An Optical Cable with Retractable Modules and a Method for Producing Said Modules

Abstract

An optical cable (1) comprises a sheath (2) surrounding a cavity (3) and a plurality of substantially parallel modules (4) arranged into said cavity (3) with a filling ratio between 20 and 50%; each of said modules (4) comprises:•four to twelve fibers (9),•A tube (5) surrounding the fibers (9) that comprises a mix of polycarbonate and a low friction polymer, chosen from the group of fluorinated polymers and polyamide; said tube (5) having a ratio between its inner d.sub.i and outer d.sub.o diameters between 0.45 and 0.55, and comprising an outer low friction polymer layer (6) having a thickness between 0.05 and 0.15 mm,•A filling ratio of said module 4 greater than 55%.

Claims

1. An optical cable (1), comprising a sheath (2) having an inner surface defining a cavity (3) and a plurality of modules (4) arranged into said cavity (3) and targeted to be parallel, said cavity having a filling ratio between 20% and 50%, each of said modules (4) comprising: four to twelve fibers (9), a tube (5) surrounding the fibers (9) and made from polycarbonate and a low friction polymer comprising polyamide and/or fluorinated polymers, said tube (5) having a ratio between its inner (d.sub.i) and outer (d.sub.o) diameters between 0.45 and 0.55, and comprising an outer low friction polymer layer (6) having a thickness between 0.05 and 0.15 mm, a filling ratio of said module (4) greater than 55%.

2. The cable (1) according to claim 1, wherein each of said modules include exactly 4 or 8 or 12 fibers.

3. The cable (1) according to claim 2, wherein for fibers having a diameter of 245 μm±10 μm the outer diameter (d.sub.o) of said modules is between 1.20 and 1.45 mm for a 4-fiber module, or between 1.55 and 1.9 mm for a 8-fiber module, or between 1.90 and 2.50 mm for a 12-fiber module.

4. The cable (1) according to claim 2, wherein for fibers having a diameter of 200 μm±10 μm the outer diameter (d.sub.o) of said modules is between 1.00 and 1.20 mm for a 4-fiber module, or between 1.25 and 1.55 mm for a 8-fiber module, or between 1.55 and 1.90 mm for a 12-fiber module.

5. The cable according to claim 1, wherein said tube is a coextruded polycarbonate and polyamide tube.

6. The cable (1) according to claim 1, wherein said tube surrounding the fibers is filled with a filling compound (10) having a viscosity between 5000 and 7000 mPa.Math.s at 25° C.

7. The cable (1) according to claim 1, wherein said tube surrounding the fibers is filled with a swellable material.

8. The cable (1) according to claim 1, wherein at least one of said modules (4) is watertight.

9. The cable (1) according to claim 1, wherein at least one of said modules comprises four fibers and has an inner diameter of 0.65 mm and an outer diameter of 1.25 mm.

10. The cable (1) according to claim 1, wherein the thickness of the outer layer (6) is 0.1 mm.

11. The cable (1) according to claim 1, wherein said low friction polymer consists essentially of PA12 type polyamide.

12. The cable of claim 1, wherein, for at least one of said modules, said tube comprises four fibers and an inner polycarbonate layer having an inner diameter of 0.65 mm and outer diameter of 1.05 mm and an outer polyamide layer having an inner diameter of 1.05 mm and an outer diameter of 1.25 mm.

13. The cable (1) according to claim 1, wherein at least two of said modules (4) have outer layers with different colors.

14. A method for manufacturing an optical cable according to claim 1, comprising a step of co-extrusion of the tube (5) from polycarbonate and a low friction polymer comprising polyamide and/or fluorinated polymers.

