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
  • G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
• • 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
  • G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
  • G02B6/4401—Optical cables
  • G02B6/441—Optical cables built up from sub-bundles

Definitions

• the present invention relates to a telecommunications cable having optical fibers contained in a retaining sheath.
• the cable is intended in particular to transmit high speed telephone and / or data processing signals, for example in local networks or as long distance cable between telephone exchanges or as distribution or connection cable for user lines which can convey telephone, data and / or image signals.
• European patent application EP 0 468 878 discloses a telecommunication cable comprising several optical fibers wrapped in a retaining sheath of small thickness that is easily tearable.
• the retaining sheath is in contact with the optical fibers to grip them.
• a sealant can fill the space between the fibers inside the sheath.
• the same holding sheath disposed directly without decoupling on one set of fibers does not degrade the transmission properties of the latter.
• the sheath ensures cohesion of the fibers to form a module having a high compactness, while allowing rapid stripping in situ when connecting to a user member or a connection between cables.
• the optical fibers are thus protected from contact with the ambient environment.
• the small thickness of the retaining sheath avoids subjecting the optical fibers to elongation and compression stresses during thermal cycles and allows economical production, in particular if it is carried out during the same manufacturing operation as the pulling of the optical fibers constituting the module, according to a technique of the multi-fiber-line wiring type.
• the module thus obtained has a significant compactness, and facilitates the connection of the cables by a simple location, an easy stripping, an aptitude for handling and a flexibility very favorable to the internal organization of the connection boxes, which can therefore made to be optimized in size and cost.
• French patent application FR 2 760 540 also relates to a cable comprising several optical fibers clamped in a sheath of the type of a microtube mounted very close to the optical fibers.
• This patent application poses a problem of increased attenuation by microbending of the optical fibers confined in the sheath when the sheath is deformed under the effect of an external stress, of mechanical or thermal origin.
• the request for patent FR 2 760 540 recommends that the sheath have, at a temperature of approximately + 20 ° C., a Young's modulus less than 200 Pa and a hardness less than 90 Shore units, and at a temperature of approximately -40 ° C, a Young's modulus less than 2000 MPa.
• the Young's modulus can be the Young's modulus in tension or the Young's modulus in bending, which differ by around 20% for polymers thermoplastics, and hardness can be expressed in Shore A units or Shore D units.
• the present invention aims to provide a fiber optic cable comprising a retaining sheath having defined mechanical characteristics relative to those of optical fibers, particularly to prevent microbending in the optical fibers when the cable is subjected to temperature variations of -40 ° C approximately to +85 ° C approximately.
• a cable comprising N optical fibers each having a core with a coefficient of thermal expansion / compression ⁇ l, a Young's modulus in tension El and a section SI and a covering with a coefficient of thermal expansion / compression ⁇ 2, a Young's modulus in tension E2 and a section S2, a retaining sheath enveloping the optical fibers, and a filling material between the optical fibers and the retaining sheath having a coefficient of thermal expansion / compression ⁇ .4, a module d 'Young in traction E4 and a section S4, is characterized in that the holding sheath has a coefficient of thermal expansion / compression ⁇ 3, a Young's modulus in traction E3 and a section S3 satisfying the following inequality:
• the material of the retaining sheath is preferably an amorphous, thermoplastic or elastomeric material, which may contain mineral fillers.
• the flexibility and ease of tearing required for the sheath are obtained for the abovementioned materials when the retaining sheath has a thickness of less than 0.3 mm and a hardness of less than 45 Shore D units.
• FIGS. 1 to 4 are section views on a large scale of fiber optic telecommunication cables according to the invention.
• Each of the telecommunication cables according to the invention shown in Figures 1 to 4 comprises several optical fibers FO.
• Each optical fiber FO is composed of a silica core 1 having a section SI typically with a diameter of 0.125 mm, and a colored identification coating 2 having a section S2 with a thickness of 0.062 mm, ie a diameter of optical fiber FO of about 0.25 mm.
• the coefficient of thermal expansion / contraction ⁇ l of the optical fiber core 1 is equal to
• optical fiber coating 2 is equal to 10 MPa.
• the retaining sheath 3 clamps a predetermined number N of optical fibers FO which is equal for example to four, or six, or eight, or twelve according to the embodiments illustrated in FIGS. 1 to 4, in order to maintain the optical fibers grouped and thus constitute a compact module.
• Most of the optical fibers at the external periphery of the module are in contact with the sheath 3.
• the holding sheath 3, called “microgaine” is extruded from a thermoplastic material defined in the following description.
• the retaining sheath 3 is very thin and has a thickness of the order of one tenth of a millimeter.
• the external diameter of the retaining sheath is of the order of a millimeter.
• the interior of the retaining sheath is filled with a filling material 4, such as gel or silicone oil, with which the optical fibers are coated prior to their passage through an extrusion die of the retaining sheath.
• the filling material 4 longitudinally seals the interior of the sheath.
• the coefficient of thermal expansion / contraction and the Young's modulus in tension of the filling material 4 are designated by ⁇ 4 and E4 and expressed in mm / mm / ° C and MPa.
• S4 denotes the section of the filling material, that is to say the cross-sectional area internal to the sheath 3, not including the sections of the optical fibers FO.
• the retaining sheath 3 can be coated with one or more colored identification films or be colored in the mass so as to distinguish it from other support sheaths.
• several fiber optic modules such as that illustrated in one of FIGS. 1 to 4, can be combined inside a protective envelope of a telecommunication cable, as shown in the aforementioned application EP 0 468 878, or can be kept in a cylindrical sheath to form a bundle of several modules, with or without central reinforcement, which is joined with other bundles of modules in a protective sheath of a telecommunication cable.
• the thermoplastic material making up the retaining sheath 3 does not alter the transmission performance and the lifetime of the optical fibers FO.
• the optical fibers according to the invention are not subjected to microbending constraints, in particular when the module is subjected to temperature variations, in particular when cold. It is recalled that an optical fiber is subjected to micro-bends when it is placed in a sinusoid with a short pitch, which decreases the optical performance of the optical fiber and particularly increases its attenuation. According to the invention, when the retaining sheath 3 contracts cold, it does not carry with it the optical fibers FO, and conversely, the group of optical fibers contained in the sheath impedes the withdrawal of the sheath for prevent optical fibers from undergoing microbending.
• the aforementioned performances of the telecommunication cable according to the invention are obtained by a selection of the coefficient of thermal expansion / contraction ⁇ 3 expressed in mm / mm / ° C, of the Young's modulus in tension E3, also called modulus or elasticity stress in tension, expressed in MPa, and of section S3, between
• the coefficient of thermal expansion / contraction ⁇ 3 of the retaining sheath 3 is for the sheath materials suitable below, typically
• a holding sheath whose Young's modulus in tension E3 and the coefficient of thermal expansion / contraction ⁇ 3 are low and whose maximum product ( ⁇ 3.E3) is less than 0.6.10 3 MPa / ° C (or 0.6.10 ⁇ 4 daN / mm 2 / ° C) achieves the targeted performance.
• the cable of the invention is flexible and the retaining sheath 3 can be easily torn manually. These latter conditions imply that the material of the retaining sheath has a hardness of less than 45 Shore D units and a thickness of less than 0.3 mm, preferably between 0.1 and 0.2 mm.
• the material of the retaining sheath produced by extrusion satisfying the above inequality is also selected to minimize as much as possible the post-extrusion sheath removals due to the relaxation of the stresses generated on the material by stretching and to avoid any risk. recrystallization of the material generating risks of putting optical fibers in microbends. The retaining sheath material therefore does not tend to recrystallize in the service range of -40 to +85 ° C.
• the material of the retaining sheath is a thermoplastic amorphous material, for example polyvinyl chloride PVC or an elastomer; or a charged thermoplastic material, for example a polyethylene, or a polyolefin such as ethylene / vinyl acetate EVA, comprising a sufficient amount of one or more of the following mineral fillers: chalk, kaolin, silica, talc, calcium carbonate , alumina or magnesium hydrate, titanium oxide.
• a thermoplastic amorphous material for example polyvinyl chloride PVC or an elastomer
• a charged thermoplastic material for example a polyethylene, or a polyolefin such as ethylene / vinyl acetate EVA, comprising a sufficient amount of one or more of the following mineral fillers: chalk, kaolin, silica, talc, calcium carbonate , alumina or magnesium hydrate, titanium oxide.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
• Insulated Conductors (AREA)
• Surface Treatment Of Glass Fibres Or Filaments (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9532897

