Optical Fiber Manufacturing Research Articles

Neck Down and Thermally Induced Defects in High-Speed Optical Fiber Drawing

The drawing speeds employed in the manufacturing of optical fibers have been rising in recent years due to growing worldwide demand. However, increasing speeds have placed stringent demands on the manufacturing process, mainly because of large temperature gradients that can generate thermally induced defects and undesirable variations in fiber characteristics. Heat transfer and glass flow that arise in drawing fibers of diameters 100–125 microns from cylindrical silica preforms of diameters 5–10 cm play a critical role in the success of the process and in the maintenance of fiber quality. This paper presents an analytical and numerical study of the optical fiber drawing process for relatively large diameter preforms and draw speeds as high as 20 m/s. The free surface, which defines the neck-down profile, is not assumed but is determined by using a balance of forces. An iterative numerical scheme is employed to obtain the profile under steady conditions. The transport in the glass is calculated to obtain the temperature, velocity and defect distributions. A zone radiation model, developed earlier, is used for calculating radiative transport within the glass. Because of the large reduction in the diameter of the preform/fiber, the velocity level increases dramatically and the geometry becomes complicated. A coordinate transformation is used to convert the computational domains to cylindrical ones. The numerical results are compared with experimental and numerical results in the literature for smaller draw speeds for validation. The effects of high draw speeds and of other physical variables on defects generated in the fiber, on the neck-down profile, and on the feasible domain for the process are determined. [S0022-1481(00)02302-1]

Asymptotic analysis of compound liquid jets at low Reynolds numbers

Asymptotic methods based on the slenderness ratio are used to obtain the leading-order equations which govern the fluid dynamics of both hollow and solid, compound jets such as those employed in the manufacture of textile fibers, composite fibers and optical fibers. These fibers consist of an inner material which may be a round jet or an annular one and which, in turn, is surrounded by an annular jet in contact with ambient air. It is shown that the leading-order equations are one-dimensional and that it is possible to obtain analytical solutions for several flow regimes for steady, compound jets. These analytical solutions are presented here. The one-dimensional leading-order equations for the fluid dynamics of annular liquid jets at low Reynolds numbers are also derived here.

Interactive data analysis in a manufacturing setting — A case study

We present a case study in the application of interactive data analysis in the context of semiconductors and optical fiber manufacturing. Our approach to interactive graphics is based on well-known principles of data analysis and interactive graphics (Chambers, Cleveland, Kleiner & Tukey 1983, Cleveland 1993, Tufte 1983, Tufte 1990, Stuetzle 1987, Becker, Cleveland & Weil 1988b, Becker, Eick & Wilks 1991, Young & Lubinsky 1995, Buja, Cook & Swayne 1996), and its implementation is written in the S-language for data analysis and graphics (Becker, Chambers & Wilks 1988a, Chambers & Hastie 1992). The case study also highlights the need for improved interactive software tools in S-based systems to support the type of programmable interactive graphics that we envision. These limitations have motivated us to explore some recent developments in software technology, such as S Version 4 (Chambers 1998), Java, LispStat (Tierney 1996), XploRe (Haerdle, Klinke, Turlach & Ardle 1995), CORBA (Siegel 1996), and PVM (Geist, Beguelin, Dongarra, Jiang, Mancheck & Sunderam 1994), and asses how they can be used to alleviate some of the deficiencies we see in existing tools.

Chemical Vapor Deposition Processes in the Manufacture of Optical Fibers

Chemical Vapor Deposition Processes in the Manufacture of Optical Fibers

Fiber optic image guide rods in ultrathin endoscopy: material problems

The results of scientific and technological experiments performed in the Glass Department of the Institute of Electronic Materials Technology in Warsaw are presented. Research on fiber optic elements are carried out in areas of light and image guides made of multicomponent glasses and light guides made from pure silica glasses. The laboratory methods of manufacturing the glass elements, which are the starting preforms for optical fibers are elaborated. These methods include selection of the proper chemical composition of glasses, preparation of optimum material batches, melting the glasses in platinum or ceramic crucibles, mechanical working (grinding and polishing) of glass blocks to obtain rods for rod-in-tube preforms. Methods of pulling glass fibers of different cross sections for several medical, technical and environmental applications are improved. A high level of techniques and technological skills in the manufacture of optical fibers make it possible to obtain a higher generation of optical fiber elements and possibly to transmit an image.

