Journal of Optics and Photonics Research
Journal of Optics and Photonics Research (JOPR) is an international, peer-reviewed journal that publishes fundamental and applied research across optics and photonics, with coverage of technologies, materials, devices, systems, and photonic integration, including intelligent modeling, design, optimization, and advanced manufacturing. JOPR particularly encourages submissions that bridge these domains, highlighting both theoretical advances and practical innovations that drive next-generation photonic science and engineering. JOPR is sponsored by The Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Shanghai University, a distinguished research institution recognized for its contributions to optical communications, specialty fibers, and photonic technologies. The journal is a Gold Open Access journal, online readers don't have to pay any fee.
First-Principle Calculations of Structural, Electronic, Elastic, and Optical Properties of XBaCl3 (X = In, Tl) Chloro-Perovskites
​To investigate the potential of barium-based halide perovskites for optoelectronic applications, we performed first-principles density functional theory calculations on XBaCl3 (X = In, Tl). These calculations were performed using the WIEN2k package, which provides detailed insights into the materials' characteristics. The code provides a silent insight into materials' characteristics and potential improvements. We employed the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) approximation to study the optimized structure, electronic, elastic, and optical properties of XBaCl3 chloro-perovskite compounds. To assess the structural stability, we are applying the Birch–Murnaghan fitting curves, confirming that each compound is structurally stable in its optimal or ground states. The IRelast Package is utilized for evaluating the elastic properties, revealing that the materials are anisotropic, brittle, and mechanically stable. In the analysis of electronic structure, the density of states and band structure were examined. It was discovered that the compounds have an indirect bandgap of 4.9 eV for InBaCl3 and 5.6 eV for TlBaCl3. Examining the total and partial density of states allowed us to trace how individual atomic orbitals shape the overall band structure. Furthermore, we also studied the optical response that comprises the dielectric function, refractive index, absorption coefficient, and reflectivity across an energy range of 0–13.5 eV. The materials are transparent to low-energy photons, absorbing light and exhibiting optical conductivity only in the ultraviolet range. This provides critical insight for developing more efficient and functional high-tech electronics and motivating further experimental investigation. Received: 1 February 2026 | Revised: 28 May 2026 | Accepted: 9 July 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study Author Contribution Statement Shujaat Ali Khan: Conceptualization, Methodology, Software, Validation, Investigation, Writing – original draft, Writing – review & editing, Visualization. Nasir Rahman: Software, Validation, Resources, Writing – original draft, Writing – review & editing, Supervision. Shah Zeb Ullah: Conceptualization, Writing – original draft, Writing – review & editing, Visualization. Muhammad Sajjad: Validation, Resources, Supervision, Project administration. Junaid Rehman: Validation, Formal analysis, Writing – review & editing, Visualization.
Copyright (c) 2026 Authors https://creativecommons.org/licenses/by/4.0/
Recent Advances in Polarization Control for Fiber Links: Mechanisms, Technologies, and Applications
Polarization control is essential for maintaining the performance and stability of fiber-optic sensing and optical communication systems, since the state of polarization in fiber links is highly susceptible to birefringence variation and environmental perturbations. This review summarizes recent advances in polarization control for fiber links from the perspectives of polarization evolution mechanisms, target performance parameters, application-specific requirements, and representative technical implementations. Passive polarization-control schemes are first discussed, with emphasis on loop-based architectures, all-polarization-maintaining configurations, and integrated passive approaches. Active polarization-control techniques are then reviewed, including manual fiber polarization controllers, Faraday-effect-based devices, lithium-niobate electro-optic controllers, and other emerging platforms such as silicon photonics and liquid-crystal-integrated devices. Their operating principles, structural characteristics, and key performance metrics are compared. Recent progress shows that the field is evolving from static and discrete schemes toward high-speed, closed-loop, and highly integrated architectures. Despite these advances, achieving a balanced combination of low loss, high extinction ratio, ultrafast response, low power consumption, compact footprint, and long-term stability remains a major challenge for practical deployment. Received: 31 March 2026 | Revised: 3 June 2026 | Accepted: 17 July 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Zhihang Zhang: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition. Yujie Zheng: Software, Writing – review & editing. Xiao Wu: Project administration. Jianhua Yang: Investigation. Heming Wei: Resources, Supervision. Long Ma: Data curation. Xiaohu Liu: Writing – original draft. Dapeng Han: Formal analysis, Funding acquisition. Lijun Miao: Investigation, Visualization. Dengwei Zhang: Software, Validation, Supervision, Project administration, Funding acquisition.
Photo-Stability of Polymethyl Methacrylate Incorporated with Vanillin and Metal Oxide Nanoparticles
The material poly(methyl methacrylate), PMMA, is used for many different purposes, ranging from high-resolution electron beam lithography for microelectronics manufacturing through medical uses such as intraocular lenses and bone cements to the manufacture of automobile taillight covers and as a shatterproof replacement for glass in aquaria, signs, and window coverings. Photostabilization is necessary to protect polymeric materials from photodegradation and photooxidation caused by aging and ultraviolet (UV) radiation. It is imperative, therefore, to modify polymeric compounds for increased resistance against degradation due to extended exposure to UV light. There have been recent advances, which have led to the development of different polymeric materials that can be used as potential photostabilizers. This work focuses on the surface modification of the polymer PMMA through incorporating inorganic metal oxide nanoparticles in the polymer backbone. Upon reacting PMMA with ethylenediamine, an amino group will react with vanillin to produce the respective Schiff's base. Incorporation of nano metal oxides (TiO2, NiO, and CuO) leads to the formation of inorganic metal oxide nanoparticles into the polymer chains. Films of the treated PMMA were made and subjected to UV irradiation to investigate the effect of the additives on the photostabilization of PMMA. The effects of additives and the type of metal oxide on the photostabilization of PMMA were evaluated by infrared spectroscopy, weight loss, surface morphological investigation, and determination of the rate constant of decomposition. PMMA treated with organic nano metal oxides showed low photodegradation as compared to pure organic-treated PMMA. Received: 25 March 2026 | Revised: 14 May 2026 | Accepted: 23 June 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Great Iruoghene Edo: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration. Emad Yousif: Conceptualization, Methodology, Software, Validation, Resources, Data curation, Writing – review & editing, Visualization, Supervision, Project administration. Mohammed H. Al-Mashhadani: Resources, Data curation, Writing – review & editing, Visualization, Supervision, Project administration.
