Fiber Drawing Process Research Articles

Optical properties and radiation hardness of Pr-doped sol-gel silica: Influence of fiber drawing process

The optical emission from the 5d – 4f allowed transition of Pr3+ ions embedded in sol-gel silica is investigated for High Energy Physics applications requiring fast scintillating materials.A complete and detailed characterization of the optical, scintillation and radiation hardness properties of Pr-doped silica is carried out employing different experimental techniques including steady-state and time-resolved photo-luminescence, radio- and thermo-luminescence, scintillation and optical absorption.Optical absorption measurements, performed after X-ray irradiation sequences up to 1kGy, evidence the formation of radiation-induced absorption bands related to point defects acting as color centers. Spontaneous partial recovery of the radiation-induced defects at room temperature, as well as after thermal treatments, is also disclosed.Particular attention is paid to the comparison between bulk silica, both before and after a melting process, and fibers. The results reveal the presence of a lower concentration of optically active defects in melted glass. Such comparison highlights a role of the fiber drawing in modifying the glass defectiveness, consisting in the occurrence of a structural reorganization of the amorphous network during the process.

Distributed fiber optic interferometric geophone system based on draw tower gratings

A distributed fiber optic interferometric geophone array based on draw tower grating (DTG) array is proposed. The DTG geophone array is made by the DTG array fabricated based on a near-contact exposure through a phase mask during the fiber drawing process. A distributed sensing system with 96 identical DTGs in an equal separation of 20 m and an unbalanced Michelson interferometer for vibration measurement has been experimentally validated compared with a moving-coil geophone. The experimental results indicate that the sensing system can linearly demodulate the phase shift. Compared with the moving coil geophone, the fiber optic sensing system based on DTG has higher signal-to-noise ratio at low frequency.

Heat Transfer Modeling of the Capillary Fiber Drawing Process

Considerable recent research has focused on the ability of microstructured fibers to exhibit diverse optical functionalities. However, accurately preserving the structure imposed at the preform stage after drawing it down to fiber, while avoiding Rayleigh–Plateau style instabilities, has proven to be a major fabrication challenge. This modeling/analytical study was carried out in support of an experimental program into possible fabrication options for various microstructured optical fibers and considers the generic case of the nonisothermal drawing of a capillary preform to fiber. Model development was carried out in two stages. Initially, a fully conjugate multiphase model, which includes all heat transfer modes within an operational fiber drawing furnace, was validated against available experimental data. To evaluate the external radiative heat flux using the net-radiation method, a Monte Carlo ray-tracing (MC-RT) method was coupled to the commercial polyflow package to obtain all view factors between the various furnace walls and the deforming preform/fiber. A simplified model was also developed (to shorten simulation run times) by explicitly calculating the convective heat transfer between the air within the furnace and the preform/fiber surface using a heat transfer coefficient determined by matching predicted results with those obtained from the multiphase model.

Reproducible fiber optofluidic laser for disposable and array applications.

Disposable sensors are widely used in biomedical detection due to their inherent safety, ease of use and low cost. An optofluidic laser is a sensitive bioassay platform; however, demonstrating its fabrication cheaply and reproducibly enough for disposable use has been challenging. Here, we report a low-cost, reproducible fiber optofluidic laser (FOFL) using a microstructured optical fiber (MOF). The MOF not only supports the whispering gallery modes for lasing but also serves as a microfluidic channel for sampling the liquid gain medium via capillary force. Because of the precise control of its geometry (δ < 0.4%) during the fiber-drawing process, good reproducibility in laser intensity (δ = 6.5%) was demonstrated by changing 10 sections of the MOF. The strong coupling between the in-fiber resonator and gain medium enables a low threshold of 3.2 μJ mm-2. The angular dependence of the laser emission was observed experimentally and analyzed with numerical simulations. An array of the FOFLs was also demonstrated. This technology has great potential for low-cost bioassay applications.

