Optical Fiber Drawing Research Articles

High-temperature resistant boron nitride-based coatings for specialty silica optical fibers

h-BN is well known for its thermal stability. h-BN coated silica optical fibers were manufactured. The coating solution is compatible with optical fiber drawing process, which allows the preparation of tens of meter of h-BN coated fibers. In addition, it is possible to use this coating material for the preparation of short length fiber samples in a post-production approach. Bentonite acts as a binder and allows the adhesion of h-BN to the silica optical fiber. The thermal stability of this protected optical fiber has been demonstrated over a short period of time (several hours) up to 900 °C and over a long period of time (1500 h) up to 800 °C in air. Moreover, the coated optical fiber can resist up to 1000 °C in neutral atmosphere (tested over 6 h).

In vivo multi-site electrophysiology enabled by flexible optrodes towards bi-directional spinal cord interrogation

Optical neural interfaces combining optogenetics and electrophysiology have been demonstrated as powerful tools for distinguishing the causal roles of neural circuits in the nervous system. Functional optrodes for multipoint stimulation and recording have already been demonstrated in the brain. However, soft and flexible multimodal optrodes for the purpose of probing the spinal cord have remained undeveloped. Here, we present the design and fabrication of a novel optrode for multi-site optical stimulation and electrical recording in the spinal cord by combining optical fiber drawing of polymer material, laser micromachining, and integration of tungsten microelectrodes in a monolithic fiber-based structure. The results from space-resolved scattering measurements, electrochemical impedance spectroscopy, and an acute in vivo electrophysiology experiment in an anesthetized rodent suggest this probe as a potential novel interface, which can serve as a part of therapeutic strategies against neurological conditions and injury in the spinal cord.

Exploring the Influence of ZnF2 on Zinc-Tellurite Glass: Unveiling Changes in OH Content, Structure, and Optical Properties.

Tellurite glasses have garnered considerable interest as optical host materials due to their advantageous properties, including low processing temperature, high resistance to corrosion and crystallization, and excellent solubility for rare earth ions. However, their applicability in the infrared (IR) region is limited by the absorption of species with distinct vibrations. The incorporation of fluorides has emerged as a promising approach to reduce hydroxyl (OH) absorption during the precursor melting process. In this study, we investigated the influence of ZnF2 on a glass matrix composed of TeO2-ZnO-Na2O, resulting in notable changes in the glass structure and optical properties, with Eu3+ serving as an environmental optical probe. The samples underwent comprehensive structural, thermal, and optical characterization. Structural analyses encompassed 19F and 125Te nuclear magnetic resonance (NMR), with the latter being complemented by mathematical simulations, and these findings were consistent with observations from Raman scattering. The main findings indicate an enhancement in thermal stability, modifications in the Te-O connectivity, and a reduction in emission intensity attributed to the effects of ligand polarizability and symmetry changes around Eu3+. Additionally, the fluorotellurite matrices exhibited a shift in the absorption edge toward higher energies, accompanied by a decrease in mid-IR absorptions, thereby expanding the transparency window. As a result, these glass matrices hold substantial potential for applications across various regions of the electromagnetic spectrum, including optical fiber drawing and the development of solid-state emitting materials.

Resolved‐detrimental surface crystallization in yttrium lanthanum gallate glasses for optical fiber applications

