Application of thermography for thermoplastic waveguide fabrication

The production of short polymer optical fibers from small material batches is valuable for materials research, especially in the investigation of copolymers. A two‐step fiber drawing process is usually used for this purpose. The drawing temperature of the individual materials is an important parameter in the process. Temperature measurements using contactless methods are preferred because they enable online monitoring and do not affect the drawing process. Such measurements can be carried out with a pyrometer, which allows the measurement of a wide range of temperatures but requires a precise adjustment of the spot to the core of the preform. To circumvent this limitation, a thermographic camera with a resolution of 134 µm per pixel in the heating zone is used. The measurement range 0–250 °C is suitable for the usual drawing conditions. The device is installed outside the resistive heating furnace. The absolute temperature is obtained by calibrating the sensor to the beam path and the material emission properties. Different materials, shapes and thicknesses lead to variations in these parameters. In this work, an analysis of the temperature calibration for poly(methyl methacrylate), poly(styrene) and the copolymers poly[styrene‐co‐(isobornyl methacrylate)] and poly[(methyl methacrylate)‐co‐(isobornyl methacrylate)] is presented. These are all thermoplastic polymers and may be used for the fabrication of polymer optical fibers. © 2018 Society of Chemical Industry     

Surfactant effect on DLP fabrication of silica fibre preforms

Three-dimensional (3D) printing based on digital light processing (DLP), for its great advantage in dealing with material and structural complexities, is being engaged for the fabrication of custom-designed silica optical fibre preforms. Resin preparation and printing are key processes critical to DLP fabrication of optical fibre preforms with high silica loading. In this work, the surfactant effect on preparation of resin and DLP printing of optical fibre preforms for higher silica loading is investigated. Based on our experimental studies of the rheological and photocuring properties of resins and the quality of printed silica fibre preforms, we find that, in the case where 2-phenoxyethanol (POE) is usually added as the surfactant, the resin has higher viscosity and results in poorer preform quality. By removing POE from resin ingredients and designing a multi-step resin processing with appropriate settling and degassing processes, fibre preforms with high silica loading up to 0.8 (w/w) have been successfully fabricated.     

Investigation of convective heating in a polymer fiber drawing process

Polymer optical fibers are drawn from a preform rod in a manufacturing process that requires heating. A polymer preform in a tubular furnace enclosure receives energy from the furnace wall via natural convection and thermal radiation. Natural convection, in comparison to radiation, contributes a smaller fraction of the total energy required during the transient heating of the preform and also during the fiber drawing. Based on numerical predictions, natural convection and radiation contribute approximately equal heating to the preform when it is initially introduced at room temperature into a preheated furnace. As the preform temperature rises, the fraction of convective heating decreases as a result of weakening of gas‐phase circulation cell(s) between the furnace wall and preform. These findings are supported by the measured temperature histories in the interior of the preforms that, for all of the cases studied, differed by less than 1.3°C from numerical predictions. Although radiation contributes a larger fraction of the total required energy, natural convection can nevertheless have a strong and detrimental effect on the fiber quality. Specifically, convective instabilities caused air temperature oscillations of 0.3 to 2°C with frequencies from 0.01 to 0.30 Hz. Experimental observations show that these gas phase temperature oscillations promote unwanted diameter variations during fiber drawing.     

An overview on fabrication methods for polymer optical fibers

An overview of the most important materials and fabrication methods for polymer optical fibers is given. In addition to conventional fabrication methods a newly developed continuous melt spinning process for graded‐index fibers is presented that uses rapid cooling in a water quench for the profile formation. The approaches presented are divided into continuous and discontinuous processes for step‐ and graded‐index profile fibers as well as microstructured polymer optical fibers. The methods are described in detail and discussed concerning their efficiency, quality of produced fibers and scalability. © 2014 Society of Chemical Industry     

Fiber‐draw‐induced elongation and break‐up of particles inside the core of a silica‐based optical fiber

Particles in the core of optical fibers are widely studied to tailor or to improve optical properties. The analysis of nanoparticles embedded in silica‐based optical fiber allowed new observations of the evolution of amorphous particles during fiber drawing. Even at the nanoscale, competition between viscous stresses and surface tension on the particles induces elongation and even break‐up of particles during the process. Indeed, particles between 140 and 200 nm diameter inside the preform can break up in fragments with diameters down to 60 nm inside the drawn fiber. Break‐up of particles appears as a new “top‐down” strategy to produce small particles. These observations are promising for micro/nanostructured and multiphasic optical fibers.     