Numerical modeling and analysis of glass fiber drawing process from large sized silica preform

Numerical modeling and analysis of glass fiber drawing process from large sized silica preform

Effect of draw ratio on fiber structure development of polyethylene terephthalate

Fiber properties are decided by its structure, and the structure are mainly formed in the fiber drawing process. In this study, the effects of the draw ratio on the fiber structure development of polyethylene terephthalate after continuous neck-drawing were investigated using simultaneous WAXD/SAXS measurements. Low-oriented amorphous as-spun fibers were drawn to a draw ratio of 3.0–4.5, at which the fiber can be stably neck drawn. WAXD and SAXS images were obtained up to 2.0 ms when the structure was mainly developed. The smectic (001′) diffraction intensity and long period increased with increasing draw ratio up to 4.2, and a larger (001′) diffraction d-spacing was observed at a draw ratio of 4.5. The results suggest that more fibrillar structures were formed with increasing draw ratio up to 4.2, and more constrained molecular bundles were formed at a draw ratio of 4.5. A larger amount of constrained fibrillar structures can bear a greater tensile force in tensile tests, therefore the drawn fibers have higher tensile strengths.

Fabrication of Metal–Polymer Nanocomposites by In-Fiber Instability

Thermal fiber drawing process has emerged as a promising nanomanufacturing process to generate high-throughput, well aligned, and indefinitely long micro/nanostructures. However, scalable fabrication of metal–polymer nanocomposite is still a challenge, since it is still very difficult to control metal core geometry at nanoscale due to the low-viscosity and high-surface energy of molten metals in cladding materials (e.g., polymer or glass). Here, we show that a scalable nanomanufacture of metal–polymer nanocomposite via thermal fiber drawing is possible. Polyethersulfone (PES) fibers embedded with Sn nanoparticles (&lt;200 nm) were produced by the iterative size reduction thermal fiber drawing. A post-characterization procedure was developed to successfully reveal the metal core geometry at submicron scale. A three-stage control mechanism is proposed to realize the possible control of the metal nanoparticle morphology. This thermal drawing approach promises a scalable production of metal–polymer nanocomposite fibers with unique physicochemical properties for exciting new functionalities.

Ligand-Driven and Full-Color-Tunable Fiber Source: Toward Next-Generation Clinic Fiber-Endoscope Tomography with Cellular Resolution.

In many biomedical applications, broad full-color emission is important, especially for wavelengths below 450 nm, which are difficult to cover via supercontinuum generation. Single-crystalline-core sapphires with defect-driven emissions have potential roles in the development of next-generation broadband light sources because their defect centers demonstrate multiple emission bands with tailored ligand fields. However, the inability to realize high quantum yields with high crystallinity by conventional methods hinders the applicability of ultra-broadband emissions. Here, we present how an effective one-step fiber-drawing process, followed by a simple and controllable thermal treatment, enables a low-loss, full-color, and crystal fiber-based generation with substantial color variability. The broad spectrum extends from 330 nm, which is over 50 nm further into the UV region than that in previously reported results. The predicted submicrometer spatial resolutions demonstrate that the defect–ligand fields are potentially beneficial for achieving in vivo cellular tomography. It is also noteworthy that the efficiency of the milliwatt-level full-color generation, with an optical-to-optical efficiency of nearly 5%, is the highest among that of the existing active waveguide schemes. In addition, direct evidence from high-resolution transmission electron microscopy together with electron energy loss spectroscopy and crystal-field ligands reveals an excellent crystalline core, atomically defined core/cladding interfacial roughness, and significant enhancements in new laser-induced electronic defect levels. Our work suggests an inexpensive, facile, and highly scalable route toward achieving cellular-resolution tomographic imaging and represents an important step in the development of endoscope-compatible diagnostic devices.

