Optical Fiber Research Articles

Optical solitons and their propagations in a time-varying coefficient modified nonlinear Schrödinger equation with non-zero boundary conditions via Riemann–Hilbert method

In this article, a time-varying coefficient modified nonlinear Schrödinger equation (tvcmNLSE) with non-zero boundary conditions (NZBCs) at infinity, phase term of which contains time-varying coefficients, is proposed to describe the nonlinear propagation behavior of optical pulses in non-uniform optical fibre. Meanwhile, the Riemann–Hilbert method (RHM) for the tvcmNLSE with NZBCs is presented for the first time. Specifically, a special transformation is constructed to convert the tvcmNLSE with NZBCs into the case with constant NZBCs, and the associated asymptotic spectral problem (ASP) is obtained. By introducing a suitable two-piece Riemann surface to map the original spectral parameter into a single-valued one, and analyzing the ASP, we construct the corresponding Jost solutions and spectral matrix, and sequentially analyze their analytical, symmetric, and asymptotic properties. Then, a generalized Riemann–Hilbert problem (RHP) is established that relates to the converted tvcmNLSE with constant NZBCs. Using the reconstruction formula, we further derive N-soliton solution with NZBCs in the absence of reflection potential, and analyze the dynamic characteristics of single and double solitons. Most notably, by modulating discrete spectral points (DSPs) and time-varying coefficients, we discover some previously unreported new waveforms, such as parabolic and periodic solitons with NZBCs. These waveforms have important implications in both theory and practice. In addition, the influences of different time-varying coefficients, NZBCs, and DSPs on soliton solutions are also discussed and analyzed. This study shows that the selection of time-varying coefficients, distribution of DSPs, and constraints from NZBCs all have significant impacts on the properties of soliton solutions.

A Fast and Accurate Mapping Method for an OPGW Tower Based on Hybrid Distributed Optical Fiber Sensing

A Fast and Accurate Mapping Method for an OPGW Tower Based on Hybrid Distributed Optical Fiber Sensing

Highly sensitive CD40L protein discrimination via label-free fiber sensing technologies.

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.

A rapid response optical fiber sensor with highly selective probe for trace detection of mercury (II) ions

A highly sensitive, selective, and well-repeatable optical fiber sensor was proposed for trace measurement of Hg2+ concentration in the water environment based on Mach-Zehnder interference. The proposed structure was prepared by splicing a piece of thin core fiber (TCF) between multimode fibers (MMF) to form MMF-TCF-MMF. A novel sensitive film 3-mercaptopropyl-trimethoxysilane (MPTMS) modified polyvinyl alcohol (PVA) has been designed and synthesized, and uniformly coated on the surface of TCF. The specific combination of Hg2+ with PVA-MPTMS sensitive film can change the effective refractive index of the coating mode, enabling the measurement of Hg2+ concentration by tracking the interference spectra. The results show that the sensitivity of the PVA-MPTMS-coated sensor can achieve 17.5 nm/μM with a detection limit of 3.42 nM in the concentration range of 0–1000 nM. The sensor represents excellent repeatability and stability and a rapid response time of roughly 90 s. Meanwhile, the proposed sensor shows a specific recognition of Hg2+ and is unaffected by many other interfering metal ions in the water, which corresponds well with the binding energy calculated by the density functional theory (DFT). The sensor for Hg2+ detection exhibits compact structure, rapid response, high selectivity and repeatability, showing promising potential applications in the field of environmental monitoring.

New insights into non-linear optical properties, photocatalytic activity, and applications of ZnSe:Cu nanoparticles prepared by microwave-assisted hydrothermal method

In the present work, semiconducting ZnSe:Cu (0, 0.1, 0.75, 1.5, 2.25 and 3 mol%) nanoparticles (NPs) were prepared by microwave-assisted hydrothermal (MAH) method at the fixed pH of 11.2. XRD patterns certified the formation of nanocrystals with the size of about 2.04–2.21 nm. Also, FESEM and TEM images confirmed the formation of round-shape NPs. UV–Vis spectra showed that the energy gap of nanoparticles decreased from 3.615 to 3.342 eV by the increment in copper impurity content. The exact value of the energy gap of NPs was determined by the absorption spectrum fitting derivative method (DASF). Results revealed that these NPs have a high potential in optical and optoelectronic applications; specially, the samples owing 1.5 and 2.25 mol% of Cu-impurity, as the best candidates for optical fiber applications, showed the highest third order non-linear optical susceptibility (χ(3)). Also, for all synthesized NPs, the optical characteristics such as the optical transition index (m), Urbach energy (Etail), dielectric constant (ε) and the refractive index (n) at the absorption edge were determined. Moreover, the amount of metallization factor was also calculated, which decreases with the increase of impurity and microwave irradiation, indicating the increase of metal affinity of the samples. Photoluminescence (PL) spectra of ZnSe NPs demonstrated a general reduction in the intensity upon the introduction of Cu. This anticipated quenching further supports their heightened photocatalytic activity. The results of photocatalytic tests indicate that the sample containing 2.25 mol% of Cu exhibits the highest rate constant value (0.0255 min−1) and achieves the maximum efficiency (75.7 % after 60 min) for degrading the DB71, establishing it as the prime candidate for photocatalytic applications.

