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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]

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]

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]

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]

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]

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]

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]

This study investigates the dynamics of boomerang solitons and their interactions in three-mode fiber under the influence of inhomogeneous effects governed by three-coupled nonlinear Schrödinger (3-CNLS) equations in GVD and nonlinearity coefficients. Also, 3-CNLS equation can be used to investigate the optical soliton propagation in three-core fibers, which contain some potential applications in the optical fiber communication system. Using the Darboux transformation method with computer simulation, the two-bright boomerang soliton solutions are attained analytically for the dispersion and nonlinearity functions. The propagation and interaction properties of boomerang solitons are investigated, while the variable coefficients are adopted as linear functions. Various interaction scenarios are illustrated by plotted figures to reveal the importance of obtained soliton solutions. The physical significance of boomerang solitons can be understood from the displayed figures. The obtained results will be benefit soliton path control and soliton phase management in an inhomogeneous three-core optical fiber. [ABSTRACT FROM AUTHOR]

Optical fibers are used in the communications, biological sensors and chemical sensors. We investigate a variable-coefficient modified Hirota equation for the amplification or absorption of pulses propagating in an inhomogeneous optical fiber. With respect to the complex envelope of the optical field, we construct the infinitely-many conservation laws based on the existing Lax pair. According to the existing Darboux transformation, we derive the three-soliton solutions, the higher-order breather solutions and breather-to-soliton transition condition. Amplitudes of the two solitons change after the interaction, while velocities of them are unchanged via asymptotic analysis. When $ P(z)=0 $ P (z) = 0 , interactions among the three parabolic or wavy solitons, interaction between the two parabolic or wavy or crooked breathers, and interactions among the three parabolic and wavy breathers are presented, where $ P(z) $ P (z) is related to the nonlinear focus length. Velocities of three solitons or two crooked breathers with $ P(z)\neq 0 $ P (z) ≠ 0 are different from those with $ P(z)=0 $ P (z) = 0. Based on the breather-to-soliton transition condition, when $ P(z)=0 $ P (z) = 0 , parabolic or wavy multi-peak and M-shaped solitons are presented; when $ P(z)\neq 0 $ P (z) ≠ 0 , the crooked periodic wave and anti-dark soliton are shown. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has gained popularity due to reduced production times of low-cost and geometrically complex structures. Due to technological constraints such as print volume, time, and thermal stability of large AM parts, adhesive joints are commonly used in assembling smaller components in large-scale polymeric structures. This work investigates the feasibility of using embedded optical fibers to monitor strain distributions within AM composite (carbon fiber/nylon) single-lap shear (SLS) joints. Internal strain distributions within the adhesive and surface strain fields of the SLS joints with AM adherends under tensile loads were obtained using optical fibers and digital image correlation, respectively. Results indicate negligible influence of optical fibers on the failure strength and axial stiffness of 3D-printed SLS joints under quasi-static loading. Higher strains were observed at the bond edges within the adhesive (using optical fiber) and the surface (using DIC) of the joints due to the rotation of the bond under loading. All specimens failed in the adherends beyond the bonded region due to their low interlaminar strength. [ABSTRACT FROM AUTHOR]

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In this paper, we skillfully utilize the discriminative ability of the discriminator to construct a conditional generative adversarial network, and propose a scheme that uses few symbols to achieve high accuracy recognition of modulation formats under low signal-to-noise ratio conditions in coherent optical communication. In the one thousand kilometres G.654E optical fiber transmission system, transmission experiments are conducted on the PDM-QPSK/-8PSK/-16QAM/-32QAM/-64QAM modulation format at 8G/16G/32G baud rates, and the signal-to-noise ratio parameters are traversed under experimental conditions. As a key technology in the next-generation elastic optical networks, the modulation format recognition scheme proposed in this paper achieves 100% recognition of the above five modulation formats without distinguishing signal transmission rates. The optical signal-to-noise ratio thresholds required to achieve 100% recognition accuracy are 12.4 dB, 14.3 dB, 15.4 dB, 16.2 dB, and 17.3 dB, respectively. [ABSTRACT FROM AUTHOR]