Silicate-clad highly Er3 +/Yb3 + co-doped phosphate core multimaterial fibers

Highly rare earth ions (RE-ions) doping phosphate glass fiber makes it possible to obtain high gain and high output power per unit length. However, high concentrations of RE-ions will cause concentration quenching and crystallization during the conventional rod-in-tube fiber drawing process. In this work, highly Er3+/Yb3+ co-doped multi-component phosphate glasses were prepared by the melt-quenching method. Through thorough investigation of 1.53μm luminescent properties of the glasses, optimal RE-ions were ascertained. The Er3+ and Yb3+ doping concentrations reach as high as 13.77×1020 and 2.295×1020ions/cm3, respectively. Then the silicate-clad highly Er3+/Yb3+ co-doped phosphate core multimaterial fibers were successfully fabricated by a molten core method. The multimaterial fibers have a large refractive index difference and good interface between the phosphate glass core and silicate glass cladding. An intense 1.53μm emission was obtained from the multimaterial fiber. The results indicate that the highly Er3+/Yb3+ co-doped multimaterial fibers are promising in applications that require high gain and high power from a short piece of active optical fiber.

Experimental and Analytical Techniques for Studying ZBLAN Crystallization in Microgravity

One of the promising new areas of materials research is in the field of microgravity. Microgravity experimentation enables new materials to be developed and traditional materials to be improved, which cannot be completed under terrestrial conditions. Recent experiments on ZBLAN (ZrF4–BaF2–LaF3–AlF3 –NaF) glass have shown that, when heated, there is a crystallization dependency on gravity. This crystallization dependency limits the optical transmissibility of this material, due to crystallites forming during the fiber drawing process. ZBLAN glass has the theoretical potential for optical transmission in the range of 0.3 –7 μm, which would facilitate much needed mid-infrared (IR) fiber technology. Past researchers have completed ZBLAN crystallizationmicrogravity experiments, with limited details on the experimental technique and analysis methods. This study demonstrates an alternative experimental technique for ZBLAN microgravity testing and postprocessing techniques that reveal crystallinity in the sample.

Integration of conductive reduced graphene oxide into microstructured optical fibres for optoelectronics applications.

Integration of conductive materials into optical fibres can largely expand functions of fibre devices including surface plasmon resonator/metamaterial, modulators/detectors, or biosensors. Some early attempts have been made to incorporate metals such as tin into fibres during the fibre drawing process. Due to the restricted range of materials that have compatible melting temperatures with that of silica glass, the methods to incorporate metals along the length of the fibres are very challenging. Moreover, metals are nontransparent with strong light absorption, which causes high fibre loss. This article demonstrates a novel but simple method for creating transparent conductive reduced graphene oxide film onto microstructured silica fibres for potential optoelectronic applications. The strongly confined evanescent field of the suspended core fibres with only 2 μW average power was creatively used to transform graphene oxide into reduced graphene oxide with negligible additional loss. Existence of reduced graphene oxide was confirmed by their characteristic Raman signals, shifting of their fluorescence peaks as well as largely decreased resistance of the bulk GO film after laser beam exposure.

Spectral characteristics of draw-tower step-chirped fiber Bragg gratings

This paper presents research results on the spectral properties of step-chirped fiber Bragg grating arrays written during the fiber drawing process into a birefringent optical fiber with an elliptical stress cladding. The dependences of resonance shift of the step-chirped fiber Bragg grating on bending, on applied tensile stress and on temperature have been investigated. A usage of such step-chirped fiber Bragg gratings in fiber-optic sensing elements creation has been considered.

Single-mode fluorotellurite glass fiber

By multi-stage rod-in-tube fiber drawing process, a single-mode fluorotellurite glass fiber was fabricated and reported for the first time. Benefiting from chemical–physical dehydration process to remove water and OH− groups, the propagation loss was decreased to 1.9dB/m at 1550nm and the infrared window is extended from 2.8μm to 4.2μm, i.e. a new kind of mid-infrared glass fiber. The fiber is with a small core of 3.52μm in diameter to meet single-mode condition, and the effective nonlinear parameter γ was estimated to be 236.7W−1km−1 at 1550nm by using continuous-wave self-phase modulation method. © 2015 Elsevier B.V. All rights reserved.

