Abstract: A method of producing a highly pure glass tube having a smooth inner surface, said method comprising the steps ofdepositing by the flame hydrolysis of a glass-forming raw material, a first layer of glass soot particles having a bulk density no greater than 0.2 g/cm.sup.3 on a seed member having a smooth and clean outer surface,depositing on the surface of the first layer of glass soot particles, a second layer of glass soot particles having a bulk density greater than that of the first layer by at least 0.03 g/cm.sup.3,drawing the seed member from the deposited two-layered glass soot preform to form a tube of glass soot particles,removing the first inner layer of glass soot particles from the second layer, either simultaneously with or subsequent to the drawing of the seed member from the soot preform, andheating and vitrifying the tubular glass soot preform to form a transparent solid glass tube.

Abstract: Apparatus for removing dust from the atmosphere around an externally heated tube (1) having a deposit being made on its inside surface from a vapor phase, said dust being removed by setting up a laminar flow of dust-free air around the tube. The apparatus includes members (7, 8, 9, 10) for setting up laminar air flows in planes parallel to the axis of the tube and on either side thereof, together with members (15, 16) for setting up flows of air perpendicularly to the axis of the tube and on either side thereof.

Abstract: A method for producing a glass preform for an optical fiber comprising flame hydrolyzing a glass raw material in an oxyhydrogen flame to form glass fine particles, depositing the glass fine particles on a seed member to produce a solid or hollow cylindrical soot preform, dehydrating by holding the whole soot preform in an atmosphere containing a dehydrating agent kept at such temperature for such period of time that the diameter of the soot preform shrinks by at least 20%, and heating and sintering the dehydrated soot preform by introducing it from its one end in an atmosphere of a pure inert gas to produce a glass preform having a uniform distribution of refractive index along its length, from which glass preform, an optical fiber having attenuation of light transmission as low as 1 dB/km or less at a wavelength of 1.30 micrometer is fabricated.

Abstract: A gas reaction apparatus for manufacturing base material of optical fiber and a multi-wall pipe type burner for the gas reaction apparatus. The gas reaction apparatus includes a mechanism which heats or heat insulates at least one of gas passages of the burner for gaseous raw material of optical fiber so as to set a saturated vapor pressure of whole kinds of the gaseous raw material higher than a partial pressure of raw material of optical fiber in the gaseous raw material when the gaseous raw material is fed through the one of the gas passages.

Abstract: A process for manufacturing optical fibers and components from bars or molds of fluoride glass draws out optical quality molds from highly pure glass. The glass is stretched or fibered into optical fibers in a dry atmosphere free of dust, organic, metallic or mineral vapors. The process leads to a low hydroxyl content fluoride glass which is used in the manufacture of optical fibers and components. The dehydration of the fluoride mixture occurs during the steps of prolonged heating at under 450.degree. C. in the presence of fluoride or ammoniumbifluoride, and of holding the molten mixture at a high temperature until dehydration occurs. The drawing out, stretching, and fibering are carried out in a vacuum.

Abstract: The method allows surface defect reduction in silica optical-fibers by enriching the external layer by silica bonded carbon atoms within the silica lattice: SiC.SiO.sub.2. Carbon is obtained from chemical reaction directly during the drawing step. Volume defects are reduced by rapidly cooling the fiber structure heated up to vitreous transition temperature.

Abstract: The method uses a raw-material and dopant-deposition technique, which requires vapor-state reactants and thermal sources for producing a temperature gradient suited to obtain a circularly and radially varying refractive-index profile in the supporting tube.

Abstract: The method of fabricating alumina-doped silica fibers allows the production of silica and dopant with reactions between gaseous chemical compounds. Alumina is obtained from a reaction between oxygen and a low-temperature vaporizable organometallic compound. The optical fibers produced do not present the refraction-index dip and exhibit low attenuation.

Abstract: A method for producing a glass preform comprising flame hydrolyzing a glass raw material in an oxyhydrogen flame to form glass fine particles of quartz, depositing the glass fine particles on a seed member to produce a solid or hollow cylindrical soot preform at least of a part of which contains GeO.sub.2, and heating and sintering the soot preform by introducing it in an atmosphere comprising an inert gas at least a part of which is kept at a temperature not lower than 1,600.degree. C. at an introducing rate not smaller than 3 mm/min, from the glass preform produced by which method, an optical fiber having longitudinally homogeneous composition and low attenuation of light transmission is fabricated.