As per the increasing demand of users, the wireless network fulfils significant challenges in terms of capacity, data rate, reduced environmental impact and better receiver performance. Radio over fiber (RoF) is the technique by which radio signal is modulated over the optical fiber link. The functioning of RoF is dependent on the optical modulator, optical fiber and photodetector. In this paper, dual parallel Mach–Zehnder modulator (DPMZM) is used, which gives good results against intermodulation distortion (IMD) errors. In order to investigate the receiver performance, positive-intrinsic-negative (PIN) and avalanche photodiode (APD) photodetectors are utilized at the receiver end. The analytical analysis of DPMZM based RoF system is analyzed, and the simulation model is implemented using OptSIM software, including PIN and APD photodetectors. The performance is scrutinized against various optical fiber lengths. The performance of the proposed model is analyzed and investigated by the presence of desired components and distorted (IMD) components for 1 and 5 km optical fiber distance between the control station and base station. [ABSTRACT FROM AUTHOR]

Radio over fiber (ROF) is a very attractive technology for the increasing demand for flexibility and transmission capacity and due to its high bandwidth and low attenuation, it offers an economic advantage. The wavelength division multiplexing (WDM) is used to multiplex the different wavelengths signals within a single optical fiber. In this paper, WDM-ROF system is analysed with different filters using an optisystem. Results were compared using max Q factor, min BER, and eye height parameters. [ABSTRACT FROM AUTHOR]

In this paper, we have presented the far field pattern in presence and absence of Kerr type nonlinearity for the first higher order mode in Dispersion shifted and dispersion flattened type optical fibers. Our analytical results are based on simple power series expressions for the first higher order (LP11) mode of aforesaid fibers, which have been formulated by Chebyshev formalism. Using the analytical expressions for the linear case, method of iteration is applied in order to predict the concerned propagation parameters in presence of Kerr type nonlinearity. We have taken some typical trapezoidal index, step W and Parabolic W fibers for our study. Our results for the far field pattern have been shown to be in excellent agreement with the exact numerical results computed by rigorous finite element technique. The simplicity and accuracy of our formalism will prove helpful to the designers for setting up of efficient low dispersion optical link. [ABSTRACT FROM AUTHOR]

Photonic crystal fiber is a category of optical fibers, getting great attention by its promise to offer a range of optical characteristics that are not achievable in conventional optical fibers. Engineered dispersion and nonlinear characteristics of photonic crystal fiber (PCF) make it an attractive candidate for nonlinear optics and advanced optical networking in the all-optical domain. An optical network consists of different optical components such as laser sources, amplifiers, regenerators, and convertors for proper signal transmission over long distances. In recent years, the performance of the components has been improving by employing the appealing properties of PCF. The PCF's application on such components is discussed, and the simulated results on gain amplification, regeneration, conversion, fiber laser are reviewed. These developments reveal that the enhanced performance provided by PCF makes it suitable for different optics applications. [ABSTRACT FROM AUTHOR]

In the context of the emerging Industry 4.0 paradigm, smart fabric sensors have been representing a novel addition to the textile industry. The proposed sensors utilize macro-bending techniques with varying fiber optic core sizes. The study involved the construction and testing of macro-bending sensors using single-mode (9 µm) and hetero-core (50-9-50 µm) fibers, configured into seven sinusoidal loops. The experiment was further extended to different types of elastic textiles. Spandex demonstrated superior linearity compared with jersey and rubber bands. The integration with the DOIT ESP32 DevKit facilitated real-time monitoring of respiratory rates. The results from the experiment indicated that the macro-bending sensor, fabricated using hetero-core optical fiber, exhibited superior sensitivity in comparison to the sensor assembled from single-mode optical fiber, with respective sensitivity values of 1.72 and 1.30 dB/cm. The designed sensors displayed closely aligned behavior during forward and reverse loading, indicating the reversibility of the fiber optic sensor. Given its simplistic design and low fabrication cost, the proposed sensor holds significant potential for practical applications. [ABSTRACT FROM AUTHOR]