AbstractGallium‐rich heavy metal oxide glasses have become highly attractive optical materials since they exhibit a wide transparency window spanning from the ultraviolet ∼270 nm up to the mid‐infrared (IR) region ∼6 μm making them promising for a future integration in optical fiber devices. Nonetheless, in most composition, surface crystallization is a key limiting factor for optical fiber drawing using the classical preform‐to‐fiber method. Herein, taking advantage of structural information from vibrational spectroscopies (Raman/IR) and 71Ga Solid‐State Nuclear Magnetic Resonance, we describe the key role of lanthanum and yttrium rare—earth elements on the glass structure and their impact on the capability to draw those new glass compositions into optical fibers. This approach emphasizes that yttrium ions as compared with lanthanum ones favor the glass disorder, increasing significantly the fraction of GaO5 units with respect to GaO4. That, combined with thermal analysis and examination of the crystallization behaviors, highlights that Y2O3 prevents the glass devitrification during the glass shaping. The smaller yttrium radius is believed to be the key physical parameter preventing the precipitation of the BayGa5‐yGey+1La3‐yO14 (y = 0, 1, 2, 3) langasite‐type crystal phase. This study remains particularly relevant and opens up the way for the development of highly robust power scaled fiber devices operating from the visible up to the challenging mid‐IR domain.

An LSTM-based adaptive prediction control model for the wire diameter control of high-precision optical fiber drawing machines

Reducing inconsistencies in fiber diameter has always been a focus of research on optical fiber drawing machines (OFDM). Based on an established mathematical model for OFDM, we adopted a long short-term memory (LSTM)-based neural network to predict fiber wire diameter and utilized these results to feedback and control the drawing speed, thereby achieving high precision control of the wire diameter. We trained the proposed network using relevant data from two different fiber drawing processes, allowing it to learn the long-term and short-term correlations in the data. Additionally, we evaluated the performance of the model using root mean square error (RMSE) and R2 as indicators. The experimental results show that network complexity has a considerable impact on the precision of fiber wire diameter prediction. We also established that two LSTM hidden layers with 64 neural units in each layer are the most suitable for the proposed network structure. The network with such a structure has the smallest RMSE value in the validation set and the largest R2 in the testing set. Subsequently, the optimal network structure was used to conduct a multi-timespan wire diameter prediction experiment. According to the experimental results, the LSTM-based wire diameter prediction model still has a satisfactory predictive effect when the time is as long as 50 s, suggesting that the precision and robustness of this network are high. When this method is applied to the actual wire drawing process, the wire diameter error can be controlled to within ± 1.8 μm when the target wire diameter is 0.66 mm, indicating that the wire diameter precision is greatly enhanced. Results indicate that using LSTM-based prediction and control effectively avoids the interference of other factors in the process of wire drawing. Therefore, we remedied the time delay issue of conventional wire diameter control methods. Also, compared with conventional methods, we achieved more precise and robust control of wire diameter.

Addition of Ag2O in Er3+ doped oxyfluorophosphate glass to allow the drawing of optical fibers

Here, Ag2O containing glasses in the NaPO3–CaF2 glass network were prepared using standard melting process. The addition of Ag2O was found to increase the thermal stability of the glass due to the decrease in the Q2 units at the expense of Q1 units, to decrease the intensity of the upconversion under 980 nm pumping and to have a small impact on the nucleation and growth mechanism. Due to the thermal stability against crystallization of the glass prepared with 4 mol % of Ag2O, we demonstrate that fiber can be drawn from this glass. Despite the formation of Ag nanoparticles at the surface of the fiber although the drawing is a fast process, light can still be confined in the fiber. The fiber exhibits a large emission band centered at 1.5 μm under 980 nm pumping.

Robust extruded tungsten tellurite glass fiber with excellent mechanical properties for infrared applications

Robust tungsten tellurite (70TZLW) glass fiber consisting of 70TeO2-16ZnO-4La2O3-10WO3 core and 70TeO2-16ZnO-5.5La2O3-8.5WO3 cladding (in mol.%) was prepared by extrusion method. Due to the adding of La2O3 and WO3, 70TZLW glass exhibits higher glass transition temperature (385–395 °C) and thermal stability (>145 °C) than those of TeO2-ZnO-Na2O glasses, which is beneficial to the drawing of optical fiber. In addition, the mean optical losses of the bare wires drawn by the core and cladding glass preform are about 1.19 dB/m and 1.16 dB/m, while that is about 1.04 dB/m for the fiber drawn from the accordingly extruded preform at the wavelength of 1310 nm. Moreover, the average mechanical bending strength of the fiber reaches to about 570 MPa with a Weibull slope of 67.4. These results show the improvement in work ability and the greater practical potential of the 70TZLW extruded fiber compared to TeO2-ZnO-Na2O fibers for infrared application.

