Fiber Curvature Research Articles

Sub-ppm CO detection in a sub-meter-long hollow-core negative curvature fiber using absorption spectroscopy at 2.3 μm

We demonstrated the sensitive CO detection in a novel hollow-core negative curvature fiber (HC-NCF) with infrared laser absorption at 2.3 μm. The HC-NCF consists of a single ring of eight nontouching silica capillaries around the air core, providing a single-mode light delivery of the 2.3-μm distributed feedback laser. A high coupling efficiency of 90% was achieved with the aid of optimal free-space coupling optics. The hollow-core fiber was used as a gas cell for gas absorption measurement of a total path length of 85 cm. Both direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) were adopted to demonstrate the sensor performance by detecting the CO line R(10) at 4297.7 cm−1. In scanned-wavelength DAS, we obtained a minimum detection limit (MDL) of 13 ppm CO, which was limited mainly by the existing mode noise in the HC-NCF. By applying a pressure difference of 0.8 bar between the two ends of the fiber, we demonstrated a very short gas loading time of only 5 s. Finally, we achieved a MDL of 0.4 ppm CO using the WMS technique, corresponding to a noise equivalent absorption of 1.6 × 10-7 cm−1.

An Inline Fiber Curvature Sensor Based on Eccentric Core Fiber and Off-Axis Air Cavity Fabry-Pérot Interferometer

In this paper, we present a highly sensitive inline fiber curvature sensor based on an eccentric core fiber (ECF) and off-axis air cavity Fabry-Perot interferometer (OACFPI). This ECF-based bending sensor is fabricated by fusion-splicing a section of ECF between a single-mode fiber and an off-axis air cavity fiber. Due to the location of the core in the ECF, a bend applied to the ECF-based OACFPI leads to elongation or shortening of the optical path length in the air cavity, which makes the system suitable for bending measurement. To analyze bending characteristics, three ECFs with different eccentric core locations are investigated separately. In addition, a swept source is employed for measurement. The experimental results demonstrate that, the bending sensitivities of the sensors at the two opposite most-sensitive directions are 0.241 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 1), 0.131 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 2), and 0.0807 nm/ $\text{m}^{\mathrm {\mathbf {-1 }}}$ (sensor 3), and −0.245 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 1), −0.156 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 2), and −0.077 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 3). The temperature sensitivities of the sensors are 0.84 pm/°C, 0.92 pm/°C, and 0.94 pm/°C, respectively. The proposed sensors are compact and versatile, and are expected to have potential applications in biomedical sensing.

Temperature-insensitive curvature sensor based on anti-resonant reflection guidance and Mach–Zehnder interferometer hybrid mechanism

A temperature-insensitive optical fiber curvature sensor based on hollow-core fiber is proposed. The hybrid guidance mechanism is a combination of anti-resonant reflecting guidance and the Mach–Zehnder interferometer. The curvature can be detected through the wavelength interval between the two kinds of lossy dips resulting from the two above-mentioned guidance mechanisms. The curvature sensitivity is −0.54 nm/m−1 and −2.02 nm/m−1 in the curvature range of [0 m−1, 7.04 m−1] and [7.04 m−1, 11.87 m−1], respectively. And the temperature cross-sensitivity of the sensor is only 5.54 pm °C−1, which makes the device attractive for potential applications in curvature measurements.

Anatomically accurate model of EMG during index finger flexion and abduction derived from diffusion tensor imaging.

This study presents a modelling framework in which information on muscle fiber direction and orientation during contraction is derived from diffusion tensor imaging (DTI) and incorporated in a computational model of the surface electromyographic (EMG) signal. The proposed model makes use of the principle of reciprocity to simultaneously calculate the electric potentials produced at the recording electrode by charges distributed along an arbitrary number of muscle fibers within the muscle, allowing for a computationally efficient evaluation of extracellular motor unit action potentials. The approach is applied to the complex architecture of the first dorsal interosseous (FDI) muscle of the hand to simulate EMG during index finger flexion and abduction. Using diffusion tensor imaging methods, the results show how muscle fiber orientation and curvature in this intrinsic hand muscle change during flexion and abduction. Incorporation of anatomically accurate muscle architecture and other hand tissue morphologies enables the model to capture variations in extracellular action potential waveform shape across the motor unit population and to predict experimentally observed differences in EMG signal features when switching from index finger abduction to flexion. The simulation results illustrate how structural and electrical properties of the tissues comprising the volume conductor, in combination with fiber direction and curvature, shape the detected action potentials. Using the model, the relative contribution of motor units of different sizes located throughout the muscle under both conditions is examined, yielding a prediction of the detection profile of the surface EMG electrode array over the muscle cross-section.