Abstract: A process for producing an aerosol stream, which is conducted through an essentially aerosol-free vapor and/or gas stream to prevent undesirable precipitation of particles contained in the aerosol stream, is augmented by additionally employing thermophoresis. For this purpose, the vapor and/or gas stream is heated to a temperature which is higher than the temperature of the aerosol stream. Thermophoresis then causes the particles to be held within the aerosol stream.

Abstract: A tubular porous silica preform is made by depositing particulate silica on a mandrel from which the preform is subsequently removed. A solid cylindrical porous silica preform is made by depositing particulate silica on an end surface of a support body. The porous preforms are then dried and the tubular preform is heated in a fluorine containing atmosphere to introduce a fluorine dopant into the silica. The rod preform is then placed inside the tubular preform and the two preforms are further dried in a chlorine atmosphere to remove residual moisture. The dual preforms are then heated in a zone sintering furnace to consolidate and collapse the porous material of the rod and tubular preforms into a transparent fused silica rod. The composite preform obtained is heated and dielectric optical waveguide drawn from it, the waveguide having a pure silica or doped silica core derived from the rod preform and a fluorine doped silica cladding derived from the tubular preform.

Abstract: A method for producing sodium-containing glasses, by a vapor deposition process wherein a vapor mixture containing a sodium fluoroalkoxide compound is reacted to provide a particulate sodium-containing vapor deposition product which can be sintered to a glass.

Abstract: Optical waveguide having a fused silica core and a fluorine doped silica cladding is made by heating a cylinder of silica in fluorine, the cylinder initially having an outer annular particulate or porous region which is dried by the fluorine and into which fluorine diffuses to lower the refractive index of the silica when fused. The cylinder is made by depositing particulate silica onto a mandrel, drying the silica in chlorine, and heating the silica to densify it. Further particulate silica is deposited and is then heated in a fluorine-containing gas to dry, fluorine diffuse, and sinter the porous outer part of the silica. The resulting tubular silica preform is heated to cause fusion of the porous silica and to collapse the tubular preform into a rod from which optical waveguide is drawn, the waveguide having a fluorine doped silica cladding. The fluorine drying and diffusion steps produce HF which is extremely corrosive.

Abstract: An improved method of forming porous glass preforms by generating glass particles from a vapor phase and applying the particles onto a substrate characterized by generating the glass particles from a vapor phase in a separate operation, collecting the particles and then subsequently applying the previously collected particles onto a deposition surface of the substrate by creating a hot zone adjacent the deposition surface and projecting the particles as a stream through the hot zone and onto the deposition surface.

Abstract: A process is disclosed for making a preform from which optical fibers may be drawn, comprising forming a tubular glass body having a hollow center and concentric layers, at least one layer being a doped layer, and each layer having different indices of refraction. A partial vacuum is formed within the interior of the tubular glass body, at least part of the glass body is softened by heating, and the softened portions of the tubular glass body are collapsed to form a preform. The pressure of the partial vacuum is selected to effectively eliminate a dip in the index of refraction of any glass fiber drawn from the preform.

Abstract: A process is disclosed for producing an optical fiber comprising forming a tubular glass body having at least one doped layer, at least one concentric layer, each layer having a different index of refraction, and a hollow center. The glass body is heated until the softening point is reached, and is then drawn into a glass fiber. During drawing, a partial vacuum is maintained in the hollow center of the tubular glass body, the partial vacuum being of sufficient magnitude to reduce the evaporation of doping material from the interior of the tubular glass body and thereby effectively prevent a reduction in the index of refraction in the center of the optical fiber.

Abstract: An arrangement for collapsing tubular formations into optical preforms includes a control arrangement which controls the pressure build-up at the downstream end of the tubular formation during all of but the last one of the collapsing increments to control the flow of a gaseous medium through the interior of the tubular formation from an upstream end to and beyond the downstream end of the tubular formation. The magnitude of the back-up pressure is controlled by a set point controller in dependence on the actual value of the back-up pressure, the set point controller being operative for counteracting any deviation from the desired pressure. The set point controller controls the flow-through cross-section of a control valve that admits a pressurized inert gas to a region situated downstream of the downstream end of the tubular formation and also downstream of the point at which the pressure build-up is being measured.

