OPTICAL FIBRE UNIT FOR AIR-BLOWN INSTALLATIONS

Abstract

An optical fibre unit includes one or more optical fibres; an outer jacket surrounding the one or more optical fibres, made of a fibre reinforced polymer comprising inorganic fibres embedded in a polymer matrix in an amount comprised between 5 and 25 wt % with respect to the weight of the fibre reinforced polymer, the inorganic fibres having a median length (d50) comprised between 50 and 250 μm; and a skin layer surrounding the outer jacket and in direct contact thereto, having a thickness comprised between 0.05 mm and 0.5 mm and being free from fibres.

Claims

1. Optical fibre unit comprising: one or more optical fibres; an outer jacket surrounding the one or more optical fibres, made of a fibre reinforced polymer comprising inorganic fibres embedded in a polymer matrix in an amount comprised between 5 and 25 wt % with respect to the weight of the fibre reinforced polymer, the inorganic fibres having a median length (d50) comprised between 50 and 250 μm; and a skin layer surrounding the outer jacket and in direct contact thereto, having a thickness comprised between 0.05 mm and 0.5 mm and being free from fibres.

2. The optical fibre unit of claim 1, wherein the outer jacket fibre reinforced polymer comprises inorganic fibres in an amount comprised between 10 and 20 wt % with respect to the weight of the fibre reinforced polymer.

3. The optical fibre unit of claim 1, wherein the inorganic fibres have a median length (d50) comprised between 100 and 200 μm.

4. The optical fibre unit of claim 1, wherein the diameter of the inorganic fibres is comprised between 14 and 16 μm.

5. The optical fibre unit of claim 1, wherein the inorganic fibres comprise glass fibres.

6. The optical fibre unit of claim 1, wherein the outer jacket polymer matrix is made of a material selected from polyethylene, polyamide or polyester.

7. The optical fibre unit of claim 1, wherein the outer jacket has a thickness comprised between 0.3 mm and 3 mm, with the outer jacket being thicker than the skin layer.

8. The optical fibre unit of claim 1, wherein the skin layer has a surface roughness which is lower than a surface roughness of the outer jacket.

9. The optical fibre unit of claim 1, wherein the skin layer has a thickness of 0.1 to 0.3 mm.

10. The optical fibre unit of claim 1, wherein the skin layer is made of a material selected from polyethylene, polyamide or polyester.

11. The optical fibre unit of claim 1, wherein the skin layer includes additives for reducing the skin layer surface frictions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further characteristics and advantages will be more apparent from the following description of some embodiments given as a way of an example with reference to the attached drawings in which:

[0028] FIG. 1 shows a sectional view of an optical fibre unit for air-blown installations according to an embodiment of the present disclosure;

[0029] FIGS. 2a and 2b are graphs showing tensile stress (in ordinate) vs. elongation (in abscissa) of samples made of glass fibre filled HDPE and samples made of unfilled HDPE;

[0030] FIGS. 3a and 3b are graphs showing flexural stress (in ordinate) vs. flexural strain (in abscissa) of samples made of glass fibre filled HDPE and samples made of unfilled HDPE;

[0031] FIGS. 4a-4i are graphs showing the distribution of the optical fibre attenuation of the optical fibre unit according to an embodiment and in an optical cable according to the prior art.

DETAILED DESCRIPTION

[0032] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0033] The present disclosure, in at least one of the aforementioned aspects, can be implemented according to one or more of the following embodiments, optionally combined together.

[0034] For the purpose of the present description and of the appended claims, the words “a” or “an” should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. This is done merely for convenience and to give a general sense of the disclosure.

[0035] FIG. 1 shows an embodiment of an optical fibre unit 1 according to the present disclosure. The optical fibre unit 1 is adapted for air-blown installations, as discussed in the introductory part of the present description.

[0036] The optical fibre unit 1 comprises one or more optical fibres 2. In the example of FIG. 1 four optical fibres 2 are provided. However, in other examples (not shown) the number of optical fibres 2 could be higher or lower. It should be noticed that the number of optical fibres 2 is not relevant for the present invention and the number of optical fibres could be any number.

[0037] Each optical fibre 2 of FIG. 1 comprises an optical core 2a, a protective coating system 2b and a buffer 2c.

[0038] The optical fibres suitable for the unit of the present disclosure may be single mode or multimode optical fibres. The optical fibres generally extend in a longitudinal direction. For example, the optical fibres 2 are arranged in a bundle.

[0039] The optical fibre unit 1 comprises an outer jacket 3 surrounding the optical fibres 2.

[0040] The outer jacket 3 is made of a fibre reinforced polymer comprising inorganic fibres embedded in a polymer matrix. The fibre reinforced polymer comprises the inorganic fibres in an amount comprised between 5 and 25 wt %, wherein “wt %” means the weight percentage of the inorganic fibres with respect to the total weight of the fibre reinforced polymer. In an embodiment, the amount of the inorganic fibres is comprised between 10 and 25 wt %, still more preferably between 15 and 20 wt %.

[0041] The inorganic fibres have a median length d50 comprised between 50 and 250 μm. As said above, the median length d50 is the value of the fibre length at 50% in the cumulative distribution. For example, when d50=100 μm, then 50% of the inorganic fibres in the polymer matrix are longer than 100 μm, and 50% are shorter than 100 μm. In an embodiment, the inorganic fibres have a median length d50 comprised between 100 and 200 μm.

[0042] The inorganic fibres can comprise, for example, glass fibres. It is to be noted that two or more different types of inorganic fibres can be embedded in the polymer matrix.

[0043] In an embodiment, the outer jacket 3 has a thickness comprised between 0.3 mm and 3 mm.

