Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/255—Splicing of light guides, e.g. by fusion or bonding
  • G02B6/2558—Reinforcement of splice joint

Definitions

• the present invention relates to the field of optical fibers.
• the present invention applies to optical fibers at least partially stripped over part of their length, for example for the formation of a component in the core of the fiber.
• the present invention aims to reconstruct the sheath of the fiber.
• the present invention applies in particular to optical fibers, whatever their type (250 ⁇ m to 400 ⁇ m) integrating a Bragg grating. Reference is usefully made to this subject in documents [1] and [2].
• the present invention is not however limited to this particular application. It can also be implemented in any application requiring local fiber reinforcement.
• optical fibers consist of a central core and an external sheath.
• the sheath of an optical fiber constitutes mechanical protection. Most often, this protection consists of an acrylate polymer. Its destruction or even its local withdrawal, justified for example by the production of a component, such as a Bragg grating, weakens the optical fiber considerably.
• the only effective technique to date for the production of a resurfacing is molding [3].
• the area to be recovered is placed in a mold.
• a polymer identical to that used for the initial sheathing of the fiber is injected into the mold, around the fiber, and polymerized.
• the optical fiber comprises a component, such as a Bragg grating, at the level of the stripped zone, which implies that the sheathing does not mechanically constrain this zone so as not to disturb the optical parameters of the network.
• this implies a value of the refractive index of the polymer adapted to the optical function photoinscribed in the fiber.
• the inventors have found experimentally that, by molding, it is very difficult to produce a sheathing of quality equivalent to the initial sheathing of the fiber.
• Several major faults are present repeatedly. Among the main ones, we can cite: - burrs due to molds (mold junction area),
• the object of the present invention is to reconstitute a homogeneous protection on a previously stripped fiber and to eliminate the defects due to manufacturing by molding. More specifically, the present invention aims to reconstitute the sheath of a locally stripped fiber by obtaining a sheathing of quality equivalent to that of the initial sheathing of the fiber and by retaining the initial flexibility of the latter as well as a volume d '' minimum space requirement. In particular, it is important that the finished product retains a flexibility close to that of the initial fiber. In this way the sheathed part can be curved or wound on short rays like a standard optical fiber (the minimum radius of curvature specified for an optical fiber is typically 15 mm).
• optical fibers obtained by implementing the method according to the present invention can in particular be used in the field of telecommunications. This implies that they retain their properties during their lifetime and under uncontrolled conditions of use (typically 20 years, from -40 ° C to + 85 ° C). This data can be verified by passing the aging tests defined by the Telcordia (ex-BelIcore) standards GR-1209-CORE and GR-1221-CORE.
• a method comprising the steps which consist in: - place a flexible tube on a bare fiber area comprising a Bragg grating,
• the tube remains attached to the fiber, at the end of the sheathing process.
• the present invention also relates to the optical fibers thus recovered.
• FIG. 1 represents a schematic sectional view of a partially stripped optical fiber
• FIG. 2 represents the step in accordance with the present invention consisting in placing a tube on the bare area of the optical fiber
• FIG. 3 represents the step consisting in injecting a polymeric material into the tube thus placed
• FIG. 4 schematizes a step consisting in polymerizing the end of the injected material opposite the injection zone
• FIG. 5 shows diagrammatically a step consisting in pressurizing the material thus injected
• FIG. 6 schematizes a step consisting in polymerizing all of the injected material
• FIG. 7 schematically shows an optical fiber thus obtained in the context of the present invention.
• An optical fiber 10 comprising a core 12 coated with a first silica sheath and possibly surrounded by an external mechanical protection sheath 14 has been shown diagrammatically in the appended figures. As illustrated in FIG. 1, for certain applications, it is this latter sheath 14 which is partially removed at 16 over part of the length of the optical fiber, for example for the production of components such as a Bragg grating, and it is precisely on this bare area 16 that the present invention proposes to reconstruct an optimal mechanical protection sheath.
• the stripped fiber 10 is cleaned with alcohol over its entire length before starting assembly. Indeed, the quality of the bonding between the fiber and the sheathing as well as the purity of the final sheathing strongly depend on the surface condition of the fiber.
• a flexible tube 20 is placed on the area 16 of bare fiber as seen in FIG. 2.
• a polymeric material 40 is injected into the tube 20 through an axial end of the latter. This step is shown diagrammatically in FIG. 3.
• the fiber 10 From the start of the injection of the material 40, until the end of the process, the fiber 10 must be kept straight, and the tube 20 centered on the bare area 16, that is to say almost identical overshoot on the part and other of this bare area 16.