A silica optical fiber doped with yttrium aluminosilicate nanoparticles for supercontinuum generation

We design and fabricate a silica optical fiber doped with yttrium aluminosilicate (YAS, Y2O3–Al2O3–SiO2) nanoparticles in the core. The optical fiber is drawn directly from a silica tube with YAG (Y3Al5O12) ceramics and silica powders (the molar ratio 1:18) in the core at the temperature of ∼1950°C. The YAS nanoparticles are formed during the optical fiber drawing process. Supercontinuum (SC) generation in the optical fiber is investigated at different pump wavelength. At the pump wavelength of ∼1750nm which is in the deep anomalous dispersion region, SC spectrum evolution is mainly due to multiple solitons and dispersive waves (DWs), and three pairs of multiple optical solitons and DWs are observed. When the pump wavelength shifts to ∼1500nm which is close to the zero-dispersion wavelength (ZDW), flattened SC spectrum with ±7dB uniformity is obtained at the wavelength region of ∼990–1980nm, and only one obvious soliton and DW are observed. At the pump wavelength of ∼1100nm, a narrow SC spectrum from ∼1020 to 1180nm is obtained in the normal dispersion region due to self-phase modulation (SPM) effect.

Raman gain of Ge-Sb-Se chalcogenide glass

Previously reported chalcogenide glass Raman fiber lasers are made of glass compositions such as As2S3 or As2Se3. However, due to the high toxicity of the element arsenic, there is a potential risk in the glass preparation, fiber drawing, and testing processes. Therefore, we need to explore new environmentally friendly chalcogenide glasses that do not contain As for Raman fiber lasers. Studies have shown that the chalcogenide glasses of Ge-Sb-Se system have excellent infrared transmissions and good environmental friendliness, and thus they are excellent candidates for chalcogenide glass Raman fiber lasers. However, their Raman gains have not been reported. Then Raman gain coefficients can be obtained by experimental measurements and theoretical analyses. The experimental method requires expensive laboratory equipments, a complex optical path, and precision adjustments. Therefore, the design and preparation of new chalcogenide glass fiber with high Raman gain require the theoretical analysis of the Raman gain characteristics in a particular glass component glass. In this work, four chalcogenide glasses, respectively, with compositions of As2S3, As2Se3, Ge20Sb15Se65 and Ge28Sb12Se60 (mol%) are prepared. Refractive indices, infrared transmission and Raman spectra of these glass samples are measured. By using spontaneous Raman scattering theory combined with the measured Raman spectral data, the values of Raman gain coefficient gR of the chalcogenide glasses are calculated and calibrated by a quartz glass sample. Results show that the gR of As2S3 glass is 6010-13 m/W at 230 cm-1 Raman shift and the gR of As2Se3 glass is 22310-13 m/W at 340 cm-1 Raman shift, which are consistent with the experimental results reported in the literature. Compared with the traditional method, the present method used for calculating the fiber Raman gain coefficient provides great convenience for exploring new chalcogenide glasses with high Raman gain. By using this method, we obtain the gR values of Ge20Sb15Se65 and Ge28Sb12Se60glasses at 200 cm-1 Raman shift, which are 21510-13 m/W and 11110-13 m/W respectively. Meanwhile, we analyze the effects of composition and network structure of chalcogenide glass samples on the Raman gain coefficient and gain spectrum. There are two Raman peaks at 165 cm-1 and 200 cm-1 Raman shift, which are attributed to Ge-Ge bond vibration and Ge-Se bond vibration of common apex GeSe4/2 tetrahedral structure respectively. It could be found that the Raman gain coefficient of Ge20Sb15Se65 glass is bigger than that of Ge28Sb12Se60glass at 200 cm-1 Raman shift because of more Ge-Se bonds. By further optimizing the ratio of components of Ge-Sb-Se chalcogenide glass, we could obtain higher Raman gain coefficient at a particular frequency shift. These results show that the Raman gain coefficient of Ge-Sb-Se chalcogenide glass without poisonous element is up to over 200 times that of the ordinary quartz glass, which provides a new possibility for environment-friendly Raman fiber laser material.