Soft robots typically involve manual assembly of core hardware components like actuators, sensors, and controllers. This increases fabrication time and reduces consistency, especially in small-scale soft robots. We present a scalable monolithic fabrication method for millimeter-scale soft-rigid hybrid robots, simplifying the integration of core hardware components. Actuation is provided by soft-foldable polytetrafluoroethylene film-based actuators powered by ionic fluid injection. The desired motion is encoded by integrating a mechanical controller, comprised of rigid-flexible materials. The robot's motion can be self-sensed using an ionic resistive sensor by detecting electrical resistance changes across its body. Our approach is demonstrated by fabricating three distinct soft-rigid hybrid robotic modules, each with unique degrees of freedom: translational, bending, and roto-translational motions. These modules connect to form a soft-rigid hybrid continuum robot with real-time shape-sensing capabilities. We showcase the robot's capabilities by performing object pick-and-place, needle steering and tissue puncturing, and optical fiber steering tasks. This work introduces a fabrication method for mechanically controllable, self-sensing soft-rigid hybrid robots. Translational, bending, and roto-translational modules are designed and assembled as a continuum robot with real-time shape-sensing. [ABSTRACT FROM AUTHOR]

The optical excitation of nitrogen-vacancy (NV) color centers in diamonds mostly results in fluorescence emission. During this process, a portion of the incident energy is transferred to phonon vibration, which heats the diamond crystal. For single NV color centers, the heat generated by the optical cycle is negligible, while for an ensemble of NV defects, the generated heat accumulates rapidly and heats the diamond. The temperature rise is rapid due to the high thermal conductivity of the diamond. In addition to the ability to be heated by light, the NV defect's unique properties also allow for the precise measurement of temperature using optically detected magnetic resonance. Here, we experimentally demonstrate that microcrystalline diamond containing NV center ensembles can be used as a self-gauged microheater. We attached a microcrystal diamond to an optical fiber in an endoscope configuration, evaluated its performance as a self-gauged heater under varied biologically relevant environments, and discussed its potential applications. In addition to the aforementioned capabilities, the NV defect enables the precise measurement of local magnetic fields. This provides a unique multimodal sensor to probe temperature-controlled magnetic phenomena at microscopic scales. [ABSTRACT FROM AUTHOR]

The integration of pressure quantification and visualization enhances pressure perception, accuracy, and efficiency. Current solutions require improvements in quantization accuracy, structural simplicity, and integration. We proposed a novel photonic skin comprising a 3 × 1 flexible optical fiber combiner, integrating red, green, and blue light emitting diode (LED) chips through three flexible optical fibers. Under pressure, changes in the optical fibers' transmission loss alter the output light intensity ratio, thus inducing a color shift at the combiner's output. This visible change can be precisely quantified using a color sensor chip. Performance metrics include sensing range up to 33N, sensitivity between 0.04 and 0.24 dB N−1, detection limit below 0.08 N, response time of 500 ms, recovery time of 400 ms, and durability exceeding 2000 cycles. A compact flexible circuit board manages light source driving, data acquisition, and wireless communication, forming a wearable photonic skin system. This system enables visual recognition and quantitative measurement of pressure across diverse scenarios, including different tactile modes, multi‐position pressure, finger bending, and neck movement. For oral occlusion force detection, the spatial separation of the sensing and visualization areas enables the system to simultaneously provide accurate measurements and intuitive visual assessment. [ABSTRACT FROM AUTHOR]

Photonic Crystal Fiber (PCF) constructions, controlled light propagation for measuring amplitude, phase, polarization and wavelength of the spectrum, and PCF-incorporated interferometry techniques are the foundations upon which sensors operate. But the existing PCF techniques have very large stretching that tends to be difficult to align due to the cross-polarization mode of the optical fiber structure. Hence, the novel Polymer graphene-based Hexagonal cladding is designed by using a hexagonal hollowed core and a cladding material of Polymethyl methacrylate reinforced with gyroidal graphene which increases confinement strength. Once the crystal structure is designed, normally the presence of substrate the Q-factors is degraded. On substrates, Q-factors are enhanced by fine-tuning the position of the neighboring holes. Hence, the novel Bilayer Grating Stratum solves the degrading issues in Q-factors, which utilizes a Silicon polyamide-coated FBG in the crystal that is incorporated using the Femto-laser technique thereby increasing the wavelength tenability. To identify the electric field pattern, the designed structure is simulated in COMSOL software. Thus, the proposed system has a high sensitivity of 22 with a low material loss of 0.1% and a low response time of 0.2 s. [ABSTRACT FROM AUTHOR]

