Second-order Fiber Research Articles

Fiber Raman Amplifier Based on Improved Whale Algorithm

In this paper, an improved whale algorithm to optimize pump power and wavelengths of second-order fiber Raman amplifier (FRA) has been proposed. Adopted by the strategies of adaptive gradients and reverse learning, the normal whale algorithm is greatly improved. An optimized FRA is designed based on the six-wavelength backward pump structure. Compared by optimizing both wavelength and power with optimizing only power, the gain flatness curves of the two algorithms, the optimal combination scheme, and the corresponding noise characteristics are got. A 6-pumped FRA has been designed in which the error of on-off gain is 0.08% and the ripple is only 0.18dB.

Fiber orientation distributions based on planar fiber orientation tensors of fourth order

Fiber orientation tensors represent averaged measures of fiber orientations inside a microstructure. Although, orientation-dependent material models are commonly used to describe the mechanical properties of representative microstructure, the influence of changing or differing microstructure on the material response is rarely investigated systematically for directional measures which are more precise than second-order fiber orientation tensors. For the special case of planar orientation distributions, a set of admissible fiber orientation tensors of fourth-order is known. Fiber orientation distributions reconstructed from given orientation tensors are of interest both for numerical averaging schemes in material models and visualization of the directional information itself. Focusing on the special case of planar orientations, this paper draws the geometric picture of fiber orientation distribution functions reconstructed from fourth-order fiber orientation tensors. The developed methodology can be adopted to study the dependence of material models on planar fourth-order fiber orientation tensors. Within the set of admissible fiber orientation tensors, a subset of distinct tensors is identified. Advantages and disadvantages of the description of planar orientation states in two- or three-dimensional tensor frameworks are demonstrated. Reconstruction of fiber orientation distributions is performed by truncated Fourier series and additionally by deploying a maximum entropy method. The combination of the set of admissible and distinct fiber orientation tensors and reconstruction methods leads to the variety of reconstructed fiber orientation distributions. This variety is visualized by arrangements of polar plots within the parameter space of fiber orientation tensors. This visualization shows the influence of averaged orientation measures on reconstructed orientation distributions and can be used to study any simulation method or quantity which is defined as a function of planar fourth-order fiber orientation tensors.

Age-Related Hearing Loss: Sensory and Neural Etiology and Their Interdependence.

Age-related hearing loss (ARHL) is a common, increasing problem for older adults, affecting about 1 billion people by 2050. We aim to correlate the different reductions of hearing from cochlear hair cells (HCs), spiral ganglion neurons (SGNs), cochlear nuclei (CN), and superior olivary complex (SOC) with the analysis of various reasons for each one on the sensory deficit profiles. Outer HCs show a progressive loss in a basal-to-apical gradient, and inner HCs show a loss in a apex-to-base progression that results in ARHL at high frequencies after 70 years of age. In early neonates, SGNs innervation of cochlear HCs is maintained. Loss of SGNs results in a considerable decrease (~50% or more) of cochlear nuclei in neonates, though the loss is milder in older mice and humans. The dorsal cochlear nuclei (fusiform neurons) project directly to the inferior colliculi while most anterior cochlear nuclei reach the SOC. Reducing the number of neurons in the medial nucleus of the trapezoid body (MNTB) affects the interactions with the lateral superior olive to fine-tune ipsi- and contralateral projections that may remain normal in mice, possibly humans. The inferior colliculi receive direct cochlear fibers and second-order fibers from the superior olivary complex. Loss of the second-order fibers leads to hearing loss in mice and humans. Although ARHL may arise from many complex causes, HC degeneration remains the more significant problem of hearing restoration that would replace the cochlear implant. The review presents recent findings of older humans and mice with hearing loss.