field emission scanning electron microscopy (FESEM)
Film and Substrate Spectral Optical Behaviors of a Tungsten Trioxide (WO3) Thin Layer Deposited on Fluorine-Doped Tin Oxide (FTO)–Coated Glass
The effective optical constants (EOCs) of a 480 nm tungsten trioxide (WO3 ) thin film deposited on fluorine-doped tin oxide (FTO)–coated glass were determined from collimated transmittance and reflectance measurements over the 250–2500 nm solar spectral range. The WO3 EOCs were obtained by fitting the experimental spectra with the four-flux model (4FM), using previously determined optical constants of the FTO and glass layers as input parameters. This work extends previous analyses of FTO–glass bilayers to a more complex WO3–FTO–glass trilayer configuration, enabling validation of the proposed framework under multilayer boundary conditions. A three-extinction matching requirement was identified from the agreement between extinction coefficients calculated from forward and backward 4FM collimated differential equations and from the EOCs under wavelength compression. In addition, a spectral limit of the optical behavior between film and substrate was consistently observed at wavelengths approximately three times the layer thickness for both FTO and WO3 layers, confirming its applicability beyond bilayer systems. Thickness gradient plots of collimated light fluxes and complex electric fields revealed the transition from substrate-like incoherent behavior to film-like coherent behavior. In the coherent regime, complex electric fields were represented through wavelength-dependent Bode and Nyquist diagrams, allowing analysis of their magnitude–phase evolution within the multilayer structure. The results provide a consistent framework for determining EOCs and identifying optical regime transitions in multilayer systems, demonstrating applicability to trilayer electrochromic structures. Received: 16 January 2026 | Revised: 30 April 2026 | Accepted: 27 May 2026 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement David Barrios-Puerto: Conceptualization, Methodology, Validation, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.
Copyright (c) 2026 Author https://creativecommons.org/licenses/by/4.0/
Performance Analysis of a 16-QAM Directly Modulated OFDM Visible Optical Wireless Link Without External Modulators
This paper presents a performance analysis of a directly modulated direct-detection orthogonal frequency division multiplexing-based visible light communication system designed for high-speed and low-complexity transmission. The proposed architecture employs 16-Quadrature Amplitude Modulation (16-QAM) and achieves a data rate of 15 Gbps over a 500 m line-of-sight link while eliminating the need for external optical modulators and transmission-line amplifiers. The system was modeled and evaluated in the OptiSystem environment using a 1024-point fast Fourier transform with 512 active subcarriers, a cyclic prefix, and a directly modulated laser operating at 550 nm. Performance was assessed in terms of bit error rate (BER), optical signal-to-noise ratio (OSNR), error vector magnitude (EVM), maximum Q factor, and received optical power. The results show that the proposed architecture maintains BER ≤ 10−3 when the OSNR is approximately 32 dB or higher, confirming the feasibility of reliable 16-QAM orthogonal frequency division multiplexing (OFDM) transmission without external amplification. In addition, the analysis demonstrates that beam divergence is a critical design factor, since larger divergence angles reduce received optical power density and degrade both BER and EVM. A comparison between theoretical and simulated received power shows close agreement, validating the adopted link-budget model. The results confirm that the proposed directly modulated OFDM architecture provides an energy-efficient and cost-effective solution for short-to-medium-range high-speed visible optical wireless communication. Received: 18 February 2026 | Revised: 20 May 2026 | Accepted: 22 June 2026 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Mahmoud Alhalabi: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration.
Study on Structural and Optical Properties of Nanocrystalline Mn–Ni Ferrites Prepared by Auto-Combustion Technique
Nanocrystalline mixed ferrites with the general formula MnxNi1-xFe2O4(x = 0.0 to 1.0, in steps of 0.2) were successfully synthesized using the auto-combustion technique. The main objective of this work was to investigate the effect of Mn substitution at Ni sites on the structural and optical properties of NiFe2O4 in the nanocrystalline regime. X-ray diffraction (XRD) reflections were consistent with the formation of a cubic spinel structure for all compositions. No additional crystalline impurity peaks were detected within the sensitivity of conventional powder XRD. The average crystallite size estimated from the Scherrer equation lies in the range of 26–33 nm, confirming the nanocrystalline nature of the synthesized powders. The slight variation in crystallite size with increasing Mn content suggests that ionic substitution influences the growth kinetics during combustion synthesis. Ultraviolet–visible (UV–Vis.) diffuse reflectance spectroscopy was used to study the optical response, and the apparent optical bandgap values were estimated from UV–Vis. absorbance data using Tauc analysis. The bandgap varies from 1.18 to 1.58 eV, revealing clear composition-dependent optical tuning. These results show that Mn substitution effectively changes the electronic structure and optical response, making MnxNi1-xFe2O4 ferrites favorable materials for optoelectronic and photocatalytic applications. Received: 29 January 2026 | Revised: 20 May 2026 | Accepted: 26 June 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Laxmi J. Hathiya: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Visualization. Hiren H. Joshi: Validation, Resources, Writing – review & editing, Supervision, Project administration.
Band-Structure Engineering of P-Doped Ge/SiGe Heterostructures for Mid-infrared Photonic Devices
This work presents a systematic theoretical investigation and band-structure engineering of p-doped Ge/Si1−xGex multiple quantum wells (MQWs) tailored for mid-infrared (MIR) photonics. Using a self-consistent 6-band k·p Poisson-Schrödinger approach, we establish a predictive simulation framework that rigorously accounts for quantum confinement, epitaxial strain, and many-body interactions. A key feature of our model is the integration of realistic graded interfacial profiles and self-consistent many-body corrections—specifically local density approximation exchange—correlation and depolarization shifts. We demonstrate that these corrections are essential to resolve the observed 8–12 meV energy blueshift in high-density hole gases (> 1018cm−3), where standard single-particle approximations fail. By systematically optimizing well geometry, doping profiles, and Ge concentration, we achieve precise spectral tunability across the strategic 6–15 μm atmospheric window. Furthermore, our transport and optical models capture the complex valence band mixing between heavy, light, and split-off hole states, providing deep insights into intersubband absorption dynamics. The model's high predictive accuracy (> 95% compared to experimental MIR absorption spectra) establishes it as an indispensable tool for the ab-initio design of CMOS-compatible MIR emitters, quantum cascade lasers, and photodetectors. Ultimately, this framework bridges the gap between fundamental valence band physics and practical device performance, accelerating the development of next-generation monolithic silicon-photonics platforms. Received: 13 January 2026 | Revised: 14 April 2026 | Accepted: 22 June 2026 Conflicts of Interest The author declares that she has no conflicts of interest to this work. Data Availability Statement Data supporting the findings of this study are available from the corresponding author upon reasonable request. Author Contribution Statement Vittoria Urso: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.