The partial exposure of submarine cable may cause damage to the metal sheath, which will affect its safe and stable operation. Existing detection methods for burial depth of submarine cables are difficult to implement and have a long detection period. In this contribution, a method is proposed to calculate the burial depth of alternating current (AC) submarine cable based on surface optical fiber monitoring temperature. According to the functional relationship between the transient temperature rise of submarine cable outer sheath above the ambient temperature and the burial depth (in the IEC‐60853 standard), the burial depth of submarine cables is calculated. The optical fiber temperature, electric load and meteorological temperature data are used for 30 consecutive days in September 2020 to calculate the change of burial depth of AC 500 kV oil‐filled submarine cable. The calculation results are basically consistent with the detection conclusion of side‐scan sonar, which shows that the method can accurately calculate the burial depth of submarine cables and locate the exposed position. This provides a theoretical basis for the intelligent operation and maintenance of AC submarine cables. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive study on the impact of irradiation optical fiber cores with a femtosecond-pulsed laser, operating at a wavelength of 1030 nm, on the signal amplitude in Rayleigh scattering-based optical frequency domain reflectometry (OFDR). The experimental study involves two fibers with significantly different levels of germanium doping: the standard single-mode fiber (SMF-28) and the ultra-high numerical aperture fiber (UHNA7). The research findings reveal distinct characteristics of reflected and scattered light amplitudes as a function of pulse energy. Although different amplitude changes are observed for the examined fibers, both can yield an enhancement of amplitude. The paper further investigates the effect of fiber Bragg grating inscription on the overall amplitude of reflected light. The insights gained from this study could be beneficial for controlling the enhancement of light scattering amplitude in fibers with low or high levels of germanium doping. [ABSTRACT FROM AUTHOR]

An advanced process for the manufacturing of aerogel-lined capillaries is presented; these are applicable as liquid-core waveguides for gaining the Raman signal of aqueous samples. With respect to the spin-coating process we have used so far for the manufacturing of aerogel-lined capillaries, the here-presented manufacturing process is advanced as it enables (i) the lining of longer capillaries, (ii) the adjustment of the lining-thickness via the lining velocity, and (iii) the reproducible generation of crack-free linings. The key parameters of the advanced process and their effect on the fabrication of aerogel-lined capillaries with optimal Raman signal gain are reported and related to the thickness and topography of the aerogel linings by the support of scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Oil pipeline projects in China are mostly long‐distance, linear projects, making pipelines vulnerable to safety problems. Consequently, pipeline monitoring is crucial for their effective maintenance. In this study, a recently developed optical fiber sensing technology was employed to monitor pipeline crossing projects and conduct tests to study the coordination deformation of buried‐pipeline‐soil systems using a comprehensive deformation monitoring system model based on optical fiber sensing technology developed for the test. The test realized three‐dimensional monitoring of the pipeline and soil deformation when lateral displacement occurred in the soil. In addition, the feasibility of monitoring the deformation of different encapsulation types of optical fiber gratings and different sheath types of distributed optical fibers was demonstrated using this test model. The test results showed that both distributed optical fibers and fiber Bragg gratings (FBGs) could effectively reflect the strain distribution status of a pipeline during deformation monitoring. However, distributed optical fibers could detect data between two points, making them more suitable for pipeline monitoring. The FBG displacement and soil‐pressure gauges could effectively monitor pipeline displacement and soil‐pressure changes, thereby providing a basis for predicting the direction of slider movement during pipeline deflection and landslide monitoring. This test realized the multiparameter monitoring of pipeline deformation, pipeline displacement, and soil pressure along the pipeline, thereby providing a theoretical basis for developing prediction and warning systems for buried pipelines. [ABSTRACT FROM AUTHOR]

