Optical communication cable having an uhmwpe reinforcement

Abstract

Disclosed is an optical communication cable (1) comprising: an optical fiber (4); a reinforcement (10) surrounding the optical fiber (4), the reinforcement (10) consisting of non-woven free fibers made of ultra-high-molecular-weight polyethylene (UHMWPE); an outer sheath (12) which surrounds the reinforcement (10) and to which the reinforcement (10) adheres, the outer sheath (12) comprising polyethylene and / or polypropylene.

Description

[0001] DESCRIPTION

[0002] TITLE: UHMWPE reinforced optical communication cable

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to an optical communication cable.

[0005] STATE OF THE ART

[0006] An optical communication cable is known from the state of the art, comprising an optical fiber, a reinforcement, and a sheath surrounding the reinforcement. The reinforcement is made of aramid. This material provides the cable with good tensile strength.

[0007] A problem that arises in such a cable, particularly when the cable is overhead, is that the reinforcement is likely to move axially relative to the sheath when the cable is pulled. The aramid fibers then slide over a length that is equivalent to the elongation of the cable. This undesirable effect is commonly referred to as "pistoning."

[0008] A solution to this pistoning problem, recommended by operators and implemented by installers, consists of creating cable coils between an anchor clamp and a box with the minimum cable winding diameter, and anchoring the reinforcements in the box by creating a braid and fixing it around the sheath using a cable tie. This solution, however, has the disadvantage of being relatively complex to implement.

[0009] STATEMENT OF THE INVENTION

[0010] An aim of the invention is to overcome the aforementioned "pistoning" problem in a simple manner.

[0011] For this purpose, an optical communication cable is proposed comprising:

[0012] - an optical fiber,

[0013] - a reinforcement surrounding the optical fiber, the reinforcement being made of free non-woven fibers made of polyethylene with a very high molar mass,

[0014] - an outer sheath surrounding the reinforcement and to which the reinforcement adheres, the outer sheath comprising polyethylene and / or polypropylene.

[0015] The proposed cable may include the following optional features, taken alone or in combination whenever technically possible.

[0016] Preferably, the polyethylene of the outer sheath is a high density polyethylene. In one embodiment, the outer sheath is made of polyethylene. In another embodiment, the outer sheath is made of polypropylene.

[0017] Preferably the cable further comprises a flame retardant sheath surrounding the optical fiber and surrounded by the reinforcement.

[0018] Preferably, the cable further comprises an internal reinforcement made of aramid, the internal reinforcement being surrounded by the flame-retardant sheath.

[0019] Also provided is a method of manufacturing the foregoing optical communication cable, the method comprising contacting the reinforcement and the outer sheath while at least one of the reinforcement and the sheath has a temperature greater than or equal to 145°C.

[0020] Preferably, the temperature is less than or equal to 185°C.

[0021] DESCRIPTION OF FIGURES

[0022] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0023] Figure 1 is a cross-sectional view of an optical communications cable according to one embodiment.

[0024] Figure 2 is a flowchart of steps of a method of manufacturing an optical communication cable, according to one embodiment.

[0025] Throughout the figures, similar elements have identical references.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring to Figure 1, an optical communication cable 1 comprises an internal part forming a subscriber cable 2.

[0028] The internal part forming a subscriber cable 2 is intended, as its name indicates, to be connected to the home of a subscriber to an FttH (“Fiber to the Home”) type network.

[0029] The internal part forming a subscriber cable 2 comprises an optical core, an internal reinforcing layer and an internal sheath 8. The internal reinforcing layer comprises at least one internal reinforcement 6. This layer may comprise several concentric internal reinforcements, i.e. arranged around each other.

[0030] The optical core 4 extends along a longitudinal axis of the cable. The optical core comprises one or more optical fibers 4. An optical fiber constitutes a basic unit for transmitting an optical signal.

[0031] In the embodiment shown in Figure 1, the optical core consists of a single optical fiber 4, but it is understood that this is not mandatory. In other embodiments, the optical core may comprise several optical fibers. In this case, the optical fibers may be grouped in the optical core according to one or more different nested levels of hierarchy. For example, the optical core may comprise several optical modules, each optical module comprising one or more optical sub-modules, each optical sub-module comprising one or more optical micro-modules, each micro-module comprising one or more optical fibers.

[0032] In particular, the optical core can be made up of a cord of 1 to 4 optical fibers or several modules made up of 2 to 12 optical fibers or even 24 optical fibers.