A novel design of symmetrical grating built on D-shaped optical fiber sensor-based surface plasmon resonance

Surface Plasmon Resonance (SPR) is an electromagnetic phenomenon that occurs during the interaction between metals and dielectric materials. Fiber sensors show much attention in the last few decades because of their extremely sensitive performance. A novel design of a Dual symmetrical grating D-shaped fiber (Dual SGD-SF) based plasmonic sensor was theoretically studied. The effects of grating depth and gold and silver thickness were investigated. For the Dual SGD-SF sensor design at analyte RI = 1.5 and grating depth = 0.3 μm, the resonance wavelength at the maximum loss was 2.4 μm. The maximum wavelength sensitivity, resolution, and FOM for Dual SGD-SF were obtained at 2000 nm/RIU, 0.00005 RIU, and 22.22 RIU−1, respectively. This design was proposed for sensing very low concentrations of analyte and helps to discover the variations of refractive indices compared to high-purity liquids. To the best of our knowledge, using a symmetrical grating design as a refractive index sensor has not previously been reported.

Optical properties of cylindrical topological photonic crystal heterostructures

This paper uses a modified transfer matrix method to investigate the optical properties of a cylindrical topological photonic crystal heterostructure composed of two cylindrical photonic crystals. Topological photonic crystals are novel structures with topological edge states capable of field confinement and robust propagation. Numerical results showed that when the sum of the phases of the reflection coefficients of the two cylindrical photonic crystals is zero, a topological edge state occurs inside their overlapping band gaps. In the linear regime, the peak frequency of the topological edge states undergoes a redshift as the incidence angle increases. An increase in the incidence angle leads to a decrease (increase) in the Full width at half maximum of the E-polarized (H-polarized) topological edge states. As the incidence angle increases, the frequency separation between the E-polarized and H-polarized topological edge states increases, causing the cylindrical heterostructure to work as a polarizer. The performance of the cylindrical topological photonic crystal heterostructure as a polarizer is evaluated in the linear and nonlinear regimes. We showed that the peak frequency of the topological edge states undergoes a redshift irrespective of their polarization state as the intensity of the input light increases. We found that the structure has a good performance in the nonlinear regime due to the higher displacement in E-polarized topological edge states compared to H-polarized topological edge states. The findings of this paper might be beneficial in the construction of polarization-maintaining optical fiber, which has specific applications in telecommunications, fiber optic sensing, interferometry, and quantum key distribution.

Diameter Optimization of No-Core Fiber for High Refractive Index Sensing

This study presents a simulation-based modal analysis to optimize the no-core fiber (NCF) sensor design for high refractive index (HRI) applications. The goal is to improve the sensitivity of the sensor towards HRI by solving problems in conventional optical fiber sensors (OFS), such as sophisticated fabrication methods, high fragility, and potential effects on long-term reliability. Furthermore, in previous work, most OFS applications focused on detecting mediums with a low refractive index (LRI). Hence, the goal of this study is to overcome these constraints. For this research, the Wave Optics module in COMSOL Multiphysics® software was used to optimize the NCF diameter, which ranged from 100 μm to 150 μm. Simulations include changes in the refractive index (RI) of the analyte in the surrounding medium of the sensor to analyse the efficiency of the NCF in HRI sensing completely, ranging from 1.46 RIU to 1.56 RIU. The performance is then assessed by monitoring the intensity change in the power spectrum, which reflects the reaction of leaky modes to various HRI conditions. The findings indicate that decreasing the size of the NCF sensor enhances sensitivity in detecting HRI mediums by amplifying the leakage loss of each order leaky mode, as opposed to a larger NCF diameter. This effect is due to the reduced confinement of modes in a smaller diameter NCF. The 100 μm diameter NCF has exceptional refractive index (RI) sensitivity and linearity, measuring 88.996 dB/RIU and 0.7783, respectively. Accordingly, NCF proves to be a promising candidate for utilization in HRI sensing applications, given its high sensitivity and straightforward fabrication, making it easily implementable and practical for real-world use.

