Fiber Drawing Research Articles

Tunable distributed sensing performance in Ca-based nanoparticle-doped optical fibers

Rayleigh scattering enhanced nanoparticle-doped optical fibers is a technology very promising for distributed sensing applications, however, it remains largely unexplored. This work demonstrates for the first time the possibility of tuning Rayleigh scattering and optical losses in Ca-based nanoparticle-doped silica optical fibers by controlling the kinetics of the re-nucleation process that nanoparticles undergo during fiber drawing by controlling preform feed, drawing speed and temperature. A 3D study by SEM, FIB-SEM and optical backscatter reflectometry (OBR) reveals an early-time kinetics at 1870 °C, with tunable Rayleigh scattering enhancement 43.2–47.4 dB, regarding a long-haul single mode fiber, SMF-28, and associated sensing lengths of 3–5.5 m. At 2065 °C, kinetics is slower and nanoparticle dissolution is favored. Consequently, enhanced scattering values of 24.9–26.9 dB/m and sensing lengths of 135–250 m are attained. Finally, thermal stability above 500 °C and tunable distributed temperature sensitivity are proved, from 18.6 pm/°C to 23.9 pm/°C, ∼1.9–2.4 times larger than in a SMF-28. These results show the promising future of Rayleigh scattering enhanced nanoparticle-doped optical fibers for distributed sensing.

Ultrafast Nanocrystallization of BaF2 in Oxyfluoride Glasses with Crystal-like Nanostructures: Implications for Upconversion Fiber Devices

Transparent glass–ceramic fibers containing fluoride nanocrystals are attracting attention as upconversion devices. In this paper, a material design is proposed that eliminates the need for heat treatment processes. The impact of short- to medium-range structures on the crystallization of glasses was investigated to enable nanocrystallization in the quenching process via ultrafast nucleation. In this study, the short- to medium-range structures of (33.3 – x/3)BaF2–xZnO–(66.7 – 2x/3)B2O3 glasses were investigated by 11B- and 19F-magic-angle spinning nuclear magnetic resonance spectroscopy, molecular dynamics simulations, and the high-energy synchrotron X-ray diffraction. After heat treatment, glasses with x > 40 formed BaF2 nanocrystals with a diameter of ∼5 nm and a small particle size distribution (<1 nm). Based on the high-energy synchrotron X-ray diffraction, the critical size of the nuclei was estimated to be 4 nm, which was similar to the size of the precipitated crystals. Obvious selectivity in the binding was observed: F– preferred Ba2+ and O2– preferred B3+, whereas Zn2+ was bound to both anions. The binding selectivity caused a bicontinuous structure of oxide and fluoride domains, and the fluoride-related structure factors and bond distance were very similar to the peak positions of the precipitated crystals. Er3+-doped glasses with x > 40 showed upconversion luminescence with a spectrum similar to that of BaF2. These results suggested the pre-existence of a crystal-like structure with a composition, density, and ordering similar to those of the precipitated crystals. Moreover, glass with the modified composition was successfully crystallized during press-quenching of the melt and the fiber drawing process. These results could facilitate the production of photonic components such as nanocrystallized glass fibers and microspheres for upconversion lasers as well as a wide variety of glass–ceramic products.

Rheological Properties of MWCNT-Doped Titanium-Oxo-Alkoxide Gel Materials for Fiber Drawing.

A strategy of doping by multi-walled carbon nanotubes (MWCNT) to enhance mechanical strength and the electrical conductivity of ceramic fibers has nowadays attracted a great deal of attention for a wide variety of industrial applications. This study focuses on the effect of MWCNTs on rheological properties of metal alkoxide precursors used for the preparation of nanoceramic metal oxide fibers. The rheological behavior of MWCNT-loaded titanium alkoxide sol precursors has been evaluated via an extensional rheometry method. A substantial decrease in elongational viscosity and relaxation time has been observed upon an introduction of MWCNTs even of low concentrations (less than 0.1 wt.%). A high quality MWCNT/nanoceramic TiO2 composite fibers drawn from the specified precursors has been validated. The MWCNT percolation, which is mandatory for electrical conductivity (50 S/m), has been achieved at 1 wt.% MWCNT doping.