Development of a Low-Cost, Arduino-Based CNC Laser Cutting and Engraving Device for Laboratory Teaching/Learning and Engineering Purposes
The article presents the design and implementation of a low-cost, easy-to-implement, Arduino-based computer-numerical-controlled (CNC) laser cutting and engraving device. By means of a CNC shield and appropriate drivers, as well as the G-code Reference Block Library firmware, the Arduino-Uno board can control the motion of the motors and the laser head of the CNC device, enabling the laser (which emits at 450 nm, providing an optical output of about 5.5 W) to perform cutting and engraving processes. The device is lightweight and compact in size (thus, portable and easy to place and store) and made up of open-source, easily available (even recycled) equipment at a cost of about 190 €. Despite its simplicity and low cost, the device can adapt to lab and medium-demand engineering environments and can operate on a wide variety of materials. The described device can also serve as a learning and teaching tool through which students have the opportunity to encounter a diverse range of engineering topics and skills and fully exploit the attractiveness and effectiveness of project-based and discovery learning. Received: 17 December 2025 | Revised: 11 March 2026 | Accepted: 13 May 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are available within the manuscript. Author Contribution Statement Georgios Akritidis: Software, Validation, Investigation, Data curation. Leonidas Dritsas: Conceptualization, Methodology, Supervision, Project administration. Gerasimos Pagiatakis: Conceptualization, Methodology, Validation, Writing – original draft, Writing – review & editing. Andreas Papadakis: Methodology, Investigation, Resources, Data curation, Writing – review & editing. Ioannis Katsiris: Investigation, Resources, Data curation, Writing – review & editing. Nikolaos Voudoukis: Investigation, Data curation, Writing – review & editing. Dimitrios Karaoulanis: Investigation, Data curation, Writing – review & editing. Dimitris Uzunidis: Investigation, Data curation, Writing – review & editing.
Advances in Optical Analysis of Materials and Complex Biological Systems Using Infrared Spectroscopy
Infrared spectroscopy (IRS) is an increasingly important optical technique because the properties of light in this part of the electromagnetic spectrum enable interactions with materials and complex biological systems that provide unique information that has both research and commercial applications. This review summarizes the basic optical principles employed in IRS systems and outlines recent technological advances that have improved the functionality and applicability of IRS instruments. The relevance of the principal practical applications of near-infrared spectroscopy (NIRS), mid-infrared spectroscopy (MIRS), and hyperspectral imaging (HI) in materials science, agriculture, and medicine is highlighted, and key progress made with the software used for the analysis of raw optical data is described. The shorter wavelengths in the near-infrared (NIR) range of the spectrum achieve greater penetration than those in the mid-NIR range. NIRS is now a prominent analytical technology, and its growing role in medicine is the principal focus of this review. MIRS is an important and widely used sample characterization and analytical technique. NIR HI enables the chemical constituents in a sample to be analyzed by capturing complete spectral data at each sample point; the unique spectral signatures generated then allow different chemicals to be visualized and identified. Received: 16 December 2025 | Revised: 4 March 2026 | Accepted: 23 March 2026 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Andrew J. Macnab: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration.
Machine Learning–Enhanced UWOC System for Robust Underwater Communication with FEC Integration
Underwater wireless optical communication (UWOC) often suffers from channel-induced bit errors that degrade adaptive threshold detection, particularly due to dynamic turbidity conditions. Standard approaches of applying mitigation techniques may improve the link performance to an extent. In this study, we have incorporated an integrated approach based on machine learning (ML) into the UWOC system, along with forward error correction (FEC), and tested it on various turbidity levels. This has significantly reduced bit errors and improved link performance. To train the ML models, experimental data were collected using an underwater testbed, with various turbidity levels up to seven nephelometric turbidity units (NTU) to simulate different underwater conditions. The results revealed that across different water models, fluctuations due to angle of arrival (AoA) changes cause a one-order change in magnitude for clear water. In contrast, for harbor water, changes occur only at short ranges. Similarly, the signal-to-noise ratio changes sharply in harbor water compared to clear water as the communication range increases. When we studied the effect of ML models and FEC, we found that an additional 5 m of error-free range can be achieved in underwater environments for 100 Mbps UWOC links using a 2-watt green laser. In different scenarios, ML models alone were able to provide an error reduction from 10−1 to 10−2 across all water conditions. Received: 6 November 2025 | Revised: 28 January 2026 | Accepted: 30 March 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Shreyas Jain: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization. Harshit Kumar Sharma: Software, Validation, Investigation. Appala Venkata Ramana Murthy: Conceptualization, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.
underwater wireless optical communication
Estimator Algorithms for Determining the Elastic Properties of Chalcogenide Glasses Based on Elemental Composition
Accurate prediction of the elastic properties of chalcogenide glasses (ChGs) remains a long-standing challenge due to the structural complexity of amorphous networks and the limited availability of reliable mechanical measurements. In this work, we develop a set of numerical estimator algorithms capable of predicting Poisson's ratio, Young's modulus, the Bulk modulus, and the Shear modulus of a ChG solely from its elemental composition. Building on our earlier density-estimator framework, we introduce two composition-based weighting schemes—XC weighting for Poisson's ratio and XMC weighting for the elastic moduli—that incorporate atomic fraction, atomic weight, and coordination number. Element-specific high- and low-concentration endpoint values are found using a reverse Monte Carlo analysis approach and interpolated using a Sigmoid functional form. The resulting estimators were applied to 171 glass compositions spanning 16 ChG families with previously reported elastic properties. Across this dataset, the estimators achieved standard deviations of approximately 2% for Poisson's ratio and less than 5.7% for the elastic moduli. These results show that the elastic properties of ChGs can be predicted with practical accuracy using only elemental composition, enabling pre-melt screening of candidate materials and reducing experimental cost and effort. Received: 9 December 2025 | Revised: 25 February 2026 | Accepted: 9 April 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing not applicable—the authors generated no new data. All elastic properties data used by the authors to develop their models, equations, and example calculations were extracted from the sources provided below [DA01-DA08] and in references [24–40]. In this regard, all data have been measured over the course of the last 20 years. In some cases, peer-reviewed journal articles for a specific glass family and/or composition's elastic properties data were not available. For reputable data sources, the authors relied on the scientific expertise of the major infrared optical chalcogenide glass manufacturing companies: Schott North America, Inc., Amorphous Materials, Inc., Vitron Spezialwerkstoffe, GmbH, and Wavelength Opto-Electronics, Singapore (using their published datasheets). DA01. Comparison of IR transmitting glasses produced by AMI (Version5). https://www.amorphousmaterials.com/app/download/6541860504/ Comparison+of+IR+Materials+ver+5.pdf DA02. Schott. (2025). IRG25 datasheet. https://www.schott.com/en-us/products/infrared-glasses-and-materials/downloads DA03. Schott. (2025). IRG22 datasheet. https://www.schott.com/en-us/products/infrared-glasses-and-materials/downloads DA04. Schott. (2025). IRG27 datasheet. https://www.schott.com/en-us/products/infrared-glasses-and-materials/downloads DA05. Vitron. (2025). IG-2 datasheet. https://www.vitron.de/upload/vitron-ig-2-datenblatt-okt-2020-1_901.pdf DA06. Vitron. (2025). IG-3 datasheet. https://www.vitron.de/upload/ vitron-ig-3-datenblatt-okt- 2020-1_55.pdf DA07. Hilton, A. R., Hayes, D. J., & Rechtin, M. D. (1974). Chalcogenide glasses for high energy laser application (Report No. TI-08-74-44). Texas Instruments. https://apps.dtic.mil/sti/html/tr/AD0782036/index.html DA08. Wavelength opto-electronic datasheets. https://wavelength-oe.com/wp-content/uploads/Chalcogenide-Materials.pdf Author Contribution Statement Richard A. Loretz: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Thomas J. Loretz: Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization, Project administration.
