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A Two-Point Propagation Field of a Single Photon: A Way to X-Ray Picometer Displacement Detection and Nanometer Resolution 3D X-Ray Micro-Tomography -
X-UV Radiative Processes in Structurally Active Media -
Algebraic Absorption in Non-Hermitian Photonic Lattices -
Fiber Bragg Grating Accelerometers: A Review from Single-Axis to Multi-Dimensional Vector Sensing
Journal Description
Photonics
Photonics
is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
- Journal Rank: CiteScore - Q2 (Instrumentation)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 13.9 days after submission; acceptance to publication is undertaken in 2.6 days (median values for papers published in this journal in the first half of 2026).
- Recognition of Reviewers: Reviewers whose reports are timely and of high quality receive an APC discount voucher for a future publication in an MDPI journal. Become a reviewer.
- Companion journals for Photonics include: Lights, Lasers and Optoelectronics.
- Journal Cluster of Atomic, Molecular, and Optical (AMO) Physics: Entropy, Photonics, Atoms, Lights, Optics, Physics and Quantum Beam Science.
Impact Factor:
2.1 (2025);
5-Year Impact Factor:
2.1 (2025)
Latest Articles
Slime-Mould-Inspired Resilient Topology Construction Algorithm for UVC/RF Heterogeneous UAV Swarms
Photonics 2026, 13(9), 892; https://doi.org/10.3390/photonics13090892 (registering DOI) - 20 Sep 2026
Abstract
Addressing the demand for highly reliable communication in unmanned aerial vehicle (UAV) swarms operating in extreme environments, this paper proposes a slime mold-inspired resilient topology construction algorithm for UVC/RF heterogeneous UAV networks, termed UVC-SMA. To overcome the limitations of conventional bio-inspired algorithms in
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Addressing the demand for highly reliable communication in unmanned aerial vehicle (UAV) swarms operating in extreme environments, this paper proposes a slime mold-inspired resilient topology construction algorithm for UVC/RF heterogeneous UAV networks, termed UVC-SMA. To overcome the limitations of conventional bio-inspired algorithms in UVC/RF heterogeneous network scenarios—including insufficient heterogeneous modeling, weak dynamic adaptability, long passive repair latency, and inadequate single-path reliability—the proposed algorithm integrates three core mechanisms. First, it constructs an energy-aware joint cost model for heterogeneous links and uses an exponential energy penalty factor to suppress energy hotspots in the network. Second, it designs a network state-driven parameter adaptation mechanism to dynamically balance the capabilities of global exploration and local exploitation. Third, it establishes an active key node protection framework with a hybrid degree-betweenness weighting, which shifts resilience optimization from post-failure reconfiguration to proactive pre-failure reinforcement and develops a K-shortest multipath routing method (K = 3) based on the reciprocal of conductivity to achieve millisecond-level path switching. The simulation results show that compared with the traditional slime mould algorithm (SMA), the UVC-SMA improves network robustness from 0.75 to 1.00, increases average residual energy by 19.5%, and reduces average node degree by 16.8%. The algorithm adopts a distributed architecture with a single iteration complexity of O(n2), which theoretically supports low-cost on-board deployment and is applicable to UAV swarm communication in highly dynamic and highly adversarial extreme environments. The reported robustness improvement from 0.75 to 1.00 is obtained under the baseline 50-node simulation configuration and cannot be guaranteed under arbitrary network or mobility conditions.
Full article
(This article belongs to the Special Issue Optical Wireless Communications (OWC) for Internet-of-Things (IoT))
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Open AccessArticle
Erbium-Doped Self-Similar Fiber Laser with a Prism-Based Spectral Filter
by
Seongmin Park and Andy Chong
Photonics 2026, 13(9), 891; https://doi.org/10.3390/photonics13090891 (registering DOI) - 20 Sep 2026
Abstract
Mode-locked fiber lasers are widely used due to their compactness and ability to generate ultrafast optical pulses. In normal-dispersion fiber lasers, including dissipative soliton (DS) and self-similar (SS) regimes, intracavity spectral filtering is essential for achieving stable pulse evolution. Spectral filters based on
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Mode-locked fiber lasers are widely used due to their compactness and ability to generate ultrafast optical pulses. In normal-dispersion fiber lasers, including dissipative soliton (DS) and self-similar (SS) regimes, intracavity spectral filtering is essential for achieving stable pulse evolution. Spectral filters based on diffraction gratings have been widely employed for this purpose. In contrast, prism-based spectral filters provide an attractive alternative, offering lower insertion loss and improved robustness against environmental contamination. Furthermore, compared to grating-based counterparts, they allow for a larger intra-cavity beam size. In this work, we demonstrate an erbium (Er)-doped SS fiber laser operating at 1550 nm that incorporates a prism-based spectral filter. The prism-based spectral filter successfully maintains SS pulse evolution in the normal-dispersion cavity for stable mode-locked operation.