Cancer Cells Sense Fibers by Coiling on them in a Curvature-Dependent Manner.

SummaryMetastatic cancer cells sense the complex and heterogeneous fibrous extracellular matrix (ECM) by formation of protrusions, and our knowledge of how cells physically recognize these fibers remains in its infancy. Here, using suspended ECM-mimicking isodiameter fibers ranging from 135 to 1,000 nm, we show that metastatic breast cancer cells sense fiber diameters differentially by coiling (wrapping-around) on them in a curvature-dependent manner, whereas non-tumorigenic cells exhibit diminished coiling. We report that coiling occurs at the tip of growing protrusions and the coil width and coiling rate increase in a curvature-dependent manner, but time to maximum coil width occurs biphasically. Interestingly, bundles of 135-nm diameter fibers recover coiling width and rate on 1,000-nm-diameter fibers. Coiling also coincides with curvature-dependent persistent and ballistic transport of endogenous granules inside the protrusions. Altogether, our results lay the groundwork to link biophysical sensing with biological signaling to quantitate pro- and anti-invasive fibrous environments.Video

Variation in KRTAP6-1 affects wool fibre diameter in New Zealand Romney ewes.

Variation in KRTAP6-1 has been reported to affect wool fibre traits in Merino cross-breed sheep and Chinese Tan sheep, but little is known about whether these effects persist in other breeds. In this study, variation in KRTAP6-1 was investigated in 290 New Zealand (NZ) Romney ewes sired by 16 different rams. Polymerase chain reaction single-stranded conformational polymorphism (PCR-SSCP) analysis revealed four variants (, , and of KRTAP6-1, and nine genotypes (AA, AB, AE, AF, BB, BE, BF, EE and FF) in these ewes. Among the 243 ewes that had genotypes with a frequency of over 5 % (i.e. AA, AB and BB), the presence of was found to be associated with reduced mean fibre diameter (MFD) and increased coefficient of variation in fibre diameter (CVFD), whereas the presence of had a trend of association with decreased coarse edge measurement (CEM). A genotype effect was also detected for MFD and CVFD. No associations were detected for fibre diameter standard deviation (FDSD), mean fibre curvature (MFC) and medulation. These results suggest that variation in KRTAP6-1 affects wool fibre diameter in NZ Romney ewes, confirming the finding in Merino cross-breed sheep.

Photothermal CO detection in a hollow-core negative curvature fiber.

We demonstrate the first, to the best of our knowledge, photothermal carbon monoxide (CO) sensor using a hollow-core negative curvature fiber. The hollow-core fiber features a typical structure of one ring cladding containing eight nontouching capillaries to form a negative curvature core-surround. The photothermal effect in a 40-μm hollow core is induced by CO absorption at 2327nm and detected by a Mach-Zehnder interferometer operating at 1533nm. By using wavelength modulation spectroscopy, we achieve a normalized noise equivalent absorption coefficient of 4.4×10-8 cm-1 WHz-1/2. As CO has a very slow vibrational-translational relaxation process, we enhance the photothermal signal by enhancing the relaxation with the water vapor additive.

Variation in ovineKRTAP8-1is associated with variation in wool fibre staple strength and curvature

AbstractKRTAP8-1was the initial high-glycine-tyrosine keratin-associated protein gene recognized in sheep, but little is known about the functional influence of this gene. The current study used polymerase chain reaction-single stranded conformational polymorphism analysis to genotypeKRTAP8-1in 391 Southdown × Merino-cross sheep from six sire-lines. Five previously described variants (namedAtoE) ofKRTAP8-1were identified with frequencies of 67.0, 14.2, 7.0, 10.7 and 1.0%, respectively. Of the four variants (A,B,CandD) that occurred at a frequency greater than 5%, the presence ofCwas found to be associated with a reduction in mean fibre curvature (MFC) and the presence ofDwas associated with an increase in mean staple strength (MSS), whereas the presence ofAhad a trend of association with reduced MSS. Associations were not identified with other wool traits. These results suggest that variation inKRTAP8-1affects MSS and MFC, and thatKRTAP8-1has the potential to be used as a genetic marker for improving these traits.