Computational Investigation of Second Harmonic Generation in KTP Crystals Using COMSOL
This study presents a COMSOL Multiphysics-based finite-element workflow for steady-state modeling of second harmonic generation (SHG) in potassium titanyl phosphate. The electromagnetic fields at the fundamental frequency 𝜔 and the second-harmonic frequency 2𝜔 are solved in the frequency domain with explicit nonlinear polarization source terms, and the resulting photon flux trends are benchmarked against the standard depletion-included slowly varying envelope approximation under an idealized phase-matched condition (Δk ~ 0). Two pump wavelengths (1064 nm and 808 nm) and their corresponding SHG wavelengths (532 nm and 404 nm) are investigated, together with parametric variations of input intensity and an effective nonlinear coefficient used in the model. The results provide spatial field maps and photon flux evolution in a reproducible finite-element method setup; reported high conversion levels should be interpreted as upper-bound trends within the simplified, lossless benchmark assumptions rather than direct bulk experimental performance predictions. The present work can serve as a practical starting point for later extensions toward tensor-resolved, dispersion-aware, and fully three-dimensional SHG models. Received: 9 December 2025 | Revised: 28 April 2026 | Accepted: 11 June 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are available within the article. Author Contribution Statement Nabeel Ahmed: Conceptualization, Methodology, Software, Formal analysis, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization. Muddasir Naeem: Validation, Formal analysis, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision. Tayyab Imran: Conceptualization, Methodology, Validation, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Supervision, Project administration.
Performance of Encoding, Encryption, and Modulation Schemes in Free-Space Optical Communication Evaluated on the Atmospheric Testbed
In this paper, we investigate the adverse atmospheric effects, including wind disturbance, dry fog, wet fog, and smoke conditions, which are simulated on an atmospheric testbed specifically built for free-space optical communication (FSOC) experiments. We have also developed an FSOC system that can modulate the optical signals with the choice of the modulation, encoding scheme, and encryption. A robust, secure link that is operated by the user from a single graphical user interface. We have further tested the secure link with two encryption schemes, three error correction codes, and five different modulation formats with various combinations and in different atmospheric conditions. We have evaluated the link performance by two important metrics, that is, execution time and bit error rates. The results obtained can explicitly show the effect of the adverse channel. Initial experiments, with a clean chamber, showed the behavior of link performance with data rate. Further results show that the smoke chamber can adversely impact the FSOC system with an early onset of error occurrence and contributes to 10–20% of additional error compared to a clean chamber. Among error correction codes, the Reed–Solomon code helps to improve the error in all adverse conditions. This study further expands to the real-time and on-field investigation of free-space optical links for better performance. Received: 27 October 2025 | Revised: 29 January 2026 | Accepted: 7 May 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Shashank Shekhar: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization. Dhanush Devappa B C: Methodology, Software, Data curation, Writing – original draft. Moksh Chandrakar: Investigation. Appala Venkata Ramana Murthy: Resources, Writing – original draft, Supervision, Project administration, Funding acquisition.
Thermographic Effects of 445 nm Laser in Periodontal and Periapical Areas Ex Vivo
The objective of the study was to evaluate heat transfer within periodontal and periapical tissues when exposed to a 445 nm diode laser operating in continuous-wave (c.w.) versus pulsed mode. Mandibular bovine anterior teeth were endodontically prepared, and posterior teeth were used for laser-assisted periodontal therapy. A 445 nm diode laser was irradiated on root canals (120 μm glass fiber) and periodontal pockets (320 μm glass fiber) for 30 s (n = 20) at 2W in c.w. and pulsed modes (15 Hz, 50% duty cycle) using non-initiated tips. The maximum temperature changes (in °C) and heat transfer in height (vertical surface temperature distribution) and width (lateral heat transfer) were captured using a thermographic infrared camera. Mean periodontal heat temperature changes (in °C) were 36.53 ± 10.32 (c.w.) and 22.32 ± 8.46 (pulsed). In the periapical areas, the temperature changes were 11.65 ± 4.46 and 7.74 ± 2.40, respectively. In the periodontal tissues, lateral heat transfer was 6.13 ± 0.85 mm in c.w. mode and 6.94 ± 1.03 mm in pulsed mode. In the periapical areas, lateral heat transfer was 4.11 ± 0.75 mm in c.w. mode and 3.59 ± 0.32 mm in pulsed mode. The vertical surface temperature distribution in periodontal tissues showed similar patterns to periapical areas with minimal difference in both modes. Within the limitations of this study, a 445 nm diode laser caused a higher temperature change in continuous waves and produced greater lateral heat transfer than vertical spread in periodontal and endodontic applications. Received: 29 November 2025 | Revised: 28 February 2026 | Accepted: 25 March 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Grace Kang: Writing – original draft, Writing – review & editing, Visualization. Jamie Wu: Investigation. Ghaedsharafi Yasamin: Validation, Investigation. Jiayue Han: Writing – original draft, Writing – review & editing, Visualization. Thomas Manders: Validation, Investigation, Writing – review & editing. Rafael Delgado-Ruiz: Software, Validations, Formal analysis, Resources, Data curation, Writing – review & editing. Georgios E. Romanos: Conceptualization, Methodology, Validation, Investigation, Resources, Writing – review & editing, Visualization, Supervision, Project administration.
