Abstract: The invention relates to apparatus for supporting a preform manufactured in an installation for manufacturing or building up preforms having supporting cores, said installation including at least rotation means having a horizontal axis of rotation and two mounting points between which the supporting core of the preform to be manufactured or built up is mounted, plasma-torch and material-supply means disposed radially relative to said supporting core and being mounted to move in axial translation relative to and parallel to the supporting core so as to make said preform around said supporting core, said apparatus being wherein it includes controlled support means constituting additional localized abutment points between said mounting points for said preform being manufactured or built up.

Abstract: A device for doping silica powder with a dopant includes an arrangement for receiving silica soot particles or previously fabricated silica granules. The particles or granules contained in the receiving arrangement are heated to a temperature sufficient to allow agglomeration of the soot particles into granules followed by densification of the granules. The receiving arrangement is fed with a precursor gas of the dopant so that the granules are heated in an atmosphere containing the precursor gas, which causes the dopant to be incorporated into the granules during their densification to produce densified and doped silica grains. The receiving arrangement is mobile so that, during their movement, each of the granules that it contains is subject to movement such that substantially all of its outside surface is exposed to the atmosphere containing the precursor gas.

Abstract: A process of fabricating an optical fiber preform, preferably a multimode optical fiber preform, having a maximum refractive index along an axis of the fiber and a lower refractive index at its periphery. The process includes the following steps: depositing successive layers onto the interior of the tube with the refractive index increasing from the first, larger diameter layer to the central layer, each layer being formed from gases which react with each other inside the tube, and varying the proportions of the gases from one layer to another to vary the index. The gases are introduced into the tube at a velocity such that the radial index profile is homogenized in the longitudinal direction. This velocity is advantageously maintained substantially the same for the fabrication of all the layers. This process produces preforms having a homogeneous index profile in the longitudinal direction.

Abstract: The method of manufacturing a preform having a supporting core by effecting successive passes with a plasma torch while material is being supplied, and by effecting at least one glazing step with the plasma torch and without material being supplied includes:a) a first glazing step effected at slow speed from a first end of the preform to the second end thereof;b) pre-separation of the preform adjacent to the first end, thereby reducing its diameter to substantially that of the supporting core;c) a second glazing step effected from the first end to the second end of the preform; andd) complete separation of the preform at the place of pre-separation.

Abstract: The invention relates to a method of performing surface treatment on a preform manufactured in an installation for manufacturing or building up preforms having supporting cores, the installation including at least rotation means having a horizontal axis of rotation and two mounting points between which the supporting core of the preform to be manufactured or built up is mounted, plasma-torch and material-supply means disposed radially relative to the supporting core and mounted to move in axial translation relative to and parallel to the supporting core so as to make the preform around the supporting core, the preform being manufactured or built up by effecting successive passes with the plasma torch while material is being supplied.

Abstract: Device for injecting non-oxidizing gas into a furnace with a graphite concentrator (12) as the heating element used to heat a primary preform in the enclosure of the furnace (14) and moving relative to the furnace in its axial direction, and comprising at the inlet orifice (24) and at the outlet orifice (26) of the enclosure a respective annular injector (40, 42) for injecting two conical curtains of non-oxidizing gas, the gas for each of the curtains being directed towards the apex of the cone and in the direction away from the enclosure (14) so as to prevent any entry into the enclosure of air that could cause combustion of the graphite.

Abstract: A method of manufacturing a multi-core optical fiber, the method including assembling together a plurality of substantially identical single-core optical fiber preforms (2', 2"), referred to as "single-core preforms", each of which includes a core bar (3) surrounded by a layer of optical cladding (4), so as to form a "multi-core preform" (10) and drawing down the multi-core preform (10) so as to obtain the multi-core optical fiber. The assembly step includes securing the single-core preforms (2', 2") to one another by fusing them over their entire lengths or over portions thereof along their tangential lines of contact (T), without inserting the multi-core preform (10) into a holding tube. A vacuum is maintained in the preform during the drawing step, the vacuum being formed before or during the drawing step.

Abstract: A device for drawing down an optical fiber preform (2) connected at one end to a feed rod (3) having an equal or smaller diameter. A chamber (11) in which the preform is drawn has an upper part (11A) with an opening (12). The opening engages the preform to seal the chamber. An enclosure (5) has a seal (6) at its upper part (5A) for sealing around the feed rod. A lower part (5B) of the enclosure contacts the upper part of the chamber to seal the chamber while the feed rod is passing through the opening.

Abstract: A device for producing spherical silica grains includes a cylinder having its axis inclined to the horizontal and an inside wall made from a material that is significantly softer than silica. The cylinder has an entry chute for non-spherical silica grains and an exit chute for spherical cylinder grains. A rotary member is rotated at high speed by a drive shaft having its axis coincident with the axis of the cylinder. The rotary member includes at least one paddle vertically aligned with the entry chute so that silica grains entering via the entry chute are thrown by the paddle against the inside wall of the cylinder and follow a path most of which is against the wall before leaving via the exit chute.

Abstract: A method of manufacturing a multi-core optical fiber, the method including assembling together a plurality of substantially identical polished single-core optical fiber preforms (2', 2"), referred to as "single-core preforms", each of which includes a core bar (3) surrounded by a layer of optical cladding (4), so as to form a "multi-core preform" (10), and drawing down the multi-core preform (10) so as to obtain the multi-core optical fiber. The assembly step includes securing the single-core preforms (2', 2") to one another by fusing them over their entire lengths or over portions thereof along their tangential lines of contact (T), without inserting the multi-core preform (10) into a holding tube. A vacuum is maintained in the preform during the drawing step, the vacuum being formed before or during the drawing step.