Micro/nanorobots with active movement capabilities provide a new option for the treatment of glioblastoma (GBM). However, the long working distance of intravenous injection and the protection of the blood‐brain barrier can prevent micro/nanorobots from reaching the target location. Photodynamic therapy (PDT) has gradually appeared in GBM treatment research. The limitation of the penetrating strength of the light source will nevertheless hinder the application range of PDT. Herein, a magnetic continuum robot (MCR) to deliver optical fibers and microrobots for combined chemotherapy and PDT of GBM is used. The prepared magnetic diatom microrobots can effectively move in biological fluids and move upstream. Vacuum loading can improve the drug loading efficiency. The photosensitizer in the frustule cavity can be explosively released in a short time through ultrasound. The chemotherapeutic drugs have long‐term and pH‐sensitivity release characteristics. In vitro cell experiments showed that the combined administration of TMZ‐loaded microrobots and photosensitizer‐loaded microrobots has a synergistic effect. The in vitro model demonstrated that an MCR can deliver an optical fiber and drug‐loaded microrobots. This enables cross‐scale delivery of microrobots and deep PDT. This delivery method may expand the drug selectivity for GBM treatment and provide a new possibility for intracranial PDT. [ABSTRACT FROM AUTHOR]

Recent studies investigated the hydrolysis of Magnesium (Mg) thin films, highlighting their potential use in biodegradable devices. Quantitatively monitoring the degradation rate and morphological changes of Mg through optical methods and light‐delivery devices offers an innovative, contactless technique, independent of electrical wiring. This method is particularly useful for challenging sensing applications. This study introduces a set of strategies based on Mg optrodes where hydrolysis drives the real‐time monitoring of biofluid penetration through thin‐film encapsulations for bioelectronics. This enables a straightforward assessment of their long‐term reliability, through a quantitative correlation between the water transmission rate (WTR) of the encapsulation and the Mg optical modifications. The optical response of the corroding Mg films deposited on glass substrates and multimode optical fibers tips, within the visible spectrum is characterized. Finally, it is demonstrated that nanopatterning of Mg films as plasmonic nanoantennas significantly enhances the sensitivity of the quantitative approach in the mid‐Infrared spectrum through localized plasmon effects. This method achieves a WTR detection of 6.9 × 10−3 gm−2 day−1 in phosphate buffer solution (25 °C), with a theoretical lower detection limit of ≈10−5 gm−2 day−1. These findings pave the way for the development of a new class of nano‐optical water‐permeation sensors. [ABSTRACT FROM AUTHOR]

AbstractThis article aims to showcase recent advances on Optical Fiber distributed strain measurement systems applied to concrete monitoring. It focuses on their ability to accurately quantify concrete strain in post-tensioned containment buildings of nuclear power plants under various conditions, including instantaneous concrete strain due to pressure tests, delayed concrete strain due to creep/shrinkage, and instantaneous concrete strain due to tendon rupture. To achieve this, the study considers several mockups including the VeRCoRs building, a 1/3 scale post-tensioned concrete containment mockup equipped with a large number of monitoring systems. This mockup facilitates the testing and qualification of distributed measurement systems within concrete structures during both operational phases (for prestressing monitoring) and pressure tests (for measuring instantaneous strain/displacement under pressure). Additionally, a post-tensioned beam was specifically designed and fabricated to examine tendon re-anchorage after cutting. Another objective is to assess various Optical Fiber Cables (OFC) from different suppliers to ensure reliable measurements. The study also aims to test different installation methods, such as embedding the OFC into concrete or attaching them to the external surface using various adhesives. [ABSTRACT FROM AUTHOR]