Nonlinear control of optical fiber diameter variations

This paper presents a simulation-based investigation of nonlinear control of optical fiber diameter variations. A model of the fiber drawing process is presented and model reference control (MRC) and quasi-nonlinear control (QNC) systems are developed, based on a nonlinear dynamical model of the fiber drawing process. Results of numerical simulation indicate that the control schemes developed in this paper provide the potential for the manufacture of optical fibers at higher speeds. Numerical experiments also indicate that the QNC methodology is robust in the presence of significant model uncertainties and external disturbances.

Wear resistance of PVD coatings in plastics processing

In view of the increasing filler content, processing temperatures and throughput in plastics, wear in processing will remain a problem. This is particularly true of processes where no surface damage is permitted because of the subsequent change of dimensions or the intoxicating effects of the loosened particles, as is the case, for instance, in the manufacture of polymeric optical glass fibres. In particular, raw materials that exhibit abrasiveness as well as corrosiveness create a severe complex tribological load. The surface of processing equipment must be hard enough to withstand the mechanical attack of the hard glass fibres and should also be corrosion resistant. The potential of PVD coatings for wear protection in plastic processing has been studied when exposed to solid as well as molten plastic raw material. Wear tests have been carried out for commercially available glass fibre-reinforced polyamide (PA) and glass fibre-reinforced polyphenylene sulphide (PPS). The methods used were the platelet apparatus for the molten materials and the DKI universal wear and friction tester for the solid raw material. It was found that PPS (compared with PA) created higher abrasion in the solid zone and lower abrasion in the plasticized stage, although it may have higher corrosiveness. Among the PVD coatings tested the best results were achieved with CrN. In comparison with standard metals used for plastics machining the results show that, in general, PVD coatings offer a good opportunity for wear protection: not so much in the solids conveying zone but more so in the melt zone. As yet little is known about the scope of multi-layered PVD coatings, in which by combining the individual layers a combined wear resistance against complex loads may be achieved.

Chemical Vapour Deposition for Optical Fibre Technology

At the beginning of the seventies, a break-through took place in the telecommunication research. The introduction of Chemical Vapour Deposition technology in the manufacture of optical fibres allowed both technical quality and economical convenience to realise optical networks, thus beginning the telecommunication revolution. Since that moment, a great development of the CVD techniques has been performed, introducing several methods to produce fibres with geometry and optical properties optimised for different applications. An overview of the different methods is given, and the problems which have been to be solved in these years are described.

Modelling of chemical vapour deposition for optical fibre manufacture

A study of numerical modelling has been carried out for chemical vapour deposition processes with applications to manufacture of optical fibres. Temperature distributions and thermophoretic particle deposition have been calculated for the modified chemical vapour deposition (MCVD) and the outside vapour deposition (OVD) processes. A two torch formulation and a heat flux boundary condition are used for MCVD and the present model is shown to be capable of predicting tube wall temperatures and deposition profiles correctly. The present results are in agreement with experimental data. For OVD modelling, nonorthogonal body-fitted coordinates have been utilized to solve a conjugate problem including the jet flow and heat conduction through a two-layered cylinder that consists of an original target and the deposited porous layers. Surface temperatures and efficiencies of particle deposition have been obtained.

