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Here, we analyzed the effect of a donor molecule (Rh6G) on the random laser emission of an acceptor molecule (Rh640 perchlorate) coated on the surface of a polymer optical fiber. Due to the energy transfer mechanism, the random lasing threshold of Rh640 perchlorate was found to be reduced in the presence of Rh6G. Also, the emission spectrum of Rh640 perchlorate was blue-shifted with the addition of Rh6G. Meanwhile, there is an enhancement in the lasing threshold of Rh6G in the presence of Rh640 perchlorate. The present study demonstrates that by properly adjusting the concentrations of both donor and acceptor molecules, we can obtain a dual-color random laser emission from polymer optical fiber. [ABSTRACT FROM AUTHOR]

Traditional silica-based optical fiber strain sensors suffer from a limited range of strain detection, mismatched mechanical performance, and complicated sensing structures that hinder their practical applications involving complex strain patterns and large strain measurement. To solve these issues, the development of novel flexible optical fiber strain sensors with distributed and multimodal strain sensing performance is critical but challenging. In this work, a flexible hydrogel optical fiber with a step-index core/cladding structure was successfully designed and fabricated using a simple thermal polymerization method involving calcium alginate and polyacrylamide. The resulting flexible fiber exhibited a large stretch deformation capacity and good optical transmission property as well as an effective and reversible strain response. Significantly, a flexible hydrogel functional fiber was further constructed by doping quantum dots with different fluorescent emission wavelengths in different positions. By exploiting a combination of emission wavelength encoding and transmission loss, the assembled flexible hydrogel functional optical fibers could distinguish and recognize the locations, magnitudes, and modes (stretch or bend) of mechanical deformation through a single wavelength of visible light (365 nm) excitation. An ultra-large dynamic range (0–120%) of axial strain and bending deformation (10°–80°) could be effectively detected. This work offers a versatile solution to develop promising stretchable and distributed fiber strain sensors. [ABSTRACT FROM AUTHOR]

To enhance the load-bearing capacity of sapphire optical fiber (SOF) in extreme environments, this study prepared SOF/(BN/SiBCN) n by optimizing the nanostructure through increased deposition temperature of BN using alternating chemical vapor deposition. Simulation results indicated an inverse correlation between the leakage loss of SOF/BN/SiBCN and BN thickness; at room temperature, the tendency for coating cracking along the radial direction of SOF/BN/SiBCN is positively correlated with BN thickness, whereas this trend reverses at 1500 °C. Mechanical testing revealed that the tensile strength of SOF/BN/SiBCN is inversely correlated with the tendency for interlayer cracking, aligning with the findings from residual stress simulations; under an air environment at 1500 °C, SOF/(BN/SiBCN) 2 exhibited the highest tensile strength, indicating that the layered matrix design effectively mitigates the risk of BN oxidation by creating barrier layers. Optical test demonstrated that the BN coating functions as a total reflection layer to suppress the scattering of optical signals on the sapphire optical fiber surface. In conclusion, the coating design of SOF/(BN/SiBCN) n could meet the material requirements for sapphire optical fiber sensors in extreme environments. [ABSTRACT FROM AUTHOR]

Single crystals of Thiourea Cadmium hydrogen borate (TCHB), a hybrid nonlinear optical (NLO) material, are grown from an aqueous solution by slow evaporation solution growth technique at ambient temperature. Characterization studies have been conducted to probe the nonlinear effects of the crystal. The crystalline nature of TCHB is explored using the single crystal X-ray diffraction technique. The chemical composition is resolved by the Fourier transform infrared (FTIR) spectroscopy and energy dispersive X-ray analysis. UV–Vis spectral studies analyze the transparency of the crystal. Optical studies illustrate the UV cut-off wavelength to be 285 nm with wide window of transparency in the infrared and visible regions. The optical and electrical conductivity studies indicate superior optical response essential for optical computing and photonic applications. The Kurtz powder test has confirmed the NLO capability. The thermal stability is analyzed through a thermogravimetric study. Dielectric and AC conductivity measurements carried out over a wide range of frequencies (100 Hz to 5 MHz) for various temperatures establish the semiconducting and photonic capacity of TCBH crystal to be used as photodiodes, optical fibres and laser lights. [ABSTRACT FROM AUTHOR]

This research focuses on the nonlinear coupled Davey–Stewartson Fokas system, which models pulse propagation in monomode optical fibers. In order to find the novel periodic and solitary wave solutions of the nonlinear coupled Davey–Stewartson Fokas system, we have employed two effective mathematical techniques named as the Sine‐Gordon expansion method and the simple equation method. We found after researching into previous literature that these novel solutions are unique and have never been reported. Some 3D and 2D graphs are also used to discuss the dynamical behavior of these new solutions. [ABSTRACT FROM AUTHOR]

The characterisation of novel materials presents a challenge that requires new and original developments. To face some of these demands for making measurements at the nanoscale, a new microsphere-assisted white light interference nanoscope performing local reflectance mapping is presented. This technique presents the advantages of being non-destructive, full-field and label-free. A 145 μm diameter microsphere, glued to the end of an optical fiber, is inserted inside the white light interference microscope to improve the lateral resolution from 940 nm to 520 nm. The acquisition and the Fourier transform processing of a stack of interference images superimposed on the virtual image produced by the microsphere allows the extraction of the local reflectance over a wavelength range of 460 nm to 900 nm and a field of view of 8 μm in diameter. The enhancement in the lateral resolution of the reflectance is demonstrated through the spectral distinction of neighboring ripples on a laser-textured colored stainless-steel sample that cannot be resolved without the microsphere, on regions with a surface of 279 × 279 nm2 horizontally spaced 279 nm apart. Future improvements could potentially lead to a lateral resolution of reflectance measurement over a 100 nm diameter area in air, paving the way to sub-diffraction reflectance mapping. [ABSTRACT FROM AUTHOR]