Full article
(This article belongs to the Special Issue Advanced Nonlinear Optics in Ultrafast Lasers: From Novel Materials to System Applications)
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Open AccessArticle
Beam Quality Optimization in Fiber Lasers via Selective Mode Attenuation Using Femtosecond-Laser-Inscribed Cladding Modulations in Few-Mode Fibers
by
Minnan Wu, Meng Wang, Qiushi Qin, Hao Li, Rong Zhao and Zefeng Wang
Photonics 2026, 13(9), 890; https://doi.org/10.3390/photonics13090890 (registering DOI) - 20 Sep 2026
Abstract
Beam quality directly determines the output performance and application effectiveness of high-power fiber lasers. Conventional control methods, such as coiling and tapering, degrade mechanical reliability and cause localized heating, while specialty fibers suffer from fabrication complexity and poor compatibility with standard components. To
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Beam quality directly determines the output performance and application effectiveness of high-power fiber lasers. Conventional control methods, such as coiling and tapering, degrade mechanical reliability and cause localized heating, while specialty fibers suffer from fabrication complexity and poor compatibility with standard components. To address these issues, this paper proposes and validates a beam quality optimization method using mode-selective loss, based on femtosecond-laser-inscribed periodic index modulation structures in the fiber cladding. Theoretical analysis clarifies the influence of mode weight on the M2 factor in a 20/400 LMA fiber and the optimization mechanism of the structure. In a kilowatt-level laser, the average M2 improvement is 19.5% above 800 W; at 1384 W, M2 drops from 3.31 to 2.67, and the R2 between beam profile and an ideal Gaussian beam increases from 0.5412 to 0.8609. This work provides a fully fiber-integrated, easily fabricated, and tunable beam quality-control solution for high-power fiber lasers.
Full article
(This article belongs to the Special Issue Advanced Fiber Laser Technology and Its Application: 2nd Edition)
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Open AccessReview
Microstructured Optical Sensors: Design, Fabrication, and Applications
by
Victor Argueta-Diaz
Photonics 2026, 13(9), 889; https://doi.org/10.3390/photonics13090889 (registering DOI) - 19 Sep 2026
Abstract
Microstructured optical sensors (MOS) have emerged as transformative photonic devices offering unprecedented sensitivity, miniaturization, and multiplexing capability. This review synthesizes the state of the field for specialists in photonics and optics, covering principal design architectures—photonic crystal fibers, microresonators, plasmonic nanostructures, and integrated waveguide
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Microstructured optical sensors (MOS) have emerged as transformative photonic devices offering unprecedented sensitivity, miniaturization, and multiplexing capability. This review synthesizes the state of the field for specialists in photonics and optics, covering principal design architectures—photonic crystal fibers, microresonators, plasmonic nanostructures, and integrated waveguide platforms—alongside the fabrication methodologies underpinning their realization. We examine four high-impact application domains: environmental monitoring, biomedical diagnostics, structural health monitoring, and food safety. A central argument runs through the review: the dominant bottleneck constraining MOS adoption has shifted from sensitivity—where many platforms now approach the physical detection limit—to the engineering triad of packaging difficulty, calibration drift, and manufacturing reproducibility. Against this backdrop, we provide frank comparative assessments of platform readiness for each application domain, distinguishing proof-of-concept demonstrations from deployable systems. A dedicated Critical Perspective section addresses the translation of laboratory sensitivity figures to field performance, the genuine and overstated contributions of machine learning, and a commercialization-readiness assessment for principal MOS platform families.
Full article
(This article belongs to the Special Issue Microstructured Optical Sensors: Design, Fabrication and Applications)
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Open AccessArticle
Measurements of Carrier Concentration, Mobility and Crystalline Properties Along the Growth Direction in MOCVD-Grown GaN-on-Sapphire by Cross-Section Raman Spectroscopy
by
Guang Chen, Manika Tun Nafisa, Yun-Chen Chung, Subiao Bian, Zhe Chuan Feng, Hsiang-Lin Liu, Kang Yang, Jixiong Li, Jeffrey Yiin, Gu Xu, Weijie Lu, Benjamin Klein, Ian Ferguson and Changcai Cui
Photonics 2026, 13(9), 888; https://doi.org/10.3390/photonics13090888 (registering DOI) - 19 Sep 2026
Abstract
GaN-on-sapphire structure is currently playing an important role in developing modern optoelectronic and electronic devices. Cross-sectional Raman scattering (RS) measurements were conducted along the growth direction of GaN-on-sapphire structures; the 4.0 μm R4 and 7.6 μm N7 layers were measured using step intervals
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GaN-on-sapphire structure is currently playing an important role in developing modern optoelectronic and electronic devices. Cross-sectional Raman scattering (RS) measurements were conducted along the growth direction of GaN-on-sapphire structures; the 4.0 μm R4 and 7.6 μm N7 layers were measured using step intervals of 0.5 μm and 1.0 μm, respectively. Characterization techniques, such as scanning electron microscopy, optical transmission and spectroscopic ellipsometry, have been applied to these GaN/sapphire structures and provide information on the crystalline properties of the two GaN films. Cross-sectional Raman measurements showed sample-dependent shifts in the fitted GaN E2(high) and E1(LO) peak positions. The fitted E2(high) peak positions were used to estimate the relative stress profiles, while spatial correlation model analysis provided model-dependent estimates of the effective phonon correlation lengths and damping constants. Longitudinal optical phonon–plasmon coupling fitting of the E1(LO) modes was used to estimate the carrier concentration and mobility. The distinctive findings may enhance the comprehension of GaN/sapphire and present valuable benchmarks for others within this field.