[0033] Each optical fiber can be clamped, semi-clamped, or loose.

[0034] The internal reinforcement layer extends around the optical fiber 4, so as to be in contact with the optical core 4. Thus, at least one internal reinforcement 6 of this layer is in contact with the optical core.

[0035] Each internal reinforcement 6 is for example made of aramid fibers.

[0036] The inner sheath 8 extends around the inner reinforcing layer, so as to be in contact with this inner reinforcing layer. Thus, at least one inner reinforcement 6 of this layer is in contact with the inner sheath 8.

[0037] The inner sheath is preferably made of a flame-retardant material, for example an LSZH (Low Smoke Zero Halogen) type material.

[0038] The internal part forming a subscriber cable 2 has, for example, a diameter of 2.3 millimeters (this diameter corresponds to the external diameter of the internal sheath 8). Alternatively, this internal part 2 has a diameter of 2.65 millimeters.

[0039] The optical communication cable 1 further comprises a reinforcement 10 and an external sheath 12.

[0040] The reinforcement 10 extends around the internal part forming a subscriber cable 8. More precisely, the reinforcement 10 extends around the internal sheath, so as to be in contact with the internal sheath 8. The reinforcement 10 is not fixed to the internal sheath 8, so as to facilitate a mutual separation of these two elements. Thus, it is easier to connect the internal part forming a subscriber cable 2 to the home of such a subscriber.

[0041] Reinforcement 10 is made of fibers made of a so-called “very high molecular weight” polyethylene (UHMWPE). This material, known in itself, is also referred to in the literature by the following synonyms:

[0042] • UHMWPE for “ultra high molecular weight polyethylene” (sometimes abbreviated to UHMW).

[0043] • High modulus polyethylene (HMPE).

[0044] • High performance polyethylene (HPPE).

[0045] As is known, this material comprises extremely long chains, of the order of several hundred thousand monomer units; this is an advantageous property, because it allows the reinforcement 10 to ensure good tensile strength.

[0046] Another advantageous property of this material is its good resistance to negative temperatures. In fact, the mechanical strength of this material increases at low temperatures.

[0047] Constituting the reinforcement 10 using fibers allows the reinforcement 10 to take different shapes, thus making it possible to adapt to different available spaces (unlike a single-piece reinforcement). Furthermore, the fibers can be stretched, which promotes the appearance of the aforementioned chains and therefore contributes to the good mechanical strength of the UHMWPE reinforcement 10. Another advantage is that these fibers easily separate from each other when the cable 1 is subsequently opened.

[0048] The outer sheath 12 extends around the reinforcement 10, so as to be in contact with the reinforcement 10.

[0049] The outer sheath 12 defines an outer surface of the optical communication cable 1. In other words, the outer sheath 12 constitutes the radially outermost portion of the optical communication cable 1.

[0050] The outer sheath 12 comprises polyethylene and / or polypropylene. The sheath is preferably made of polyethylene. Alternatively, the sheath is made of polypropylene.

[0051] Preferably, the polyethylene of the outer sheath 12 is a high-density polyethylene (HDPE). In particular, this polyethylene may or may not be of the UHMPE type. Preferably, this polyethylene is not of the UHMPE type in order to reduce the manufacturing cost of the optical communication cable 1.

[0052] Not only is the reinforcement 10 in contact with the outer sheath, but the reinforcement 10 adheres to the sheath 12. The polyethylene or polypropylene of the outer sheath 12 and the very high molecular weight polyethylene of the reinforcement 10 are two materials that are naturally compatible with each other, so that such adhesion is facilitated.

[0053] The diameter D of the optical communication cable 1 (corresponding to the diameter of its external surface) is for example 5 millimeters.

[0054] The optical communication cable 1 may also comprise external reinforcements 14 embedded in the external sheath. These external reinforcements 1 are for example two in number, and diametrically opposed relative to the longitudinal axis of the cable.

[0055] Each external reinforcement 14 has, for example, a diameter of 0.8 millimeters, 1.2 millimeters, 1.4 millimeters or 1.6 millimeters.

[0056] Each external reinforcement 14 is for example of the FRP type.

[0057] Referring to Figure 2, a manufacturing method of the optical communication cable comprises the following steps.

[0058] In a preliminary step 100, the reinforcement 10 and the sheath are formed 12, for example by extrusion.