Near‐infrared II (NIR‐II, 900–1880 nm) fluorescence confocal microscopy offers high spatial resolution and extensive in vivo imaging capabilities. However, conventional confocal microscopy requires precise pinhole positioning, posing challenges due to the small size of the pinhole and invisible NIR‐II fluorescence. To simplify this, a fiber optical wavelength division multiplexer (WDM) replaces dichroic mirrors and traditional pinholes for excitation and fluorescence beams, allowing NIR‐IIb (1500–1700 nm) fluorescence and excitation light to be coupled into the same optical fiber. This streamlined system seamlessly integrates key components—excitation light, detector, and scanning microscopy—via optical fibers. Compared to traditional NIR‐II confocal systems, the fiber optical WDM configuration offers simplicity and ease of adjustment. Notably, this simplified system successfully achieves optical sectioning imaging of mouse cerebral blood vessels up to 1000 µm in depth. It can discern tiny blood vessels (diameter: 4.57 µm) at 800 µm depth with a signal‐to‐background ratio (SBR) of 5.34. Additionally, it clearly visualizes liver vessels, which are typically challenging to image, down to a depth of 300 µm. [ABSTRACT FROM AUTHOR]

An optical fiber biosensor based on tapered noncore fiber (NCF) and coupling effect between surface plasmon resonance (SPR) and localized surface plasmon resonance is proposed in this paper. The sensor consists of two multimode fibers and a tapered NCF spliced in the middle. The tapered fiber with a waist diameter of 40 μm is fabricated by flame-heated drawing technology, and then a layer of Au film of 50 nm thickness is deposited on the surface of the taper waist. Au nanoparticles (AuNPs) are immobilized on the surface of the Au film by using the rich functional groups of polydopamine (PDA). The sensitivity is improved by reducing the diameter of the NCF and the electric field coupling between the Au film and AuNPs. The refractive index sensitivity of the sensor is increased to 3558 nm/RIU in the detection range of 1.335–1.365, which is about 1.8 times higher than that of Au-NCF sensor without tapering and AuNPs. Goat anti-rabbit IgG was fixed on the sensor surface through the adhesion effect of PDA and used for the specificity detection of rabbit IgG. The sensitivity and limit of detection (LOD) of the proposed biosensor are 1.16 nm/(μg/ml) and 0.017 μg/ml, respectively. The proposed biosensor has low manufacturing cost and high biological sensitivity, which has potential applications in low concentration biomolecular detection and human health monitoring. [ABSTRACT FROM AUTHOR]

The deployment and advancement of high‐bandwidth communication networks, quantum information systems, and sensing platforms relying on multi‐core optical fibers (MCFs) are challenged by the scarcity of cost‐effective, compact, and efficient optical interfacing components. This study introduces an unprecedented 3D‐printed 1 × 4 splitter for MCFs fabricated with 2‐photon polymerization‐based direct laser writing. The pivotal element is a triangular cross‐section 3D multimode interference (MMI) coupler, supplemented with S‐bends and adiabatic tapers to facilitate the splitting of a signal from a single core of a single‐mode fiber into four cores of a multi‐core fiber. All components are initially designed and assessed to minimize loss and polarization dependence across the C‐ and L‐bands using optical simulation. Subsequently, a proof‐of‐concept model of the splitter, compactly integrated within the fiber volume, featuring a remarkably short length of 180 µm and insertion loss of ≈−3 dB, is fabricated. The manufacturing speed, minimal loss, component compactness, and flexibility of the approach, collectively present promising avenues for pioneering developments in MCF‐coupling components. [ABSTRACT FROM AUTHOR]

As China enters the stage of deep coal mining, the accidents caused by roof failure pose increasingly serious threats. Current research on roof failure zones often use single methods, but single geophysical data may result in multisolution issues during interpretation. This paper employed similar simulation experiments, exploring the strain failure characteristics and the changes in apparent resistivity caused by stress variations, taking the 11-3106 working face of a mining area as the research object. Through optical fiber strain and apparent resistivity, the locations and degrees of fracture in postmining rock strata were identified. The feasibility of using distributed optical fiber sensing and the parallel electrical method for qualitative and quantitative analysis of mining-induced fractures was verified. The results showed that optical fiber strain increased significantly at the location of rock fracture, with apparent resistivity anomalies rising correspondingly. The peak strain region corresponded well with the region of apparent resistivity anomalies. In a similar simulation with a geometric ratio of 1:100, the height of the caving zone was measured to be 31.65 cm, with a caving-to-mining ratio of 6.33. In the field working face, the caving zone height was 29.47 m, with a caving-to-mining ratio of 6.01, consistent with the actual conditions of the 11-3106 working face. [ABSTRACT FROM AUTHOR]

To investigate the reasonable width of a coal pillar in the downward mining section of close-distance coal seams, the stress state of any point below the residual coal pillar in the overlying goaf and the width of a small coal pillar were studied by theoretical calculation, numerical simulation, similar simulation and field monitoring. The findings indicate that the width range of the small coal pillar is 7.92~11.42 m. The 4-1 coal seam is in the stress reduction zone when it is more than 16.6 m horizontally from the border of the residual coal pillar above it. In addition, the peak stress is situated inside the elastic zone of the coal pillar and is lower than the coal pillar's bearing limit when a small coal pillar of 8 m is maintained. With the help of distributed optical fiber monitoring to model the coal pillars' stress distribution, it is found that 8 m simulated coal pillars have a certain bearing capacity. The practical findings demonstrate that the 8 m small coal pillar that was left on the site satisfies the demand, and the convergence of the roadway's floor and roof, and its two sides fall within the controllable range. The findings of the study offer a reference for the location of a return air roadway and the width of section coal pillars in the downward mining of close-distance coal seams. [ABSTRACT FROM AUTHOR]

A key challenge toward future quantum internet technology is connecting quantum processors at metropolitan scale. Here, we report on heralded entanglement between two independently operated quantum network nodes separated by 10 kilometers. The two nodes hosting diamond spin qubits are linked with a midpoint station via 25 kilometers of deployed optical fiber. We minimize the effects of fiber photon loss by quantum frequency conversion of the qubit-native photons to the telecom L-band and by embedding the link in an extensible phase-stabilized architecture enabling the use of the loss-resilient single-click entangling protocol. By capitalizing on the full heralding capabilities of the network link in combination with real-time feedback logic on the long-lived qubits, we demonstrate the delivery of a predefined entangled state on the nodes irrespective of the heralding detection pattern. Addressing key scaling challenges and being compatible with different qubit systems, our architecture establishes a generic platform for exploring metropolitan-scale quantum networks. [ABSTRACT FROM AUTHOR]