The development of bend‐induced effectively single‐mode fiber with a square cross‐section and flat top‐hat intensity distribution is reported using core topology nanostructuring dedicated to femtosecond laser ablation systems. The fiber's core comprises 5419 silica and germanium‐doped silica nanorods with a diameter of 430 nm each arranged into a hexagonal lattice. The distribution of the rods is calculated using in‐house developed code based on the Monte Carlo algorithm to obtain a target shape of mode and intensity distribution. As a proof‐of‐concept, a silica nanostructured fiber with a 24 µm core is developed and verified against the purity of mode guidance, bending, and guiding losses. It is shown that for a wavelength of 1030 nm, the fiber is effectively single‐mode with 96% mode purity when bending with a radius of 20 cm is applied. The fiber has a measured mode area of 360 µm2, numerical aperture of 0.03, and total losses of 0.07 dB m−1. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) conventionally occurs at the interface of a thin metallic film and an external dielectric medium in fiber optics through core‐guided light. However, this work introduces theoretical and experimental evidence suggesting that the SPR in optical fibers can also be induced through light scattering from Au nanoparticles (NPs) on the thin metallic film, defined as nanoparticle‐induced SPR (NPI‐SPR). This method adheres to phase‐matching conditions between SPR dispersion curves and the wave vectors of scattered light from Au NPs. Experimentally, these conditions are met on an etched optical fiber, enabling direct interaction between light and immobilized Au NPs. Compared to SPR, NPI‐SPR exhibits stronger field intensity in the external region and wavelength tuning capabilities (750 to 1250 nm) by varying Au NP diameters (20 to 90 nm). NPI‐SPR demonstrates refractive index sensitivities of 4000 to 4416 nm per refractive index unit, nearly double those of typical SPR using the same optical fiber configuration sans Au NPs. Additionally, NPI‐SPR fiber configuration has demonstrated its applicability for developing biosensors, achieving a remarkable limit of detection of 0.004 nm for thrombin protein evaluation, a twenty‐fold enhancement compared to typical SPR. These findings underscore the intrinsic advantages of NPI‐SPR for sensing. [ABSTRACT FROM AUTHOR]

Coal seam mining causes fracture and movement of overlying strata in goaf, and endangers the safety of surface structures and underground pipelines. Based on the engineering geological conditions of 22,122 working face in Cuncaota No.2 Coal Mine of China Shenhua Shendong Coal Group Co., Ltd. a similar material model test of mining overburden rock was carried out. The subsidence of overburden rock was obtained through the full-section strain data of distributed optical fiber technology, and the characteristics of mining surface subsidence were studied. The Weibull model was used to adjust the mathematical form of the first half of the surface subsidence curve via the MMF function. On this basis, the prediction model of coal seam mining surface subsidence was established, and the parameters of the prediction model of surface subsidence were determined. The test results show that with the advancement of coal seam mining, the fit goodness of the surface subsidence prediction curve based on the MMF optimization model reaches 0.987. Compared with the measured values, the relative error of the surface subsidence prediction model is reduced to less than 10%. The model displays good prediction accuracy. The time required for settlement stability in the prediction model is positively correlated with parameter a and negatively correlated with parameter b. The research results can be further extended to the prediction of overburden "three zones" subsidence, and provide a scientific basis for the evaluation of surface subsidence compression potential in coal mine goaf. [ABSTRACT FROM AUTHOR]

Optical hydrogen sensors can use optical fiber as the medium for light transmission or sensing, and realize hydrogen detection based on the relevant physicochemical properties of hydrogen-sensitive materials, which have excellent characteristics such as intrinsic safety, good stability, small size, high specificity, and easy to network. However, conventional hydrogen-sensitive materials such as palladium metal typically require large thicknesses to achieve good performance, but this can exacerbate the mechanical deformation of the palladium metal during hydrogenation and thus shorten the service life of the sensor. In response to this issue, a hydrogen sensor based on hyperbolic metamaterials and ultrathin Pd films is proposed. The control of the Pd film thickness to be less than 0.02 μm ensures that mechanical deformation does not occur during the formation of hydrides in the Pd film. The calculations indicate that the sensor sensitivity can be maintained at approximately 2300 even when the thickness of the palladium film is reduced to 0.011 μm. This work provides a promising solution for high-performance optical hydrogen detection, characterized by high sensitivity, low latency, and low cost. • Designed & demoed hydrogen sensor using hyperbolic metamaterials (HMMs). • Even with a thickness of Pd as thin as 0.011 μm, the sensor can still achieve a sensitivity of 2300. • Robust against parameter changes like incidence angle and layer thickness, adaptable for diverse real-world applications. • Expands HMMs' application range and introduces an innovative path for stable, efficient, high-sensitivity hydrogen sensors. [ABSTRACT FROM AUTHOR]