[0059] In particular, the reinforcement 10 is formed from UHMWPE fibers.

[0060] At least one of the reinforcement 10 and the outer sheath 12 is heated, such that the heated element reaches a temperature greater than or equal to 145°C. This temperature is higher than the melting point of the reinforcement 10.

[0061] Preferably, the heated element is an extrudate, that is to say that this element is formed by extrusion. In this case, the temperature rise of the element is the direct consequence of the extrusion carried out.

[0062] In a contacting step 102, the reinforcement 10 and the outer sheath 12 are brought into contact. This step is carried out once each heated element has reached a temperature greater than or equal to 145°C.

[0063] During this contact, the outer UHMPE fibers of the reinforcement 10 and the outer sheath 12 fuse due to the heating. Thanks to this fusion, these two elements adhere to each other. Thanks to this adhesion, the pistoning problem mentioned in the introduction is overcome. It should be noted that the UHMPE fibers in contact with the sheath are not always the same, which makes it possible to obtain strong cohesion of the assembly.

[0064] An additional advantage provided by the materials of the reinforcement 10 and the outer sheath 12 is that such adhesion can be achieved without the need for an additional adhesive, such as glue.

[0065] By making reinforcement 10 in UHMWPE, we obtain an adhesion force much higher than that provided by an aramid reinforcement under the same conditions.

[0066] It is preferable that the temperature reached by the reinforcement 10 during the heating step remains less than or equal to 185°C. Indeed, exceeding such a temperature would risk breaking the long chains of the UHMWPE used in the reinforcement 10, which would degrade the tensile strength performance of this reinforcement.

[0067] Comparative tests were carried out to evaluate the impact of the aforementioned heating on the tensile strength performance of the UHMWPE reinforcement 10. Let S be the cable section, expressed in mm 2, and E the elastic modulus of the cable (expressed in MPa). An average value of the product ES for the cable (expressed in Newtons), and the Young's modulus of a strand of the reinforcement, expressed in GPa, were measured at different extrusion temperatures. These tests reveal that the ES value of the cable decreases at 200°C while it is equivalent at 150°C and 175°C. These tests are summarized in the table below:

[0068] The other steps of the method leading to obtaining the optical communication cable 1 are known from the state of the art.

[0069] As indicated previously, the optical communication cable 1 can be used to connect an external connection point and a subscriber optical outlet, by installation both in conduit and overhead and this without splicing (at the point of penetration of the subscriber's home). The external sheath 12 can easily be removed, releasing the internal part forming a subscriber cable 2. The internal part 2 thus exposed can then be laid in a duct, glued or stapled up to the subscriber's optical outlet. It has been described previously that the cable 1 comprises a single internal part 2. Of course, in other embodiments not illustrated, the cable 1 could comprise several internal parts 2.

Claims

DEMANDS 1. Optical communication cable (1) comprising: - an optical fiber (4), - a reinforcement (10) surrounding the optical fiber (4), the reinforcement (10) being made of free non-woven fibers made of ultra-high molecular weight polyethylene (UHMWPE), - an outer sheath (12) surrounding the reinforcement (10) and to which the reinforcement (10) adheres, the outer sheath (12) comprising polyethylene and / or polypropylene.

2. Cable according to the preceding claim, in which the outer sheath is made of polyethylene.

3. Cable according to any one of the preceding claims, wherein the polyethylene of the outer sheath (12) is high-density polyethylene (HDPE).

4. Cable according to claim 1, in which the outer sheath is made of polypropylene.

5. Cable according to any one of the preceding claims, further comprising a flame-resistant sheath (8) surrounding the optical fiber (4) and surrounded by the reinforcement (10).

6. Cable according to the preceding claim, further comprising an internal reinforcement (6) made of aramid, the internal reinforcement being surrounded by the flame-resistant sheath (8).

7. Cable according to any one of the preceding claims, obtained by a process comprising bringing the reinforcement (10) and the outer sheath (12) into contact while at least one of the reinforcement (10) and the sheath (12) has a temperature greater than or equal to 145°C and less than or equal to 185°C.

8. Method of manufacturing an optical communication cable (1) according to any one of the preceding claims, the method comprising bringing the reinforcement (10) and the outer sheath (12) into contact while at least one of the reinforcement (10) and the sheath (12) has a temperature greater than or equal to 145 °C.

9. A method according to the preceding claim, wherein the temperature is less than or equal to 185 °C.

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