Ytterbium (Yb)-doped fibers using aluminophosphosilicate (Yb-APS) host glass offer significant advantages over conventional aluminosilicate (Yb-AS) fibers, such as strong photodarkening resistance, higher RE-ion solubility and lower Numerical Aperture (NA), making them ideal for high-power laser applications. However, achieving optimal performance in Yb-APS fiber fabrication poses various challenges, including maintaining a precise Al3+/P5+ ratio (1:1), minimizing the central dip in the refractive index profile (RIP), ensuring proper dopant distribution, and reducing background loss. We introduce a new fabrication method for Yb-APS fiber to address these challenges. This approach entails first synthesizing amorphous Yb³⁺: AlPO 4 particles, then incorporating them into the fiber core using a hybrid technique that merges Vapor Phase Delivery (VPD) with solution doping (SD). We extensively utilized various materials and optical characterizations, including XRD, FTIR, Raman spectroscopy, FESEM, and XPS, to fine-tune the composition of Yb³⁺: AlPO 4. The optical characterization of the developed preform sample, including absorption, emission, and luminescent lifetime measurements, was conducted to assess the fabrication technique's suitability. The results confirmed the successful incorporation of Yb-ions into the preform core, with peaks consistent with reported values. The fiber's attenuation loss was measured, showing approximately 10 dB/km at 1200 nm. This indicates that the particles dissolved smoothly during preform and fiber processing, resulting in minimal scattering loss in the fiber core. The developed fiber demonstrated NA of 0.1, uniform RIP along the preform length with significant reduction of the central dip formation and improved spectral performance (∼1.7X broader bandwidth) compared with an equivalent Yb-AS fiber. These findings suggest the Yb-APS fiber's overall effectiveness and structural robustness, highlighting the potential of the proposed fabrication method for high-power fiber laser applications. [ABSTRACT FROM AUTHOR]

The coupled higher-order nonlinear Schrödinger equations (CHNLSEs) are investigated in this paper. This model mimic the actuation of the solitons through multimode fibers. The technique of improved modified extended tanh function is used to conduct the study. Many exact solutions are achieved like bright solitons, dark solitons and singular solitons. Moreover, singular periodic solutions, Weierstrass elliptic function solutions, hyperbolic and Jacobi elliptic solutions are raised. Using 3D and 2D graphs, the physical behavior of the produced solutions is illustrated. [ABSTRACT FROM AUTHOR]

Delamination is a prevalent type of damage in composite laminate structures. Its accumulation degrades structural performance and threatens the safety and integrity of aircraft. This study presents a method for the quantitative identification of delamination identification in composite materials, leveraging distributed optical fiber sensors and a model updating approach. Initially, a numerical analysis is performed to establish a parameterized finite element model of the composite plate. Then, this model subsequently generates a database of strain responses corresponding to damage of varying sizes and locations. The radial basis function neural network surrogate model is then constructed based on the numerical simulation results and strain responses captured from the distributed fiber optic sensors. Finally, a multi-island genetic algorithm is employed for global optimization to identify the size and location of the damage. The efficacy of the proposed method is validated through numerical examples and experiment studies, examining the correlations between damage location, damage size, and strain responses. The findings confirm that the model updating technique, in conjunction with distributed fiber optic sensors, can precisely identify delamination in composite structures. [ABSTRACT FROM AUTHOR]

Polymer optical fibers (POFs), including side‐emitting POF (SEPOF) and end‐emitting POF (EEPOF) are developed for luminous textiles. The SEPOF is more common for usage but suffers from significant intensity decay, which limits its effective usage length. In contrast, the EEPOF can provide a much more stable side illumination behavior than SEPOF since the light is largely confined within the EEPOF, while its side illumination requires special treatment. In this work, 0.5 mm diameter EEPOFs were firstly assembled into bundles with 10 EEPOFs (B10) and 15 EEPOFs (B15), and then twisted. The morphology, tensile properties, and side illumination behavior of the twisted EEPOF bundles are evaluated. With an increased twisting degree, the initial modulus of twisted sample B10 increases (due to shortening of bundle diameter) from 1.06 to 1.17 GPa while the initial modulus of twisted sample B15 decreases from 1.01 to 0.91 GPa. The increased twisting degree also results in the higher flexibility (indirectly connected with modulus) of the twisted EEPOF bundles. Besides, the increased twisting degree results in a higher side illumination intensity meantime causes a decreased side illumination intensity along the light penetration path. When the twisting degree is low (e.g., 10 T m−1), the highest decrease rate of side illumination intensity along the light penetration path is found. [ABSTRACT FROM AUTHOR]

Structural health monitoring is essential for the lifecycle maintenance of tunnel infrastructure. Distributed fiber‐optic sensor (DFOS) technology, which is capable of distributed strain measurement and long‐range sensing, is an ideal nondestructive testing (NDT) approach for monitoring linear infrastructures. This research aims to develop a distributed sensing network utilizing DFOS for structural integrity assessment of concrete immersed tunnels. The primary innovations of this study lie in the development of a general flowchart for establishing a sensing network and obtaining reliable field data, as well as its subsequent validation through a detailed case study. Concentrated joint deformations in typical immersed tunnels, detectable by the DFOS, are key indicators of structural integrity. This study addresses crucial elements of field monitoring system design, including the selection of appropriate optical fibers or cables and the determination of vital interrogator system parameters. It also covers sensor parameter determination, installation techniques, field data collection, and postanalysis. Furthermore, this research is exemplified by a case study that illustrates the successful implementation of a distributed sensing network in an operational immersed tunnel, and monitoring data reveals cyclic structural deformations under impacts of daily tide and seasonal temperature variations. The data obtained from this network play a significant role in subsequent condition assessments of tunnel structures. The research findings contribute to the assessment of large‐scale infrastructure health conditions through the application of DFOS monitoring. [ABSTRACT FROM AUTHOR]