Abstract: A method for producing a glass preform for an optical fiber by an outside vapor-phase deposition method, which comprises forming fine glass particles by jetting gaseous glass raw material and fuel gas from a first burner to deposit the particles on a seed rod to form a soot rod at such a temperature that a specific bulk density of the soot rod being formed is low and subsequently heating the soot rod by a second burner so as to increase the bulk density of the soot and then sintering the soot rod to obtain a transparent glass preform for an optical fiber, by which method, a highly pure glass preform is produced in a good deposition yield without cracking.

Abstract: The process of manufacturing optical fibers of extremely low loss in the medium infrared permits the fabrication of glass preforms having as basic materials metal-fluorides obtained from vapor-phase reactants.

Abstract: A method for producing an optical fiber preform comprising injecting a glass raw material, a gaseous fluorine-containing material and oxygen gas from a first nozzle, inactive gas from a second nozzle which surrounds the first nozzle and hydrogen gas from a third nozzle which surrounds the second nozzle, flame hydrolyzing the glass raw material to synthesis fine glass particles and depositing the fine glass particles on a tip of a rotating seed rod to produce the optical fiber preform containing fluorine.

Abstract: Glass preforms for optical fibers or the like having refractive index profiles which vary in stepped or graded fashion across the preform, are made from porous glass preforms by introducing a first dopant into the porous preform during manufacture, partially sintering the preform to selectively modify the internal surface area thereof, introducing a second vapor-infusible dopant into the selectively sintered preform to cause selective doping of the porous glass, and then consolidating the resulting doped preform to clear glass.

Abstract: Integrated optical waveguides, for example planar waveguides with stripes of guiding material formed integrally on a substrate, are manufactured by depositing the doped glass guiding material by plasma chemical vapor deposition. Several substrates can be arranged in a suitably shaped apparatus so that deposition can take place on all of them at once.

Abstract: In an optical fiber preform fabrication method having the steps of decomposing a glass raw material in a flame so that fine glass particles are produced; depositing the fine glass particles on a seed rod to form a porous preform; and consolidating the porous preform into a transparent optical fiber preform, use is made of a burner having a raw material supply orifice for supplying the glass raw material and a plurality of flame forming orifices disposed around the raw material supply orifice sequentially for forming a plurality of flames, respectively. The flame speed V.sub.k of a kth flame, the flame speed V.sub.k+1 of a (k+1)th flame surrounding outwardly of the kth flame and the flow speed Vm of the glass raw material are determined in a suitable manner. The glass raw material is supplied to the maluti-flame produced by the burner in which the kth flame is positioned rearwardly of the (k+1)th flame to synthesize the fine glass particles.

Abstract: A method for continuously melting a glass by means of a high-frequency electromagnetic field in a melting tube is provided. In this technique, the electromagnetic field is coupled in the melt by means of a coil present within a cooling jacket surrounding the melting tube. A grounded screen and a tube of insulating material are present between the wall of the melting tube and the coil. The melt traverses a heating zone and a refining zone, and a solid elongated body is withdrawn from the bottom of the melting tube.

Abstract: This disclosure describes a novel method of coating a substrate, e.g., a transparent glass substrate, with a very thin inorganic coating of predetermined varying composition, e.g. an electrically-conductive tin oxide coating. The coating is carried out in such a way that quality control problems associated with leakage of the coating reactants from the reaction zone are virtually eliminated. The resulting coating can exhibit excellent non-iridescent properties even at thicknesses well below on micrometer.

Abstract: A method for producing a directed aerosol stream from gaseous and/or vapor phase reactants by conveying the gaseous and/or vapor phase reactants including vaporous silicon tetrachloride, water vapor, and at least one vaporous, fluorine-containing hydrocarbon to a reaction site; reacting the reactants at the reaction site in a flame-free chemical reaction to produce an aerosol composition constituted of solid silicon dioxide particles which include silicon dioxide doped with fluorine, whereby the optical index of refraction of the solid silicon dioxide particles is reduced; and causing the aerosol composition to flow as an aerosol stream from the reaction site and immediately surrounding the aerosol stream with a moving, essentially aerosol-free, gas and/or vapor stream to form a directed aerosol stream enveloped in the aerosol-free stream.