Mitigating Surface-Roughness Effects in the BaTiO3 Top Protective Layer of a Divergence Beam Surface Plasmon Resonance Sensor Using Savitzky–Golay and Whittaker Filters
Surface roughness in the top protective layer of a surface plasmon resonance (SPR) sensor degrades performance by introducing reflectivity fluctuations, broadening the resonance dip, and reducing the accuracy of resonance-angle estimation. In practice, obtaining a perfectly uniform barium titanate (BaTiO3) protective coating over a commercially sized SPR chip is difficult; therefore, signal processing strategies that compensate for roughness are of practical interest. In this study, a periodic roughness profile is used to model thickness fluctuations in a 3 nm BaTiO3 overlayer, and the resulting impact on SPR performance is analyzed theoretically using the transfer matrix method. Two digital smoothing approaches, the Savitzky–Golay (SG) filter and the Whittaker filter, are then evaluated as post-processing tools. The results show that the roughness height of 1 nm can reduce the signal-to-noise ratio (SNR) to approximately 6.4 dB and broaden the resonance feature sufficiently to compromise reliable detection. Among the tested methods, the Whittaker filter yields the most faithful recovery of the SPR curve, improving resonance-position accuracy by a factor of 119.14 relative to the rough signal, whereas the SG filter provides an improvement factor of 18.81. The Whittaker filter also increases the SNR to 26.44 dB, which signifies enhancement by 75% and preserves sensor sensitivity (390.12°/refractive index unit (RIU)), which remains close to the ideal value of 396.27°/RIU and detection accuracy more effectively than the SG filter. These findings indicate that Whittaker smoothing is a practical, low-cost computational strategy for mitigating roughness-induced degradation in high-sensitivity SPR biosensors. Received: 11 November 2025 | Revised: 28 April 2026 | Accepted: 29 May 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data supporting the findings of this study are available within the article, and no external dataset was generated or analyzed. Author Contribution Statement Jordan H. Hossea: Conceptualization, Methodology, Formal analysis, Resources, Writing – original draft, Visualization. Athuman O. Mfinanga: Software, Validation, Investigation, Writing – review & editing, Supervision.
Tunable Phase Shifters for 6G Beamforming Networks
The deployment of 6G network requires multiple number of antennas at the base station with multiple signals that undergo constructive interference to create thinner beams with more energy so as to mitigate path loss. This will support higher data rates, lower latency levels, and improved energy efficiency. This paper proposes a phase-shifting technology for beamforming that focuses radio energy to a specific user equipment, thus maximizing spectral efficiency. We present a novel approach of phase-shifting technology by generating tunable microwave pulses using the slicing-level technique in an optoelectronic oscillator (OEO) setup. Two laser sources undergo intensity and phase modulation using a well-characterized Mach–Zehnder modulator and a phase modulator. Modulating signals in the range of 100 kHz–13.3 MHz are used to generate microwave waveforms. Repetition-rate-tunable pulses are generated from the microwave waveforms using the slicing-level technique. Photonic-assisted tunable pulses generated have a pulse width ranging from 0.6 ns to 7.5 μs and a duty cycle ranging from 17% to 96% optimized for phase shifting (𝜑) of signals, with potential for multiple antenna elements, which act as time delays aimed at creating constructive interference of the beams that form a concentrated beam of energy. This work successfully creates phase shifters ranging from 14° to 299° that can be used to steer antennas for 6G network by controlling pointing angles at the antenna array terminals, which creates a multiplex transmission line as a linear combination of signals. Received: 30 October 2025 | Revised: 30 January 2026 | Accepted: 19 May 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are available within the manuscript. Author Contribution Statement Victor Chepkech Naibei: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Dismas Choge: Validation, Formal analysis, Resources, Writing – review & editing, Supervision, Project administration. James Jena: Methodology, Investigation. David Waswa: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing – review & editing, Supervision, Project administration, Funding acquisition. Duncan Kiboi Boiyo: Validation, Writing – review & editing.
Effect of Temperature on the Dispersion Properties of Water-Filled Photonic Crystal Fibers
This study aimed to dynamically control the optical dispersion properties of water-filled photonic crystal fibers (PCFs) by adjusting their temperature and the wavelength of the applied pulse (0.8–1.5) nm. Using numerical modeling (finite element method), the effect of hole diameter (1.5–4.5 μm) and temperature (15–95 °C) on the zero-dispersion wavelength (ZDW) was analyzed. The results showed that increasing the hole diameter reduced the ZDW from 1.1324 to 1.0216 μm (at 15 °C) and increased the maximum positive dispersion (from 38.67 to 53.24 ps/nm/km). Increasing the temperature also shifted the ZDW toward longer wavelengths of 36.5 nm with a tuning accuracy of ±5 nm. This behavior is due to the decrease in the refractive index of water with temperature, which alters the balance between material and wave dispersion. The importance of these results extends beyond the theoretical aspect, as they constitute a qualitative addition in two critical technical fields: first, in optical communications systems, where this dynamic control opens the way to designing fibers capable of handling multiple wavelengths with enhanced performance, and second, in the field of supercontinuum generation research and its advanced applications, where these smart, thermally tunable fibers could contribute to the development of highly efficient nonlinear optical devices, such as amplifiers and ultrafast light sources, placing them at the heart of promising future technological applications. Received: 16 October 2025 | Revised: 23 January 2026 | Accepted: 27 March 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Mohammed Salim Jasim AL-Taie: Conceptualization, Software, Investigation, Data curation, Writing – original draft, Supervision. Hayder Ahmed Hasan: Methodology, Validation, Resources, Project administration. Mohammed Kadhum Hamad: Formal analysis, Writing – review & editing, Visualization.
Scaling Rules for TM Modes in Thin–Film Optical Waveguides
Three-media planar dielectric nonmagnetic optical waveguides represent basic structures employed in integrated optics and sensing. The previously published scaling rules for transverse electric (TE) and transverse magnetic (TM) modes in these structures were characterized with different sets of parameters for TE and TM cases. The latter case which is more involved received less attention. The present work suggests an alternative approach where both TE and TM modes are characterized by the same set of three parameters, that is, normalized frequency or film thickness, normalized guide index, and asymmetry measure. A complete specification of the TM modes requires an additional parameter, that is, the ratio of the index of refraction in the film to that in the substrate. The TE and TM solutions for the normalized guide index and the normalized guide thickness are displayed in common charts as functions of normalized frequency. This provides an improved insight into the differences between the TE and TM guided modes. Received: 16 October 2025 | Revised: 24 February 2026 | Accepted: 28 April 2026 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Štefan Višˇnovský: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration.