Optimization of Second-Order Fiber Raman Amplifier Based on the Improved Whale Algorithm

Optimization of Second-Order Fiber Raman Amplifier Based on the Improved Whale Algorithm

Asymptotic fiber orientation states of the quadratically closed Folgar–Tucker equation and a subsequent closure improvement

Anisotropic fiber-reinforced composites are used in lightweight construction, which is of great industrial relevance. During mold filling of fiber suspensions, the microstructural evolution of the local fiber arrangement and orientation distribution is determined by the local velocity gradient. Based on the Folgar–Tucker equation, which describes the evolution of the second-order fiber orientation tensor in terms of the velocity gradient, the present study addresses selected states of deformation rates that can locally occur in complex flow fields. For such homogeneous flows, exact solutions for the asymptotic fiber orientation states are derived and discussed based on the quadratic closure. In contrast to the existing literature, the derived exact solutions take into account the fiber-fiber interaction. The analysis of the asymptotic solutions relying upon the common quadratic closure shows disadvantages with respect to the predicted material symmetry, namely, the anisotropy is overestimated for strong fiber-fiber interaction. This motivates us to suggest a novel normalized fully symmetric quadratic closure. Two versions of this new closure are derived regarding the prediction of anisotropic properties and the fiber orientation evolution. The fiber orientation states determined with the new closure approach show an improved prediction of anisotropy in both effective viscous and elastic composite behaviors. In addition, the symmetrized quadratic closure has a simple structure that reduces the effort in numerical implementation compared to more elaborated closure schemes.

Research on second-order Raman fiber amplifier based on particle swarm optimization

In order to further improve the performance index of second-order Raman fiber amplifier, the main parameters of second-order RFA were analyzed. First, a structural model that can be controlled by optical switches and switched between two modes of traditional second-order and traditional first-order RFA is designed. It is proved through simulation that second-order RFA can increase the system gain and improve noise performance. The gain performance of first-order RFA is optimized. The optimization goal is to reduce the flatness. The particle swarm optimization algorithm is used to optimize the configuration of the wavelength and power of the pump light. After further structural improvement, a second-order RFA with a gain of 24.50 dB and a gain flatness of 0.98 dB were achieved in a 100 nm bandwidth. These results provide a reference for the design of second-order RFA with better performance in the future.

On the use of orientation tensors to represent prepreg platelet orientation state and variability

Prepreg platelet molding compounds (PPMCs) have mesoscale (platelet scale) features that are not found in injection molding materials. Beyond the fiber orientation state, the platelet normal orientation state and the expected orientation state variabilities are desirable outputs from flow simulations of PPMC systems. However, theoretical understanding and efficient numerical molding simulation capabilities have primarily been developed for injection molding. Using exact solutions of Jeffery’s equation, two methods are developed: approximation of the second-order normal orientation tensor as a function of the second-order fiber orientation tensor and estimation of the variability in predicted orientation tensors due to scale similarity of the platelets and typical molded geometry thicknesses. These methods are validated using orientation state data obtained from computed tomography for five replicates of a PPMC bracket structure. Finally, the methods are applied as postprocessing of a fiber orientation simulation results, showing good comparison with the experimental data. The developed methods allow existing simulation capabilities to be applied to PPMCs as a reduced order model to enable efficient design iterations for PPMC manufacturing.

A novel pseudo-grain approach for the estimation of the elastic stress distributions within the matrix of short fiber-reinforced polymers

Abstract The aim of the work is to provide a new methodology for the calculation of the linear elastic stress distributions within the matrix of a short fiber-reinforced Representative Volume Element (RVE) with misaligned fibers, without relying on complex algorithms for the generation and solution of the microstructure. For this purpose, a Pseudo-Grain approach is adopted, the novelty of which lies in the computation of local stress distributions through the analytical combination of numerical solutions from unidirectional (UD) grains that can be easily and quickly solved through commercial codes. The new approach consists in two steps: i) the application of Voigt boundary conditions to Finite Element (FE) models (grains) with fully aligned fibers and ii) the mathematical combination of the computed Stress Cumulative Distribution Functions (S-CDF) on the basis of the second-order Fiber Orientation Tensor (FOT) of the microstructure of interest. The latter can be generally derived from process simulations or experimental analyses. The method is validated by comparing the resulting stress fields with those calculated from actual RVEs with different fiber volume fractions, fiber aspect ratios and Fiber Orientation Tensors, showing a very good agreement.