[0044] In an embodiment, the outer jacket 3 is based on a polymeric material like polyethylene, polyamide or polyester.

[0045] The Applicant has tested samples made of fibre reinforced polymer of the type used for the outer jacket of the optical fibre unit according to the present disclosure for evaluating the mechanical properties of the same compared to the mechanical properties of a polymeric sample of the type used for the outer jacket in a known optical fibre unit. FIG. 2a is a graph of tensile stress (as σ [MPa], in ordinate) vs. elongation (as ε [%], in abscissa) of five samples made of HDPE glass fibre filled according to the disclosure, and FIG. 2b is an analogous graph of tensile stress vs. elongation of five samples made of the same HDPE, but unfilled. The tests have been performed according to IEC 60811-2-1 (2001) at a speed of 50.0 mm/min. As can be seen from the graphs in the FIGS. 2a and 2b, both for HDPE glass fibre filled according to the disclosure and for unfilled HDPE show a similar tensile behaviour and fracture occurs at about 700% of elongation, showing that the addition of inorganic fibres to the polymeric material does not substantially impair its mechanical properties.

[0046] Similar tests have been performed for evaluating the flexural properties. Particularly, FIG. 3a is a graph of flexural stress (as σ.sub.f [MPa], in ordinate vs. flexural strain (as ε.sub.f [%], in ordinate) of three samples made of HDPE glass fibre filled according to the present disclosure, and FIG. 3b is an analogous graph of flexural stress vs. flexural strain of three samples made of the same HDPE, but unfilled. The tests have been performed according to ASTM D790-10 at a speed of 1.20 mm/min. As can be seen from the graphs in the FIGS. 3a and 3b, both the HDPE glass fibre filled according to the present disclosure samples and the unfilled HDPE samples show a 3% flexural strain at a flexural stress of about 8 MPa, showing that the addition of inorganic fibres to the polymeric material does not substantially impair its mechanical properties.

[0047] Referring again to FIG. 1, the optical fibre unit 1 comprises a skin layer 4 surrounding and in direct contact with the outer jacket 3. The skin layer 4 has a thickness comprised between 0.05 mm and 0.5 mm. Preferably, the skin layer thickness is comprised between 0.1 mm and 0.3 mm. The outer jacket 3 is thicker than the skin layer 4.

[0048] The skin layer 4 has a surface roughness which is lower than the surface roughness of the outer jacket 3 containing inorganic fibres. This improves the optical fibre unit blowability because the friction between the duct wall and the optical fibre unit is reduced.

[0049] The skin layer 4 can be made of a material like polyethylene (PE), polyamide (PA) or a polyester. In an embodiment, the material of the skin layer 4 is similar or the same as that of the outer jacket 3.

[0050] The skin layer 4 material can include additives and/or lubricants for further reducing the above-mentioned friction. In an embodiment, the additives/lubricants can be selected from waxes or fatty acid amides.

[0051] The skin layer 4 can be extruded over the outer jacket 3 or coextruded with the same.

[0052] The Applicant has tested an optical fibre unit according to the present disclosure for evaluating the optical fibre attenuation as a function of the temperature. Particularly, an optical fibre unit according to the present disclosure, having an outer jacket with glass fibres embedded in a HDPE matrix (with no skin layer as not relevant for the performance of the fibres as a function of the temperature), has been compared to a comparative optical fibre unit according to the known art having an unfilled HDPE outer jacket. The “optical fibre attenuation” is the reduction in intensity of the light beam with respect to distance travelled through the optical fibre.

[0053] FIGS. 4a-4i are graphs showing the distribution (in ordinate) of the optical fibre attenuation (as db/Km, in abscissa), at a wavelength of 1550 nm, in all the optical fibres of the optical fibre unit according to the present disclosure (dashed line) and in the optical fibres of the comparative optical cable unit (continuous line). The distribution is shown for different temperatures after two temperature cycles (the same fibres were used for all the cycles), particularly: [0054] First cycle: [0055] @ −10° C. (FIG. 4a) [0056] @ −20° C. (FIG. 4b) [0057] @ +70° C. (FIG. 4c) [0058] Second cycle: [0059] @ −10° C. (FIG. 4d) [0060] @ −20° C. (FIG. 4e) [0061] @ −30° C. (FIG. 4f) [0062] @ −40° C. (FIG. 4g) [0063] @ +70° C. (FIG. 4h) [0064] @ +20° C. (FIG. 4i)

[0065] The above-mentioned graphs show that during the first cycle the optical fibre attenuation of the optical cable unit of the present disclosure is slightly better than that of the comparative optical cable unit. The first cycle of tests is introductory to the second cycle, the results of the latter being the test bench for understanding the optical cable behaviour once installed. During the second cycle, the optical fibre unit according to the present disclosure always showed a substantially better behaviour than that of the comparative optical cable unit. In particular, the curve representing the distribution of the optical attenuation in the optical fibres of the optical fibre unit according to the present disclosure is generally narrower than the one of the optical fibre unit of the known art, and this means a more uniform behaviour for the optical fibres in the units of the invention. Also, according to the British Telecommunications specification CW1854 (2019) for air blown fiber, during test, maximum variation of fibre attenuation should be 0.10 dB/Km. As shown in Table I, the attenuation peak of the optical fibres in the unit of the invention varied of 0.06 dB/Km at most, while the attenuation peak of the optical fibers in the comparative unit varied of 0.11 dB/Km (thus unsuitable for the BT standard).

TABLE-US-00001 TABLE I Peak (mean value) (dB/Km) −10° C. −20° C. −30° C. −40° C. +70° C. +20° C. Dashed curve 0.19 0.20 0.21 0.24 0.19 0.18 Continuous 0.20 0.22 0.24 0.29 0.19 0.18 curve