An Asymptotic Energy Equation for Modelling Thermo Fluid Dynamics in the Optical Fibre Drawing Process

Microstructured optical fibres (MOFs) are fibres that contain an array of air holes that runs through the whole fibre length. The hole pattern of these fibres can be customized to manufacture optical devices for different applications ranging from high-power energy transmission equipment to telecommunications and optical sensors. During the drawing process, the size of the preform is greatly scaled down and the original hole pattern result might be modified, potentially leading to unwanted optical effects. Because only a few parameters can be controlled during the fabrication process, mathematical models that can accurately describe the fibre drawing process are highly desirable, being powerful predictive tools that are significantly cheaper than costly experiments. In this manuscript, we derive a new asymptotic energy equation for the drawing process of a single annular capillary and couple it with existing asymptotic mass, momentum, and evolution equations. The whole asymptotic model only exploits the small aspect ratio of a capillary and relies on neither a fitting procedure nor on any empirical adjustable parameters. The numerical results of the simplified model are in good accordance with experimental data available in the literature both without inner pressurization and when internal pressure is applied. Although valid only for annular capillaries, the present model can provide important insights towards understanding the MOF manufacturing process and improving less detailed approaches for more complicated geometries.

Effect of B2O3 and Li2O on vibrational, thermal and optical properties of 50Bi2O3-15PbO-(35-x)B2O3-xLi2O (0 ≤ x ≤ 25 mol%) glasses

Bi2O3 based glasses have been proven as promising optical materials with regard to their 6 s2 lone pair electrons. By melt quenching, the highly thermal stable glasses 50Bi2O3-15PbO-(35-x)B2O3-xLi2O (where 0 ≤ x ≤ 25 mol%) were prepared. The short range order of the glasses was verified with XRD and DSC measurements. DSC analysis showed that thermal parameters varied non-linearly with increase of Li2O. Density (ρ), molar volume (Vm), oxygen packing density (OPD) and oxygen molar volume (Vo) were calculated and their compositional dependency was discussed in detail. Energy dispersive X-Ray (EDX) spectrometry analysis validated the stoichiometry of sample composition. FTIR analysis illustrated that the glass network comprise of BiO3, BiO6, BO3 and BO4 structural units together with non-bridging oxygens. The computed optical properties like optical band gap (Eopt), refractive index (n), Urbach energy (∆E), molar refraction (RM), metallization criterion (M) and oxide ion polarizability (αO2-) were observed to be non-linearly varied with the addition of Li2O. The interplay between the structural roles of Li2O and Bi2O3 was instrumental for the observed variations in all the properties. BiPBL4 glass showed the highest thermal stability (175 °C) and the high kgl value among the glass series. The incorporation of Li2O in presence of low mol% of B2O3 with Bi2O3-PbO endowed these glasses to have the low phonon energy. The analysis carried out in this work showed that these glasses might useful for optoelectronic devices and optical fiber drawing applications.

Fiber drawing ability and loss optimization of niobium rich borophosphate optical glass fibers

Here we explore the manufacturing of niobium-rich borophosphate glasses into fibers with optical quality. Glass preforms of composition [(100-x) (0.95 NaPO3 + 0.05 Na2B4O7) - x Nb2O5] with x = 37, 38, 39, 40 were synthetized and thermally drawn. Viscosity measurements performed in the softening point range show that the optical fiber drawing temperature gradually increases with the amount of niobium oxide. X-ray diffraction and Raman structural analysis performed post drawing demonstrate that the BPN glass with 39% Nb2O5 represents the upper limit for fiber drawing under oxygen. Subsequently, preform quenching protocol was optimized to mitigate the density fluctuations within the glass matrix related to convection flows and compare with the conventional cast-in-mold method. Optical transmission and shadowscopy imaging highlight the improvement in the optical quality of the glasses produced following this new protocol. This observation is confirmed by cut back loss measurements which show a decreasing in the attenuation from 6.04 dB/m to 3.19 dB/m between the two methods. One believes the manufacturing of niobium rich borophosphate fibers with improved optical quality highlights their potential to be used as near-infrared highly nonlinear waveguide devices.

