Abstract: The present invention provides an installation for fabricating or overcladding an optical fiber preform, which installation includes an inductive torch for producing a plasma from a plasma generating gas and material feed means and is characterized in that said plasma generating gas is a mixture of a first gas chosen from diatomic gases and mixtures of at least two gases and argon in a proportion by volume from 0.5% to 10%.

Abstract: The present invention provides an installation for fabricating or overcladding an optical fiber preform, which installation includes an inductive torch for producing a plasma from a plasma generating gas and material feed means and is characterized in that said plasma generating gas is a mixture of a first gas chosen from diatomic gases and mixtures of at least two gases and argon in a proportion by volume from 0.5% to 10%.

Abstract: The invention relates to the field of optical fibres, to optical-fibre preforms and to processes for producing a final optical-fibre preform obtained by plasma built-up on a primary preform. The invention relates especially to a final optical-fibre preform comprising a primary preform (3) obtained by a VAD deposition process or an OVD deposition process, a silica sleeve tube (4) surrounding the primary preform (3), and a built-up layer (5) made of silica particles surrounding the silica sleeve tube (4).

Abstract: The invention provides a low cost method of manufacturing high capacity preforms by chemical vapor deposition. More particularly, there is described a method of manufacturing an optical fiber preform, which method comprises the steps of providing a substrate tube of silica doped with sufficient chlorine to obtain an OH concentration of less than 100 ppb and doped with sufficient fluorine proportional to the chlorine doping to obtain a refractive index that is lower than that of a natural silica, depositing inner cladding and an optical core inside the substrate tube, collapsing the substrate tube to form a primary preform, and depositing outer cladding of said natural silica on the resulting primary preform. The invention is applicable to manufacturing optical fibers.

Abstract: The invention relates to a method of doping silica with fluorine. The method described comprises mixing a powder of silica granules with a solid fluorine compound, thermally decomposing the solid fluorine compound under an inert atmosphere, and densifying the granules to obtain dense grains of doped silica. It is preferable to use ammonium bifluoride. The invention is applicable to preparing high index silica glass, in particular for fabricating optical fiber preforms.

Abstract: The invention provides a step index optical fiber which presents cladding having an index lower than the index of silica and a core with an index higher than the index of silica. The fiber is obtained by drawing a preform made by chemical vapor deposition using a deposition tube of index lower than the index of silica. Inner cladding of index substantially equal to the index of the deposition tube, and then a core of index higher than the index of the inner cladding are deposited in succession therein. The invention makes it possible to obtain a fiber having a large effective area, reduced attenuation, and suitable for being fabricated at low cost by chemical vapor deposition.

Abstract: In an FCVD process for producing preforms for dispersion shifted optical fiber or dispersion compensating optical fiber having a core comprising a central portion, an inner cladding, a ring, and an outer cladding by depositing layers, the layers of the preform corresponding to the inner cladding and to the ring of the optical fiber have a phosphorus content not greater than 0.1 wt %.

Abstract: The method is designed to be implemented in an installation provided with means enabling a preform held between two points by supporting end-pieces to be rotated and to be moved in translation. Heater means for heating the preform by means of a plasma torch are associated with material supply means, so as to enable the preform to be manufactured in layers. Preform/torch relative displacements, with or without material being supplied, lead either to a new layer of material being deposited on the preform, or to the most recent layer deposited being glazed. Said method interposes a one-ended reduction in layer length, starting from one of the intermediate layers, while a succession of concentric layers are being deposited on the preform in a manner such that the lengths of the layers are progressively reduced so that the preform tapers towards it ends. The one-ended reduction leads to a limitation of the thickness of a determined segment at the level of the layer deposited immediately prior to the reduction.

Abstract: A method for reducing the hydrogen aging loss of silica optical fibers by irreversible reaction of the peroxide defects with deuterium is described. This method comprises the step of contacting the optical fiber with deuterium by exposure to a gas mixture containing deuterium at a temperature compatible with the fiber without exposing the fiber to any further activation, and subsequently the step of degassing the fiber in a neutral atmosphere. The invention relates further to a process of producing optical fibers with low hydrogen aging loss wherein an optical fiber is treated using the method for reducing the hydrogen aging loss. Finally, the invention relates to optical fibers with low hydrogen aging loss obtainable by this process and telecommunication cables produced using these optical fibers. Using the new method, an activation step using intense light and/or elevated temperature is not necessary to achieve the reaction of peroxide defects in silica with deuterium.

Abstract: A method for reducing the hydrogen aging loss of silica optical fibers by irreversible reaction of the peroxide defects with deuterium is described.

Abstract: The invention relates to the field of processes for manufacturing optical fiber preforms. This is a process for manufacturing optical fiber preforms that includes a step of drawing the preform with a draw ratio that remains constant for the same preform and may vary from one preform to another depending on their respective mean diameters so as to reduce the variation in mean diameter between preforms or else a process for manufacturing optical fiber preforms that includes a step of compressing the preform with a compression ratio that remains constant for the same preform and may vary from one preform to another depending on their respective mean diameter so as to reduce the variation in mean diameter between preforms.