Abstract: A method for producing spherical silica grains using a cylinder having its axis inclined to the horizontal and having an inside wall made from a material that is significantly softer than silica. The cylinder has an entry chute for non-spherical silica grains and an exit chute for spherical cylinder grains. According to the method, a rotary member is rotated at high speed by a drive shaft having its axis coincident with the axis of the cylinder. The rotary member includes at least one paddle vertically aligned with the entry chute so that silica grains entering via the entry chute are thrown by the paddle against the inside wall of the cylinder and follow a path most of which is against the wall before leaving via the exit chute. As a result, the silica graining have a spherical shape.

Abstract: A method of applying an amorphous boron-based protective coating to an optical fiber comprising an optical core enclosed in optical cladding, both made of a silica-based material, wherein the boron is applied to the surface of said optical fiber chemically from the vapor phase at a temperature lying in the range 1050.degree. C. to 1250.degree. C., by reducing boron chloride BCl.sub.3 by means of hydrogen H.sub.2. The amorphous boron protective coating imparts mechanical protection to the fiber, and enhanced abrasion resistance, enabling the fiber to be used in optical cables of high capacity and that are highly compact. The thickness of the resin coating can be about half that required when a carbon protective coating is used, and can even be eliminated. The coating further provides sealing properties comparable to those provided by a carbon coating.

Abstract: An optical fiber comprising an optical core enclosed in optical cladding, both made of a silica-based material, and a protective layer constituted by amorphous boron. The amorphous boron layer is deposited on a non-crystalline carbon which is itself deposited directly on the optical cladding. Also, a method is provided for depositing an amorphous boron layer on an optical fiber and includes a deposition step of depositing a layer of carbon on the fiber, followed by a subsequent step of depositing the amorphous boron protective layer chemically from the vapor phase on the layer of carbon.

Abstract: The present invention relates to an induction plasma torch of the type used in plasma deposition methods for depositing pure or doped silica when manufacturing preforms for optical fibers, the plasma torch comprising:a "reaction" tube inside which a plasma production zone is located;means for injecting reagents for forming the pure or doped silica to be deposited into the tube towards the plasma production zone;feed means for feeding plasma-generating gases into the tube towards the plasma production zone; andan induction coil surrounding the tube for supplying the energy required to form the plasma;wherein the tube is protected against the thermal cycles due to variations in the temperature inside the tube by means of a protective lining deposited on the inside wall of the reaction tube at the plasma production zone so as to surround the zone, the lining being made of a material based on silica, and having a thickness of less than 2 mm.

Abstract: A method of detecting variation in the diameter of an optical fiber includes the following steps:transversely illuminating a portion of the fiber by means of an incident light beam,measuring a radiation pattern produced by the fiber portion in a predetermined acute angular sector around the fiber, anddetecting variation in the diameter of the optical fiber causing modification of the angular radiation pattern produced in this way.The angular sector is defined by angles of 90.degree. and 105.degree. or by angles of 255.degree. and 270.degree..

Abstract: Dispersion-shifted monomode optical fibers have an effective mode surface area greater than 65 .mu.m.sup.2 by optimization of the geometrical characteristics that characterize the fibers. The fibers have substantially zero chromatic dispersion in the vicinity of 1.55 .mu.m, and they include an optical core having a central portion, a first layer having an index lower than the index of the central portion, and a second layer having an index higher than the index of the first layer and higher than the index of the optical cladding.

Abstract: Method of manufacturing a multi-component glass cylindrical part comprising the operations of providing a vertical cylindrical cavity lined with porous membranes whose inside dimensions are very slightly larger than those of the glass cylindrical part and in which can slide a cylindrical pedestal, providing a seed mass of the glass on the pedestal, heating the seed mass until it melts, injecting a gas continuously into the porous membranes to form and maintain a layer of gas between the porous membranes and the molten seed mass preventing any contact between the molten seed mass and the porous membranes, feeding the molten seed mass from the top of the cavity by continuously dispensing a powder made up of the components of the glass, varying the composition of the powder as the cylindrical part is formed, so that the glass cylindrical part has a composition that varies in the longitudinal direction, and lowering the pedestal as the cylindrical part is formed.

Abstract: To modify the longitudinal pitch distribution of a diffraction grating, longitudinal dimensional variation is imparted, over time, to a support along the entire length of a line on which said support carries, at least indirectly, a succession of diffraction elements of the grating. By way of example, the support is an auxiliary part on which an optical fiber is stuck, said fiber including said grating. An elongation coefficient dl/l represents the local relative value of dimensional variation. This value varies along said line. The invention is particularly applicable to making variable pitch light-refracting filters in optical fiber telecommunications systems.

Abstract: A method of using a plasma to build up an optical fiber preform consists in injecting hydroxyl ions in a controlled manner into the build-up silica that is deposited on the preform. The invention is applicable to the manufacture of optical fibers, in particular monomode fibers.

Abstract: This invention concerns an apparatus for checking the thickness and uniformity of a coating made of conducting material deposited on an elongated insulating body, this apparatus comprising:a sensor sensitive to the presence of the elongated body and forming part of an electrical circuit powered by a power supply voltage (24),measurement instruments (25) to measure an electrical quantity that is a function of the thickness of the conducting coating, at the output of the circuitequipment for processing the electrical quantity to deduce the thickness of the conducting coating,wherein the sensor consists of a condenser (10) containing two plates separated from each other by an air gap containing a dielectric material, this condenser being adapted to enable the elongated body to pass through the air gap.