Family Applications (1)

Country Status (12)

Families Citing this family (24)

Family Cites Families (7)

• 1998
  • 1998-11-18 FR FR9814519A patent/FR2785994B1/fr not_active Expired - Fee Related
• 1999
  • 1999-10-26 AU AU63465/99A patent/AU6346599A/en not_active Abandoned
  • 1999-10-26 CA CA002349921A patent/CA2349921A1/en not_active Abandoned
  • 1999-10-26 BR BR9914888-9A patent/BR9914888A/pt not_active IP Right Cessation
  • 1999-10-26 SK SK652-2001A patent/SK6522001A3/sk not_active Application Discontinuation
  • 1999-10-26 WO PCT/FR1999/002609 patent/WO2000029892A1/fr not_active Application Discontinuation
  • 1999-10-26 JP JP2000582840A patent/JP2002530693A/ja not_active Withdrawn
  • 1999-10-26 EP EP99950842A patent/EP1131661A1/fr not_active Ceased
  • 1999-10-26 CN CN99813396A patent/CN1326556A/zh active Pending
  • 1999-10-26 HU HU0104462A patent/HUP0104462A3/hu unknown
  • 1999-10-26 KR KR1020017006267A patent/KR20010101031A/ko not_active Application Discontinuation
• 2001
  • 2001-05-04 US US09/848,435 patent/US6334015B2/en not_active Expired - Fee Related

Non-Patent Citations (1)

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