Photonics in Smart Clothing for Personalized Medicine
The implementation of mobile health (m-Health) technologies into personalized healthcare systems requires substantial financial investment and the engagement of diverse social resources. Mobile systems integrated into smart clothing represent one of the key directions for the future development of healthcare, particularly with the emergence and deployment of high-speed 5G/6G networks. Underpinning this transition from traditional treatment models—based on diagnosis, medical history, and test results—is the concept of disease prevention and real-time early intervention. Prototypes of m-Health systems developed over the past decade, leveraging photonics and flexible electronics, open new frontiers in healthcare delivery. 5G/6G technologies enhance the efficiency of m-Health in smart clothing through features such as massive multiple-input multiple-output data transmission, secure communication protocols, wireless charging, and energy-efficient operational modes. Smart clothing equipped with embedded multispectral sensors, combined with big data analytics and m-Health systems, enables continuous health monitoring, facilitating timely detection and prevention of diseases. This review-conceptual article presents key aspects of designing prototypes of smart clothing based on thin-film micro- and nanoelectronics. It addresses scientific, technical, and social dimensions of implementing these solutions, including the development and investigation of multispectral sensors, aimed at enhancing healthcare system efficiency, improving patients' quality of life, and laying the foundation for future personalized medicine. Received: 12 September 2025 | Revised: 31 December 2025 | Accepted: 27 January 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Irina Veshneva: Methodology, Software, Validation, Formal analysis, Writing – review & editing. Rustam Singatulin: Conceptualization, Methodology, Validation, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.
Observable Effects and Peculiarities of the Low-Energy Quantum Gravity
The existence of a background of ultra-strongly interacting gravitons is a key postulate of the author's low-energy gravity model. Side effects of the model due to photons interacting with this background may be important for cosmology, and their observation would be essential to support the model. The most important such effect is the quantum redshift mechanism, which may constitute an alternative to the generally accepted mechanism associated with the expansion of the universe. The model should have a weakening of the light flux due to a change in the number of photons, which replaces the influence of dark energy. Scattered photons may form a new background that can be detected by deep space missions. Some important predictions of the model are tested using observational data sets of Supernovae Ia (SNe Ia), compact quasars, and Lyman-alpha emitters. The article shows that the linear function H(z) of the model satisfactorily describes the results of measurements of the Hubble parameter. Using a trial function for the weakening parameter, the possibility of a different interpretation of the Hubble tension is illustrated. The increasing angular diameter distance of this model is fitted to a set of 120 measurements of the angular sizes of compact quasars with redshifts of 0.46–2.76 with independent calibration of their linear sizes. Attention is drawn to the possibility of a false interpretation of changes in the measured sizes of Lyman-alpha emitters observed by the James Webb Space Telescope in the redshift range of 3–7 as evolutionary effects in the Lambda Cold Dark Matter (ΛCDM) model, since these changes can be due to the increasing angular diameter distance of this model. Received: 14 August 2025 | Revised: 10 October 2025 | Accepted: 1 January 2026 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are openly available at https://doi.org/10.1007/s41114-022-00040-z, reference number [9]; https://doi.org/10.1088/0004-637X/746/1/85, reference number [19]; https://doi.org/10.1051/0004-6361/201730551, reference number [25]; and https://doi.org/10.3847/1538-4357/ae24e4, reference number [26]. Author Contribution Statement Michael A. Ivanov: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization.
Comprehensive Analysis of Structural, Optical, Topographical, and Photosensing Characteristics of CuZnO Thin Films Synthesized via Facile Chemical Route
This study outlines the low-cost synthesis of copper-doped zinc oxide (Cu:ZnO) thin films using a chemical bath deposition method performed at 50 °C. A detailed investigation of their structural, optical, and electrical properties was conducted. X-ray diffraction confirmed the successful integration of copper within the ZnO lattice, resulting in a hexagonal Wurtzite structure and an average crystallite size of 17.18 nm. The Williamson-Hall method revealed compressive strain within the films, which is expected to influence their optical and electronic behavior. UV–Vis absorption analysis showed significant light absorption in the visible spectrum, with an absorption edge close to 700 nm, indicating a band gap of approximately 2.67 eV. Topographical analysis highlighted variations in grain structure and surface roughness. Current-voltage characteristics, measured both in darkness and under 100 W light exposure, demonstrated linear behavior indicative of ohmic contact. A notable rise in photocurrent under illumination resulted in about 78.7% photosensitivity at a bias of +2 V, confirming efficient photocarrier generation. Received: 26 August 2025 | Revised: 9 January 2026 | Accepted: 31 March 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not ​applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Harshal P. Borse: Conceptualization, Methodology, Investigation, Data curation, Writing – original draft. Neha P. Chaware: Methodology, Software, Investigation. Manohar R. Patil: Writing – review & editing. Arun V. Patil: Writing – review & editing. Nanasaheb P. Huse: Conceptualization, Methodology, Software, Validation, Resources, Data curation, Writing – review & editing, Visualization, Supervision.​
Evaluation and Characterization of the Optical Properties of NBR Rubber/N220 Granular Carbon Black Composites
This study investigates the optical and dielectric properties of nitrile butadiene rubber (NBR) reinforced with varying concentrations of N220 carbon black (CB). Ultraviolet (UV)–visible spectroscopy, in the range of 200–800 nm, was used. The optical spectrum showed a high absorption peak at approximately 220 nm, indicating that the material is suitable as a strong absorber of ultraviolet radiation. The direct optical band gap decreases slightly from 5.55 eV to 5.34 eV as CB content increases. The Urbach energy values, around 1.5 eV, suggest the formation of structural disorder and band tail states induced by CB–rubber interfacial interactions. The optical parameters such as extinction coefficient and refractive index exhibit characteristic variations around 220 nm, corresponding to strong absorption and high photon–carrier coupling. Dispersion behavior, interpreted through the Wemple–DiDomenico and Sellmeier models, reveals consistent variations in the effective oscillator energy, dispersion energy, and oscillator length strength. Dielectric analysis demonstrates that both the static and high-frequency dielectric constants are sensitive to CB loading, while the real part of the dielectric constant dominates over the imaginary component across the spectrum. Generally, the optical and dielectric findings demonstrate that the incorporation of N220 CB substantially modifies the energy band structure, optical dispersion, and charge carrier dynamics of NBR composites. These characteristics suggest their promising potential for optoelectronic and UV-sensing applications, where tunable optical absorption and dielectric response are critical. Received: 24 August 2025 | Revised: 10 November 2025 | Accepted: 23 December 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement K. Alfaramawi: Conceptualization, Formal analysis, Resources, Writing – review & editing. S. Abboudy: Formal analysis, Resources, Data curation, Writing – review & editing, Visualization, Supervision, Project administration. L. Abulnasr: Formal analysis, Investigation, Data curation, Writing – review & editing. S. Ebrahim: Investigation, Writing – review & editing. Ahlam K. Yousif: Methodology, Data curation, Writing – original draft.