Physicochemical Properties and Fiber-Drawing Ability of Tellurite Glasses in the TeO2-ZnO-Y2O3 Ternary System

Glasses in the TeO2-ZnO-Y2O3 (TZY) ternary system are examined in the present work. The vitrification domain of the chosen oxide matrix is determined and differential scanning calorimetry as well as X-ray diffraction measurements are carried out. The material characterizations reveal that Y2O3 incorporation cannot exceed 5 mol.% without causing detrimental crystallization within the glass. Optical transmission and refractive index investigations are conducted on compositions yielding fully amorphous samples. Next, the fiber drawing ability of selected yttrium-containing zinc-tellurite glasses is assessed and fiber-attenuation measurements in the mid-infrared are presented. Finally, a multimode step-index fiber is fabricated by combining a TZY cladding glass with a La2O3-based tellurite core glass. It is believed that yttrium-containing glasses could prove useful in association with other high glass transition temperature (>300 °C) TeO2-based materials for the design of robust optical fibers with precisely engineered refractive index profiles.

Design of a dielectric chiral micro-structured fiber applied in a fiber optic current sensor

During the process of drawing the screwed silicon-based fiber, there will be a uniform rotation rate in it, which results in a decrease of circular polarization degree of the fiber. In order to solve this problem, we presented a kind of dielectric chiral micro-structured fiber owing higher circular polarization degree. Meanwhile, the air holes of fiber will collapse during the progress of fiber drawing, which will change the position of air holes. As a result, the circular polarization degree of the fiber decreases. In order to reduce the change of circular polarization degree caused by the position fluctuation of the air holes, a highly symmetrical micro-structured dielectric chiral fiber was firstly designed in this paper. Then, we established a physical error model considering the fluctuation of the air holes’ position which was the design basis of the air holes’ position, size, and chiral parameters of the specific microstructure fiber. Next, comparing the circular polarization degree S3 of screwed silicon-based fiber and that of the dielectric chiral micro-structured fiber by simulation, it was proved that the dielectric chiral micro-structured fiber we designed has a higher circular polarization degree S3 than that of screwed silicon-based fiber. Finally, we applied the fiber designed in this paper as the fiber sensing coil in a fiber optic current sensor, and compared it with the fiber optic current sensor utilizing the original fiber sensing coil in ratio error. The simulation results proved that compared with the original system, dielectric chiral micro-structured fiber utilized as the fiber sensing coil in a fiber optic current sensor will decrease the ratio error by an order of magnitude in theory.

Various colloid systems for drawing of aluminum oxide fibers

The aim of this study was to develop new low-cost synthesis routes to produce aluminum oxide ceramic fibers for high temperature insulation. The co-precipitation and sol gel chemistry provided the basic of the syntheses. The starting materials were varied from inorganic Al salts (nitrate and chloride) to organic Al compounds (acetate and isopropoxide). The influence of various chemical additives such as polymers, surfactants, basic and gelation agents has been determined on the fiber parameters. Important task was to find the appropriate and efficient fiber drawing technique and heat treatment. The solvent spinning technique has been proved to be an optimal device to produce fibers qualified for high temperature insulation. These fibers can be characterised by diameter of 10–20 μm and the length of 5–15 cm. The techniques as SEM, NMR spectroscopy, DLS, DTA, WAXS, the measurement of tensile strength, thermal conductivity, and heat resistance were aimed to characterise the fibers.

One-step drawing of continuous basalt fibers coated with palladium nanoparticles and used as catalysts in benzyl alcohol oxidation

The continuous basalt fibers (CBFs) coated with palladium (Pd) nanocatalysts were prepared via one-step drawing strategy by using dispersion of Pd/montmorillonite (Pd@MMT) as the sizing. The prepared composite fibers (Pd@MMT/CBFs) were woven into fabrics and were used as fixed-bed catalyst for oxidation of benzyl alcohol (BzOH). The woven Pd@MMT/CBFs monolith was featured with “three-dimensional architecture” which afforded excellent catalytic performance (conversion 96%, selectivity 90%) and superior resistance to sustaining liquid flow shock. It was found that the tensile strength of CBFs was well preserved even the catalyst was exposed to a violent flow of BzOH+H2O2 at velocity of 0.1–0.6 m/s, and the mass loss was < 2.0% demonstrating rockiness stability of such CBFs-based catalysts.

Toughening Wet-Spun Silk Fibers by Silk Nanofiber Templating.