Full article
(This article belongs to the Special Issue Advances in Raman Spectroscopy)
Open AccessArticle
Intravascular Photoacoustic Viscoelasticity Imaging
by
Xiangmei Tian, Heng Zhang and Pingping Wang
Photonics 2026, 13(9), 887; https://doi.org/10.3390/photonics13090887 (registering DOI) - 19 Sep 2026
Abstract
Plaque rupture drives acute cardiovascular events and originates from a mechanical imbalance between fibrous cap integrity and lipid core loading. This process reflects the coupled elastic and viscous behavior of plaque components, and viscoelasticity therefore serves as a biomechanical marker for stability assessment.
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Plaque rupture drives acute cardiovascular events and originates from a mechanical imbalance between fibrous cap integrity and lipid core loading. This process reflects the coupled elastic and viscous behavior of plaque components, and viscoelasticity therefore serves as a biomechanical marker for stability assessment. In this study, an intravascular photoacoustic viscoelasticity imaging (IVPAVEI) method was developed for the quantification of the plaque viscosity–elasticity ratio through phase delay analysis between the photoacoustic signal and laser pulse. A miniature probe with a diameter of 1.1 mm was integrated into the IVPAVEI system, rendering it suitable for intravascular applications. The capacity of the system to discriminate tissues with distinct viscoelastic properties was validated by resolution experiments in phantom. In situ evaluations were performed on rabbit aortic plaques, and IVPAVEI captured subtle viscoelastic changes before overt morphological lesions emerged. This minimally invasive approach thus enables the early detection of atherosclerotic plaques and holds potential for identifying lesions with high progression risk in future clinical practice.
Full article
(This article belongs to the Special Issue Advanced Technologies in Biophotonics and Medical Physics)
Open AccessArticle
Research on Crosstalk Suppression Technology of Wavelength Division Multiplexing for Fiber-Optic Sensing Based on Fabry–Perot Interference
by
Zijie Hua, Zheng Liu, Ji Xia, Fuyin Wang, Qiong Yao and Shuidong Xiong
Photonics 2026, 13(9), 886; https://doi.org/10.3390/photonics13090886 (registering DOI) - 19 Sep 2026
Abstract
Aiming at the severe inter-channel crosstalk and degraded detection accuracy existing in wavelength division multiplexing (WDM)-based fiber Fabry–Perot (F-P) sensor arrays, this paper proposes a multi-channel WDM crosstalk suppression technique based on phase-shifting diversity demodulation. A theoretical crosstalk model is constructed, and analysis
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Aiming at the severe inter-channel crosstalk and degraded detection accuracy existing in wavelength division multiplexing (WDM)-based fiber Fabry–Perot (F-P) sensor arrays, this paper proposes a multi-channel WDM crosstalk suppression technique based on phase-shifting diversity demodulation. A theoretical crosstalk model is constructed, and analysis reveals that WDM crosstalk depends on four key parameters: wavelength diversity group number k, channel extinction ratio ε, amplitude of the measured signal As, and wavelength interval m. Numerical simulations and experiments are performed on a dual-channel WDM sensing system to evaluate the influences of these parameters on the crosstalk suppression performance. Results verify that the proposed crosstalk suppression technique can remarkably suppress inter-channel crosstalk compared with the system without crosstalk suppression, and the fundamental-frequency crosstalk suppression level is improved by 33.8 dB. For engineering optimization, there exist an optimal wavelength diversity group number and an optimal wavelength interval to achieve maximum crosstalk attenuation. Moreover, the proposed technique relaxes the strict extinction ratio requirements for WDM devices and mitigates the hardware limitations in large-scale array systems. This method effectively addresses the crosstalk bottleneck of fiber F-P sensor arrays under WDM configuration, and provides theoretical guidance and an engineering optimization strategy for large-scale underwater fiber F-P WDM sensing arrays.
Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
Open AccessArticle
Tunable Multicriticality in a Dissipative Superradiant Phase Transition via Optical Squeezing
by
Yuanyi Huang, Gui-Lei Zhu, Lin Cheng and Xiaoguang Wang
Photonics 2026, 13(9), 885; https://doi.org/10.3390/photonics13090885 (registering DOI) - 18 Sep 2026
Abstract
Dissipation can fundamentally reconstruct the multicritical structure of driven-dissipative light–matter systems. In the interpolating Dicke–Tavis–Cummings model, cavity loss eliminates the -symmetric superradiant phase on the Tavis–Cummings line and splits the original multicritical point into
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Dissipation can fundamentally reconstruct the multicritical structure of driven-dissipative light–matter systems. In the interpolating Dicke–Tavis–Cummings model, cavity loss eliminates the -symmetric superradiant phase on the Tavis–Cummings line and splits the original multicritical point into a pair of dissipation-induced tricritical points. Here, we show that intracavity optical squeezing provides a coherent means of continuously reshaping this loss-generated multicritical structure. The single-mode parametric interaction acts asymmetrically on the two cavity quadratures, thereby deforming the phase boundaries and continuously tuning the dissipation-induced tricritical points. We analytically determine the phase boundaries and the evolution of the tricritical structure with the parametric gain and cavity dissipation, and show that the two tricritical points coalesce in the weak-loss limit. Photon-number fluctuations provide clear quantum signatures of the squeezing-controlled multicritical structure.
Full article
(This article belongs to the Special Issue Advanced Light Manipulation via Nanostructures and Light–Matter Interaction)
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Open AccessArticle
Effect of Annealing Treatment on Laser-Induced Damage Characteristics of Non-Quarter-Wave HfO2/SiO2 Antireflection Films
by
Yifei Chen, Jin Zhang, Changxin Xiong, Weijun Tong, Haoze Du, Yuming Deng and Quanrong Deng
Photonics 2026, 13(9), 884; https://doi.org/10.3390/photonics13090884 (registering DOI) - 18 Sep 2026
Abstract
High-power laser systems impose stringent requirements on the laser-induced damage threshold of optical thin films. Post-deposition thermal annealing has been demonstrated as an effective approach to enhancing the LIDT of HfO2-based coatings; however, its effects on antireflection coatings—particularly those employing non-quarter-wave
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High-power laser systems impose stringent requirements on the laser-induced damage threshold of optical thin films. Post-deposition thermal annealing has been demonstrated as an effective approach to enhancing the LIDT of HfO2-based coatings; however, its effects on antireflection coatings—particularly those employing non-quarter-wave designs that offer industrial advantages such as fewer layers and lower fabrication cost—remain insufficiently investigated. In this work, non-quarter-wave HfO2/SiO2 multilayer antireflection films were fabricated by ion beam-assisted electron beam evaporation, and the effects of thermal annealing on their laser-induced damage characteristics were systematically investigated. Experimental results show that the effect of thermal annealing between 300 and 700 °C on the laser damage resistance of the antireflection coating is not monotonic: the laser-induced damage threshold rises from 27.6 J/cm2 in the as-deposited state to 36.7 J/cm2 at 500 °C, an improvement of approximately 33.1%, and then falls at 600 °C and 700 °C, while remaining above the as-deposited value throughout. This non-monotonic behavior originates from a competition between two contributions. On the one hand, the repair of oxygen vacancies, the densification of the film, and the growth of the crystallites continuously reduce the population of initiating absorbers and improve heat dissipation. On the other hand, the penalties arising from the exhaustion of the free volume and from the accumulation of tensile stress accelerate in the upper part of the temperature range, and their influence on the threshold progressively outweighs the gain produced by the former. Annealing at 500 °C is therefore the optimum state determined by this competition.
Full article
(This article belongs to the Special Issue Advanced Photonic Sensing Technologies for Optical Fiber Devices)
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Open AccessArticle
A Rapid Eyebox Characterization Method for Near-Eye Display Systems Based on Sampling Efficiency Optimization and Error Modeling
by
Hengshen Xu, Yuqian Li, Chunqiang Huang and Yueqiang Hu
Photonics 2026, 13(9), 883; https://doi.org/10.3390/photonics13090883 (registering DOI) - 18 Sep 2026
Abstract
The standardized eyebox measurement method for AR devices specified in IEC 63145-20-10:2019 is associated with a large traversal range, lengthy measurement time, high operational complexity, and limited accuracy in exit pupil distance positioning. To address these limitations, a predictive framework for eyebox sampling
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The standardized eyebox measurement method for AR devices specified in IEC 63145-20-10:2019 is associated with a large traversal range, lengthy measurement time, high operational complexity, and limited accuracy in exit pupil distance positioning. To address these limitations, a predictive framework for eyebox sampling optimization and error estimation based on exit pupil distance is proposed. A geometric optics model describing the relationship between exit pupil distance and eyebox search range is established, and conversion equations for eyebox dimensions at different exit pupil distances are derived. Furthermore, quantitative models for sampling efficiency and measurement error are developed, revealing the relationships among exit pupil distance, sampling interval, measurement efficiency, and characterization accuracy. Based on these models, the trade-off between measurement efficiency and accuracy can be quantitatively predicted and optimized prior to measurement. Experimental validation was conducted on a commercial AR headset using a Riedel I29 optical measurement system, including optical axis alignment, eyebox center localization, exit pupil distance configuration, search range determination, and luminance-ratio-based sampling. The results demonstrate that increasing the exit pupil distance from the standard 16 mm to 38 mm reduces the number of sampling points by 77.99%. Through joint optimization of exit pupil distance and sampling interval, the sampling quantity can be further reduced by up to 94.07% while maintaining a measurement error below 5.1%. The predicted eyebox dimensions and measurement errors show good agreement with both experimental measurements and results obtained using the standard procedure. Without requiring additional hardware, the proposed framework simplifies measurement operations and provides a quantitative basis for balancing efficiency and accuracy. The framework is applicable to both manual and automated measurement scenarios and offers a practical and theoretically grounded solution for eyebox characterization and optical performance evaluation in AR near-eye display systems.
