quality inputs are simulated from HR via controlled degradations (e.g., bicubic downsampling and frequency-truncation-based degradation) to enable paired quantitative evaluation. We designed a hierarchical comparative experiment to systematically evaluate the performance differences of CNN (SRCNN/FSRCNN), GAN (Real-ESRGAN), and Transformer (SwinIR) architectures on nucleus and whole-cell structure datasets. This study reveals a significant decoupling between “visual sharpness” and “signal fidelity”: while Real-ESRGAN can generate highly impactful high-frequency textures, its checkerboard effect in the spectrum and random residuals in the error map expose serious “illusion” risks, making it unsuitable for precise quantitative analysis. All ground-truth (HR) images used in this study are experimentally acquired fluorescence microscopy data; the corresponding low-quality inputs are simulated from HR via controlled degradations (e.g., bicubic downsampling and frequency-truncation-based degradation) to enable paired quantitative evaluation. Full article

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

16 pages, 5134 KB

Open AccessArticle

Development of a Compact Laser Collimating and Beam-Expanding Telescope for an Integrated ⁸⁷Rb Atomic Fountain Clock

by Fan Liu, Hui Zhang, Yang Bai, Jun Ruan, Shaojie Yang and Shougang Zhang

Photonics 2026, 13(2), 142; https://doi.org/10.3390/photonics13020142 - 31 Jan 2026

Abstract

In the rubidium-87 atomic fountain clock, the laser collimating and beam-expanding telescope plays a key role in atomic cooling and manipulation, as well as in realizing the cold-atom fountain. To address the bulkiness of conventional laser collimating and beam-expanding telescopes, which limits system [...] Read more.

In the rubidium-87 atomic fountain clock, the laser collimating and beam-expanding telescope plays a key role in atomic cooling and manipulation, as well as in realizing the cold-atom fountain. To address the bulkiness of conventional laser collimating and beam-expanding telescopes, which limits system integration and miniaturization, we design and implement a compact laser collimating and beam-expanding telescope. The design employs a Galilean beam-expanding optical path to shorten the optical path length. Combined with optical modeling and optimization, this approach reduces the mechanical length of the telescope by approximately 50%. We present the mechanical structure of a five-degree-of-freedom (5-DOF) adjustment mechanism for the light source and the associated optical elements and specify the corresponding tolerance ranges to ensure their precise alignment and mounting. Based on this 5-DOF adjustment mechanism, we further propose a method for tuning the output beam characteristics, enabling precise and reproducible control of the emitted beam. The experimental results demonstrate that, after adjustment, the divergence angle of the output beam is better than 0.25 mrad, the coaxiality is better than 0.3 mrad, the centroid offset relative to the mechanical axis is less than 0.1 mm, and the output beam diameter is approximately 35 mm. Furthermore, long-term monitoring over 45 days verified the system’s robustness, maintaining fractional power fluctuations within ±1.2% without manual realignment. Compared with the original telescope, all of these beam characteristics are significantly improved. The proposed telescope therefore has broad application prospects in integrated atomic fountain clocks, atomic gravimeters, and cold-atom interferometric gyroscopes. Full article

(This article belongs to the Special Issue Progress in Ultra-Stable Laser Source and Future Prospects)

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