High-resolution optical fiber underwater acoustic sensor enhanced by PDMS coating

This study introduces a high-resolution optical fiber underwater acoustic sensor utilizing a Fabry-Perot (FP) interferometer design. The sensor consists of a single-mode fiber (SMF) integrated with polydimethylsiloxane (PDMS), forming an FP cavity at the coated SMF terminus. The exceptional elasticity of PDMS amplifies vibrations from acoustic stimuli, modulating the FP cavity for effective acoustic wave detection. This integration of the probe within a single fiber, along with the PDMS coating technique, enhances the sensor’s SNR, resolution, and frequency response. The sensor’s simplicity, cost-effectiveness, superior signal-to-noise ratio, and low power consumption make it a promising tool for underwater acoustic applications.

FiberFlex: Real-time FPGA-based Intelligent & Distributed Fiber Sensor System for Pedestrian Recognition

In recent years, security monitoring of public places and critical infrastructure has heavily relied on the widespread use of cameras, raising concerns about personal privacy violations. To balance the need for effective security monitoring with the protection of personal privacy, we explore the potential of optical fiber sensors for this application. This paper proposes FiberFlex, an intelligent and distributed fiber sensor system. Ultizing FPGA high-level synthesis (HLS) acceleration, FiberFlex offers real-time pedestrian detection by co-designing the entire pipeline of optical signal acquisition, processing, and recognition networks based on the principles of optical fiber sensing. As a promising alternative to traditional camera-based monitoring systems, FiberFlex achieves pedestrian detection by analyzing the vibration patterns caused by pedestrian footsteps, enabling security monitoring while preserving individual privacy. FiberFlex comprises three modules: First , fiber-optic sensing system: A fiber-optic distributed acoustic sensing (DAS) system is built and used to measure the ground vibration waves generated by people walking. Second , algorithms: We first collect the training data by measuring the ground vibration waves, label the data, and use the data to train the neural network models to perform pedestrian recognition. Third , hardware accelerators: We use HLS tools to design hardware modules on FPGA for data collection and pre-processing, and integrate them with the downstream neural network accelerators to perform in-line real-time pedestrian detection. The final detection results are sent back from FPGA to the host CPU. We implement our system FiberFlex with the in-house built DAS system and AMD/Xilinx Kintex7 FPGA KC705 board and verify the whole system using the real-world collected data. We conduct recognition tests on 5 test subjects of varying ages, heights, and weights in a fixed sensing area. Each subject experienced 20 real-time recognition tests using their daily walking habits, and the subjects were given adequate rest between tests. After 100 tests on five test subjects, the overall real-time recognition accuracy exceeded \(88.0\%\) . The whole system uses 55 watts of power, 33 watts in the optical DAS system, and 22 watts in the FPGA. Relying on its end-to-end interdisciplinary design, FiberFlex seamlessly combines fiber-optic sensors with FPGA accelerators to enable low-power real-time security monitoring without compromising privacy, making it a valuable addition to the existing security monitoring network. According to FiberFlex, more valuable research can be conducted in the future, such as fall monitoring for the elderly, migration of identification networks between different application scenarios, and improvement of anti-interference performance in more complex environments. In future perception networks, where the “eyes” are not feasible, let's use fiber optic touch instead.

Photoinduced bending in bimorph optical fibers

Optomechanical materials directly generate work from light through physical deformation upon illumination. Here, we report an optical fiber-based optomechanical actuator that undergoes bending when illuminated by actinic light. A model for light-induced bending curvature as a function of geometrical and material properties was developed to aid in design. Polymer fibers were fabricated and filled directly during the draw with a molten azobenzene derivative. Upon illumination, photoactivated motion is observed and quantified with an optical lever beam approach.

Tunable-Nanoisland-Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection

Tunable-Nanoisland-Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection

Fabrication of PANI/GO/Pd nanocomposite based tapered optical fiber for hydrogen gas sensing applications

Hydrogen (H2) is viewed as a promising solution for future energy demands because of its effectiveness, widespread availability, environmentally friendly properties, and sustainability. The study focuses on developing and evaluating H2 gas sensors based on optical fiber coated with nanocomposites such as polyaniline (PANI), graphene oxide (GO), and palladium (Pd) as sensing layers. An optical transducing channel was developed using a 125 μm diameter multimode optical fiber to improve the light field. The optical fiber was reduced to 20 μm and coated with the PANI/GO/Pd nanocomposite using drop casting. The proposed optical fiber sensor achieved a sensitivity of 9.79/vol%. The response and recovery time were calculated at room temperature and found to be 60 and 190 s, respectively. Overall, the developed optical fiber sensor shows high stability and excellent selectivity to H2 gas when compare to other gases such as NH3 and CH4.