Regenerated silk fibers typically fall short of silkworm cocoon fibers in mechanical properties due to reduced fiber crystal structure and alignment. One approach to address this has been to employ inorganic materials as reinforcing agents. The present study avoids the need for synthetic additives, demonstrating the first use of exfoliated silk nanofibers to control silk solution crystallization, resulting in all-silk pseudocomposite fibers with remarkable mechanical properties. Incorporating only 0.06wt% silk nanofibers led to a ≈44% increase in tensile strength (over 600MPa) and ≈33% increase in toughness (over 200kJkg-1 ) compared with fibers without silk nanofibers. These remarkable properties can be attributed to nanofiber crystal seeding in conjunction with fiber draw. The crystallinity nearly doubled from ≈17% for fiber spun from pure silk solution to ≈30% for the silk nanofiber reinforced sample. The latter fiber also shows a high degree of crystal orientation with a Herman's orientation factor of 0.93, a value which approaches that of natural degummed B. mori silk cocoon fiber (0.96). This study provides a strong foundation to guide the development of simple, eco-friendly methods to spin regenerated silk with excellent properties and a hierarchical structure that mimics natural silk.

Development of Flexible Biceps Tremors Sensing Chip of PVDF Fibers with Nano-Silver Particles by Near-Field Electrospinning.

Polyvinylidene fluoride (PVDF) and AgNO3/PVDF composite piezoelectric fibers were prepared using near-field electrospinning technology. The prepared fibers are attached to the electrode sheet and encapsulated with polydimethylsiloxane to create an energy acquisition device and further fabricated into a dynamic sensing element. The addition of AgNO3 significantly increased the conductivity of the solution from 40.33 μS/cm to 883.59 μS/cm, which in turn made the fiber drawing condition smoother with the increase of high voltage electric field and reduced the fiber wire diameter size from 0.37 μm to 0.23 μm. The tapping test shows that the voltage signal can reach ~0.9 V at a frequency of 7 Hz, and the energy conversion efficiency is twice that of the PVDF output voltage. The addition of AgNO3 effectively enhances the molecular bonding ability, which effectively increases the piezoelectric constants of PVDF piezoelectric fibers. When the human body is exercised for a long period of time and the body is overloaded, the biceps muscle is found to produce 8 to 16 tremors/second through five arm flexion movements. The voltage output of the flexible dynamic soft sensor is between 0.7–0.9 V and shows an orderly alternating current waveform of voltage signals. The sensor can be used to detect muscle tremors after high-intensity training and to obtain advance information about changes in the symptoms of fasciculation, allowing for more accurate diagnosis and treatment.

Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete

Integration of fiber reinforcement in high-performance cementitious materials has become widely applied in many fields of construction. One of the most investigated advantages of steel fiber reinforced concrete (SFRC) is the deceleration of crack growth and hence its improved sustainability. Additional benefits are associated with its structural properties, as fibers can significantly increase the ductility and the tensile strength of concrete. In some applications it is even possible to entirely replace the conventional reinforcement, leading to significant logistical and environmental benefits. Fiber reinforcement can, however, have critical disadvantages and even hinder the performance of concrete, since it can induce an anisotropic material behavior of the mixture if the fibers are not appropriately oriented. For a safe use of SFRC in the future, reliable non-destructive testing (NDT) methods need to be identified to assess the fibers’ orientation in hardened concrete. In this study, ultrasonic material testing, electrical impedance testing, and X-ray computed tomography have been investigated for this purpose using specially produced samples with biased or random fiber orientations. We demonstrate the capabilities of each of these NDT techniques for fiber orientation measurements and draw conclusions based on these results about the most promising areas for future research and development.

Development of gradient index microlenses for the broadband infrared range.

The development of gradient index free-form micro-optic components dedicated to the mid-infrared range is challenging due to the lack of appropriate technology. We propose a method for developing gradient index components for broadband infrared range beyond the transmission window of silicate glass based on nanostructurization using a stack-and-draw fiber drawing technique. A proof-of-concept microlens is developed and verified experimentally in the wavelength range 1.5-4.3 µm. The microlenses are composed of a set of nanorods with a diameter of 940 nm made of a pair of SiO2-PbO-Bi2O3-Ga2O3 based glasses ordered into the preliminary calculated binary pattern. The pattern forms effectively continuous parabolic refractive index distribution for infrared range according to Maxwell-Garnett effective medium model. The development of individual microlenses with a diameter of 118 µm and focal length of 278 µm at the wavelength of 3.75 µm are reported. A large array of 737 microlenses with an individual diameter of 125 µm and focal length of 375 µm is also presented and analyzed.