Abstract: In the manufacture of preforms for metal halide optical fibers by the vapor deposition of metal halide layers on the inside surface of a silicate glass substrate tube, silicon release from the tube side wall by fluorine-containing reactants used in the vapor deposition process is reduced by the preliminary application of a slurry coating of a sinterable, fluorine-resistant metal halide or other glass composition which is dried and sintered to a passivation layer.

Abstract: Fluorine is selectively added to a cladding portion of a glass preform by producing a soot preform which comprises a core portion and a cladding portion under such conditions that an additive concentration or a bulk density of the outermost part of the core portion is to be larger than that of the inner part thereof and heating the soot preform in an atmosphere containing fluorine or fluorine-containing compound at least for some period to obtain a transparent glass preform.

Abstract: The process allows a uniform layer of glass particles, forming the preform, to be deposited on the internal wall of a supporting tube rotated around its axis. A suitable relationship is provided to determine the temperature distribution in the deposition zone. The apparatus makes use of different types of heat sources for generating inside the tube a temperature with the distribution required by the process.

Abstract: A vapor phase method for the synthesis of MgO--Al.sub.2 O.sub.3 --SiO.sub.2 products, including MgO--Al.sub.2 O.sub.3 --SiO.sub.2 glasses of optical quality, wherein SiCl.sub.4, aluminum halide, and organometallic magnesium vapors are oxidized by flame oxidation and the oxides collected and sintered to glass or ceramic products, is described. A added shield gas stream is provided during flame oxidation of the vapors to reduce or prevent MgCl.sub.2 by-product formation at the burner and in the product.

Abstract: A preform from which lightguide fiber is drawn is made by depositing optically suitable layers of doped silicon dioxide on an inner wall of a rotating glass tube (31) which is exposed to a moving zone of heat (56) which is provided by a torch assembly (50) during a deposition mode and during a collapse mode. After the deposition mode and generally prior to the collapse mode, one end portion of the tube is at least partially closed in order to allow pressurizing of the tube during collapse. This is accomplished with a pivotally mounted tool (70) which straddles the torch assembly to cause an internally water cooled contact device (92) to be disposed within the confines of the torch. Further, the contact device is configured to provide a curved lead-in from the tube to the at least partially closed portion. The use of separate apparatus for initially closing the tube provides control of the sealed-off portion and prevents an irregular cross-section from being propagated along the length of the tube.

Abstract: Infrared optical fibres are provided with hermetic coatings (6) by decomposition or reaction of volatile compounds of the coating material at the surface of the fibre. Materials having melting points greater than the fibre's glass transition temperatures may thus be applied at temperatures lower than the glass transition temperatures. The fibre (1) may be sufficiently hot from a preceding fibre formation (2,3) process in line with the coating process to enable the decomposition or reaction, or additional heating of the fibre by radiation may be necessary in the reaction chamber (7).

Abstract: Low signal attenuation optical fibers and methods for making such fibers mimimize the internal and interface defects while providing high throughput by radial deposition of successive particulate layers about a small diameter start element and co-vitrification of the layers followed by drawing to the small final diameter that is desired. Radial vapor deposition of an interface layer on the start element, followed by an encompassing core and then a cladding provides boundaries that form transitional continuums after the structure has been vitrified. The start element remains as part of the core but is so small as to have no discernible effect on light propagation, and the number of interfaces in the light propagating portion is limited by maintaining the ratio of the cladding thickness to the core radius to less than 1.5 in the initial preform. By drawing this preform to form separate rods, additional cladding is applied to form a fiber preform from which optical fibers may be drawn.

Abstract: Manufacture of optical fibre preforms. A material such as Si, Ge and B.sub.2 O.sub.3 is evaporated in vacuo into a silica tube and is made to condense therein as a viscous liquid which is then oxidized. The operation may be repeated several times with different materials. In this way the tube is clad from within in such a way that the optical index of refraction increases from the periphery inwards. Upon completion of the cladding the tube is collapsed into a rod which is then used for drawing optical fibres.

Abstract: The present invention relates to a method for producing a directed aerosol stream by a flame free reaction which is conducted while enveloped within an aerosol free gas and/or vapor stream. It is particularly suitable for use in coating systems, as it permits economical coating without so-called wall deposits.