Full article
(This article belongs to the Special Issue Recent Research on Optical Sensing and Precision Measurement)
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Open AccessArticle
An Improved Robust Multibasin Profiling Framework with Physics-Protected Selective Structured-Residual Refinement for Thin-Film Thickness Inversion
by
Guangshuo Wu, Yixuan Huang, Wenhui Ma, Zhi Zhang, Lihan Yang and Hao Zheng
Photonics 2026, 13(9), 882; https://doi.org/10.3390/photonics13090882 (registering DOI) - 18 Sep 2026
Abstract
Recovering thin-film thickness from reflectance spectra becomes unreliable when measurements contain sparse outliers, competing thickness minima, or structured mismatch with the nominal optical model. We use a robust multibasin framework in which a Tukey profile first establishes a thickness anchor. A local structured-residual
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Recovering thin-film thickness from reflectance spectra becomes unreliable when measurements contain sparse outliers, competing thickness minima, or structured mismatch with the nominal optical model. We use a robust multibasin framework in which a Tukey profile first establishes a thickness anchor. A local structured-residual correction is then allowed only in directions that do not reproduce the main thickness-sensitive spectral variation. First-order sensitivity is protected explicitly, and second-order protection is adjusted with an observation-specific curvature-overlap coefficient . A frozen gate decides whether the refined candidate replaces the anchor; otherwise, the anchor is returned unchanged. The method was tested in an independent-seed numerical study with 7200 observations spanning three optical systems, three thicknesses, and four contamination conditions. Unprotected residual flexibility did not improve accuracy, whereas adaptive protection reduced the pre-gating mean absolute error to 0.216601 nm. Selective gating reduced harmful accepted refinements from 923 to 495 while retaining 93.28% of beneficial refinements. We then applied the frozen procedure, without experiment-specific retuning, to five physical SiO2/Si specimens measured at three spatial positions each. Relative to independent model-based ellipsometric references, the specimen-level mean absolute error was 0.374 nm, with relative errors of 0.01–0.15% and within-specimen spatial SDs of 0.16–0.34 nm. These results show that structured residual correction can improve thickness recovery when thickness-sensitive directions are protected and refinement is not forced on every spectrum.
Full article
(This article belongs to the Section Data-Science Based Techniques in Photonics)
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Open AccessArticle
Acceptance Mode Dependent Transfer of Non-Common Path Aberrations to Null Leakage in Mid-Infrared Nulling Interferometry
by
Yangdi Hu, Junru Feng, Jiankai Zhu, Tong Zhao, Huizhe Yang and Yonghui Liang
Photonics 2026, 13(9), 881; https://doi.org/10.3390/photonics13090881 (registering DOI) - 18 Sep 2026
Abstract
Mid-infrared nulling interferometry enables thermal characterization of warm exoplanets, but non-common path aberrations (NCPA) degrade starlight suppression by creating complex amplitude mismatch between interferometer arms. We investigate how architecture and NCPA spatial structure jointly determine null leakage and stability at
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Mid-infrared nulling interferometry enables thermal characterization of warm exoplanets, but non-common path aberrations (NCPA) degrade starlight suppression by creating complex amplitude mismatch between interferometer arms. We investigate how architecture and NCPA spatial structure jointly determine null leakage and stability at . A unified statistical framework combines free-space propagation, a Houizot chalcogenide fiber, and a Labadie-type waveguide with extended Sauvage-type NCPA screens and adaptive optics (AO) residuals in nested Monte Carlo simulations. The mean raw null is governed mainly by the combined aberration amplitude of the two arms and depends only weakly on its allocation between them. AO residuals set leakage floors that depend on the reception configuration. Cases with similar mean raw nulls can still have different dispersions. Compared with free space, the single-mode spatial filters lower the mean leakage and reduce fluctuations, and they are less sensitive to the allocation of amplitude error between the arms. Their performance depends on modal selectivity: larger energy fractions in azimuthally symmetric radial modes are associated with poorer mean nulls and greater AO-driven fluctuations. These results show that NCPA tolerances cannot be specified by global wavefront error amplitude alone. They should also account for aberration spatial content and the modal projection imposed by the transmission architecture.