Compositional dependence of crystallization in Ge–Sb–Se glasses relevant to optical fiber making

For fiber‐optic mid‐infrared bio‐ and chemical‐sensing, Ge–Sb–Se glass optical fibers are more attractive than Ge–As–Se because of: (i) lowered toxicity and (ii) lower phonon energy and hence transmission to longer wavelengths, with potential to reach the spectral “fingerprint region” for molecular sensing. There is little previous work on Ge–Sb–Se fibers. Here, fibers are fabricated from two glass compositions in the Ge_xSb₁₀Se_90?x atomic (at.) % series. Both glass compositions are of similar mean‐coordination‐number, lying in the overconstrained region, yet of different chemical composition: stoichiometric Ge₂₅Sb₁₀Se₆₅ at. % and non‐stoichiometric Ge₂₀Sb₁₀Se₇₀ at. %. Thermal analysis on bulk glasses has previously shown that the former exhibited the maximum glass stability of the series. However, during fiber‐drawing of Ge₂₅Sb₁₀Se₆₅ at. %, the preform tip is found to undergo surface‐devitrification to monoclinic GeSe₂ alone, the primary phase, no matter if the preform is an annealed, as‐melted rod or annealed, extruded rod. The heating rate of the preform‐tip to the fiber‐drawing temperature is estimated to be up to ~100°C/min to ~490°C. Lower heating rates of 10°C/min using thermal analysis, in contrast, encourage crystallization of both Sb₂Se₃ and GeSe₂. The non‐stoichiometric: Ge₂₀Sb₁₀Se₇₀ at. % composition drew successfully to low optical loss fiber, no matter whether the preform was an annealed, as‐melted rod or annealed, extruded rod.     

Effects of thermal environment on dehydroxylation of porous silica preform in two-step CVD synthesis

Two-step chemical vapor deposition (CVD) method is a promising technique for industrial fabrication of low-hydroxyl silica glass ingot, in which a porous silica preform is first synthesized by flame hydrolysis deposition, which is subsequently sintered and vitrified to form silica glass. During sintering hydroxyls can be easily removed through the small pores in porous silica preform, which is called dehydroxylation. A deep understanding of the heat and mass transport characteristics involved in the dehydroxylation process is prerequisite to its controlling. In our previous work, a numerical model was developed to simulate the sintering and dehydroxylation of porous silica preform considering heat and mass transfer in porous media at high temperatures, chemical reaction of dehydroxylation, and volume shrinkage of preform. The results revealed that the dehydroxylation effect largely depends on the temperature fields in the furnace. In present work, the influences of thermal environments, including heating curve, heater position, and crucible structure on the dehydroxylation process of porous silica preform are systematically studied by numerical methods. Based on the results, increasing temperature at either stage is helpful for hydroxyl removal as well as increasing the hydroxyl distribution uniformity. However, long-time exposure to 1500°C will instead worsen the dehydroxylation effect. Compared to top or bottom heating, side heating is more beneficial to hydroxyl removal. To improve the dehydroxylation condition at the bottom of porous silica preform, a novel crucible structure is designed which shows better performance than the ordinary crucible. At last, an optimized heating scheme is proposed in this study, which obtains much better dehydroxylation effect than other cases.     

Adhesion of polymers to reinforcing fibres

A single fibre pull out technique is presented which makes it possible to measure the strength in the interface between fibre and polymer with high precision even if the embedded length of the fibre is short. The method allows measurements for all kinds of fibres in thermoplastic or thermosetting polymers. The effect of fibre surface treatment can be investigated as well as the effect of morphology or internal stresses in the polymer. Examples are given. The shear strength results are compared with results of tensile shear tests performed on symmetrically notched unidirectional reinforced composite samples. The correlation is good and it is shown that the new single fibre pull out method is able to give a better discrimination between the composites than other methods. An analysis of mechanical stress induced during the pull out demonstrates the use and limitation of this method.     