Plasmonic tilted fiber Bragg gratings (TFBGs) have emerged as versatile tools for refractometric analyses and biochemical sensing. Their applications have significantly blossomed these last years, from proteins and cellular bioassays to operando monitoring in batteries, to cite just a few. They are widely recognized for their cutting‐edge performance and low limits of detection, arising from their dense multimodal spectral nature featuring tens of narrowband cladding mode resonances. Their comb‐like spectrum is so rich that numerous demodulation techniques have been reported, without benchmark of their relative performance while they possess important distinctions. This review highlights developments in detangling techniques from the pioneering works based on single‐peak analysis up to the most recent approaches involving Fourier analysis, the implementation of machine learning, and cascaded spectral decomposition processes. To fairly compare the different techniques of the literature, we implemented each analysis on original experimental refractometric calibrations, revealing the assets of the most updated methods. This paper therefore reviews these demodulation techniques based on the same datasets, obtained under the same conditions. We show and discuss the results obtained from bioassays and pinpoint the importance of advanced analytical methodologies to maximize the reproducibility, reliability and performance of plasmonic‐based TFBGs biosensors. [ABSTRACT FROM AUTHOR]

The recombinant Cluster of Differentiation 40 Ligand (CD40L) can be expressed in various cells and is closely related to various types of cancer. This association underscores the critical need for expedited and precise measurement of CD40L levels in clinical fluid specimens. A novel optical fiber biosensor has been devised, employing single-mode fibers that are sandwiched around a coreless fiber, with the diameter refined by etching with hydrogen fluoride. This innovative configuration allows for light transmission through the evanescent field, thereby enhancing the sensor's sensitivity to changes in the surrounding refractive index. Employing chemical binding techniques, CD40 was securely immobilized onto the fiber's surface, facilitating the detection of CD40L. The sensor exhibited a sensitivity of 1.126 nm (μg mL−1)−1 and a detection limit of 0.68 nM. Furthermore, the sensor's specificity for CD40L was validated using authentic clinical serum samples spiked with artificial analytes. In addition, the specificity of CD40L of the proposed sensor was proved using natural clinical serum samples with added artificial analyte, assisted by the ELISA method, and the results ideally conformed with the detection of standard samples. With the aid of the ELISA method, the outcomes were found to be in excellent agreement with those from standard sample detection. Consequently, the findings indicate that this sensor provides a specific, label-free, and highly sensitive method for CD40L detection, showcasing its significant potential for applications in molecular biology research. [ABSTRACT FROM AUTHOR]

Ultrafast fiber lasers constitute a flexible platform to investigate new solitary wave concepts. To surpass the low energy limitation of the conventional solitons generated in standard telecom fibers, successive breakthroughs have promoted the usage of an important frequency chirping within fiber oscillators. This lead to original solitary wave regimes such as stretched-pulse, all-normal-dispersion, and self-similar dynamics. We here revisit ultrafast fiber lasers built from standard optical fibers featuring solely anomalous dispersion. We propose a new cavity design enhancing key dissipative effects with contained frequency chirping and demonstrate the generation of high energy pulses in the few-picoseconds regime. The involved intracavity dynamics blends conventional and dissipative soliton features in an unseen way with low- and high-energy propagation regions, allowing an increased flexibility and novel scalability prospects. The authors revisit ultrafast fiber lasers with anomalous dispersion to propose a new laser design enhancing dissipative effects. Their approach yields high-energy few-picosecond pulses, blending soliton features for improved flexibility and scalability. [ABSTRACT FROM AUTHOR]

TBM has been widely used in underground engineering and construction, but there is no precedent for the application of open TBM in the inclined shafts of coal mines, which brings new challenges to the support system. The distribution of the axial forces on anchors and the range of loosening of the surrounding rock are crucial considerations in tunnel support design. Existing methods for measuring the axial forces in anchors and determining the extent of loosening in the surrounding rock typically remain at the inspection level, lacking long-term and real-time monitoring capabilities. This paper presents a new self-sensing anchor with embedded optical fibers (made using an improved stirrer) and proposes an intelligent tunnel rock monitoring system. The paper also outlines a method for identifying loosening zones in surrounding rock based on monitoring data and theoretical analysis. Installing self-sensing anchors in the deep sections of the rock surrounding a tunnel provides three-dimensional, round-the-clock real-time monitoring of the axial forces acting on the anchors, using new technology and methods to recognize the deformation characteristics of loosening zones within the surrounding rock. This new self-sensing fiber optic anchor was first applied to an open TBM tunneling project in an inclined shaft in the Kekegai coal mine, and monitoring data indicate that self-sensing optical fiber anchors can accurately reflect stress patterns in real time. The axial force curve can be divided into four segments: the borehole area, the loosening zone, the stable zone, and the anchoring zone. Consequently, it accurately identifies the thickness of loosening zones at different positions within the tunnel's surrounding rock. This information is compared and verified against results obtained from bolt dynamometers and borehole inspection. On this basis, an intelligent monitoring system was established to provide a basis for making engineering construction decisions, which makes tunnel construction smarter and helps technicians timely adjust TBM driving and support parameters. [ABSTRACT FROM AUTHOR]

This paper investigates new analytical wave solutions for the fractional Kuralay-IIB equations (FK-IIBE), including a new definition of the fractional derivative. This model works in disciplines such as ferromagnetic materials, optical fibers, wave mixing, and nonlinear optics. The integrable motion of space curves can be determined by our governing model. This research holds great importance in the area of optical fibers, exact and analytical solitons solution. The polynomial method’s complete discrimination system (CDSPM) is used to identify a variety of exact and analytical soliton solutions such as periodic, hyperbolic, rational, Jacobian elliptic (JE), and trigonometric functions. Additionally, we also convert the JE function into a solitary wave (SW) solution. To provide a comprehensive understanding of the dynamic aspects of the system, we also address bifurcation points, quasi-periodic behavior, sensitivity analysis, Poincarè maps, time series profile, and critical solution conditions. The research offers straightforward, efficient algorithms that can consistently and effectively address FK-IIBE. Machine learning technologies are also utilized to satisfy the criteria defined by dynamic analysis. Python regression learner tools are used for reverse engineering to analyze the mathematical model’s equilibrium based on parameter intervals and thresholds determined by dynamical analysis. [ABSTRACT FROM AUTHOR]