Crack resistance, strength and dynamic fatigue of quartz fibers with copper coatings

Metallized coatings can significantly improve the operational properties of quartz fibers. The research was conducted to determine the crack resistance, strength and dynamic fatigue of optical fibers without any coating and with copper coatings. The microhardness of quartz fibers was measured by the diamond indentation of end surfaces. The stress intensity parameter K1cwas found from the A. Niihara semi-empirical dependence. The geometry of indentation and radial cracks was studied using a scanning electron microscope. The crack resistance of uncoated quartz turned out to be almost 3 times less as compared to the copper coating fiber, which is presumably due to the additive contribution of compressive stresses on fiber surfaces and quartz wetting with copper. Copper-coated optical fiber drawing increases the tensile strength, crack resistance and dynamic fatigue parameter, and it is the main resource for maintaining operation in the conditions of a statistical approach to structural strength. Comparative tests were conducted to check the optical fiber strength by two-point bending and axial tension methods. Experimental tests conducted to check the ultimate mechanical strength of quartz optical fibers showed a significant spread of data, which indicates the presence of cracks of various sizes in a brittle solid and is a characteristic feature of brittle fracture as suggested by the A. Griffiths theory. In addition, it was assumed that the chaotic distribution of defects and microcracks extends along the entire length of a brittle solid, a quartz optical fiber in this case. A statistical model based on the Weibull distribution was used to describe surface microcracks depending on the fiber length. As a result, Weibull graphs were plotted in coordinates connecting the probability of failure with the strength, fiber length and parameter describing the ultimate strength.

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.

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.

Specialty optical fiber fabrication: fiber draw tower based on a CO laser furnace

An experimental, laboratory-scale optical fiber drawing tower based on CO laser heating has been developed and used to fabricate speciality optical fiber. The CO laser was utilized in a symmetric four beam heating system. The localized and responsive heating time of the laser-based furnace was beneficial for manufacturing crystalline core fibers, specifically, silicon core optical fibers. Moreover, the specific absorption properties of the CO laser radiation in silica have been evaluated with the aid of finite element modeling. In comparison to the more traditional C O 2 laser, CO lasers were found to improve temperature uniformity and heating times while minimizing surface evaporation.

Manufacturing of GLS-Se glass rods and structured preforms by extrusion for optical fiber drawing for the IR region

Chalcogenide glasses are amorphous solid materials formed from chalcogen elements bonding with metals to form typically in binary or tertiary compounds. One family of chalcogenide glasses, based on gallium and lanthanum sulphides, possesses properties important for the infrared (IR) window transmissions and IR applications; these include thermal stability, high solubility of rare earth ions, low phonon energy and high laser damage threshold. Efforts have been made to produce new chalcogenide glasses that can extend the IR transmission window further into the IR. Work has led to the successful melting of a selenium-modified gallium lanthanum sulphide (GLS-Se) glass that can transmit up to 15 μm, however these glasses have, to date, only been demonstrated in bulk glass form. We aim to develop processes for the fabrication of chalcogenide optical fiber to exploit the properties of chalcogenide glasses. Several potential applications include sensing for the civil, medical, and military areas, as these materials offer transmission over much of the molecular fingerprint region (2 to 25 μm). The aim of our work is to understand and control the thermal properties and stability of GLS-Se glasses without compromising their optical properties, in order to produce transparent glass rods and demonstrate the feasibility in fabrication for structured optical preforms by extrusion, as the first step to achieve optical fiber from GLS-Se glass.