The multi-positon and breather positon solutions for the higher-order nonlinear Schrödinger equation in optical fibers

Abstract Under investigation in this paper is the higher-order nonlinear Schrödinger equation, which can imitate the ultrashort pulses propagation in optical fibers. The modulation instability is analyzed based on the plane-wave solution. With the help of the generalized Darboux transformation, the
second-, third- and fourth-order positon solutions are constructed. Furthermore, the second-, third- and fourth-order breather positon solutions are obtained, and the influences of parameters for the characteristics of solutions are analyzed.

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Comment on “Optical solitons for 2D-NLSE in multimode fiber with Kerr nonlinearity and its modulation instability”

Most recently, Baber et al. (Optical solitons for 2D-NLSE in multimode fiber with Kerr nonlinearity and its modulation instability, Mod. Phys. Lett. B (2024) 2450341, doi:10.1142/S021798492450341X2450341-1) claimed to have obtained exact solutions of a two-dimensional nonlinear Schrödinger equation with an instantaneous Kerr nonlinearity that governs beam movement within a multimode optical fiber featuring a parabolic index shape, using the Jacobi Elliptic Function Expansion. Additionally, they have analyzed the modulation instability for the underlying model. It is the aim of this comment to point out that all results found in that work and published in the journal Mod. Phys. Lett. B (doi:10.1142/S021798492450341X2450341-1) are all erroneous, from the exact solutions of the considered equation to the modulation instability of the underlying model.

Exploring the dynamical behaviour of optical solitons in integrable kairat-II and kairat-X equations

The current research focusses on the establishment of an analytical approach known as the Riccati Modified Extended Simple equation Method (RMESEM) for the development and assessment of optical soliton solutions in two important Kairat equations. These models are known as Kairat-X equation (K-XE) and the Kairat-II equation (K-IIE), which describe the trajectory of optical pulses in optical fibres. Using RMESEM, the soliton solutions in five families–the periodic, rational, hyperbolic, rational-hyperbolic, and exponential functional families–are achieved for the targeted models. A set of 3D, 2D, and contour visualisations are presented to visually illustrate the dynamics of some produced optical soliton solutions which demonstrates that the due to the axial-periodic perturbation, the optical soliton solutions exhibit fractal phenomena in the realm of K-IIE whereas in the setting of K-XE the optical solitons adopt the form of kink solitons such as solitary kink, lump-type kink, dromion and periodic kink soliton structures. Moreover, our suggested RMESEM illustrates its usefulness by building a multitude of optical soliton solutions, providing valuable insights into the dynamics of the targeted models and indicating potential uses in addressing other nonlinear models.

In-depth analysis of optical fiber displacement sensor design process

In-depth analysis of optical fiber displacement sensor design process

Optical fiber shape reconstruction algorithm based on 3D Euler spiral model

Abstract This paper presents a reconstruction algorithm that uses a 3D Euler spiral model to construct the microsegment of a 3D space curve to improve the reconstruction efficiency. Euler spiral is a curve whose shape information changes linearly with arc length, which improves the current assumption of the reconstruction algorithms that the shape information of the micro-segment is constant, and effectively reduces the number of interpolations required, and thus improves the efficiency of the shape algorithm. To verify the effectiveness of this algorithm, a method for constructing random space curves is proposed. Three random space curves of different lengths are reconstructed and the results are compared with the reconstruction algorithms based on the homogeneous transformation matrix and Bishop frame. The results show that this model can significantly improve the efficiency of the algorithm. Under the random space curves of 1 m, 10 m, and 100 m, the efficiency is enhanced by about 15, 27, and 30 times respectively. Prepare a shape sensor with a length of 1465mm to verify the highest reconstruction accuracy of 3D Euler spiral model, which is consistent with the simulation results. The results provide a solid foundation for further research in the field of shape sensing, and show potential for promoting the development of applications that rely on real-time shape measurements.

Laser Doppler velocimetry based on multi-core fiber

Fiber laser doppler velocimetry has the advantages of high measurement accuracy, wide measurement range and non-contact measurement. Usually, fiber optic bundles are used in traditional measurement systems. Multi-core fiber (MCF) is a new structure of optical fiber with multiple cores in the same cladding and a uniform core layout. Compared to traditional fiber bundles, multi-core fibers have advantages in integration and volume. Therefore, by taking advantage of the special spatial arrangement of cores and compact structure of MCF, we investigate the laser doppler velocimetry system. The main work includes:1. Simulation and analysis of double-beam interference fringes based on MCF; 2. Construct a laser doppler velocimetry system based on MCF, and verify the feasibility of the experimental system. Our method provides an effective solution for fiber laser doppler velocimetry.