Abstract: A method for fabricating a single mode fiber preform is described. The method consists of placing a core rod in a glass lathe, sliding a barrier tube over the core rod, partially attaching the barrier tube to the core rod, rotating and heating the barrier tube, and traversing the heat source until the barrier tube collapses onto the core rod. A second tube of high purity quartz called a primary jacket tube is then slipped over the combination fabricated from the core rod and barrier tube, rotating and heating the primary jacket tube, and traversing the heat source until the primary jacket tube collapses onto the barrier tube.

Abstract: A method for producing a glass preform for optical fibers by heating a glass soot preform consisting of glass fine particles made mainly of silicon oxide, which method comprises the steps of:(1) heating the glass soot preform to dehydrate and to remove impurities therefrom;(2) heating the glass soot preform in a gas atmosphere containing at least fluorine or fluorine-based compound to add fluorine to the glass soot preform; and(3) heating the glass soot preform to make it transparent, from the transparent preform prepared by which method, an optical fiber having superior transmission characteristics can be prepared.

Abstract: The inert or oxidizing auxiliary gases used in the manufacture of optical waveguides often contain traces of water which can be the cause of disruptive OH groups in the glass fiber. According to the invention, this disruption is overcome by reducing the hydroxyl content of optical waveguides by treating the auxiliary gases with heavy water (D.sub.2 O), so as to replace the hydrogen atom in the OH groups with deuterium, and then subjecting the gases to a drying step. Preferably, the auxiliary gases are subjected to a preliminary drying prior to treatment with D.sub.2 O.

Abstract: A method for fabricating preforms for drawing into single mode optical fibers having core and cladding doped with different amounts fluorine. A pure fused silica start rod is first coated with a layer of soot which is then dehydrated, doped with a first level of fluorine, and then consolidated. This structure, which is an intermediate preform, is then drawn down until its area weighted average index of refraction is such that it would perform as a core in a fiber. If not, it is recoated and drawn down further until it will behave as a core upon further reduction in size. The intermediate preform is then recoated with another layer doped with a higher concentration of fluorine so that it will act as a cladding layer over the first fluorinated layer whose index is higher because of a lower concentration of fluorine. This final structure serves as a preform from which the desired fiber can be drawn.

Abstract: The effluent of a process for making a preform from which an optical fiber is drawn is directed into a scrubber (40) of a loop (20) where it is treated with an aqueous solution to provide a solvent mixture which comprises particulates and a solvent solution including germanium. Subsequently, the solvent mixture is moved into a first filter system (55) which provides a filtrate free of particulates above a first size that is returned to the scrubber for reuse and a residue. Then the residue from the first filter system is moved into a second filter system (80) which provides a filtrate free of particulates larger than a second size that is smaller than the first size and a residue. The filtrate from the second filter system also is returned to the scrubber for reuse while the residue from the second filter system is recirculated therethrough.

Abstract: An optical fiber which has just been drawn from an optical preform is provided with two external hermetic coatings. The primary coating is a metallic or dielectric coating provided by, for example, using a heterogeneous nucleation thermochemical deposition (HNTD) technique. This technique involves passing the fiber through a reaction zone which contains a gaseous medium that includes a reactant which decomposes, or a mixture of reactants which chemically react, at a predetermined temperature, to form the material of the coating. Such predetermined temperature is available from the heat of the fiber forming process which is retained at the fiber surface by means of a shielding element so that additional heating means is not required. The second coating may be deposited, by for example, using an HNTD or a chemical vapor deposition process. The resulting fiber may then be provided with an additional polymer coating layer.

Abstract: A porous glass optical waveguide preform is formed by depositing a coating of glass particulate material on the lateral surface of a core which may be a porous glass body continuously produced by the axial deposition of glass particles. The core rotates and moves longitudinally in one direction with respect to two flame hydrolysis burners which emit streams of glass particles having different compositions. In addition, the two burners reciprocatingly move with respect to a portion of the length of the core. The speed of each burner varies as it traverses along its path of reciprocating motion. The thickness of the layer produced by a burner at a given point is inversely related to the speed of the burner as it passes that point. The layers formed by the completion of a single traverse by both burners combine to form a conically-shaped layer, the composition of which varies from the base toward the apex thereof.

Abstract: An optical fibre capable of monomode transmission in, and having a wavelength of zero dispersion in, the 1.55 .mu.m window and having a core comprising silica and germanium dioxide and a cladding comprising silica is drawn from an appropriate preform at a temperature in the range from 1900.degree. C. to 2000.degree. C. Fibres thus produced have low loss compared with fibres drawn at higher temperature.