Bismuth (Bi) and Germanium (Ge) co‐doped silica glass and fiber, as advanced gain media with broadband near‐infrared (NIR) emission and amplification, have promise for extending communication bandwidth. However, efficiently modulating the NIR emissions of bismuth to cover the C+L communication bands remain a significant challenge. In the study, a high‐temperature and high‐pressure reduction treatment on Bi/Ge co‐doped silica glass is employed to tailor the coordination environment around bismuth active center. This method facilitated the creation of new bismuth NIR luminescence centers, resulting in the luminescence spectrum with a peak position at 1550 nm and a FWHM exceeding 350 nm. The changes in the bismuth coordination environment are elucidated using HRTEM, photoluminescence decay, temperature‐dependent emission, EXAFS and CW‐EPR. Furthermore, the feasibility of this method in Bi/Ge co‐doped silica fiber is validated, and obtained >5 dB amplification in the range of 1400–1700 nm. This coordination engineering method holds significant potential for widespread application in Bi/Ge co‐doped silica glass and optical fiber is believed. It presents a promising prospect for expanding communication bandwidth by effectively modulating the NIR emissions of bismuth to cover the S to U communication band. [ABSTRACT FROM AUTHOR]

Fluorescence intensity ratio (FIR) thermometers have obtained great attention in industrial production, medical diagnosis and scientific research. However, the sensitivity has a large decline at high temperatures, which seriously limits the practical applications. Here, the Yb,Er,Tm:Sc 2 O 3 single crystal fibers were grown by laser-heated pedestal growth (LHPG) technique and its multi-mode FIR thermometry based on thermal coupled energy levels (TCLs) and non-thermal coupled energy levels (NTCLs) has been well demonstrated. The temperature measuring range of Yb,Er,Tm:Sc 2 O 3 single crystal fibers covers 298–973 K, with an increase of 2 orders of magnitude in absolute sensitivity. The relative sensitivity is higher than 0.02 % K−1 in the whole T-range of 298∼973 K, with a maximum value of 1.02 % K−1. Especially at the high temperatures of 973 K, it can still maintain 0.31 % K−1. This work proposes an innovative fluorescence intensity ratio detection strategy to achieve complementary disadvantages between TCLs and NTCLs and provides an effective method for improving detection sensitivity. [ABSTRACT FROM AUTHOR]

Featured Application: The displacement sensor developed in this work provides a robust and highly sensitive solution for measuring small displacements in industrial and scientific environments. It can be employed in precision machinery, robotics, and instrumentation, where detecting minimal movements with high accuracy is critical. Additionally, it holds potential for applications in optical metrology, structural health monitoring, and micro-mechanical systems, providing an adaptable and cost-effective tool for precise displacement measurements. This paper presents a displacement sensor designed to achieve the Optical Vernier Effect (OVE) through a simple yet robust configuration, enhancing sensitivity and precision in small displacement measurements. The sensor structure comprises a few-mode fiber (FMF) placed between two single-mode fibers (SMF) in an SMF-FMF-SMF (SFS) configuration. A series of distinct configurations of concatenated Mach–Zehnder fiber interferometers (MZFI) were examined, with the lengths of the reference FMF (FMFRef) and sensing FMF (FMFSen) adjusted to track the spectral envelope shifts. The results demonstrate that the direction of the spectral shift is governed by the ratio between the FMFRef and FMFSen lengths. The sensor achieved a sensitivity of up to 39.07 nm/mm and a magnification factor (M factor) of up to 50.09, demonstrating exceptional precision and adaptability across a range of applications. The proposed configuration also enhances the overall sensor performance, highlighting its potential for broader use in fields requiring precise displacement monitoring. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride has attracted significant interest in heterogeneous photocatalysis due to its activity under visible‐light irradiation. Herein, we report on using carbon nitride‐coated NMR tubes for in situ studies of photocatalytic reaction mechanisms. In a first step, we exploited carbon nitride‐coated crimp vials as batch photoreactors for visible photocatalytic fluorinations of unactivated C(sp3)−H bonds, with moderate to excellent yields and reusability over multiple cycles. Eventually, carbon nitride‐coated NMR tubes were used as a photoreactor by coupling them with optical fiber irradiation directly inside the spectrometer. This enabled us to follow the reaction with in situ NMR spectroscopy identifying reactive intermediates otherwise elusive in conventional analyses. The method provides advantages for the study of photocatalytic mechanisms of complex reactions and substantially reduces the need of comparative tests for depicting reaction intermediates and conversion pathways. [ABSTRACT FROM AUTHOR]

Electrochromic (EC) fibers capable of optical transmission, reflection, and emission modulation are highly desired for promising applications in electronic display, adaptive camouflage, and visual sensation. However, the non‐uniform electric field of the fiber structure and the lack of electrochemically stable transparent conductive electrodes still limit the practical applications of EC fibers. In this work, scalable EC fibers with long‐range modulation performance and electrochemical stability are fabricated using Ag@Au nanowires (AANWs) nanonetwork and parallel dual‐electrode. Benefiting from the electrochemically resistant Au shell layer that inhibits the oxidation of the nanonetwork electrodes, the EC fibers still maintain excellent EC performance even after 300 color changes. The synergistic interaction between the unique AANWs nanonetwork and the parallel dual‐electrode structure enables the 10 m‐long EC fibers to maintain rapid switching speeds and excellent color uniformity. Additionally, the utilization of mechanical looms to weave long EC fibers has facilitated the practical application of EC fibers in wearable displays, adaptive camouflage, and visual sensation. [ABSTRACT FROM AUTHOR]

This work discusses label-free biosensing application of a double-layer optical fiber interferometer where the second layer tailors the reflection conditions at the external plain and supports changes in reflected optical spectrum when a bio-layer binds to it. The double-layer nanostructure consists of precisely tailored thin films, i.e., titanium (TiO2) and hafnium oxides (HfO2) deposited on single-mode fiber end-face by magnetron sputtering. It has been shown numerically and experimentally that the approach besides well spectrally defined interference pattern distinguishes refractive index (RI) changes taking place in a volume and on the sensor surface. These are of interest when label-free biosensing applications are considered. The case of myeloperoxidase (MPO) detection—a protein, which concentration rises during inflammation—is reported as an example of application. The response of the sensor to MPO in a concentration range of 1 × 10−11–5 × 10−6 g/mL was tested. An increase in the MPO concentration was followed by a redshift of the interference pattern and a decrease in reflected power. The negative control performed using ferritin proved specificity of the sensor. The results reported in this work indicate capability of the approach for diagnostic label-free biosensing, possibly also at in vivo conditions. [ABSTRACT FROM AUTHOR]

This article describes a case study of a failure in which voice calls on the Hikari Denwa IP telephone service were being disconnected due to DHCP (Dynamic Host Configuration Protocol) conflicts. This is the eighty-fourth article in a series on telecommunication technologies. [ABSTRACT FROM AUTHOR]