An Investigation of the Viscous Flow Problem Associated with the Heating of the Glass Preform During Optical Fiber Processing

ABSTRACTA thermal study of the optical fiber manufacturing process involves some of the most challenging, and in some cases, unsolved fundamental problems in heat transfer and fluid Mechanics. The heating stage of the process, where the glass cylinder (preform) is heated radiantly by the cylindrical muffle furnace, greatly influences the resultant quality of the fiber. During the process a neckdown region is formed that is characterized by the stretching of the glass. The two-dimensional transient equations of motion and Mass conservation, with viscosity dependent on temperature, were solved to obtain the velocity profiles in the glass and the shape of the neckdown region. Axial velocity contours and the neckdown profiles were examined for various drawing conditions. Differences between the new method presented here and existing one-dimensional method were examined. The analysis can be used for drawing of other materials such as metals and polymers, and the modeling is applicable to other viscous liquids.

The formation and deposition of SiO 2 aerosols in optical fiber manufacturing torches

Pyrogenic silica particle formation for optical waveguide manufacturing precludes the empirical approach to process control and optimization. The intimate coupling of flame chemistry, particle formation, and subsequent deposition necessitates the development of mathematical models which reproduce the intrinsic physics of the system, along with non-intrusive optical diagnostics to probe the extensive process parameter space. We present sheet-beam laser scattering and thermal tagging techniques to measure particle distribution and velocity, respectively. This information is used to compare particle deposition model calculations with data collected. In addition, two distinct particle formation mechanisms, oxidation and hydrolysis, have been observed which have profound effects on particle deposition efficiencies. Model calculations agree well with data and predict accurately the very high deposition efficiencies ( ca 100%) observed in the oxidation mode of particle formation.

Directions in Optical Fibers

Optical-fiber communications has developed into a multi-billion dollar industry during the past decade. More than 3 million kilometers of optical fiber are installed annually. AT&T has been a leader in optical communication systems; the company's representative accomplishments include the first full lightwave system trial (in Chicago in 1977) and the first transoceanic optical-fiber systems (in 1989). AT&T is one of the world's largest manufacturers of optical fiber and cable. This article will discuss the relationship between optical-fiber manufacturing and material research and development. Future directions and challenges will be identified.

Ultrapurification of SiCl4 by photochlorination in a bubble column reactor

AbstractThe development and performance of a bubble column photoreactor for ultrapurification of SiCl4 is described. Trichlorosilane (SiHCl3), the principle contaminant in SiCl4 commercially available for use in optical fiber manufacture, is converted to SiCl4 and HCl by UV‐initiated photochlorination. Studies of the homogeneous photochlorination kinetics and of Cl2 gas absorption in a bubble column were undertaken. In addition, an extensive set of data was collected from continuous‐flow bubble column reactor (BCR) runs. The rate of photochlorination in the BCR was found to be mass‐transfer‐limited. A simple model of BCR performance, incorporating the effect of Cl2 mass transfer rate enhancement by chemical reaction, was tested that agrees well with the experimental data. The BCR was found to be operable over a wide range of SiHCl3 concentrations and SiCl4 feed rates, and capable of lowering the concentration of SiHCl3 in product to below measurable levels (<1 ppm).

Deposition of lognormally distributed aerosols accounting for simultaneous diffusion, thermophoresis and coagulation

A moment model to predict deposition rates of lognormally distributed aerosols onto cylindrical surfaces in cross flow was developed taking into account diffusion, thermophoresis and coagulation. The results of the moment model are in excellent agreement with the solution of Friedlander [Friedlander (1977) Smoke, Dust and Haze. Wiley, New York] for the limiting case of monodisperse aerosols in absence of coagulation. Deposition rates for polydisperse aerosols determined by the moment model are in good agreement with solutions obtained by integrating Friedlander's monodisperse aerosol results over the entire size distribution. Deposition rates have also been determined due to diffusion accounting for coagulation, and due to diffusion and thermophoresis accounting for coagulation having applicability in deposition of high concentration aerosols encountered in industrial systems such as manufacture of optical fibers by the OVD process or heat exchangers in boilers.