Full article
(This article belongs to the Special Issue State-of-the-Art Optical Systems for Astronomy)
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Open AccessArticle
Bridging Visible and SWIR Spectroscopy via Dual-Spectrometer for Skin Tissue Characterization
by
Guancheng Li, Wenxuan Li, Yunfei Li and Fuhong Cai
Photonics 2026, 13(9), 880; https://doi.org/10.3390/photonics13090880 (registering DOI) - 18 Sep 2026
Abstract
The optical response of skin tissue in the near-ultraviolet to short-wave infrared band (350–2350 nm) contains rich physiological information such as hemodynamics, hydration status, and lipid metabolism. However, due to limitations in detector technology, conventional spectroscopic systems often use a single type of
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The optical response of skin tissue in the near-ultraviolet to short-wave infrared band (350–2350 nm) contains rich physiological information such as hemodynamics, hydration status, and lipid metabolism. However, due to limitations in detector technology, conventional spectroscopic systems often use a single type of detector: silicon-based CCD (effective wavelength ≤ 1100 nm) captures visible blood features but cannot cover the long-wave vibration bands of water/lipids, while InGaAs (effective wavelength ≥ 900 nm) is sensitive to long-wave water/lipid absorption but misses the strong blood absorption in the visible region. This spectral detector segmentation leads to a separation of blood features from tissue background signals. In addition, traditional single source-probe distance measurement only probes one depth and cannot observe tissue information at different depths by varying the source-probe distance. This study employs a dual-spectrometer splicing architecture to achieve seamless continuous spectral measurement across 350–2350 nm by amplitude registration and normalization in the overlapping region. Using the thumb, palm, and arm as representative sites, we systematically analyzed spectral differences under varying vascular densities and fat backgrounds and successfully extracted absorption features of major chromophores including blood, water, and lipids. The results showed that the dual-spectrometer splicing method achieved smooth transitions in the overlapping region across different sites, validating its reliability. Spectral differences across sites were mainly characterized by hemoglobin absorption features in the visible region and water/lipid vibrational absorption features in the short-wave infrared region. These findings demonstrate the feasibility of dual-spectrometer splicing for broadband tissue spectral acquisition, enabling simultaneous capture of multi-component signals, and providing a new technical approach for non-invasive tissue composition analysis.
Full article
(This article belongs to the Special Issue Recent Progress in Biomedical Optical Technologies)
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Open AccessArticle
Optimising Material Ratios for Full-Colour 3D-Printed Dental Restorations
by
Philipp Nguyen, David Hevisov, Markus Wagner, Joachim Jelken, Florian Foschum and Alwin Kienle
Photonics 2026, 13(9), 879; https://doi.org/10.3390/photonics13090879 - 17 Sep 2026
Abstract
Accurate colour reproduction remains a challenge in manufactured dental restorations because tooth appearance depends on wavelength-dependent absorption and scattering, geometry, illumination, and viewing conditions. We present a measurement- and simulation-based workflow for determining 3D-printable multi-material compositions. We demonstrate our workflow by reproducing the
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Accurate colour reproduction remains a challenge in manufactured dental restorations because tooth appearance depends on wavelength-dependent absorption and scattering, geometry, illumination, and viewing conditions. We present a measurement- and simulation-based workflow for determining 3D-printable multi-material compositions. We demonstrate our workflow by reproducing the appearance of the 16 VITA classical A1–D4 shade guide colours with a set of six Stratasys Vero and VeroUltra photopolymers. Each reference tooth was recorded in a photobox using a camera with six narrow-band spectral filters spanning 450 nm to 700 nm. A physics-based, GPU-accelerated Monte Carlo light transport simulation was then used inversely to recover the six material concentrations that minimised the CIE colour difference between the measured and simulated appearance considering all six wavelength bands. Additionally, we compared four colour optimisation strategies for determining material compositions. We further investigated metamerism in the colour optimisation by independently the illuminant and comparing a single- and double-light-source setup. These variations produced substantial changes in the resulting colour differences. With the given material set, the resulting mixtures reproduced all 16 teeth across the shade guide with a mean colour difference of CIE over the evaluated tooth regions. Crucially, the printing materials require optical characterisation only once, after which new target teeth need only be spectrally measured to determine their printable compositions. More broadly, the framework provides a general route from spectral measurements to physically realisable multi-material reproductions, extending beyond dental applications.
Full article
(This article belongs to the Special Issue Computational Optical Imaging: Progress and Future Prospects)
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Open AccessCommunication
Far-Field Raman–Nath Diffraction of Polychromatic Light and a Ternary Data Transmission Scheme
by
Jyun-Ping Chang, Cheng-Mu Tsai and Pin Han
Photonics 2026, 13(9), 878; https://doi.org/10.3390/photonics13090878 - 17 Sep 2026
Abstract
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Raman–Nath diffraction is produced by a thin acoustic beam. The standing sound wave acts as a thin phase grating, causing monochromatic light to interact with it and diffract into multiple orders. This phenomenon is typically used to redistribute light intensity at specific angles.