NTT Access Network Service Systems Laboratories is promoting research and development (R&D) of optical fiber facility technologies that contributes to the sustainable development of communications networks. This article outlines the R&D of large-capacity and advanced optical fiber facilities for the All-Photonics Network, which is one of the three key elements of IOWN (the Innovative Optical and Wireless Network) concept advocated by NTT. This article also introduces the R&D activities of optical fiber facilities in response to social changes and demands such as the decrease in the working population, diversification of communication services, and reduction in environmental impact. [ABSTRACT FROM AUTHOR]

NTT Access Network Service Systems Laboratories is conducting research and development to support access networks in the fields of optical fiber access, infrastructure, access system, wireless access, and operation technologies. To advance the Innovative Optical and Wireless Network (IOWN) from concept to implementation by 2030, we introduce our vision of a future access network and our efforts to implement it. [ABSTRACT FROM AUTHOR]

In large scale manufacturing, polymeric materials for cable jackets are subjected to high temperature and shear, what can induce degradation processes. In result, changes in structure of polymer materials can occur what is critical for their applications. Permanent market pressure on increase of productivity and product reliability as well as rigorous administrative regulations in telecommunication industry are the driving forces for development and introduction of new advanced Flame Retardant Non-corrosive jacketing materials. Despite many studies, their behavior is still neither well characterized nor understood in large-scale production. The object of studies was characterization of a relationship between processing conditions and effects of degradation of FRNC cable materials. The main goal was to find the processing factors limiting the production speed. Materials taken into consideration were two commercially available thermoplastic FRNC compounds dedicated to fiber optic cables, based on linear low-density polyethylene/ethylene–vinyl acetate composites with high loading of aluminum trihydroxide and magnesium dihydroxide fillers. Thermal degradation of cable materials was studied with use of thermogravimetry and rheometry. The series of jacket samples under different processing conditions were produced. Material processing behavior was characterized, and tensile and heat aging performance of cable jacket were tested. The results showed that the primary limiting factors for line speed increase were the melt pressure and jacket tensile performance, but neither the shrinkage nor extruder motor load. The result and general approach to the FRNC investigation can be successfully used in cable industry or in other industries involving the extrusion of FRNC materials. [ABSTRACT FROM AUTHOR]

This study delves into utilizing the Kudryashov auxiliary equation method on the time-fractional (3+1)-dimensional Sasa–Satsuma equation, pivotal for transmitting ultra-fast pulses in optical fibers. The main aim is to generate a variety of optical solitons for the time-fractional nonlinear (3+1)-dimensional Sasa–Satsuma model, including dark, bright, singular, and straddled solitons. These solitons are derived from exponential and hyperbolic function-type solutions, presenting novel findings not previously reported. The study demonstrates the effectiveness of the implemented method in deriving analytical solutions for fractional differential equations. The (3+1)-dimensional Sasa–Satsuma model's potential in optical fiber transmission is highlighted, offering significant insights into generating optical solitons and their applications. [ABSTRACT FROM AUTHOR]

This paper applies the extended direct algebraic method (EDAM) for the first time to obtain the soliton solutions of the fractional Sasa–Satsuma equation (FSSE) with the descriptions of two fractional derivatives. To evaluate the optical soliton and some other solutions of the FSSE, the presented research applies the fractional beta and conformable derivatives. As a useful result of this research, several types of solitons have been identified, such as the single soliton, M-shaped, W-shaped, combined dark-bright, smooth dark, sharp dark, dark-bright, anti-bell shaped, and periodic. Among the nonlinear optics fields expanding at the fastest rate are optical solitons. A fundamental equation in the theory of optical fibers and telecommunications is the fractional Sasa–Satsuma equation. The transmission of femtosecond pulses in optical fibers as well as the interaction and propagation of ultrashort pulses in the sub-picosecond or femtosecond region are influenced by this equation. Additionally, the physical properties of the completed solutions are illustrated via contour, 3D, and 2D graphs. The EDAM is a practical and effective technique that offers a variety of avenues for future investigation. The fresh versions of the findings presented here have not been published in the full body of literature before. [ABSTRACT FROM AUTHOR]

Oriented to the multicore fiber-based space-division multiplexing (SDM) networks, the inter-core coupling in multicore fiber is desired to transfer signals between cores. In this paper, we proposed and designed an integrated optical coupler based on three-core fiber (TCF) with long-period gratings (LPGs). The TCF with three cores distributed in the cladding connected with single-mode fiber at both ends through adjacent cores. The self-coupling characteristics of TCF are studied firstly, and the effects of core pitch and coupling distance on coupling efficiency are analyzed to rule out the direct coupling between adjacent cores, indicating that coupling distance increases with the core pitch increases. With LPGs induced in TCF, coupling between core mode and cladding mode in each individual core is realized, and then the power at resonance wavelength transfers among cores through the overlapped cladding modes. Moreover, with the LPGs, the efficient coupling among adjacent cores in TCF has been realized at the C-band. In addition, the influence of structural parameters such as core pitch, grating duty cycle and coupling co-efficiency do affect the coupling efficiency of TCF-LPGs. By adjusting the structural parameters properly, coupling efficiency of ~ 66% could be achieved to equalizing the output power in three cores. Therefore, the proposed TCF-LPGs could be used as an optical coupler, which would be helpful in multicore fiber-based SDM networks. [ABSTRACT FROM AUTHOR]

Optical reflection is an important concern in all commercial optical systems because of their potential performance degradation effects. Various approaches are employed to minimize the reflections in the optical couplings/connections, such as anti-reflective (AR) coating, index-matching fluids, and angled surfaces/facets. This manuscript investigates the Optical Return Loss (ORL) of different kinds of angled-facet waveguides using the power overlap between the incoming mode and the reflected one. We present a novel and straightforward analytic method to analyze the reflectance of tilted-facet waveguide modes with the advantage of no analytical approximation of the guided modes profiles that can be used to design integrated photonic waveguides. The dependence of the reflectance on the Mode Field Diameter (MFD) of optical fibers is examined. It is shown that an angle of 6 ∘ is sufficient to get an ORL of - 50 dB for an SMF-28 optical fiber. For High Numerical Aperture (HNA) fibers, an angle greater than 15 ∘ is necessary to achieve - 25 dB. In silicon photonics edge couplers, the reflectance is - 25 dB when the coupler is 15 ∘ tilted for the Transversal Electric (TE) polarization. Finally, the mode reflectance of a typical edge-emitting diode laser is also calculated for a tilted interface in two directions, and a dramatic difference between the reflectances is noticed, which is caused by the mode asymmetry. [ABSTRACT FROM AUTHOR]

