Installation of aerial optical cable with reduced piston effect

Abstract

The invention relates to an optical cable installation comprising at least one optical connection box (20) and at least one optical cable (28) connected to said at least one optical connection box, said at least one optical cable (28) comprising: - a central mechanical reinforcement carrier (32), - at least one optical fiber module (34) arranged around the central mechanical reinforcement carrier (32), - at least one holding wire (38) wrapped around said at least one optical fiber module (34) to hold said at least one optical fiber module (34) against the central mechanical reinforcement carrier (32), and wherein the central mechanical reinforcement carrier (32) is fixed to said at least one optical connection box (20) to limit a longitudinal movement of said at least one optical fiber module (34) therein along a protective sheath (40). Figure for abstract: Fig. 5

Description

Title of the invention: Aerial optical cable installation with reduced pistoning effect

[0001] The present invention relates to the connection of optical cables comprising a plurality of optical fibers.

[0002] In particular, the present invention relates to an optical cable installation comprising an optical connection box and at least one optical cable connected to the optical connection box.

[0003] An optical telecommunications network connects different subsets together to enable data exchange between these subsets. Such an optical telecommunications network consists of branches, formed by optical cables, and nodes connecting the different branches together to create a mesh of a given territory.

[0004] A part of this optical telecommunications network located near buildings and individual houses is terrestrial, in particular aerial. The optical cables are connected together at optical connection boxes, called splice protection boxes. The purpose of these optical connection boxes is to protect and receive the splices of the optical fibers contained in the optical cables. In other words, the optical fibers are connected together inside the optical connection box so as to serve a portion of the network, a building or an individual house.

[0005] [Fig.l] is a schematic view illustrating a part of an optical telecommunications network between a ROP distribution cabinet and dwellings 12. An aerial optical cable 10 is supported by pylons 11 and connected to the dwellings 12. To do this, connection boxes are arranged on the pylons 11 at the junction points of individual optical fibers 2A. The optical fibers of the aerial optical cable 10 are connected by means of splices to the individual optical fibers 2A inside the connection boxes.

[0006] Aerial optical cables comprise a plurality of optical fiber modules arranged around a central carrier. Each optical fiber module comprises a tube and a plurality of optical fibers extending inside this tube. A retaining wire is generally wrapped around the optical fiber modules to secure them to the central carrier. A protective sheath surrounds the assembly formed by the central carrier, the optical fiber modules and the retaining wire.

[0007] The aerial optical cable is subject to harsh climatic conditions which can lead to significant variations in the dimensions of the optical cable, particularly in length. When the outdoor temperature is high, the optical cable elongates, while in winter, when the outdoor temperature is low, the optical cable shrinks and decreases in length. Such a variation in cable length also occurs when it is subjected to stresses related to wind and overloading with snow or ice.

[0008] Due to the structure of the cable and the materials present, the variation in length experienced by the core formed by the central carrier, the optical fiber modules and the support wire is different from that experienced by the protective sheath. A relative displacement therefore occurs between the core of the optical cable and the protective sheath during such a variation in length. This phenomenon is called "pistoning" (also known in English as the "pistoning effect"). This pistoning phenomenon is all the more significant when the optical cable is subjected to a very low temperature, to significant frost or snow loads, particularly in winter and to high temperatures, to strong winds, particularly in summer. This effect is also amplified when the cable is very long (e.g. beyond 200m).

[0009] This relative movement results in a tendency for the core of the optical cable to come out of the protective sheath when the temperature of the optical cable drops. Conversely, the core of the optical cable shrinks inside the protective sheath when the temperature of the optical cable and / or the constraints (wind / frost) increase. This shrinkage therefore tends to place greater stress on the optical fibers, which can lead to a reduction in the quality of the transmitted signal or even a cutoff of this signal by the optical fibers inside this core.

[0010] The solutions for limiting the effects of pistoning depend on the composition of the optical cable, in particular the tubes surrounding the optical fibers. These tubes can be rigid and hard tubes (generally called "loose tubes" in English) or flexible and soft tubes (generally called "micro-bundle" in English).

[0011] Rigid tubes or "loose tubes" generally have a thickness greater than 0.2 mm and are intended to form a rigid barrier to protect optical fibers. These rigid tubes cannot, for example, be torn by an operator with bare hands. A tool is therefore necessary to strip such a tube.

[0012] The mechanical characteristics of these rigid tubes allow the application of a covering force making it possible to significantly reduce the pistoning phenomenon. In other words, a covering force holding the tubes against the central carrier can be applied without damaging the optical fibers inside these tubes.