Abstract: A method of manufacturing an optical fiber preform (3) comprising: forming at least one silica-based outer deposition layer (23) by depositing silica on a primary preform (24) constituted by a bar mainly comprising silica and including a silica-based outer peripheral portion (22), the method being characterized in that the viscosity of the outer deposition layer (23) is adjusted to be substantially identical to the viscosity of the outer peripheral portion (22) of the primary preform (24) by adding to the silica, over a substantial portion of the outer deposition layer (23), at least one compound selected from the group formed by the following compounds: CaF2, MgF2, AlF3, B2O3, and Al2O3.

Abstract: The invention relates to a method of doping silica with fluorine. The method described comprises mixing a powder of silica granules with a solid fluorine compound, thermally decomposing the solid fluorine compound under an inert atmosphere, and densifying the granules to obtain dense grains of doped silica. It is preferable to use ammonium bifluoride. The invention is applicable to preparing high index silica glass, in particular for fabricating optical fiber preforms.

Abstract: The invention provides a step index optical fiber which presents cladding having an index lower than the index of silica and a core with an index higher than the index of silica. The fiber is obtained by drawing a preform made by chemical vapor deposition using a deposition tube of index lower than the index of silica. Inner cladding of index substantially equal to the index of the deposition tube, and then a core of index higher than the index of the inner cladding are deposited in succession therein. The invention makes it possible to obtain a fiber having a large effective area, reduced attenuation, and suitable for being fabricated at low cost by chemical vapor deposition.

Abstract: Natural or synthetic silica is deposited on a preform set into rotation in front of a plasma torch which moves back and forth substantially parallel to a longitudinal direction of the preform, a first feed duct feeds the plasma with grains of natural or synthetic silica while a second feed duct feeds the plasma with a fluorine or chlorine compound, preferably a fluorine compound, mixed with a carrier gas. Any sodium or lithium contained in the grains of natural or synthetic silica react with the fluorine or chlorine of the fluorine or chlorine compound, thereby making it possible to improve the optical quality of fibers drawn from a preform built up with natural or synthetic silica, and to do so at reduced cost.

Abstract: The invention provides a low cost method of manufacturing high capacity preforms by chemical vapor deposition. More particularly, there is described a method of manufacturing an optical fiber preform, which method comprises the steps of providing a substrate tube of silica doped with sufficient chlorine to obtain an OH concentration of less than 100 ppb and doped with sufficient fluorine proportional to the chlorine doping to obtain a refractive index that is lower than that of a natural silica, depositing inner cladding and an optical core inside the substrate tube, collapsing the substrate tube to form a primary preform, and depositing outer cladding of said natural silica on the resulting primary preform. The invention is applicable to manufacturing optical fibers.

Abstract: A process is described for making silica powder by a sol-gel process whereby an aqueous suspension is made of a silica-based raw material which includes particles containing chlorine, the pH of the suspension is adjusted to a value from 3 to 4.5 if necessary, the suspension is gelled, the gel obtained is dried and the dried gel is fractionated into silica granules. The silica-based raw material preferably includes particles containing chlorine having a specific surface area less than 80 m2/g and less than 5 wt. % relative to the total quantity of particles containing chlorine of silica particles having a specific surface area from 150 m2/g to 300 m2/g. The use of such powder to manufacture an optical fiber preform is also described.

Abstract: The invention relates to an optical fiber preform comprising an optical core, optical cladding, and an outer sheath, in which the outer sheath includes a peripheral zone containing 20% to 100% by weight alumina and 80% to 0% by weight silica. Such a preform makes it possible to obtain optical fibers having improved mechanical strength and improved impermeability to hydrogen.

Abstract: Silica granules made up of mutually agglomerated silica soot particles are treated by placing the granules in a crucible inside a furnace which contains an inert gas mixed with a chlorine-containing compound and in which the temperature lies in the range 1000° C. to 1500° C. According to the invention, a crucible is used that is made of porous graphite firstly to increase the surface area of the crucible through which the chlorine-containing compound diffuses. This gives rise to faster exchange between the granules and the gas for given partial pressure of the chlorine-containing compound, thereby improving purification. Secondly, the difference between the chemical natures of the silicas and the crucible make the two materials inert relative to each other so that the granules do not adhere to the walls of the crucible, thereby making it possible to recover the granules without having to apply any mechanical operation that might contaminate them.

Abstract: The deposit of natural or synthetic silica comprises a preform (1) set into rotation (7) in front of a plasma torch (3) which moves back and forth substantially parallel to a longitudinal direction (L) of the preform (1), a feed duct (9) for feeding the plasma with grains of natural or synthetic silica (11), characterized in that the same feed duct (9) feeds the plasma with a fluorine or chlorine compound, preferably a fluorine compound, mixed with a carrier gas (15). Sodium or lithium contained in the grains of natural or synthetic silica reacts with the fluorine or chlorine of the fluorine or chlorine compound, making it possible to improve the optical quality of fibers built up with the natural or synthetic silica at reduced cost.