15. The method of claim 14, wherein said step of co-extrusion of the tube is driven at a speed of at least 150 m/min.

16. An optical cable (1), comprising a sheath (2) having an inner surface defining a cavity (3) and a plurality of substantially parallel, unstranded modules (4) arranged within said cavity (3), said cavity having a filling ratio between 20% and 50%, wherein each of said modules (4) comprises: four to twelve fibers (9), a multilayer tube (5) surrounding the fibers (9) and comprising a polycarbonate inner layer and a low friction polymer outer layer comprising polyamide and/or fluorinated polymers, said multilayer tube (5) having a ratio between its inner diameter (d.sub.i) and outer diameter (d.sub.o) between 0.45 and 0.55, and said low friction polymer outer layer (6) having a thickness between 0.05 and 0.15 mm, wherein each of said modules (4) has a filling ratio greater than 55%.

17. The cable (1) according to claim 16, wherein each of said modules (4) comprises a multilayer tube (5) consisting of a polycarbonate inner layer and a contiguous, low friction polyamide outer layer.

Description

5. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention can be better understood with reference to the following description and drawings, given by way of example and not limiting the scope of protection, and in which:

[0052] FIG. 1 is a schematic view of the cross section of a cable according to an embodiment of the invention;

[0053] FIG. 2 is a schematic view of the cross section of a module according to an embodiment of the invention.

[0054] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

6. DESCRIPTION OF AN EMBODIMENT

[0055] The present invention relates to optical cables, modules and fibers. Many specific details of the invention are set forth in the following description and in FIGS. 1 and 2. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description.

[0056] The foregoing is described in relation to a particular embodiment of the invention, in which modules comprise four fibers. It must be understood that modules according to the invention may also comprise eight or twelve fibers, although this is not described in the following exemplary embodiment.

[0057] Moreover, the following exemplary embodiment describes a co-extruded tube made from a mix of PC and PA. It must be understood that any other low friction polymer may replace polyamide, notably a polymer chosen from the group of fluorinated polymers.

[0058] FIG. 1 illustrates schematically an optical cable 1. Cable 1 is defined about an axis of revolution X that is orthogonal to the plan of FIG. 1. Cable 1 comprises a sheath 2 that defines the outline of cable 1. This sheath 2 is a reinforced plastic tube and features a certain thickness which value is equal to the difference between its outer diameter and its inner diameter D. The sheath inner wall defines a cavity 3 in which a number N of modules 4 is arranged. Each of these modules 4 is defined about an axis of revolution Y that is substantially parallel to the axis of revolution X of cable 1. Each module 4 features an outer diameter d.sub.o. According to the formula mentioned here above, the filling ratio within the cavity 3 is ranging from 20 to 50%.

[0059] FIG. 2 illustrates schematically a module 4. This module 4 is defined about an axis of revolution Y that is orthogonal to the plan of FIG. 2. Module 4 comprises a tube 5 that defines its outline. The inner diameter d.sub.i of the tube 5 is 0.65 mm whereas its outer diameter d.sub.o is 1.25 mm. Tube 5 is the result of the co-extrusion of an outer PA layer 6 and an inner PC layer 7, bonded one with the other. The respective thicknesses of the PA and PC layers are 0.1 and 0.2 mm. The tube's inner wall defines a cavity 8 in which four optical fibers 9 (N.sub.f is then equal to 4) are arranged. The rest of the cavity is filled with an optical cable filling compound 10, whose viscosity is between 5000 and 7000 mPa.Math.s at 25° C., such as cable gels marketed under the trade name Unigel©. Each of the optical fibers is defined about a revolutionary axis that is substantially parallel to the axis Y of module 4. Each fiber features an outer diameter d.sub.f. According to embodiments of the invention and following the formula mentioned here above, the filling ratio within module 4 is above 55%.

[0060] As mentioned above, tests have been conducted in order to challenge the thermal stability of a module according to the invention. In this matter, 1 km of such module in a free coil has been operated under temperatures ranging between −30° C. to +70° C. As a result, the change in attenuation of a light signal with a wavelength of 1625 nm has been measured under 0.15 dB/km for a fiber of the known G657A2-type (BendBright.sup.XS© FTTH optical fiber, produced by Prysmian Group). Such a minimization of the light attenuation in an optical fiber is undoubtedly a major performance that distinguishes the module according to the invention from the prior art.