Design of fiber-reinforced variable-stiffness composites for different open-hole geometries with fiber continuity and curvature constraints

In this study, the optimum design of fiber-reinforced composite plates with different hole geometries for various load conditions is investigated. Strain energy/compliance is optimized using three different design methodologies: constant-stiffness (CS), variable-stiffness (VS), and variable-stiffness with least-squares & continuity constraints (LSC). In all the cases, variable-stiffness and LSC designs both reveal better structural performance with reduced compliance and less stress concentrations around the hole in comparison to the optimum constant-stiffness designs. The compliance significantly decreases after optimization especially for the bi-axial loading case. Most importantly, the LSC method allows manufacturable fiber angle distributions that satisfy the maximum curvature limit, making the proposed LSC method applicable to well-established variable-stiffness manufacturing techniques such as 3-D printing and automated fiber placement. The benefits obtained by using variable-stiffness becomes less pronounced as the hole size decreases with respect to the area of the plate. The use of variable-stiffness is found to be more advantageous over shape-optimization methods of constant-stiffness composites. The comparison to the literature findings (Huang et al., 2016) reveals that 13% further reduction in structural compliance with the proposed LSC design method is possible. The proposed design method provides manufacturable variable-stiffness composites with significant improvements in structural performance.

Positively curved Killing foliations via deformations

We show that a compact manifold that admits a Killing foliation with positive transverse curvature fibers over finite quotients of spheres or weighted complex projective spaces provided that the singular foliation defined by the closures of the leaves has maximal dimension. This result is obtained by deforming the foliation into a closed one while maintaining transverse geometric properties, which allows us to apply results from the Riemannian geometry of orbifolds to the space of leaves. We also show that the basic Euler characteristic is preserved by such deformations. Using this fact, we prove that a Riemannian foliation of a compact manifold with finite fundamental group and nonvanishing Euler characteristic is closed. As another application, we obtain that, for a positively curved Killing foliation of a compact manifold, if the structural algebra has sufficiently large dimension, then the basic Euler characteristic is positive.

Preclinical evaluation of porcine colon resection using hollow core negative curvature fibre delivered ultrafast laser pulses.

Ultrashort pulse lasers offer great promise for tissue resection with exceptional precision and minimal thermal damage. Surgery in the bowel requires high precision and minimal necrotic tissue to avoid severe complications such as perforation. The deployment of ultrashort lasers in minimally invasive or endoscopic procedures has been hindered by the lack of suitable optical fibres for high peak powers. However, recent developments of hollow core microstructured fibres provide potential for delivery of such pulses throughout the body. In this study, analysis of laser ablation via a scanning galvanometer on a porcine colon tissue model is presented. A thermally damaged region (<85 μm) and fine depth control of ablation using the pulse energies 46 and 33 μJ are demonstrated. It is further demonstrated that such pulses suitable for precision porcine colon resection can be flexibly delivered via a hollow core negative curvature fibre (HC-NCF) and again ablation depth can be controlled with a thermally damaged region <85 μm. Ablation volumes are comparable to that of early stage lesions in the inner lining of the colon. This study concludes that the combination of ultrashort pulses and flexible fibre delivery via HC-NCF present a viable route to new minimally invasive surgical procedures.

Curvature sensor based on SMF taper in fiber loop ring down system

Abstract In this paper, a fiber curvature sensor based on single-mode fiber (SMF) taper structure in combination with fiber loop ring down (FLRD) technique is proposed. The curvature is sensed by the ring-down time altered by the bending loss of the SMF taper with different curvature. In the experiment, five SMF tapers with waist diameters from 44.1 to 65.4 μm were tested, with the curvatures in the range of 0–8.33 m−1. The sensitivity of the SMF taper with 44.1 μm and 65.4 μm waist diameters were 0.725 μs/m−1 and 0.328 μs/m−1 respectively. Then the way of comparing the sensitivities with different units was supposed. Compared with other curvature sensors, the system has the advantages of simple structure, high sensitivity and low cost.