In this article, we analyze the traveling wave solutions of the dimensionless time dependent Paraxial equation. In Paraxial approximation the partial differential approximation is responsible for optical wave propagation. The proposed equation is used when light or electric currents pass through optical systems such as lenses, mirrors, and optical fibers. An extended hyperbolic function method is used to construct traveling wave solutions. By using the proposed method in the Paraxial equation, different types of soliton solutions such as dark solitons, bright solitons, periodic solutions and singular soliton solutions are recovered. These solutions are obtained by carefully choosing the values of certain parameters involved in the method and model. Our findings are original and can greatly contribute to understanding the propagation of light waves. Some important requirements for the validity of solutions are also discussed. In addition, line plots and surface diagrams are presented to demonstrate the physical and behavioral significance of our findings for the proposed model. [ABSTRACT FROM AUTHOR]

The ability to transmit data at a high transmission rate is one of the main challenges that has limited the performance of visible light networking systems. In this paper, we present an eight-core photonic crystal fiber designed for multiplexing (MUX) operations at wavelengths of 1.32, 1.3, 1.54, 1.19, 1.4, 0.98, 1.35, and 1.1 µm to overcome this issue. Various MUX parameters, such as transmission rate and normalized power, are examined in this numerical study. A multiplexer is a device that enables multiple messages or signals to be conveyed simultaneously through a single communication channel. A specific type of optical fiber, called photonic crystal fiber (PCF), is used in this context, which has a cladding made of photonic crystals surrounding the fiber core. The fiber features a periodic arrangement of tiny air holes along its length, creating a low-loss periodic dielectric material known as a photonic crystal. In this new design, silica rods are employed instead of multiple air-hole zones along the fiber's length to adjust the coupling length between adjacent channels. The results indicate that after 5.5 mm of light propagation, the operating wavelengths can be effectively multiplexed. [ABSTRACT FROM AUTHOR]

The statistical characteristics of bubble plumes generated by inclined liquid jets remain inadequately understood, particularly regarding their spatial evolution. This study employs an optical fiber probe for sequential multi-point measurements to investigate the evolution of bubble plumes produced by shallow-angle inclined jets impacting both quiescent fluid and crossflow. Measurements of air volume fractions reveal that crossflow significantly attenuates the jet's penetration capability. Under both conditions, the bubble size distributions exhibit power-law behavior, with variations in the exponents observed at different spatial locations. In quiescent water, a power-law exponent of −2 is observed within the jet impact region, where the strong shear effect of the oblique jet introduces more large bubbles and extends their survival time. This exponent gradually decreases with increasing distance from the jet's influence. In the presence of crossflow, the bubble size spectrum closely resembles that observed under breaking waves. This similarity arises because the jet induces intense surface overturning and fragmentation, becoming the primary source of bubble entrainment. Multi-point measurements further indicate that bubble fragmentation dominates near the free surface, while bubble coalescence becomes more prevalent at greater depths. The results for the bubble velocity distribution indicate that, under both conditions, the distribution of high-speed bubbles follows a power law with an exponent of −6. However, the physical mechanisms driving this behavior remain unclear. [ABSTRACT FROM AUTHOR]

In the fabrication of optical fibers, the viscosity of the glass varies dramatically with temperature so that heat transfer plays an important role in the deformation of the fiber geometry. To date, models of fiber drawing processes have either assumed isothermal conditions or that advection is the dominant heat-transfer mechanism, with conduction therefore neglected. While advective heat transfer and neglect of conduction are valid in the fast process of drawing a preform to a fiber, heat conduction is also important in the slow process of extruding a fiber preform. In this paper, we derive and solve, in the context of pulled extrusion, a coupled heat and fluid flow model that incorporates heat conduction. The dramatic variation of viscosity with temperature means that this problem is extremely challenging to solve via standard numerical techniques and we therefore develop a novel finite-difference numerical solution method that proves to be highly robust. We use this method to show that conduction significantly affects the size of internal holes at the exit of the device and hence has important consequences for the process of manufacturing optical fibers. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate stable radio frequency (RF) transfer via metropolitan optical fiber link in the Beijing area. The phase variation of the RF signal is compensated by a phase conjugation method incorporating two high-performance phase-locked loops. The wavelength conversion module extends the transmission length to 200 km with only two parallel 50 km dark optical fibers available. We optimize the configuration of dispersion compensation and optical amplification due to the high loss (0.31 dB/km) of the optical fiber link. At the same time, comparative experiments verify the short-term instability limitation that arises from the group velocity dispersion of the optical fiber link. The measured standard Allan deviation of the 2.4 GHz RF transmission system with dispersion compensation is 4.5 × 10−14/1 and 2.6 × 10−17/20 000 s, which is superior to that of the reference rubidium clock. The short-term instability of the system is deteriorated to 2.5 × 10−13/1 s without dispersion compensation. [ABSTRACT FROM AUTHOR]

A two-color homodyne Mach–Zehnder optical fiber interferometer is developed for the measurement of electron and neutral particle densities in a high-density capsule θ-pinch device. The interferometer leverages the disparate contributions of distinct particles to the refractive index across two discrete wavelengths of 1310 and 1550 nm and incorporates the contributions of both electron and neutral particle densities to the phase shift in the plasma. The temporal evolutions of line-integrated electron and neutral argon densities are successfully measured by the interferometer. Comparing the electron density waveforms under various working gas pressures as well as the results obtained using the monochromatic and two-color measurements, it is inferred that the influence of neutral particle density can be neglected when measuring the electron density using a long-wavelength laser. Moreover, the maximum electron density is linearly correlated with the capacitor bank voltage for the θ-pinch device (5–9 kV). Overall, the proposed interferometer is capable of simultaneously measuring the electron and neutral particle densities. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is among the top analytical techniques for ultra-low-dense organic matter, crucial to the search for life and analysis of celestial body surfaces in space exploration missions. Achieving the ultimate sensitivity of in-situ Raman spectroscopy necessitates a breakthrough in detecting inelastically scattered light. Single-photon detectors (SPDs) operating in photon counting mode, which can differentiate between Raman and luminescence responses, are promising candidates for the challenging scientific requirements. Since large SPD arrays are not yet commercially available, a dispersive element can be adapted to a single-pixel detector. By exploiting chromatic dispersion in optical fibers and picosecond-pulsed excitation, we delay the arrivals of different spectral components onto a single-pixel SPD. This method also separates weak Raman signals from stronger luminescence through correlated time-domain measurements. We study the impact of fiber properties and the excitation wavelength of a pulsed laser on the spectral resolution of the fiber-dispersive Raman spectrometer (FDRS). Additionally, we demonstrate the FDRS's potential for studying biomarkers and discuss its feasibility for analyzing inclusions in ice matrices. [ABSTRACT FROM AUTHOR]