Second-order fiber interleaving filter based on polarization-diversified loop

A second-order fiber interleaving filter that can provide a channel interleaving capability in second-order comb spectra is proposed and demonstrated on the basis of a polarization-diversified loop comprised of a four-port polarization beam splitter, four rotatable half-wave plates (HWPs), and three high birefringence fiber (HBF) segments. Each HBF segment is positioned between two adjoining HWPs, and two HWPs located among the three HBF segments determine the effective angular orientation difference among their principal axes, or fast and slow axes. At specific orientation angles of the four HWPs, second-order comb spectra such as flat-top and narrow-band ones could be obtained with a free spectral range (FSR) of ∼0.792 nm. In particular, the frequency interleaving of these second-order comb spectra, that is, a half FSR switching, could be implemented by controlling two out of four HWPs, which is the first demonstration of the interleaving operation in second-order comb spectra without expensive birefringence modulators. These spectral characteristics of the proposed filter were theoretically predicted and experimentally demonstrated.

Negative axial strain sensitivity in gold-coated eccentric fiber Bragg gratings.

New dual temperature and strain sensor has been designed using eccentric second-order fiber Bragg gratings produced in standard single-mode optical fiber by point-by-point direct writing technique with tight focusing of 800 nm femtosecond laser pulses. With thin gold coating at the grating location, we experimentally show that such gratings exhibit a transmitted amplitude spectrum composed by the Bragg and cladding modes resonances that extend in a wide spectral range exceeding one octave. An overlapping of the first order and second order spectrum is then observed. High-order cladding modes belonging to the first order Bragg resonance coupling are close to the second order Bragg resonance, they show a negative axial strain sensitivity (−0.55 pm/με) compared to the Bragg resonance (1.20 pm/με) and the same temperature sensitivity (10.6 pm/°C). With this well conditioned system, temperature and strain can be determined independently with high sensitivity, in a wavelength range limited to a few nanometers.

Prediction of effective elastic properties of fiber reinforced composites using fiber orientation tensors

The main objective of this work is to give an answer to the question: is it sufficient to consider only the second-order fiber orientation tensor as microstructure variable describing the orientation distribution of short-fiber reinforced composites (SFRCs) in the prediction of effective elastic properties? This question is addressed in the context of SFRCs on the one hand with an overall transversal symmetric orientation distribution of fibers and, hence, effective transversally isotropic properties, and on the other hand with experimentally determined microstructure data using micro-computed tomography. Applying the maximum entropy principle, it is shown, how the fiber orientation distribution function (FODF) can be estimated by relying on the second and/or the fourth-order orientation tensor, only. Both estimates are used within the self-consistent and the interaction direct derivate approach to calculate the effective linear elastic properties. It is shown, that the predicted stiffness tensors significantly depend on the estimation of the FODF. Relative deviations of up to 20% in terms of stiffnesses and up to 46% in terms of Young's modulus are observed. For the experimentally determined microstructure, small deviations of up to 4.3% are found.

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Optical Fiber Sensor Based on Second-Order Superstructure Fiber Bragg Grating

Simulation study for prediction of short Fiber Orientation reinforced thermoplastics

The purpose of this paper is the simulation image processing of thermoplastic reinforced with short fibers with an established code in Matlab for the determination of the sizes, orientation, and the ambiguity of the fibers. Which gives a general idea about what happens before crystallization in the mold.Generally, the simulation of short fiber orientation involves coupled analysis of flow, temperature, moving free surface, and fiber kinematics. For the governing equation of the flow, Hele-Shaw flow model along with the generalized Newtonian constitutive model has been widely used. The kinematics of a group of fibers is described in terms of the second-order fiber orientation tensor.