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Raman–Nath diffraction is produced by a thin acoustic beam. The standing sound wave acts as a thin phase grating, causing monochromatic light to interact with it and diffract into multiple orders. This phenomenon is typically used to redistribute light intensity at specific angles. The correspondence relationship applies to the spatial distribution of monochromatic light and transforms it into a spectral distribution of polychromatic light. This demonstrates that angular diffraction orders in the spatial domain correspond to wavelength orders in the spectral domain. Numerical results show that the amplitude of various spectral orders can be controlled by adjusting acoustic wave intensity. This property is proposed for use in achieving ternary digital data transmission.
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Open AccessArticle
End-to-End Calibration and Performance Validation of a Chromatic Confocal Displacement System with a Reproducible All-Spherical Objective
by
Yunling Ni, Yangdong Zhou, Wenting Chen, Ruipeng Wu, Fei Wang and Lu Yin
Photonics 2026, 13(9), 877; https://doi.org/10.3390/photonics13090877 - 17 Sep 2026
Abstract
Chromatic confocal studies often report optical design and metrology performance using non-equivalent metrics, limiting reproducibility and practical comparison. We present a design-to-validation study built around a reproducible four-element, three-group all-spherical objective using CDGM catalog glasses. The objective provides an NA of 0.25, a
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Chromatic confocal studies often report optical design and metrology performance using non-equivalent metrics, limiting reproducibility and practical comparison. We present a design-to-validation study built around a reproducible four-element, three-group all-spherical objective using CDGM catalog glasses. The objective provides an NA of 0.25, a 40 mm working distance, and a nominal 2.100 mm focal shift over 400–700 nm. The workflow separates calibration residuals, independently referenced errors, fixed-position repeatability, and paired-step response, and incorporates manufacturing-tolerance analysis. A monotonic PCHIP calibration produced a 2.31 mm empirical operating interval, while measurement and simulation agreed within 2.90% over their common 440.7–700 nm band. Positions excluded from calibration yielded an uncorrected RMSE of 1.561 µm. Under a predeclared engineering criterion, 1.0 µm centrally and 1.5 µm across the full range were the smallest tested steps that passed. Tolerance analysis identified cemented-group decenter as the dominant sensitivity with assembly refocusing. The principal contribution is a reproducible catalog-glass prescription combined with an error-separated validation protocol that establishes practical performance boundaries without conflating repeatability with absolute accuracy.
Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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Open AccessArticle
High-Resolution Fabry–Pérot Interferometric Strain Sensor for Mortar
by
Jie Huang, Zewei Wu, Biyao Shi, Zihui Liu, Shan Wang and Yan Tang
Photonics 2026, 13(9), 876; https://doi.org/10.3390/photonics13090876 - 17 Sep 2026
Abstract
Continuous measurement of small deformation in cementitious materials requires both sensitive displacement readout and control of environmental effects. This study develops a long-gauge strain sensor based on a low-finesse extrinsic Fabry–Pérot interferometer (EFPI). Axial displacement of a 250 mm mortar prism is transferred
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Continuous measurement of small deformation in cementitious materials requires both sensitive displacement readout and control of environmental effects. This study develops a long-gauge strain sensor based on a low-finesse extrinsic Fabry–Pérot interferometer (EFPI). Axial displacement of a 250 mm mortar prism is transferred to an external reflector, and the air cavity length is recovered from swept-wavelength reflection spectra. Loading–unloading measurements cover a nominal strain range of 0–10,000 µε. A separate incremental test resolves a nominal 2 nm displacement step, equivalent to 8 nε, with a local strain-response slope of 0.960 and R2 = 0.99550. For 100 consecutive readings at a chamber setting of 20 °C, the sample standard deviation is 1.162 nε; division by the local response slope gives an estimated input-referred noise-equivalent strain of 1.21 nε (1σ). These short-term metrics do not establish long-term accuracy. During 14-day monitoring, individual mortar prisms with water-to-cement ratios of 0.4, 0.5, and 0.6 reach apparent compressive strains of 452.0, 532.5, and 599.7 µε, respectively. The results demonstrate the feasibility of continuous long-gauge optical monitoring.