[0013] Flexible tubes or "micro-bundles" form a very thin skin around the optical fibers, generally less than or equal to 0.2 mm. Thus, the flexible tubes can be torn manually so that they greatly facilitate the handling of the optical cable during a connection operation. However, the flexibility of these tubes does not allow the application of a wrapping force identical to that of rigid tubes, avoiding the phenomenon of pistoning.

[0014] To avoid pistoning in optical cables comprising flexible tubes, the known solutions depend on the length of the optical cable considered, in particular for optical cables having a length less than or greater than 200m.

[0015] When the cable is less than 200m long, the ends of the reinforcing fibers, for example aramid, surrounding the core of the optical cable are rolled up and fixed to the protective sheath using a collar. In other words, an operator removes a portion of the protective sheath at one end of the cable to reveal the reinforcing fibers. These reinforcing fibers are folded, folded against the protective sheath and fixed to it. The effectiveness of this technique is however debated and has not shown conclusive results, in particular when the temperature variations and / or the stresses on the cable are significant.

[0016] When the cable has a length greater than or equal to 200m, coiling loops are made on the optical cable at the level of the pylon on which the connection box is installed. Thus, an additional length of optical cable is necessary and used to increase the friction inside the cable and therefore limit the relative movements inside it. Although effective, this solution results in very high costs when applied to each connection point of the network.

[0017] There is therefore a need for a practical and less expensive solution making it possible to limit, or even eliminate, the pistoning effect in an optical cable comprising flexible tubes or “micro-bundles”.

[0018] For this, the invention proposes an optical cable installation comprising an optical connection box and at least one optical cable connected to the optical connection box, said at least one optical cable comprising: - a central mechanical reinforcement carrier, - at least one optical fiber module arranged around the central mechanical reinforcement carrier, said at least one optical fiber module comprising a micro-tube and a plurality of optical fibers extending inside the micro-tube, - at least one holding wire wrapped around said at least one optical fiber module to hold said at least one optical fiber module against the central mechanical reinforcement carrier, and - a protective sheath arranged around said at least one retaining wire, in which the central mechanical reinforcement carrier is fixed to the optical connection box to limit longitudinal movement of said at least one optical fiber module inside along the protective sheath.

[0019] The attachment of the central mechanical reinforcement carrier to the optical connection box makes it possible to form a fixed support point on the core of the optical cable, i.e. the central mechanical reinforcement carrier, said at least one optical fiber module and said at least one retaining wire. This fixed support point combined with the covering force of said at least one retaining wire on said at least one optical fiber module makes it possible to limit pistoning inside the optical cable.

[0020] When the micro-tubes are too flexible to be subjected to a wrapping force eliminating the pistoning, the fixed support point created by the central mechanical reinforcement carrier fixed to the optical connection box makes it possible to significantly limit the pistoning despite a reduced wrapping force. This reduced wrapping force is preferably chosen so as not to damage the optical fibers present inside the micro-tube.

[0021] It is thus possible to avoid the known solutions of rolling up and then tightening the reinforcement wires against the protective sheath as well as coiling the optical cable onto a fixed point, such as a pylon, upstream of the optical connection box. The connection operation is thus made easier and much less expensive.

[0022] According to particular embodiments: - the micro-tube of said at least one optical fiber module has a thickness less than or equal to 0.2 mm, - the micro-tube of said at least one optical fiber module has an elongation at break of less than or equal to 300%, preferably less than 200%, more preferably between 80% and 200%, - the micro-tube of said at least one optical fiber module has a breaking load of less than or equal to 20 MPa, preferably less than or equal to 15 MPa, - the micro-tube of said at least one optical fiber module is made of a material comprising halogens or a material with a low halogen content, and / or of a material with low smoke emission, and / or a non-flame-propagating material, - said at least one optical cable comprises a plurality of optical fiber modules wound around the central mechanical reinforcement carrier according to a predetermined winding pitch, said at least one holding wire being wrapped around the plurality of optical fiber modules to hold said plurality of optical fiber modules against the central mechanical reinforcement carrier, - said at least one holding wire is wrapped around said at least one optical fiber module with a wrapping force less than or equal to 3 N, - the optical connection box forms a housing for receiving said at least one optical cable and comprises a means for fixing the central reinforcement carrier mechanics at the level of said receiving housing, - the optical connection box is a splice protection box comprising at least one splice support cassette configured to receive a splice of at least one optical fiber of said at least one optical fiber module.