• the tube 20 may not be perfectly coaxial with the fiber 10. It may even be brought temporarily into contact with the fiber 10, by an axial generator, to thus provide a large space between the fiber 10 and the tube 20, to facilitate the injection of the polymeric material 40. Of course, thereafter, the tube 20 can be made coaxial with the fiber 10.
• a syringe 30 which has a needle 32 of suitable size and quality so as not to deteriorate the sheathing of the fiber and to ensure rapid filling of the tube 20.
• the material 40 being injected through a first end of the tube 20 the air initially present in the tube 20 is ejected through the second end of the latter.
• the sheath 14 of the fiber, on either side of the stripped area 16 must remain bonded to the fiber 12 after stripping.
• the angle made by the polymer front 40 with the stripped fiber 12 is not critical.
• the polymerization of the material 40 can be carried out in several ways (hot, cold, under UV, etc.). In the context of the present invention, very preferably UV polymerization is chosen. Indeed, it is well suited for carrying out local polymerization. In addition, this type of treatment ages the tube 20 less than a thermal polymerization.
• a plug 42 is created on the axial end of the tube 20 opposite the injection end, so as to stop the progression of the injected polymer 40 and to facilitate the pressurization thereof.
• the polymer 40 is placed under pressure , by forced injection, during polymerization.
• a step-by-step polymerization (from the stopper 42 to the syringe 30) is carried out until reaching a few millimeters from the needle 32.
• the withdrawal of the syringe 30 is carried out by always injecting polymer 40 so as not to create bubbles in the polymer.
• the entire assembly is placed under ultraviolet radiation, as shown diagrammatically in FIG. 6, in order to ensure complete polymerization of the material 40 over the entire length.
• the experiments carried out by the inventors have given excellent results. They showed excellent bonding over the entire length between the fiber 10, the cladding obtained by the material 40 and the tube 20. They made it possible to remove all the defects observed previously with molding and demolding. They have also shown good mechanical strength and a sheathing capable of withstanding extreme weather conditions (from -40 ° C to + 85 ° C in particular).
• the method proposed in the context of the present invention allows industrial mass production.
• the polymer 40 is preferably formed from an acrylate polymer, such as for example the material sold under the name DSM-950-106 (Desolyte).
• the polymeric material 40 meets the parameters below:
• the tube 20 must have a good specific flexibility to allow winding or curvature of the recovered fiber over a small radius. It may for example be a tube based on a silicone material or a material chosen from the family of thermoplastic polyester elastomers.
• the tube 20 has a length at least 2 cm longer than the length of the stripped area 16. Thus, the tube 20 projects at least 1 cm, preferably on either side of the stripped area 16. Typically, for a bare area less than or equal to 2 cm, the tube 20 has a length of the order of 4 cm.
• the internal diameter of the tube 20 must be such that the minimum space cleared between the fiber 10 and the tube 20 allows acceptable progression of the polymer 40 during the injection.
• the spacing between the fiber 10 and the interior of the tube 20 is related to the viscosity of the polymer 40 used.
• the internal diameter of the tube 20 is typically of the order of 0.5 mm, while for fibers of diameter between 250 ⁇ m and 400 ⁇ m, the internal diameter of the tube 20 is typically of the order of 0.650 mm.
• the spacing between the fiber 10 and the interior of the tube 20 is typically of the order of 125 ⁇ m.
• the external diameter of the tube 20 is of the order of 900 ⁇ m.
• the tube 20 is translucent. This makes it possible to control the progress of the polymer material 40 in the tube 20.
• the tube 20 must also be transparent to UV to allow polymerization.
• the internal diameter of the injection needle 32 is preferably greater than 250 ⁇ m. This diameter is linked to the viscosity of the polymer 40.
• the outside diameter of the needle 32 is less than or equal to 450 ⁇ m, preferably. This diameter is linked to the free spacing in the tube 20 and to the elasticity of the latter.
• the tube 20 is formed of a tube marketed under the name Hytrel (Hytrel is a registered trademark of Du Pont de
• Nemours flexible D46 with a length of 4 cm, while the needle is a 26Gx1 / 2 needle with an external diameter of 450 ⁇ m and an internal diameter greater than 250 ⁇ m.
• a tube is part of the family of thermoplastic polyester elastomers. It is a copolyester based on polyether and polyester segments.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Manufacturing & Machinery (AREA)
• Plasma & Fusion (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)
• Surface Treatment Of Glass Fibres Or Filaments (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Cites Families (13)

• 2000
  • 2000-08-03 FR FR0010257A patent/FR2812728B1/fr not_active Expired - Fee Related
• 2001
  • 2001-08-03 JP JP2002517563A patent/JP2004506232A/ja active Pending
  • 2001-08-03 US US10/343,677 patent/US6915043B2/en not_active Expired - Fee Related
  • 2001-08-03 AU AU2001282263A patent/AU2001282263A1/en not_active Abandoned
  • 2001-08-03 WO PCT/FR2001/002540 patent/WO2002012934A2/fr active Application Filing
  • 2001-08-03 EP EP01960867A patent/EP1305660A2/de not_active Withdrawn

Non-Patent Citations (1)

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