Advances in Gain Control Techniques for Bismuth-Doped Fiber Amplifier
With the explosive growth of global data traffic, extending communication bandwidth is one of the important methods to alleviate the pressure on communication capacity. As the core device of an optical fiber communication system, the bandwidth extension of the optical amplifier is an indispensable research focus. Bismuth-doped fiber amplifier (BDFA) has been widely studied because of its unique broadband luminescence characteristics. In wavelength division multiplexing systems, the signal power fluctuates as the signal goes up and down, and the network is reconstructed. This results in a gain variation of the BDFA, which deteriorates the transmission system performance. The introduction and application of gain control technology can solve this problem well. In addition, the endogenous pump generated by the gain control structure can be combined with the characteristics of bismuth-doped fiber to achieve low-cost and efficient broadband amplification. The combination of these two technologies provides inspiration for the development and application of a broadband amplifier. Received: 20 August 2025 | Revised: 13 October 2025 | Accepted: 18 December 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The data that support the findings of this study are openly available in Forc-Photonics at https://www.forc-photonics.ru/bi-doped-fibers. Author Contribution Statement Lihong Wang: Methodology, Formal analysis, Investigation, Writing – original draft, Visualization. Ge Wu: Methodology, Investigation, Writing – original draft, Visualization. Yidan Zhao: Validation, Investigation, Writing – review & editing. Jingjing Zheng: Conceptualization, Writing – original draft, Writing – review & editing, Project administration, Funding acquisition. Li Pei: Resources, Supervision. Tigang Ning: Supervision.
On the Influence of Gravity on the Deviation of the Direction of Light Propagation and Gravitational Time Slowdown
It has been established that the change in the direction of light propagation near massive astronomical bodies, such as the Sun, occurs due to the refraction of light in the cosmic environment. The role of the gravitational field is exclusively to increase the density of the cosmic environment as it approaches a massive body. The gravitational field has no direct effect on the light beam or photons. The incompatibility of the energy of gravitational processes with the idea of the interaction of space-time with objects of physical reality, including massive bodies and photons, has been established. Space-time is not an object of physical reality. It has been established that due to the decrease in the optical density of the cosmic environment as it moves away from a massive body, a gravitational red shift occurs. The idea of gravitational time dilation is devoid of physical (common) sense. It is not time that slows down. It is the physical processes that occur with material objects that slow down. Received: 2 July 2025 | Revised: 27 August 2025 | Accepted: 10 October 2025 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Igor P. Popov: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.
Copyright (c) 2025 Author https://creativecommons.org/licenses/by/4.0/
Features of Restoration of Orientation of Nematic Liquid Crystals After Pulse Shift
The aim is to study the processes of restoring the orientation of nematic liquid crystals (LCs) after a pulse shift. A sample of 4-octyl-4'-cyanobiphenyl was examined. The thickness of the LC layers ranged from 35 to 105 microns. The research methods included an experimental study of the effect of a mechanical shear pulse on thin layers of homeotropically oriented LCs (the Foner method) and theoretical modeling based on the Eriksen–Leslie equations. The experiment was carried out on a multilayer cell. Changes in the orientation of molecules were studied using optical imaging and recording of electrical signals. The obtained results showed a significant change in the temporal dynamics of light transmission and the angles of rotation of the director with a change in the amplitude and duration of the pulse. The main results showed that director relaxation occurs exponentially, and nonlinear effects such as the formation of domain structures and orientation waves were observed at amplitudes from 200 to 350 microns. At the same time, the relaxation time decreases rapidly. The proposed theory made it possible to explain the observed effects and calculate the relaxation time spectra. A satisfactory agreement was found between the theoretical and experimental relaxation time. The results obtained are important for improving the performance of LC-based devices such as displacement sensors, as well as understanding the fundamental mechanisms of the functioning of LC materials. Received: 10 July 2025 | Revised: 4 September 2025 | Accepted: 26 September 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Olga Denisova: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing. Yaroslava Abramishvili: Formal analysis, Investigation, Writing – original draft, Visualization.
orientation relaxation in liquid crystals
Copyright (c) 2025 Authors https://creativecommons.org/licenses/by/4.0/
First-Principles Study of the Structural, Electronic, and Optical Properties of NaTaO3
This study applies first-principles density functional theory calculations to systematically analyze the structural, electronic, and optical behaviors of the NaTaO3 perovskite. Different structures were evaluated for the studied material. The computations were performed using the full-potential linearized augmented plane wave approach together with local orbitals. In order to incorporate exchange–correlation effects, we applied the generalized gradient approximation (GGA) method, which is known to underestimate the bandgap value. To address this limitation, the Tran-Blaha modified Becke–Johnson exchange potential approximation is utilized for enhanced accuracy. The study provides a description of the bulk modulus and pressure derivative of orthorhombic NaTaO3 (Pbnm), as well as its density of states and electronic band structure. The structural parameters and stability derived from our calculations are in good agreement with both previous theoretical studies and available experimental data. Electronic structure analysis indicates that the material behaves as a semiconductor, exhibiting direct bandgaps of 3.15 eV using the Tran-Blaha modified Becke–Johnson (TB-mBJ) approach and 2.75 eV within the GGA framework. NaTaO3 exhibits an increase in its bandgap, accompanied by an improvement in physical properties within the TB-mBJ. We present a detailed discussion of the material's optical characteristics. The findings related to its electronic and optical properties indicate strong potential for optoelectronic applications within the visible and ultraviolet spectral ranges. Received: 7 August 2025 | Revised: 13 October 2025 | Accepted: 20 November 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Saadi Berri: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Nadir Bouarissa: Validation, Formal analysis, Writing – review & editing.