Investigating the Effect of Drawing Process Parameters on Borosilicate Glass Fiber Thickness

Borosilicate glasses have many usage areas due to high thermal and chemical resistance with a very low thermal expansion coefficient. The number of waste borosilicate glasses is increasing in direct proportion to their usage areas. Creating new usage areas by recycling these glasses will provide cost savings. In this paper, the fiber drawing method is used to recycle borosilicate glass. The aim of this article is to investigate the effect of winding speed and temperature of drawing process on fiber thickness. The fiber drawing process was performed at specific temperatures (1100 °C, 1200 °C, and 1300 °C) and at specific winding speeds (50 rpm, 175 rpm, and 300 rpm). In this context, the thermal behavior of borosilicate glasses was determined by DSC and TGA analysis. The structural, elemental, and chemical corrosion resistance properties of borosilicate glass fibers were examined by SEM, XPS, and corrosion test, respectively. The results show that the fiber thickness increased with the increase in the amount of material fed in the crucible, while it decreased with the increase of fiber drawing speed and time.

The Fabrication of an Eccentric Three-Core Fiber and Its Application as a Twist Sensor

The fabrication and application for twist sensing of an eccentric three-core fiber (3CF) were demonstrated. The fiber was made by a stack-and-draw technique, in which silica rods and core canes were put in a tube and drawn on a fiber drawing tower. Three cores formed a Mach&#x2013;Zehnder interferometer (MZI), where the lights transmitted in the three cores interfered with each other, resulting in the formation of envelopes on spectrum. Because two of the cores were off-axis, phase differences among the cores varied with twist due to different stretches on each core, which caused shift of the spectral envelopes of the interference signal. Wide-range twist measurement can be realized with relatively high sensitivity by tracking lower dips of the envelopes. Experimental results revealed that the dips shift quadratically with twist angle, which means that the sensitivity increases with twist. The compensation of temperature influence was also implemented by inscribing a Bragg grating on one of the cores with femtosecond laser. Because the fiber can be mass-produced, it is suitable for twist sensing in practical application for its low cost.

Development of a Multimaterial Optical Fiber for Fully Distributed Magnetic Sensing Applications

A novel multimaterial fiber optic magnetic sensing design is presented and evaluated in this letter. The multimaterial optical fiber has demonstrated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ &lt; 0.2\ n\epsilon $</tex-math></inline-formula> sensitivity to external magnetic fields over a 2-m gauge length. Intended for immediate use in unconventional oil and gas (UOG) and measuring while drilling (MWD), this instrument could have wide-ranging subsurface sensing applications. Composed of fused silica cladding, internally distributed ferromagnetic nickel, and a series of fiber Bragg gratings, the multimaterial structure has been consistently drawn to over 1 km of length on a fiber draw tower. Due to the consistency of manufacturability and high magnetic sensitivities over long lengths, the proposed design may be considered a competitive magnetic sensor in UOG and MWD applications.

A Temperature-Insensitive Bidimensional Curvature Sensor Employing C-Fiber-Based Fabry–Pérot Air Cavity

A bidirectional curvature sensor based on C-fiber-based Fabry-Pérot interferometer (FPI) is proposed and validated in this work. Well-established glass processing techniques and fiber drawing procedures are used to fabricate the C-fiber, which is then fusing-spliced between two single-mode fibers (SMFs) to form an FPI. When the FPI cavity undergoes bending deformation, the variation of the optical path will cause a change of the interference phase difference, resulting in a spectral shift. The shifting direction of the interference spectrum could also be used to identify the bending direction. Moreover, the FPI cavity length has a direct influence on the curvature sensing performance of the proposed sensor, and the smaller the length, the higher the sensitivity. Bending measurement and orientation recognition are experimentally investigated in two opposite directions, namely, the 0°and 180°direction. The maximum sensitivity as high as 3.434 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is obtained within a curvature range of 0.373-1.585 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in the 0°direction using a FPI cavity length of 104.81 um. It also features a low thermal sensitivity of 0.893 pm/°C. The proposed sensor is ultra-compact, easy-to-fabricate and cost effective, which makes it a promising candidate for the bending monitoring at some specific points or ultra-short distances, such as the bend-determination of joint of a robot arms or micron-scale thin films.

Investigation of the TeO2/GeO2 Ratio on the Spectroscopic Properties of Eu3+-Doped Oxide Glasses for Optical Fiber Application.