Variation in the ovine KAP8-1 gene affects wool fibre uniformity in Chinese Tan sheep

Chinese Tan sheep are known for producing ‘spring-like’ crimped wool fleeces that consist of both fine wool fibres (non-medulated) and heterotypic wool fibres (frequently medulated). The genetic basis of these unique characteristics is poorly understood. Wool fibres are comprised of hard alpha-keratins embedded in keratin-associated proteins (KAPs). Variation in the KAP8-1 gene (KRTAP8-1) was investigated in Chinese Tan sheep, and the effect of variation in the gene on four key wool traits [mean fibre diameter (MFD), fibre diameter standard deviation (FDSD), coefficient of variation of fibre diameter (CVFD) and mean fibre curvature (MFC)] was investigated for both the fine and heterotypic wool fibres. Three previously identified ovine KRTAP8-1 variants (A, D and E) were detected, but two other previously identified variants (B and C) were not present in these Tan sheep. Of the six genotypes (AA, AD, AE, DD, DE and EE) observed, the effect of the genotype on wool traits were analysed for the three (AA, AE and EE) where the genotype frequency was greater than 5%. Genotype was found to have an effect (P = 0.022) on CVFD in the fine wool. These results suggest that variation in KRTAP8-1 affects fibre uniformity in Tan sheep.

High-resolution distributed shape sensing using phase-sensitive optical time-domain reflectometry and multicore fibers.

In this paper, a highly-sensitive distributed shape sensor based on a multicore fiber (MCF) and phase-sensitive optical time-domain reflectometry (φ-OTDR) is proposed and experimentally demonstrated. The implemented system features a high strain sensitivity (down to ∼0.3 µɛ) over a 24 m-long MCF with a spatial resolution of 10 cm. The results demonstrate good repeatability of the relative fiber curvature and bend orientation measurements. Changes in the fiber shape are successfully retrieved, showing detectable displacements of the free moving fiber end as small as 50 µm over a 60 cm-long fiber. In addition, the proposed technique overcomes cross-sensitivity issues between strain and temperature. To the best of our knowledge, the results presented in this work provide the first demonstration of distributed shape sensing based on φ-OTDR using MCFs. This high-sensitivity technique proves to be a promising approach for a wide range of new applications such as dynamic, long distance and three-dimensional distributed shape sensing.

Multi-Objective Optimization of Variable-Stiffness Composites Fabricated by Tailored Fiber Placement Machine

A multi-objective optimization method for the laminated composite fabricated by a tailored fiber placement machine that is an application of embroidering machine is presented. The mechanical properties of composite with curvilinear fibers including stiffness, volume fraction, and density are variable depending on curvatures of fibers. The present study first measures the relation between curvatures and mechanical properties. The measured results indicate that the stiffness of composite decreases linearly as the curvature increases. Then, the obtained relation is applied to the multi-objective optimization where the maximum principal strain and magnitude of curvature are employed as objective functions. Obtained Pareto optimum solutions are widely distributed ranging from the solutions with curvilinear fibers to those with straight fibers, and the curvilinear fiber has still advantages over straight fiber even its weakened stiffness.

On the accuracy of localised 3D stress fields in tow-steered laminated composite structures

Variable Angle Tow (VAT) composites offer increased freedom for tailoring material properties compared to traditional straight-fibre composites. This increased freedom leads to greater design flexibility for enhanced structural performance but comes at the cost of more complex, spatially-varying displacement, strain and stress fields. To maximise the utility of VAT composites, a computationally efficient, yet accurate, numerical framework is needed. To this end, we employ a modelling approach that builds upon the recently developed, hierarchical Serendipity Lagrange finite elements. Three-dimensional (3D) stress distribution is obtained using the present modelling technique and verified against 3D finite element solutions, as well as other formulations available in the literature. A key advantage of the present approach is the ability to predict accurate 3D stress fields efficiently, i.e. with reduced computational effort, including around local features such as geometric, kinematic or constitutive boundaries. Moreover, the present work concerns the peculiarities of commonly used mathematical expressions for describing spatially varying fibre orientations across VAT laminates. The presence of an absolute value in the function used to describe fibre orientation can lead to discontinuities in fibre angle slope and curvature. In turn, these discontinuities lead to mathematical singularities in the constitutive relations along the laminate. If this singularity is not appropriately modelled as a boundary of the continuum, but rather as an interior point of the continuum, stresses may be predicted inaccurately. Compared to other models in the literature, our method is capable of unveiling detailed 3D stresses readily and accurately also in the vicinity of this singularity.