The Transformative Role of Biophotonics in Rapid, Real-Time, and in Situ Studies of Microbial Structure, Cellular Processes, and Interactions
Photonics and optical technologies provide powerful, noninvasive means to study microorganisms, including those that remain unculturable, by detecting light signals arising from specific structural and biochemical features. These include intrinsic chromophores such as aromatic amino acids, nicotinamide adenine dinucleotide hydride, and flavins; spectral signatures of functional groups in proteins, lipids, and nucleic acids; refractive index contrasts from cell walls and organelles; and scattering patterns shaped by microbial morphology. This review synthesizes current advances in applying optical and photonic methods to microbial research, with the explicit aim of showing how these tools enable in situ, real-time characterization of microbial structure, metabolic state, behavior, and interactions. We overview high-resolution imaging modalities (confocal, multiphoton, and super-resolution microscopy) for visualizing morphology and dynamics, spectroscopic techniques (Raman, surface-enhanced Raman scattering, Fourier transform infrared spectroscopy, fluorescence) for label-free molecular fingerprinting, and biosensors (fiber-optic, plasmonic, lab-on-chip) for rapid detection. We also examine light-based manipulation strategies (optogenetics, optical tweezers, laser ablation) that allow precise control of microbial processes and discuss emerging integrations with artificial intelligence analytics, quantum sensing, and space-adapted photonics. By linking the physical principles of signal generation to microbial targets, we highlight how photonics is transforming microbial ecology, diagnostics, and biotechnology and identify the technical challenges driving the development of next-generation optical tools. Received: 1 August 2025 | Revised: 20 October 2025 | Accepted: 28 November 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Abdul Rafay Rafiq: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Muhammad Abdullah Farooq: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Hamza Tariq: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Ahsan Raza: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Zeeshan Zafar Iqbal: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization.
BOL and EOL OSNR Margins in 10,000 km Pb/s DWDM Unregenerated All-Optical Lightwave Transmission Systems in the 2000 nm Band
We report the calculation of beginning-of-life and end-of-life (EOL) optical signal-to-noise ratio (OSNR) margins in designs of 10,000 km terrestrial and subsea Pb/s capacity all-optical (without O-E-O regeneration) dense wavelength division multiplexed lightwave systems in the 2000 nm band. Our margin analysis follows the OSNR budget tables originally designed for 1550 nm subsea lightwave transmission systems employing erbium-doped fiber amplifiers, as adapted for novel hybrid Tm-Ho-doped fiber amplifiers and hollow core fibers designed to operate in the 2000 nm region off the spectrum. Our analysis shows that ideal simulated losses of ≤ 0.0325 dB/km at 2000 nm in the novel hollow core transmission fibers are required for successful EOL system operation in the terrestrial lightwave system design, when assuming that the effective deployed loss = ideal loss + 0.030 dB/km. We discuss the implications of this analysis in the context of terminal tolerances, manufacturing and environmental impairments, Q-factor time variations, customer margins, and the anticipated aging behavior of the novel 2000 nm hollow core transmission fiber. Received: 15 May 2025 | Revised: 29 July 2025 | Accepted: 28 August 2025 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data for the 700 mW 1190 nm fiber-coupled PM-packaged pump diode are openly available at https://www.innolume.com/fabry-perot-laser-diodes/fiber-coupled-single-mode-laser-diode-at-1195nm-5/. Other data are available from the corresponding author upon reasonable request. Author Contribution Statement Robert E. Tench: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition.
Remaining Life Estimation of Power Towers Using Strain Sensor Data and LSTM Sequence to Sequence Models
This study investigates the effectiveness of embedding fiber Bragg grating (FBG) sensors in power transmission towers to assess the remaining service life of the structures following impacts from strong winds and hurricanes. FBG sensors monitor the structural integrity of the tower using online measurement of strain variations at critical structural points. The novelty of this work lies in employing a compact long short-term memory (LSTM) framework to estimate the remaining useful lifetime (RUL) from real-time FBG sensor data under both stable and fluctuating wind conditions. To estimate RUL of the tower, LSTM neural network has been implemented, providing predictive insights for proactive maintenance and risk mitigation. A prototype transmission tower was built and experimentally evaluated in a wind tunnel to assess the effectiveness and performance of the proposed RUL model. To simulate different hurricane categories, the experiment was conducted across wind speeds between 0 and 150 mph. FBG sensors installed at critical locations continuously captured real-time strain data, which was transmitted via a low-power micro FBG interrogator to a computer for input into the RUL prediction model. The proposed three-layer LSTM converges rapidly, reducing training and validation loss by nearly two orders of magnitude within 40 epochs, and achieves robust RUL predictions with an average bias of about 50 s on the test set. To quantify structural health, a mathematical health indicator was formulated based on the observed strain responses. The FBG sensors demonstrated high effectiveness in accurately detecting strain variations and monitoring the tower's dynamic behavior under extreme wind loads. The findings support the implementation of condition-based maintenance strategies, enhance safety assessments, and enable early failure detection. This approach not only improves operational reliability but also facilitates timely intervention and maintenance during critical events. Received: 26 June 2025 | Revised: 12 September 2025 | Accepted: 11 November 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Yu Shi: Methodology, software, formal analysis, data curation, writing – original draft, writing – review & editing, visualization, supervision, and project administration. Abolghassem Zabihollah: Conceptualization, methodology, software, validation, investigation, resources, data curation, writing – original draft, writing – review & editing, visualization, supervision, and project administration. Yao-Chi Yu: Methodology, software, formal analysis, data curation, and writing – original draft. Arunima Pathak: Investigation, writing – original draft, and visualization. Oluwaseyi Oyetunji: Investigation.
Performance Analysis of RSA Encrypted Secure Free-Space Optical Communication Link Under Adverse Atmospheric Conditions Implemented on a Testbed
The increasing interest in the field of free-space optical communication (FSOC) can be attributed to the rising demand for an alternate communication system that can replace the existing communication systems. FSOC ranges from a few meters of indoor communication to a few kilometers of terrestrial range to satellite communication. The challenges posed vary in different scenarios. For indoors, major challenges are the artificial light sources, and for outdoors, it is the atmospheric channel-related concerns, such as fog, smoke, wind flow, and the turbulence of the channel. These adverse atmospheric conditions will degrade the link performance. On the other hand, the demand for secure communication links from the physical layer to the network layer is ever-increasing. In this paper, we have conducted a simulation study for various modulation techniques in different atmospheric conditions and have demonstrated the integration of a Rivest–Shamir–Adleman (RSA) encrypted link that offers security along with various digital modulation schemes. We have designed a lab-level setup for FSOC and developed various testbeds to simulate adverse atmospheric conditions. We tested FSOC link performance by measuring the bit error rate with various modulation schemes, that is, OOK (NRZ, RZ), PPM, and DPIM formats, along with RSA on the testbed. Received: 28 April 2025 | Revised: 24 June 2025 | Accepted: 2 September 2025 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Dhanush Devappa B C: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Chandani Kashyap: Validation, Investigation, Data curation. Shreyas Jain: Validation, Formal analysis, Data curation, Writing – review & editing. Soumit Banerjee: Methodology. Appala Venkata Ramana Murthy: Conceptualization, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.