[0023] The invention also relates to a method for connecting an optical cable to an optical connection box, comprising the following steps: - provide an optical cable installation as mentioned above, - removing a portion of the protective sheath and a portion of said at least one retaining wire so as to release said at least one optical fiber module and the central mechanical reinforcement carrier, - fixing the central mechanical reinforcement carrier to the mechanical reinforcement housing to limit longitudinal movement of said at least one optical fiber module along the protective sheath, - engaging at least one optical fiber of said at least one optical fiber module in the optical connection box so as to be able to connect it to another optical fiber. Brief description of the drawings

[0024] The attached drawings illustrate the invention:

[0025] [Fig-1] represents a diagram of an optical telecommunications network.

[0026] [Fig.2] represents a front view of an optical connection box of an ins installation of optical cable belonging to an optical telecommunications network as illustrated in [Fig.l].

[0027] [Fig.3] shows a cross-sectional view of an optical cable of an optical cable connection installation.

[0028] [Fig.4] represents a perspective view of an optical cable as illustrated in [Fig.3] partially stripped so as to observe the different layers making up this optical cable.

[0029] [Fig.5] shows a detailed front view of the optical junction box as illustrated in [Fig.2] with an optical cable engaged through one of its openings, the optical cable being stripped over a portion of its length with fiber optic modules rolled up and a central support fixed to the optical junction box. Description of embodiment(s)

[0030] The inventive concept is described more fully below with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. In the drawings, the size and relative sizes of the elements may be exaggerated for clarity. Like numerals refer to elements if military in all the drawings. However, this inventive concept may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that this description is complete, and communicates the scope of the inventive concept to those skilled in the art.

[0031] A reference throughout the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the occurrence of the phrase "in an embodiment" at various locations throughout the specification does not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Furthermore, the term "comprising" does not exclude other elements or steps.

[0032] An optical cable installation is proposed, preferably aerial. By "aerial" is meant the fact that the cable is intended to be arranged in contact with the open air, i.e. on the surface. Preferably, the aerial cable is intended to be fixed to a pylon or between two pylons. Thus, the aerial optical cable is not intended to be installed underground. The aerial cable is therefore subject to external conditions, in particular temperature.

[0033] This optical cable installation may be part of an optical telecommunications network as illustrated in [Fig.l].

[0034] The optical cable installation comprises at least one optical cable and at least one optical junction box. This optical junction box is a splice protection box. Its purpose is to protect and receive the splices of the optical fibers contained in the optical cables. In other words, the optical fibers are connected together inside the optical junction box so as to serve a portion of the network, a building or an individual house. Thus, the optical junction box houses incoming optical fibers and outgoing optical fibers connected together inside the optical junction box.

[0035] Such an optical connection box is visible in [Fig.2]. The optical connection box 20 comprises a housing 22 and a plurality of splice support cassettes 24 arranged inside the housing 22.

[0036] The box 22 forms an external envelope of the optical connection box 20 making it possible to protect the elements arranged within it from the external environment, in particular from wind and rain. The box 22 forms a plurality of openings 26 allowing the introduction of optical cables 28 inside the box 22. These openings 26 constitute housings for receiving optical cables 28. In part In particular, these openings 26 are cutouts made in a wall of the box 22 so as to form a passage between the internal cavity of the box 22 and the exterior of the box 22.

[0037] In the example of [Fig. 2], an optical cable 28 is arranged through an opening 26 located in the lower part of the box 22. The optical cable 28 has been stripped over a part of its length to release a portion of the length of optical fiber modules 34 so as to be able to connect the optical fibers 30 inside them. These optical fibers 30 are connected inside the splice support cassettes 24. These splice support cassettes 24 are configured to receive a splice of at least one optical fiber 30 of an optical fiber module 34.

[0038] The optical cable 28 of the optical cable installation is to be connected inside the optical connection box 20. An example of such an optical cable is visible in Figures 3 and 4.

[0039] The optical cable 28 comprises a central mechanical reinforcement carrier 32 and a plurality of optical fiber modules 34 arranged around the central mechanical reinforcement carrier 32. The central mechanical reinforcement carrier 32 will be referred to below as "central carrier 32" for the sake of clarity of exposition.

[0040] The central carrier 32 has the function of supporting a portion of the mechanical forces to which the optical cable 28 is subjected, in particular bending forces and longitudinal forces. The central carrier 32 may be made of fiber-reinforced plastic (called "FRP" or "Fiber Reinforced Plastic" in English), glass-reinforced plastic (called "GRP" or "Glass Reinforced Plastic" in English) or aramid-reinforced plastic (called "ARP" or "Aramid Reinforced Plastic" in English). The central carrier 32 may be of any shape. Advantageously, the central carrier 32 is of circular section so as to have a balanced arrangement of the optical fiber modules 34 around it and uniform resistance to the forces. Alternatively, several central mechanical reinforcement carriers 32 may be arranged inside the optical fiber modules 34.