All-Optical Fiber Anemometer Based on the Pitot-Static Tube

An optical fiber anemometer based on the Pitot-static tube is reported. The device was fabricated in a 3-D printer, and the pressure difference was assessed by means of a latex rubber diaphragm with a mounted fiber Bragg grating probe, so the membrane deflection is obtained in terms of the fiber curvature. The sensor characteristics were first obtained by the simulation in order to determine the correlation between the Bragg wavelength shifts and the airflow speed. Next, the device was experimentally evaluated in a wind tunnel, allowing for the assessment of a 20–36-m/s dynamic range, with 24.9-pm/(m/s) maximum sensitivity and 0.04-m/s resolution. Finally, the system was tested on the measurement of cyclic airflow speeds for predicting the applied speed according to the calibration curve, yielding reproducible results with an average error of 0.98 m/s, which is comparable to other reported sensors based on more complex designs and interrogation setups.

Hollow-core negative curvature fibers for application in optical gas sensors

We demonstrate the potential of applying hollow core and negative curvature optical fibers (HC-NCF) as efficient sensors to monitor the concentration of three high-toxicity gases: methane (CH4), carbon monoxide (CO), and nitrogen monoxide (NO). Numerical simulations demonstrate that the insertion of holes in such fibers guarantees the entry of these gases into their hollow core and allows strong interaction of these gases with the low-loss mode propagating in the HC-NCF. This interaction between light and gas in spectral regions with high gas absorption allows one to monitor reduced concentrations of these gases present in the environment simply by monitoring the optical power at the fiber output. The results show a linear behavior of propagation losses as a function of concentrations of 0% to 100% of CO and NO gas, and for concentrations of 0% to 5% of CH4 gas. This linearity between the propagation losses and the variation of the concentrations of gases in the environment can promote its application in healthcare and environment, to monitor low concentrations of gases ensuring high speed and accuracy.

Electron microscopy and tomography reveal that sodium 2-naphthalene sulfonate incorporated into perming solutions swells and tilts trichocyte intermediate filaments causing straightening of curly Japanese human hair.

A new hair-care process has been specifically developed for the straightening of curved Japanese woman's hair . The process included sodium 2-naphthalene sulfonate (SNS) in the reduction and oxidation steps of a conventional perming process. Our objective was to develop an understanding of how this process caused hair straightening by measuring the changes to morphology and ultrastructure between untreated, conventionally permed and SNS permed hair. Untreated and SNS permed Merino wool fibres were used to confirm structural changes. Japanese hair samples were measured for single-fibre curvature before and after perming treatments. A silver staining method was developed to stain hair fibres without changing fibre curvature so that transmission electron microscopy could be used to measure changes in the lateral dimensions of all structural components from the cellular to protein filament level. Electron tomography determined intermediate filament slopes and slope changes after SNS perming relative to the central longitudinal axis of the fibre. SNS perming was found to cause greater lateral swelling than conventional perming of: the paracortical cells of wool; the cuticle, the cuticular cell membrane complex and the macrofibrillar centre-to-centre distance of hair; and of the intermediate filaments in wool and hair. In curved hair, SNS perming caused the intermediate filaments of the helical macrofibrils to simultaneously swell and to tilt further, resulting in the slight longitudinal contraction of the macrofibrils. The overall swelling and tilting was greatest in the helical macrofibrils of Type B cortical cells predominately located in the convex fibre half. The presence of a higher percentage of helical macrofibrils in the convex fibre half than in the concave fibre half caused a contraction differential between the two halves leading to straighten of the curved fibre. A mechanical model was proposed to explain how SNS perming straightened curly hair. The effects of conventional and SNS perming on the morphological and ultrastructural components of curved Japanese hair and high-curl Merino wool fibres have given clear insights into understanding the mechanism of fibre curvature change.

Research on Optical Fiber Sensor Based on Underwater Deformation Measurement.

With the increase in the scale and complexity of underwater engineering, safety problems caused by underwater deformation have become increasingly prominent. Although the intensity fiber curvature sensor can be used for curvature monitoring on the ground, its sensing mechanism is still under investigation. This paper establishes the mathematical model of optical power relative loss and bending radius during deformation of the fiber sensitive region and uses the optical power meter to measure light intensity loss in the sensitive region, which verifies the correctness of the model and reveals the sensing mechanism of the intensity fiber curvature sensor, then optimizes the sensor signal conditioning circuit, applies the sensor to the single-point deformation curvature measurement, and analyzes its measurement error and accuracy. It is proved that the linear measurement range of the sensor is improved when compared with existing similar products.