Numerical and experimental study of the glass flow and heat transfer in the continuous glass fiber drawing process

The manufacturing process of glass fibers used for the reinforcement of composite materials consists in drawing a free jet of a molten glass at high temperature into fibers using a winder. This process is sensitive to numerous disturbances that can cause the fiber to break during the drawing process, and thus reduce the process efficiency. The underlying physics of the forming of a single fiber is investigated here through numerical simulations, and results are validated with measurements obtained on a dedicated experimental unit. Both a two-dimensional axisymmetric and a simplified one-dimensional model are used to simulate the high-temperature region before glass transition. The influence of key parameters and physical mechanisms on the internal stress is investigated through a sensitivity analysis. The simplified model is then used to identify the optimal operating window and to assess the impact of temperature inhomogeneities at the bushing plate. Results show that the initial region close to the tip is critical, and that a low cooling rate reduces the stress. Operating at high tip temperature, large drawing velocity and small tip radius is then found to be the best strategy to minimize the stress. Finally, it is shown that the heat pattern of the bushing plate is one of the most important causes for disturbance in the process.

Role of Optical Fiber Drawing in Radioluminescence Hysteresis of Yb-Doped Silica

Point defects in the host lattice of a scintillator material can trap carriers, slowing down their migration or even preventing their transfer to luminescent centers. Such competition schemes between defects and luminescent centers may explain also the hysteresis effect, which consists of a progressive enhancement of scintillation efficiency with accumulated dose. We propose a comparison between the scintillation hysteresis effect of Yb-doped sol–gel silica glasses in bulk and fiber forms, and we correlate them with traps monitored by wavelength-resolved thermally stimulated luminescence in both materials. The results demonstrate that the fiber-drawing process is responsible for modifications of the defectiveness of the glass network, with a change of the local distribution of the traps surrounding the luminescent center. The consequence of such modifications is the removal, in the fiber samples, of the thermally stimulated luminescence peak ascribed to traps closer to Yb ions and unstable at room tempera...

Higher-order mode suppression in chalcogenide negative curvature fibers.

We find conditions for suppression of higher-order core modes in chalcogenide negative curvature fibers with an air core. An avoided crossing between the higher-order core modes and the fundamental modes in the tubes surrounding the core can be used to resonantly couple these modes, so that the higher-order core modes become lossy. In the parameter range of the avoided crossing, the higher-order core modes become hybrid modes that reside partly in the core and partly in the tubes. The loss ratio of the higher-order core modes to the fundamental core mode can be more than 50, while the leakage loss of the fundamental core mode is under 0.4 dB/m. We show that this loss ratio is almost unchanged when the core diameter changes and so will remain large in the presence of fluctuations that are due to the fiber drawing process.

The influence of the fiber drawing process on intrinsic stress and the resulting birefringence optimization of PM fibers

The propagation properties of optical fibers can be significantly influenced by intrinsic stress. These effects are often undesired but in some cases essential for certain applications, e.g. in polarization maintaining (PM) fibers. In this paper, we present systematic studies on the influence of the fiber drawing process on the generated stress and demonstrate an approach to significantly increase the stress induced birefringence of PM-fibers. It is shown that the thermal stress caused by the material composition is superimposed with the mechanical stress caused by the fiber fabrication process. This intrinsic stress has a strong effect on the optical and mechanical properties of the glass and thus influences the fiber stability and modal behavior. By applying a thermal annealing step, the mechanical stress due to the fiber drawing process can be canceled. It is shown that this annealing step compensates the stress reducing influence of the drawing process on the birefringence of PM-fibers with panda structure. The comparison of the intrinsic stress states after fabrication with the state after the additional high temperature annealing step clearly shows that it is possible to improve the overall birefringence of panda fibers using appropriate preparation steps.

Modified rod-in-tube for high-NA tellurite glass fiber fabrication: materials and technologies.

In this paper, we report the whole fabrication process for high-numerical aperture (NA) tellurite glass fibers from material preparation to preform fabrication, and eventually, fiber drawing. A tellurite-based high-NA (0.9) magneto-optical glass fiber was drawn successfully and characterized. First, matchable core and cladding glasses were fabricated and matched in terms of physical properties. Second, a uniform bubble-free preform was fabricated by means of a modified rod-in-tube technique. Finally, the fiber drawing process was studied and optimized. The high-NA fibers (∅(core), 40-50 μm and ∅(cladding), 120-130 μm) so obtained were characterized for their geometrical and optical properties.