This study presented an analysis of the TeO2/GeO2 molar ratio in an oxide glass system. A family of melt-quenched glasses with the range of 0–35 mol% of GeO2 has been characterized by using DSC, Raman, MIR, refractive index, PLE, PL spectra, and time-resolved spectral measurements. The increase in the content of germanium oxide caused an increase in the transition temperature but a decrease in the refractive index. The photoluminescence spectra of europium ions were examined under the excitation of 465 nm, corresponding to 7F0 → 5D2 transition. The PSB (phonon sidebands) analysis was carried out to determine the phonon energy of the glass hosts. It was reported that the red (5D0 → 7F2) to orange (5D0 → 7F1) fluorescence intensity ratio for Eu3+ ions decreased from 4.49 (Te0Ge) to 3.33 (Te15Ge) and showed a constant increase from 4.58 (Te20Ge) to 4.88 (Te35Ge). These optical features were explained in structural studies, especially changes in the coordination of [4]Ge to [6]Ge. The most extended lifetime was reported for the Eu3+ doped glass with the highest content of GeO2. This glass was successfully used for the drawing of optical fiber.

Effects of temperature on melt electrospinning with auxiliary heating: experiment and simulation study

In this study, the effect of the heating temperature of the spinneret on the melt electrospinning process under the condition of application of auxiliary heating was investigated, in a systematical and comprehensive way. The temperature distribution of the melt jet during the melt electrospinning process was simulated by finite element software in order to provide a good deal of insight into the experimental results. In addition, high-speed photography was adopted to capture images of jet formation and jet motion during the melt electrospinning process. The experimental results indicated that the cooling rate of the polypropylene jet decreases obviously under the condition of auxiliary heating; in addition, the higher spinneret temperature leads to greater drafting force, a drawing fiber drafting rate, and greater jet whipping motion, which is conducive to secondary drawing and refinement of the jet.

Drawing-tower inscription of apodized fiber Bragg grating arrays using a rotated focusing cylindrical lens

Large-scale, densely distributed fiber Bragg grating (FBG) arrays have a wide range of applications in industrial safety surveillance. Due to the limitation of inscription pulse-width, most grating interrogators have difficulties distinguishing each grating when the spacing between adjacent gratings reduces to specific small values. Multiple gratings within a fiber section are generally deemed as a single sensing element, and their superposed reflection spectra are acquired for necessary sensing information. The challenge is that serious crosstalk exists in multiple gratings caused by the accumulation of sidelobes from numerous reflections. Such crosstalk, indeed, can be eliminated when the sidelobe suppression ratio (SLSR) is kept high, which has been a long-term difficulty in such systems. In this work, we propose and experimentally demonstrate a novel and simple online fabrication technique for writing apodized fiber Bragg grating (AFBG) arrays during fiber drawing by simply rotating a focusing cylindrical lens for modified pulse intensities. At four degrees rotation angle, the fabricated AFBG has good performance and consistency with full width at half maximum (FWFH) of 0.088 nm, and the SLSR on the long-wavelength side is maintained as high as 20.8 dB. Experimental results further prove that using this fiber-based system, a hot spot of 10 cm size can be well perceptive over one-km fiber length, and the minimum measurable temperature change is 6 ℃. This work clearly addresses a reliable and potential method for the online fabrication of AFBG arrays with suppressed sidelobe-induced crosstalk.

Optical fibres with an inscribed fibre Bragg grating array for sensor systems and random lasers

We report the latest results on inscribing extended fibre Bragg grating (FBG) arrays upon fibre drawing, obtained at the Kotelnikov Institute of Radioengineering and Electronics of RAS. The properties of these structures are considered, and examples of their application in sensor systems of microwave dense wavelength multiplexing and as a basis for designing single-frequency fibre lasers are considered. The optical and laser characteristics of FBG arrays, inscribed (using 248-nm UV laser radiation) both in standard single-mode telecommunication fibres of the SMF-28 type and in erbium-doped active fibres, are investigated.

Fabrication of Silica Optical Fibers: Optimal Control Problem Solution

In this work, a new approach to solving problems of optimal control of manufacture procedures for the production of silica optical fiber are proposed. The procedure of silica tubes alloying by the Modified Chemical Vapor Deposition (MCVD) method and optical fiber drawing from a preform are considered. The problems of optimal control are presented as problems of controlling distributed systems with objective functionals and controls of different types. Two problems are formulated and solved. The first of them is the problem of the temperature field optimizing in the silica tubes alloying process in controlling the consumption of the oxygen–hydrogen gas mixture (in the one- and two-dimensional statements), the second problem is the geometric optimization of fiber shape in controlling the drawing velocity of the finished fiber. In both problems, while using an analog to the method of Lagrange, the optimality systems in the form of differential problems in partial derivatives are obtained, as well as formulas for finding the optimal control functions in an explicit form. To acquire optimality systems, the qualities of lower semicontinuity, convexity, and objective functional coercivity are applied. The numerical realization of the obtained systems is conducted by using Comsol Multiphysics.