Abstract: A method of producing a preform for light waveguides wherein glass-forming chlorides, e.g. SiCl.sub.4 and/or GeCl.sub.4, are reacted with water vapor to form a glass forming layer, e.g. SiO.sub.2 soot. This reaction advantageously takes place at relatively low temperatures, e.g. 20.degree. C.-800.degree. C. Surprisingly, almost no SiO.sub.2 deposition takes place on higher heated surfaces, e.g. in the reaction chamber. Elimination of annoying OH.sup.- ions is possible.

Abstract: A single-mode optical waveguide is constructed in a manner such that the core thereof is subjected to a stress-induced birefringence. A single-mode optical fiber preform is formed by a CVD process. A pair of longitudinally extending holes is formed on opposite sides of the core, spaced slighty therefrom. A stress rod having a TCE different from that of the cladding portion of the preform is inserted into each hole. The space between the holes and the rods is evacuated. The resultant composite structure is drawn into an optical fiber. A similar method is used to form a fiber having multiple light conducting cores, this method differing in that the rods which are inserted into the holes are formed of a glass having a refractive index greater than that of the cladding portion of the preform.

Abstract: Technique for making glass having a predetermined refractive index profile using fluorine doping and fluorine etching. A substrate glass body is coated with a plurality of successively applied vapor deposited glass layers wherein each succeeding layer is built with a larger quantity of fluorine than the adjacent preceding layer. The amount of the doping in each layer is such as to achieve the desired refractive index profile. Fluorine etching is employed to provide a uniform core before the glass body is heat fused into a rod-like structure suitable for the preparation of light waveguides for use in optical communications technology.

Abstract: A method of fabricating an optical glass base material by injecting and depositing fine glass particles produced by chemically reacting glass stock which comprises means for growing the fine glass particles in a depositing direction to form porous rod-shaped base material, support means for supporting the porous rod-shaped base material after growing, and heat treatment means for sintering at least the outer periphery of the rod-shaped base material in a semisintering state before supporting the rod-shaped base material by said support means to harden the same. Thus, since the rod-shaped base material is held in the stable state through the support means, the mechanical strength of the base material is strengthened strength by the semisintering hardening through the heat treating means before being supported by the support means, the base material is not deformed nor damaged in the supported state, and a large base material may be fabricated.

Abstract: A method of preparing an optical fiber includes the steps of applying a first cladding layer of a sinterable, glasseous particulate matter providing a selected index of refraction to a support surface, forming at least one longitudinally-extending groove in the layer prior to sintering, applying a deposit of glasseous particulate matter in said groove to ultimately define a core stripe having an index of refraction greater than that of the previously applied layer, applying a covering layer of glasseous particulate matter, sintering the various layers and the core strip to provide an optical fiber preform, and drawing the preform to provide an optical fiber having a rotationally non-symmetric characteristics with a core of higher index of refraction than the surrounding cladding.

Abstract: Preforms for drawing into glass fibers are relatively quickly produced by extruding filaments or tapes from polysiloxanes and/or heteropolysiloxanes and curing such filaments. A cylindrical wound body is produced from such cured filaments by winding such filaments onto an arbor. The wound body is converted, by heating in an oxidizing atmosphere, into an oxide body comprised of SiO.sub.2 and, under certain conditions, containing doping amounts of select heteroelements present in the heteropolysiloxane. After removal of the arbor, a gas stream containing chlorine gas is flushed at a temperature of about 1000.degree. to 12000.degree. C. through the oxide body to remove any traces of water and the dry oxide body is sintered into glass at a temperature of about 1200.degree. 1500.degree. C. The tubular preform thereby attained is collapsed and a glass fiber is drawn therefrom. This process is particularly suitable for the fabrication of gradient optical fibers.

Abstract: A process whereby an optical fiber is hermetically coated with a layer of aluminum oxide. The fiber is reacted pyrolytically with organo aluminum derivatives or other aluminum compounds, either in the form of vapor or atomized spray, to produce the desired coating. The thickness can be varied by changing reaction parameters. A buffer is also applied to the coated fiber. The end product is a glass fiber impervious to gases and fluids in the environment, especially H.sub.2 O, and one of improved abrasion resistance, hardness and strength.