[0041] Each fiber optic module 34 comprises a micro-tube 36 and a plurality of optical fibers 30 extending inside the micro-tube 36. The micro-tube 36 is preferably made in the form of a flexible tube or “micro-bundle”.

[0042] To obtain this flexibility, the micro-tube has an elongation at break of less than or equal to 300%, preferably less than 200%, more preferably between 80% and 200%. In addition, the micro-tube 36 preferably has a breaking load of less than or equal to 20MPa, preferably less than or equal to 15MPa. Such a micro-tube 36 can thus be torn manually. The micro-tube 36 preferably has a thickness of less than or equal to 0.2mm. The micro-tube 36 is made of a material comprising halogens or a material with a low halogen content. (commonly referred to as zero halogen). The microtube 36 material may also be low smoke and / or flame retardant.

[0043] The micro-tube 36 in the form of a “micro-bundle” is to be contrasted with rigid tubes (called “loose tubes” in English) which form a rigid shell around the optical fibers.

[0044] The optical fiber modules 34 are preferably wound around the central carrier 32 according to a predetermined winding pitch. A plurality of holding wires 38 are wrapped around the optical fiber modules 34 to hold them against the central carrier 32. Generally, at least one holding wire 38 can be used. The term “wrapping” means interlacing or helically winding strands of wire around a core, here the plurality of optical fiber modules 34, in order to constrain it against the central carrier 32. This constraint can be controlled as a function of the wrapping force applied by the holding wires 38.

[0045] The holding wires 38 are wrapped around the optical fiber modules 34 with a predetermined wrapping force. This wrapping force is preferably less than or equal to 3 N. It is indeed important not to wrap the holding wires around the microtubes 36 with too great a force, for example similar to that used for rigid tubes or “loose tubes”, to avoid any risk of deterioration of the optical fibers. For comparison, rigid tubes or “loose tubes” are generally wrapped around the central carrier with a wrapping force greater than or equal to 5 N.

[0046] The holding threads 38 can be made of aramid, polyester, glass, or any other material suitable for wrapping.

[0047] The optical cable 28 also comprises a protective sheath 40 forming a layer around the micro-tubes 36 and the holding wires 38. The protective sheath 40 may be reinforced by one or more peripheral carriers 42.

[0048] The optical cable 28 also comprises a layer of fibers 44, for example made of aramid, between the retaining wires 38 and the protective sheath 40.

[0049] In this optical cable installation, the central carrier 32 is fixed to the optical connection box 22 so as to limit longitudinal movement of the optical fiber modules 34 relative to the protective sheath 40. As indicated above, temperature variations or constraints (wind, frost) experienced by the optical cable 28 can cause a pistoning phenomenon between the optical fiber modules 34 and the protective sheath 40, which risks altering the signal transmitted by the optical fibers 30 or damaging these same optical fibers 30.

[0050] The wrapping of the holding wires 38 around the optical fiber modules 34 makes it possible to limit the movements between the optical fiber modules 34 and the central carrier 32. Thus, the fixing of the central carrier 32 to the optical connection box 20 contributes to forming a support point for the entire core of the optical cable 28, i.e. the central carrier, the optical fiber modules 34 and the holding wires 38. The pistoning phenomenon is thus greatly limited thanks to this assembly of the optical cable 28.

[0051] This pistoning limitation solution is particularly suitable for optical cables 28 comprising flexible micro-tubes 36 which can only be wrapped around the central carrier 32 with little effort. It is thus possible to benefit from the advantages of flexible micro-tubes 36 or “micro-bundles” while limiting the pistoning phenomenon.

[0052] With reference to [Fig.5], an example of fixing the central carrier 32 to the optical connection box 20 is illustrated.

[0053] The optical cable 28 is inserted through an opening 26 formed in the casing 22. The optical cable 28 is stripped over a portion of its length so as to reveal the optical fiber modules 34. In particular, the protective sheath 40, the peripheral carriers 42, the fibers 44 and the holding wires 38 are removed over this portion of the length of the optical cable 28. Thus, the optical fiber modules are free to be handled by an operator.

[0054] The optical fiber modules 34 are spaced apart so as to access the central carrier 32 which is fixed to a wall of the box 22 by means of a fixing means 46. This fixing means 46 may be a clamping collar itself fixed to the box 22, a movable plate capable of compressing the central carrier 32 or any other means making it possible to prevent the central carrier 32 from moving, in particular longitudinally.