Application of an atmospheric-pressure microwave plasma to the optical fiber manufacturing process

An atmospheric-pressure CVD method is described that uses microwave plasma for manufacturing preforms that are used in the production of optical fibers for telecommunication. The method takes advantage of the very high deposition efficiency and high deposition rates attained when using microwave plasma as well as of efficient glassing of oxide layers by means of the traditional system of burners. A simple theoretical model that allows calculations of close-to-reality plasma temperature profiles is presented.

Stress in optical waveguides 1: Preforms

The intrinsic stress properties of GeO2- and F-doped optical fiber preforms have been investigated in detail. The materials were prepared by low-pressure plasma-induced chemical vapor deposition (PCVD), and the dopant concentrations cover the range normally used in optical fiber manufacture (+1% > Δ > −1%). Homogeneously doped preform regions exhibit a constant stress level. This level is exclusively dependent on dopant concentrations. In GeO2-doped silica the stress increases linearly with the dopant concentration. For F-doped silica, however, this dependency is strongly nonlinear. A negative stress difference between undoped PCVD material and the substrate tube material can be explained by the reduced thermal expansion coefficient of PCVD-SiO2 caused by chlorine incorporated during the deposition step. The experiments agree excellently with theoretical predictions based on thermal expansion data.

Fluorine doping and etching reactions of freon 12 in optical fiber manufacture

The chemistry of reactions of CF <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> CI <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> used in optical fiber manufacture has been studied by infrared spectroscopy. Evidence is pesented to support a model of fluorine doping based on trichlorofluorosilane oxidation. Carbonyl fluoride has been identified as a major intermediate in the etching process.

Some aspects of glass science evolution

The development of halide glasses gives rise to several problems. From a basic point of view, the occurrence of glasses in numerous unexpected systems makes the prediction of glass forming ability a matter of reflection. An approach which encompasses kinetical, thermodynamical and structural aspects would be helpful for further investigations. Progress may be expected from computer simulations and calculations. Surface problems appear to be critical in various aspects of fluoride glass technology. They include hydrolysis, phase separation and diffusion processes. Finally, the reduction of the impurity level will be a major problem with respect to the manufacturing of ultra low loss optical fibers. During the next twenty years, numerous new glass forming systems will be investigated. Heavy metal oxide glasses will be synthesized. Increasing contents of nitrogen will be incorporated in glasses. New halide glasses will be discovered, especially in chloride, bromide, and mixed halide systems. Materials will be developed for optical transmission beyond 10 μm. Optical fibres lower than 10 −2 dB/km in attenuation will be achieved. BeF 2 fibres will be used for UV transmission. New sources and detectors will be available in the medium infrared range. Finally, new data and new concepts will provide a better understanding of glass structure, devitrification processes and optical losses.

A process for recovering germanium from effluents of optical fiber manufacturing

Germania is the primary dopant used to control the refractive index profile in optical waveguides. However, its poor efficiency of incorporation and its high cost create a need for recovery. This paper describes a system to recover the unused germanium from the manufacturing effluents. Briefly, the process includes 1) a gas scrubber to incorporate the unreacted germanium into solution, 2) a recirculation system to increase the germanium concentration, 3) a reaction to form a germanium precipitate, and 4) a filtration step to isolate the germanium-containing solids. The process is capable of recovering greater than 95 percent of the unreacted germanium.

Nonionizing radiation aspects of optical fiber manufacturing.

Evaluation of the spectral distribution of the electromagnetic emissions from a system composed of a hydrogen-oxygen torch and a glass tube, used in the manufacturing of glass rods from which optical fibers are drawn, indicated levels in the visible and infrared portion of the electromagnetic spectrum that necessitated a specific type of eye protection to be worn by employees operating this equipment. Specific eye wear which provided qualities of both being lightweight and reducing transmission of all three major regions of the electromagnetic spectrum (ultra-violet, visible, infrared) were specified.