Pressure Effects on Structured Optical Fibre Drawing by Modified Single-Capillary Modelling

The impact of drawing pressure on the structure of solid-core structured optical fibres (SOFs) is investigated. A modified single-capillary model to cater for multi-capillary structural constraint in the radial axis within a larger single capillary draw, whilst retaining analytical simplicity, is proposed and shown to give improved fits with experimental data. For the cases we have experimented, an effective pressure is found approximately one-fifth less than that of the applied air pressure, based on the model and contributed from the interplay of applied pressure and the surface tension associated with the structure. In addition, the proposed model indicates that when birefringent SOFs with asymmetric holes having thinner walls were examined, the reduction in effective pressure is found to be about one-quarter of the pressure applied – it is larger than the uniform case and supports the explanation. Thus the model offers a simple and useful relation between the structure and draw pressure in fabricating structured optical fibre.

Adaptive wire diameter control of the high-precision optical fibre drawing machine

Different from the conventional methods such as the Proportional-Integral-Derivative (PID)-based method, an adaptive control algorithm (ACA) is proposed in this paper to control the wire diameter of high-precision fibre drawing machines (FDMs). A simple FDM model is established to acquire the relationship between fibre diameter and drawing velocity before the ACA is introduced. The comparison simulation of the accuracy of fibre diameter between the proposed ACA and traditional PID is made, and the ACA is applied to actual fibre drawing processes, so as to validate the ACA. The comparative results show that the fluctuation of filament diameter is smaller and the accuracy is higher under the ACA control. In actual fibre filament drawing processes, the ACA can limit the diameter error within ±2μm, which meets the production requirements.

Investigation of oversized channels in tubular fibre drawing

In a previous study, we compared experiments on drawing of axisymmetric tubular optical fibres to a mathematical model of this process. The model and experiments generally agreed closely. However, for some preforms and operational conditions, the internal channel of the drawn fibre was larger than predicted by the model. We have further investigated this phenomenon of an oversized channel with to determine the mechanism behind the size discrepancy. In particular we have explored the possibility of channel expansion similar to ‘self-pressurisation’ in fibres drawn from preforms that have been first sealed to the atmosphere, as previously described by Voyce et al. [J. Lightwave Technol. 27, 871 (2009) 10.1109/JLT.2007.916489]. For this, two pieces from each of two preforms with different inner to outer diameter ratios were drawn to fibre, one open to the atmosphere and the other with a sealed end. In addition, we have sectioned a cooled neck-down region from a previous experiment, for which the fibre had an oversized channel compared to the model prediction, and measured the cross-sectional slices. We here compare this new experimental data with the predictions of the previously derived model for drawing of an unsealed preform and a new model, developed herein, for drawing of a sealed tube. We establish that the observed oversized channels are not consistent with the self-pressurisation model for the sealed tube.

Investigation of ZnSe stability and dissolution behavior in As-S-Se chalcogenide glasses

Optical composite fibers based on active transition metal (TM)-doped semiconductor crystals are being investigated for use in mid-infrared (mid-IR) fiber laser systems. This study evaluates a candidate glass matrix system assessing its key physical properties and suitability for optical fiber drawing and examines the stability of TM-doped ZnSe crystals during processing. Results indicate that despite excellent refractive index matching between crystal and glass matrix and good fiber draw attributes, the stability of the crystalline dopant within the glass melt is severely impacted by melt conditions. The time and temperature dependence of this stability is mapped by X-ray diffraction (XRD) and second-harmonic generation (SHG) microscopy, illustrating how these tools can be used to track the phase stability and robustness throughout the melting process. Results show that in a range of sulfo-selenide based matrices, dissolution and re-precipitation of Zn-containing crystalline phases is a dominant mechanism.

A two-dimensional asymptotic model for capillary collapse

Abstract