A study of the influence of controlled corona treatment on UHMWPE fibres in reinforced vinylester composites

In order to illuminate the mechanisms of corona discharge treatment on ultra‐high molecular weight polyethylene (UHMWPE) fibre, the effects of corona treatment power and time are discussed in detail. The surface‐roughness and tensile‐failure characteristics of the polyethylene fibre were determined by a scanning electron microscope (SEM). The photos from the SEM showed that the size and number of the micro‐pits on the fibre surface increase with increase of corona power. The oxygen‐containing groups on the fibre surface could be detected by Fourier‐transform infrared attenuated total reflectance and also increased gradually with increase of corona power. The T‐peel strength of composites increased from the corona treatment, and then showed a maximum value at a corona treatment time about 0.1 s with increase of treatment time. However, the tensile strength of the fibre was reduced with increase of corona power and the failure mechanism obviously changed after the treatment. The ballistic impact energy absorption of UHMWPE fibre/vinylester composite was obtained after fragment simulating projectiles (FSP) impact tests. After 6‐kW corona treatment for 0.075 s, the impact energy absorbed by the laminate reached a maximum value. Copyright © 2003 Society of Chemical Industry     

Surface Analysis and Treatment of Extruded Fluoride Phosphate Glass Preforms for Optical Fiber Fabrication

Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N‐FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride‐based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low‐loss fluoride phosphate optical fibers.     

Synthesis of aligned titanium-based oxide fibre arrays

A successful method based on the electrospinning technique to prepare continuous, parallel, well-aligned, inorganic fibre arrays was developed in this work. An ultra-high-molecular-weight polymer was used to suppress jet whipping motion to synthesise continuous, well-aligned, fibre arrays via electrospinning. Ultra-long, parallel, well-aligned, titanium-based oxides including TiO₂, Li₂TiO₃, and ZnTiO₃ binary and ternary ceramic fibres were prepared by the modified electrospinning method, which is rather difficult to do by other methods when trying to synthesise a well-aligned final structure. The effects of electrospinning conditions, such as the applied voltage, ratio of organic solvent to inorganic solvent, solvent type, and collecting drum rate of rotation on the size and morphology of the fibres was studied to demonstrate the growth mechanism of the prepared fibre arrays. The technique based on the ultra-high-molecular-weight polymer and electrospinning developed in this work can be extended to other ternary oxide nanofibre fabrication, and is beneficial for the development of one-dimensional nanostructures in optical and electrical fields.     

Fabrication and analysis of side‐emitting poly(methyl methacrylate) fibres with non‐circular cross‐sections

We present a novel type of side‐light‐emitting fibre with trilobal cross‐section. The fibre is especially designed for indirect illumination applications and the special shape of the filament cross‐section permits the formation of a distinct asymmetric radiation pattern. These fibres can focus the radially emitted light on particular locations, e.g. in order to cure resins or polymers at well‐defined positions, or may be used as indirect illumination sources in car interiors. The polymer material is commercial optical‐grade poly(methyl methacrylate) (PMMA) that is compounded with different concentrations of a TiO₂‐nanofiller‐modified PMMA. © 2018 Society of Chemical Industry     

The influence of ultraviolet radiation on the optical properties of glass fibre reinforcements for polyurethane matrix composites

Polyurethanes represent one of the most frequently used polymeric matrixes in composites. Although there have been many studies focused on the weather resistance of polyurethanes, this important property is unheeded during the reinforcing phase. In this article, the effects of ultraviolet (UV) radiation on the changes in optical properties of commercially available glass fibre reinforcements containing various polymeric binders used as compatibilising agents for the polymeric matrix in the final composite products were studied. The standardised experiments were performed using accelerated ageing equipment, q‐lab ultraviolet tester, in dry mode. Chemical modification of the binder in the form of polyesters or silanes by UV irradiation was studied using Fourier Transform–infrared spectroscopy. Changes in the optical properties caused by the degradation processes of polymeric components due to UV irradiation were evaluated based on colour changes in the examined samples using the yellowness index; statistical evaluation of the data obtained was conducted with an Anderson–Darling test of normality and an ANOVA test. It was demonstrated that both the amount of the binder and the glass fibre reinforcement's construction play a more important role than the chemical structure of the binder.     

Shear properties of C/C-SiC sandwich structures

Carbon fiber reinforced carbon-silicon carbide (C/C-SiC) sandwich structures have been developed using the Liquid Silicon Infiltration process and the in situ joining method. They offer high mass-specific stiffness, low thermal expansion, and high environmental stability. Potential application areas are highly precise satellite structures, like optical benches. In this study, sandwich samples were manufactured using prepregs based on 2D carbon fibre fabrics and a phenolic resin precursor. Carbon fibre reinforced polymer preforms for folded and grid-cores, as well as for the skin panels were manufactured using autoclave technique. In the second step, the sandwich components were pyrolyzed, leading to C/C preforms. For the build-up of the sandwich samples, two skin panels were joined to a core structure and subsequently, the resulting C/C sandwich preform was siliconized. C/C-SiC sandwich samples were tested under shear load. Shear strength, modulus, and fracture strain were determined and compared to the results obtained by analytical calculation. The shear properties were dependent on the fiber orientation in the core structure as well as on the core type and orientation. The sandwich shear stiffness obtained in the tests was close to the expected theoretical values, calculated on the basis of the material properties and the core geometry.     