Guided waves (GW) allow fast inspection of a large area and hence have received great interest from the structural health monitoring (SHM) community. Fiber Bragg grating (FBG) sensors offer several advantages but their use has been limited for the GW sensing due to its limited sensitivity. FBG sensors in the edge-filtering configuration have overcome this issue with sensitivity and there is a renewed interest in their use. Unfortunately, the FBG sensors and the equipment needed for interrogation is quite expensive, and hence their number is restricted. In the previous work by the authors, the number and location of the actuators was optimized for developing a SHM system with a single sensor and multiple actuators. But through the use of the phenomenon of acoustic coupling, multiple locations on the structure may be interrogated with a single FBG sensor. As a result, a sensor network with multiple sensing locations and a few actuators is feasible and cost effective. This paper develops a two-step methodology for the optimization of an actuator–sensor network harnessing the acoustic coupling ability of FBG sensors. In the first stage, the actuator–sensor network is optimized based on the application demands (coverage with at least three actuator–sensor pairs) and the cost of the instrumentation. In the second stage, an acoustic coupler network is designed to ensure high-fidelity measurements with minimal interference from other bond locations (overlap of measurements) as well as interference from features in the acoustically coupled circuit (fiber end, coupler, etc.). The non-sorting genetic algorithm (NSGA-II) is implemented for finding the optimal solution for both problems. The analytical implementation of the cost function is validated experimentally. The results show that the optimization does indeed have the potential to improve the quality of SHM while reducing the instrumentation costs significantly. [ABSTRACT FROM AUTHOR]

Embedded fiber Bragg gratings are increasingly applied for in-situ strain measurement in fiber-reinforced plastics, integral to high-end aerospace equipment. Existing research primarily focuses on in-plane strain measurement, limited by the fact that fiber Bragg gratings are mainly sensitive to axial strain. However, out-of-plane strain measurement is equally important for comprehending structural deformation. The birefringence of fiber Bragg gratings shows promise for addressing this problem; yet, the strain transfer relationship between composites and optical fibers, along with the decoupling method for multi-directional strains, remains inadequately explored. This study introduces an innovative method for multi-directional strain measurement in fiber-reinforced plastics using the birefringence of a single-fiber Bragg grating. The strain transfer relationship between composites and embedded optical fibers was derived based on Kollar's analytical model, leading to the development of a multi-directional strain decoupling methodology. This method was experimentally validated on carbon fiber/polyetherimide laminates under thermo-mechanical loading. Its reliability was confirmed by comparing experimental results and finite element simulations. These findings significantly broaden the application scenarios of fiber Bragg gratings, advancing the in-situ measurement technology crucial for the next generation of high-end aerospace equipment. [ABSTRACT FROM AUTHOR]

A new pickup structure was introduced and modified to improve the resolution of the linear Sagnac optical fiber acoustic sensing system. The maximum strains corresponding to the material, diameter, wall thickness, and height of the pickups were analyzed by simulation. An aluminum cylinder with a diameter of 110 mm, a wall thickness of 3 mm, and a height of 120 mm was chosen as the basic pickup. A four-groove pickup with a vertical width of 80 mm and a horizontal width of 20 mm was introduced to improve the sensitivity of the system. The experiments showed that the average peak-to-peak sensitivity of the four-groove pickup increased by 215.54% to 106.806 mV/Pa. The improved pickup can be applied in areas to monitor the situation of invasion of the Sagnac optical fiber acoustic sensing system. [ABSTRACT FROM AUTHOR]

Speckles are ubiquitous phenomena associated with multi‐spatial‐mode optics, which may reduce detection efficiency and induce modal noise if the photoresponse of the detector is polarization‐dependent. Thus far, they limit the performance of superconducting nanowire single‐photon detectors (SNSPDs) coupled with multimode optical fibers (MMF). To solve this problem, here, it is shown that SNSPDs patterned into the fractal geometry is insensitive to speckles and generates minimal modal noise that would otherwise be induced by the polarization‐dependent local device efficiency of the meander and spiral SNSPDs. Using this advantageous property of the fractal SNSPDs, 78±2%$78 \pm 2\%$ system detection efficiency at the wavelength of 1530 nm and 42‐ps timing jitter is demonstrated when we couple a fractal SNSPD with 50‐micrometer‐core, step‐index MMF. This work not only demonstrates a scheme to achieving high system detection efficiency for MMF‐coupled SNSPDs that can be used in many applications, but also provides insight on how engineered nanostructures of photodetectors can reduce modal noise when detecting light from multiple spatial modes. [ABSTRACT FROM AUTHOR]

The different types of optical soliton solutions are investigated for the 2-dimensional nonlinear Schrödinger equation with an instantaneous Kerr nonlinearity. This equation contains the beam propagation in a multimode optical fiber with a parabolic index profile. Different soliton solutions are examined, such as Breather waves, Lump waves, Mixed types, Periodic cross kink, Multiwave, M-shape, M-shape rational one, two kinks, and rogue waves. To obtain these optical solitons, we apply the Hirota bilinear transformation approach. These results are spectral, temporal, and spatial features of ultrashort light pulses that can be controlled in novel ways by this kind of nonlinear multimode optical fiber, which is gaining popularity. Moreover, the 3-dimensional, 2-dimensional, and contour plots are drawn for some solutions that show their physical interactions by selecting different parameters. These results are very helpful for further study of dynamical systems. [ABSTRACT FROM AUTHOR]