Efficient coupling between optical fibers and on-chip photonic waveguides has long been a crucial issue for photonic chips used in various applications. Edge couplers (ECs) based on an inverse taper have seen widespread utilization due to their intrinsic broadband operation. However, it still remains a big challenge to realize polarization-insensitive low-loss ECs working at the O-band (1,260–1,360 nm), mainly due to the strong polarization dependence of the mode coupling/conversion and the difficulty to fabricate the taper tip with an ultra-small feature size. In this paper, a high-efficiency and polarization-insensitive O-band EC is proposed and demonstrated with great advantages that is fully compatible with the current 130-nm-node fabrication processes. By introducing an asymmetric bi-level dual-core mode converter, the fundamental mode confined in the thick core is evanescently coupled to that in the thin core, which has an expanded mode size matched well with the fiber and works well for both TE/TM-polarizations. Particularly, no bi-level junction in the propagation direction is introduced between the thick and thin waveguide sections, thereby breaking the critical limitation of ultra-small feature sizes. The calculated coupling loss is 0.44–0.56/0.48–0.61 dB across the O-band, while achieving 1-dB bandwidths exceeding 340/230 nm for the TE/TM-polarization modes. For the fabricated ECs, the peak coupling loss is ∼0.82 dB with a polarization dependent loss of ∼0.31 dB at the O-band when coupled to a fiber with a mode field diameter of 4 μm. It is expected that this coupling scheme promisingly provides a general solution even for other material platforms, e.g., lithium niobate, silicon nitride and so on. [ABSTRACT FROM AUTHOR]

Within the realm of optical neural interfaces, the exploration of plasmonic resonances to interact with neural cells has captured increasing attention among the neuroscience community. The interplay of light with conduction electrons in nanometer-sized metallic nanostructures can induce plasmonic resonances, showcasing a versatile capability to both sense and trigger cellular events. We describe the perspective of generating propagating or localized surface plasmon polaritons on the tip of an optical neural implant, widening the possibility for neuroscience labs to explore the potential of plasmonic neural interfaces. [ABSTRACT FROM AUTHOR]

Advances in imaging tools have always been a pivotal driver for new discoveries in neuroscience. An ability to visualize neurons and subcellular structures deep within the brain of a freely behaving animal is integral to our understanding of the relationship between neural activity and higher cognitive functions. However, fast highresolution imaging is limited to sub-surface brain regions and generally requires head fixation of the animal under the microscope. Developing new approaches to address these challenges is critical. The last decades have seen rapid progress in minimally invasive endo-microscopy techniques based on bare optical fibers. A single multimode fiber can be used to penetrate deep into the brain without causing significant damage to the overlying structures and provide high-resolution imaging. Here, we discuss how the full potential of high-speed super-resolution fiber endoscopy can be realized by a holistic approach that combines fiber optics, light shaping, and advanced computational algorithms. The recent progress opens up new avenues for minimally invasive deep brain studies in freely behaving mice. [ABSTRACT FROM AUTHOR]

Significance: Over more than 300 years, microscopic imaging keeps providing fundamental insights into the mechanisms of living organisms. Seeing microscopic structures beyond the reach of free-space light-based microscopy, however, requires dissection of the tissue--an intervention seriously disturbing its physiological functions. The hunt for low-invasiveness tools has led a growing community of physicists and engineers into the realm of complex media photonics. One of its activities represents exploiting multimode optical fibers (MMFs) as ultra-thin endoscopic probes. Employing wavefront shaping, these tools only recently facilitated the first peeks at cells and their sub-cellular compartments at the bottom of the mouse brain with the impact of micro-scale tissue damage. Aim: Here, we aim to highlight advances in MMF-based holographic endomicroscopy facilitating microscopic imaging throughout the whole depth of the mouse brain. Approach: We summarize the important technical and methodological prerequisites for stabile high-resolution imaging in vivo. Results: We showcase images of the microscopic building blocks of brain tissue, including neurons, neuronal processes, vessels, intracellular calcium signaling, and red blood cell velocity in individual vessels. Conclusions: This perspective article helps to understand the complexity behind the technology of holographic endo-microscopy, summarizes its recent advances and challenges, and stimulates the mind of the reader for further exploitation of this tool in the neuroscience research. [ABSTRACT FROM AUTHOR]