편광상이 고리 기반 2차 광섬유 유연 빗살 필터의 투과 스펙트럼 특성 분석

편광상이 고리 기반 2차 광섬유 유연 빗살 필터의 투과 스펙트럼 특성 분석

Periodical spectral holes along fiber dispersion at the second-order modulation instability sideband

We present the modulation instability as well as four-wave mixing spectrum in a dispersion-shifted fiber at the input of a pump light accompanied with a seed one by solving the nonlinear Schrodinger equation. It is found that an extraordinary phenomenon of periodical spectral holes occurs along the second-order fiber dispersion at the second-order modulation instability sideband. Furthermore, the periodical spectral holes exhibit a side-selection characteristic that they only exist at the opposite side of the seed light. We interpret these phenomena as originating from the periodical power variation caused by four-wave mixing between the pump and the seed light.

Competition between modulation instability and four-wave mixing in the dispersion-shifted fiber

We demonstrate the modulation instability (MI) and four-wave mixing (FWM) spectra at the input of a pump accompanied with a seed in the dispersion-shifted fiber. By numerically solving the nonlinear Schrodinger equation, it is confirmed that there are two regions as the absolute value of the second-order fiber dispersion decreases, where MI and FWM dominates, respectively. We attribute this phenomenon to the competition between MI and FWM. Furthermore, for the FWM-dominating region, it can be divided into two subregions according to the different power levels of MI, which mainly results from the power transfer between MI and dispersive wave. Our results may lead to a further understanding of nonlinear interactions in optical fiber.

Output Characterization of Random Fiber Laser Formed by Dispersion Compensated Fiber

Random lasing (RL) characteristics of second-order random fiber laser formed solo by dispersion compensated fiber are studied. It is found that the threshold of first-order RL is only 0.45 W. In addition, a special route to stable second-order lasing is revealed, i.e., a special arc-shape output spectrum of second-order RL and three chaotic regimes during evolution from the first RL to the second-order one with increased pump power.

Grating-Outcoupled Radiation in Second-Order Fiber Bragg Gratings

The experimental results of the radiation for second-order fiber Bragg gratings, which are made of a single-mode photosensitive fiber (PS-1500; Fiber-Core Corp.) and a single-mode fiber (SMF-28; Corning Inc.), by a phase mask writing fabrication technique are explored. For PS-1500 fiber Bragg gratings, the maximum radiation efficiency of −23.5 dB at resonance λ = 1,539.34 nm with a very narrow bandwidth (about 0.02 nm) are measured from a 10-mm-diameter photo-detector, while for SMF-28 fiber Bragg gratings, the maximum radiation efficiency is −34.6 dB (λ = 1,538.03 nm) with a bandwidth of 0.06 nm. The total efficiencies of the radiation are about −16.8 dB for PS-1500 fiber Bragg gratings and −28.1 dB for SMF-28 fiber Bragg gratings.

All-Fiber Spectroscope with Second-Order Fiber Bragg Grating for Rotational Raman Lidar

ABSTRACT Owing to the second-order fiber Bragg grating possessing narrower reflectivity bandwidth than first-order, an all-fiber spectroscopic filter with several second-order fiber Bragg gratings and optical fiber couplers in the visible region is designed to extract interest rotational Raman spectra. Considering the inference fringe visibility of inscribing fiber Bragg grating and the fiber core index dispersion effect, numerical simulations are made by the improved mathematical model based on an exponential photorefractive dynamic, and its simulative results show better agreement with the experimental data. We propose an all-fiber spectroscopic configuration, which could balance lidar sensitivity against signal-to-noise ratio for optimizing remote sensing performance by fiber Bragg gratings serially. Simulative results show that the thumb principle for fabricating second-order fiber Bragg grating is the increasing gratings length, and that this all-fiber spectroscope can achieve >70 dB suppression to elastic scattering and efficiently extract the rotational Raman signal for profiling atmospheric temperature.