Multimaterial Fibers

Recent progress in combining multiple materials with disparate optical, electronic, and thermomechanical properties monolithically in the same fiber drawn from a preform is paving the way to a new generation of multimaterial fibers endowed with unique functionalities delivered at optical fiber length scales and costs. A wide range of unique devices have been developed to date in fiber form-factor using this strategy, such as transversely emitting fiber lasers, fibers that detect light, heat, or sound impinging on their external surfaces, and fibers containing crystalline semiconductor cores. Incorporating such fibers in future fabrics will lead to textiles with sophisticated functionality. Additionally, long-standing issues in traditional applications of optical fibers have been addressed by multimaterial fibers, such as photonic bandgap guidance in hollow-core all-solid-cladding fibers and imparting mechanical robustness to soft-glass mid-infrared fibers. We review recent progress in this nascent but rapidly growing field and highlight areas where growth is anticipated. Furthermore, the insights emerging from this research are pointing to new ways that the fiber drawing process itself may be leveraged as a fabrication methodology. In particular, we describe recent efforts directed at appropriating multimaterial-fiber drawing for chemical synthesis and the fabrication of nanostructures such as nanowire arrays and structured nanoparticles.     

新型纤维增强水泥复合材料研究的进展

对五种新型纤维增强水泥复合材料的复合原理、制作技术、性能与应用等方面的研究进展分别作了介绍和评述,并指出了有待进一步研究的问题。     

Fabrication of a graded‐index polymer optical fiber preform without cavity via the automatic refilling process

When two monomers with different densities and refractive indices are polymerized under a centrifugal force field, a cavity is generated in the rotational axis as a result of inherent volume shrinkage. Accordingly, an additional monomer‐refilling process is necessary to compensate for the undesirable cavity. In this study, we modified the stepwise refilling process to an automatic process and have successfully fabricated a graded‐index polymer optical fiber preform without a cavity. The process could also reduce the processing time and enhance the transmission speed of a polymer optical fiber compared with the stepwise process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Numerical Modelling of the Flow of Fibre Suspensions through a Planar Contraction

This study presents results of numerical simulations of the flow of fibre suspensions in a Newtonian fluid through a 4:1 planar contraction. Two approaches are adopted to determine the fibre orientation. The first one uses orientation tensors defined as dyadic products of the orientation vector, while the second one is based on the fibre aligned assumption. An implicit time discretization scheme and a mixed finite element method based on the introduction of the rate of deformation tensor as an additional unknown are used to obtain the steady‐state flow. The numerical technique we use allows us to examine the flow of fibre suspensions in both dilute and semi‐dilute regimes at high values of the parameters controlling inertial and fibre effects. The predicted flow patterns and fibre orientation are discussed, and a systematic comparison between the predictions of the two approaches is presented.     

Fireproof viscose fibres

A modifying bath composition was developed for manufacture of fireproof viscose fibres used for fabrication of textiles with a fireproofing effect and resistant to laundering. The existence of a chemical reaction in the viscose fibre (VF)—Pyrofax (PF) system was demonstrated and the mechanism of action of PF in thermoly sis and combustion was determined. Multicomponent bath compositions were developed for manufacturing fibres with high oxygen indexes and a high yield of carbonized residue which can be promising as reinforcing systems in creation of PCM and for fabrication of carbon fibres. Translated from Khimicheskie Volokna, No. 4, pp. 37–39, July–August, 1998.     

Evolution of the structure and mechanical performance of Cansas-II SiC fibres after thermal treatment

Herein, an in-depth analysis of the effect of heat treatment at temperatures between 900 and 1500 °C under an Ar atmosphere on the structure as well as strength of Cansas-II SiC fibres was presented. The untreated fibres are composed of β-SiC grains, free carbon layers, as well as a small amount of an amorphous SiC_xO_y phase. As the heat-treatment temperature was increased to 1400 °C, a significant growth of the β-SiC grains and free carbon layers occurred along with the decomposition of the SiC_xO_y phase. Moreover, owing to the decomposition of the SiC_xO_y phase, some nanopores formed on the fibre surface upon heating at 1500 °C. The mean strength of the Cansas-II fibres decreased progressively from 2.78 to 1.20 GPa with an increase in the heat-treatment temperature. The degradation of the fibre strength can be attributed to the growth of critical defects, β-SiC grains, as well as the residual tensile stress.