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(This article belongs to the Special Issue Advanced Optical Fiber Sensors for Harsh Environment Applications, 2nd Edition)
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Open AccessArticle
Application of Parallel-Coupled Ring Resonators in Optical Resonance Gyroscopes with Low-Coherent Radiation Sources
by
Alina V. Gorelaya, Yurii V. Filatov, Egor V. Shalymov, Vladimir Yu. Venediktov and Anastasia V. Venediktova
Photonics 2026, 13(9), 875; https://doi.org/10.3390/photonics13090875 - 17 Sep 2026
Abstract
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The most promising class of optical gyroscope from the miniaturization point of view is the resonant optical gyroscope with a low-coherence radiation source. The present study briefly discusses the principles of operation of the main types of such resonators. One of the most
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The most promising class of optical gyroscope from the miniaturization point of view is the resonant optical gyroscope with a low-coherence radiation source. The present study briefly discusses the principles of operation of the main types of such resonators. One of the most significant drawbacks of the resonant optical gyroscope with a low-coherence radiation source is its low energy efficiency. Only a small portion of the radiation carrying information about the angular velocity is directed from the source to the photodetector, specifically the radiation at frequencies corresponding to the eigenfrequencies of the ring resonator, the rest of the radiation being scattered on the unused ports of the resonator and converted into heat. It has been shown that the use of parallel-connected ring resonators can increase the energy efficiency of resonant gyroscopes with low-coherence radiation sources by an order of magnitude, from a few percent to tens of percent. It has also been theoretically demonstrated that this can reduce the contribution of shot noise and thermal noise of the photodiode by several times and increase the sensitivity of the gyroscope.
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Open AccessArticle
High-Speed Waveguide InP/InGaAs UTC-PDs for over 200 Gb/s/λ Optical Transmission
by
Han Ye, Qin Han, Liyan Geng and Hua Yang
Photonics 2026, 13(9), 874; https://doi.org/10.3390/photonics13090874 - 16 Sep 2026
Abstract
Scaling of artificial intelligence data centers is pushing the aggregate speed of photonic transceivers over 1.6 Tb/s and even 3.2 Tb/s, which in the multi-channel configuration accounts for a 200 Gb/s data transmission speed for each wavelength. Uni-traveling carrier photodetectors have proved high
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Scaling of artificial intelligence data centers is pushing the aggregate speed of photonic transceivers over 1.6 Tb/s and even 3.2 Tb/s, which in the multi-channel configuration accounts for a 200 Gb/s data transmission speed for each wavelength. Uni-traveling carrier photodetectors have proved high bandwidth performance utilizing ultra-fast carrier transit and ultra-small junction capacitance, while few reports discuss the effect of the coplanar lines on bandwidth. In this work, the parasitic effect of coplanar lines is studied, and a modified structure is designed for an InP-based waveguide uni-traveling carrier photodetector. Simulation results reveal a promotion rather than deterioration effect in PD frequency response from the coplanar lines after optimization, and the circuit analysis predicts a parasitic capacitance decrease over 40 fF, which is larger than the 23 fF junction capacitance itself. The fabricated photodetector verifies a 69% increase in bandwidth up to 120 GHz for the same active area at an external responsivity of 0.476 A/W. The eye-diagrams of 100 GBd and 140 GBd under PAM4 format also indicate huge potential for over 200 Gb/s/λ photodetection.
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(This article belongs to the Special Issue Photonic Integrated Circuits: From Fundamentals to Emerging Technologies)
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Open AccessArticle
Dynamic Imaging Simulation and Angular Measurement Performance Degradation of Interferometric Star Trackers
by
Shuai Yao, Hongyuan Wang, Weifeng Du, Zhiqiang Yan and Xunjiang Zheng
Photonics 2026, 13(9), 873; https://doi.org/10.3390/photonics13090873 - 16 Sep 2026
Abstract
Interferometric star trackers (ISTs) achieve high-precision angular measurement by encoding the stellar incident direction into multichannel interference phases. Besides image smearing, platform motion continuously changes the interference phase during a finite exposure, an effect not captured by conventional geometric star-image models. However, the
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Interferometric star trackers (ISTs) achieve high-precision angular measurement by encoding the stellar incident direction into multichannel interference phases. Besides image smearing, platform motion continuously changes the interference phase during a finite exposure, an effect not captured by conventional geometric star-image models. However, the quantitative relationship between platform motion characteristics and interferometric measurement degradation, which is essential for dynamic performance assessment and system-level optimization of ISTs, remains insufficiently characterized. We develop a full-link dynamic imaging model that incorporates broadband stellar radiation, multiple synthetic diffraction orders, multichannel energy modulation, exposure integration, and detector noise. The four-channel response is expressed as the temporal mean of a complex interference phasor, whose magnitude and argument define the modulation retention factor and dynamic phase bias, respectively. Static angular scanning experiments yield correlation coefficients above 0.97 between simulated and measured channel responses. Under a locally linear phase-to-angle relationship along the interferometric sensing direction, constant-rate motion produces a sinc response, whereas integer-cycle periodic jitter produces a zeroth-order Bessel response. For noninteger-cycle jitter, the response additionally depends on the exposure-to-jitter period ratio and initial phase. When constant-rate motion and periodic jitter coexist, they modulate the same phasor and produce a generally nonseparable response. Within the investigated parameter range, the maximum absolute difference in modulation retention between the coupled response and the independent sinc–Bessel product reaches approximately 0.58. This peak occurs near a normalized phase sweep of 1 and a normalized jitter-induced phase amplitude of 0.8. The model provides a basis for defining dynamic operating limits and selecting exposure parameters and platform stability requirements for ISTs.
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(This article belongs to the Special Issue Advances in Nonlinear Optical Imaging)
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