Abstract: The present invention relates to a perfluorinated plastic graded-index optical fiber 51, including a core 52 of fluorinated polymer doped with a fluorinated compound, an optical cladding 53 in fluorinated polymer with an index less than that of said core 52, surrounding said core 52, as well as a strengthening layer 54 in polymer material, surrounding said optical cladding 53. The invention is remarkable in that the optical fiber 51 further includes a protective layer 55 in a photo-crosslinkable resin surrounding said strengthening layer 54, and the polymer material of the strengthening layer 54 is a material different from that of the protective layer 55.

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 preform overcladding device is provided. The preform overcladding device includes an injector for providing particles having a predetermined material, and a preheater for preheating the particles provided by the injector. The preform overcladding device also includes a heater for heating and depositing onto a preform the particles preheated by the preheater.

Abstract: A method and associated apparatus for increasing the over cladding rate in perform production while maintaining the integrity of the glass quality of the cladding. The method and apparatus are designed to utilize the full capacity of the generator to thereby improve the overall deposition speed without sacrificing the glass quality. In particular, it is estimated that the process of the present invention will increase the deposition speed by approximately 50% and still obtain suitable glass quality. This object is achieved by utilizing two plasma torches, instead of just one, that are driven by the same power generator.

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: In the method, a suspension of silica particles in water is provided, the suspension is gelled, the resulting gel is dried under microwaves, the dried gel is fractioned into silica granules having a diameter lying in the range 10 .mu.m to 1000 .mu.m, having an apparent density of about 0.5 g/cm.sup.3 to 0.6 g/cm.sup.3, and a porosity of less than 20%, and the granules are screened in the range 100 .mu.m to 500 .mu.m. The suspension in water of silica particles is made by mixing silica soots having a size of less than 0.1 .mu.m and silica grains having a size greater than 1 .mu.m. Its maximum concentration in total weight is greater than that of a suspension of synthetic soots on their own, thereby making it possible to increase the production capacity of the method. Advantageously, the out-of-range granules rejected by the screening are recycled as silica grains for the aqueous suspension, thereby making it possible to increase the accumulated production efficiency of the method.

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 fiber-drawing furnace includes a graphite tube positioned vertically, heated by induction, and subjected internally to an inert atmosphere, said tube internally defining a fiber-drawing chamber. In the furnace said graphite tube is a double-walled tube having an inner wall and an outer wall, its inner wall is porous and separates the fiber-drawing chamber from a peripheral chamber defined between the walls and subjected to a flow of inert gas which diffuses through said porous wall into said fiber-drawing chamber. Application to drawing down an optical-fiber preform.

Abstract: In order to manufacture a fiber by drawing a preform, said preform is made by collapsing a thick-walled silica tube having a reduced pressure established therein and heated in successive passes. The tube is prevented from ovalizing by beginning each pass with a portion bearing against a coaxial internal conical guide. The invention is applicable to low cost fiber manufacture.