[0055] The fixing means 46 is preferably arranged close to an opening 26 of the optical connection box 20. The optical connection box 20 may comprise a plurality of fixing means 46. The optical connection box 20 may in particular comprise as many fixing means 46 as openings 26.

[0056] The fixing means 46 is preferably arranged facing an opening 26, more preferably aligned with this opening 26. It is thus easier to fix the central carrier 32.

[0057] The optical connection box 20 further comprises a clamping means 48 for clamping the protective sheath 40. The clamping means 48 makes it possible to clamp the entire optical cable 28, in particular the protective sheath 40 with the optical fiber modules 34 and the central carrier 32. The clamping means 48 forms a support point for the optical cable 28 at the optical connection box 20. The clamping means 48 is arranged upstream of the fixing means 46 along the optical cable 28, just upstream of the stripped portion thereof.

[0058] The invention further proposes a method for connecting such an optical cable 28 to the optical connection box 20. The operator first removes a portion of the protective sheath 40 and a portion of said at least one retaining wire 38 so as to release the optical fiber modules 34 and the central carrier 32.

[0059] The central carrier 32 is then fixed to the optical connection box 20 to limit longitudinal movement of the optical fiber modules 34 along the protective sheath 40.

[0060] The optical fibers 30 contained in the optical fiber modules 34 are then engaged in a splice support cassette so that they can be connected to other optical fibers.

Claims

Claims

1. An optical cable installation comprising at least one optical connection box (20) and at least one optical cable (28) connected to said at least one optical connection box, said at least one optical cable (28) comprising: - a central mechanical reinforcement carrier (32), - at least one optical fiber module (34) arranged around the central mechanical reinforcement carrier (32), said at least one optical fiber module (34) comprising a micro-tube (36) and a plurality of optical fibers extending inside the micro-tube (36), the micro-tube (36) of said at least one optical fiber module (34) having a thickness less than or equal to 0.2 mm and an elongation at break less than or equal to 300%,- at least one holding wire (38) wrapped around said at least one optical fiber module (34) with a wrapping force less than or equal to 3 N to hold said at least one optical fiber module (34) against the central mechanical reinforcement carrier (32), and - a protective sheath (40) arranged around said at least one holding wire (38), in which the central mechanical reinforcement carrier (32) is fixed to said at least one optical connection box (20) to limit a longitudinal movement of said at least one optical fiber module (34) inside along the protective sheath (40).,

2. Optical cable installation according to claim 1, wherein the micro-tube (36) of said at least one optical fiber module (34) has an elongation at break of less than 200%, more preferably between 80% and 200%.

3. Optical cable installation according to claim 1 or 2, wherein the micro-tube (36) of said at least one optical fiber module (34) has a breaking load less than or equal to 20MPa, preferably less than or equal to 15MPa.

4. An optical cable installation according to any one of the preceding claims, wherein the micro-tube (36) of said at least one optical fiber module (34) is made of a material comprising halogens or a low halogen content material, and / or of a low smoke emission material, and / or a flame-retardant material.

5. An optical cable installation according to any one of the preceding claims, wherein said at least one optical cable (28) comprises a plurality of optical fiber modules (34) wound around the central mechanical reinforcement carrier (32) at a predetermined winding pitch, said at least one holding wire (38) being wrapped around the plurality of optical fiber modules (34) to hold said plurality of optical fiber modules (34) against the central mechanical reinforcement carrier (32).

6. Optical cable installation according to any one of the preceding claims, wherein said at least one optical connection box (20) forms a receiving housing for said at least one optical cable (28) and comprises means for fixing the central mechanical reinforcement carrier (32) at said receiving housing.

7. An optical cable installation according to any one of the preceding claims, wherein said at least one optical connection box (20) is a splice protection box comprising at least one splice support cassette (24) configured to receive a splice of at least one optical fiber (30) of said at least one optical fiber module (34).

8. A method of connecting an optical cable (28) to an optical connection box (20), comprising the following steps: - providing an optical cable installation according to any one of the preceding claims, - removing a portion of the protective sheath (40) and a portion of said at least one holding wire (38) so as to release said at least one optical fiber module (34) and the central mechanical reinforcement carrier (32), - fixing the central mechanical reinforcement carrier (32) to the optical connection box (20) to limit a longitudinal movement of said at least one optical fiber module (34) along the protective sheath (40), - engaging at least one optical fiber (30) of said at least one optical fiber module (34) in the optical connection box (20) so as to be able to connect it to another optical fiber (30).

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