RESTITUTION OF CLADDING FOR OPTICAL FIBRE SPLICE

Abstract: The invention concerns a mould for reconstituing an outer plastics cladding layer on a splice region comprising the stripped, spliced ends of optical fibres. The mould includes a flexible body (10) in the form of a unitary plastics moulding having, generally parallel to a planar portion of the surface, a straight, uniform-section bore (12) for accommodating the splice region, the entire length of the bore (12) communication with the planar portion of the surface by means of a longitudinal cut (13), the adjacent portion of the mould being capable of flexure to open the longitudinal cut (13) and to broaden the uniform-section bore (12) for access to its interior. The invention also concerns a method of splicing optical fibres which incorporates the mould as just defined.

Description: This invention relates to a mould for and a method of splicing optical fibres having a glass core and at least one plastics cladding layer. The splicing method is especially useful in the jointing of optical fibre cable, for example submarine cable, in the factory. It is known from the specification of European patent Application No.206545 and Japanese Application No.A-55-157708 to carry out a moulding of a plastics cladding for a fibre optic cable joint by using a two part mould where the two parts are brought together to complete the moulding process. The mould parts may be separate or joined by a hinged part. The purpose of the invention is to provide a simple mould for, and quick method of, splicing optical fibres, which reliably results in a splice of high strength and in which the resulting clad optical fibre has a uniform outer diameter even over the spliced region. According to a first aspect of the present invention a mould for reconstituting an outer plastics cladding layer on a splice region which comprises stripped, spliced ends of optical fibres, said mould having a planar surface portion and a bore of uniform cross-section substantially parallel to said surface portion for accommodating the splice region, comprises a flexible unitary plastics body in which the entire length of the bore communicates with the planar surface portion by means of a longitudinal slot; and the portions of the flexible body adjacent the slot can be flexed so as to widen the longitudinal slot and to broaded the bore for access to its interior. According to a second aspect of the present invention a method of splicing optical fibres having a glass core and at least one plastics cladding layer for use with a mould as above comprises: stripping the or each cladding layer from the fibre ends, fusion splicing the bare fibre ends, placing the resulting splice region in the bore of the mould, and filling the gap between the bare splice region and the inner wall of the bore with a curable plastics material, by applying the plastics material drop-wise over the splice region; the dimensions of the gap having been so chosen in relation to the viscosity of the plastics material so that the plastics is distributed around the spliced ends by surface tension effects; closing the flexible mould (10) so that the bore walls close together and assume an internal shape complementary to that of the cladding layer or layers whereby to expel the surplus plastics material, curing the plastics material remaining within the mould, and opening the mould by flexure. This method allows the cladding to be reconstituted around the bare splice region precisely to the diameter of the original cladding or other required diameter. Further, a splice of high mechanical strength is ensured by fusion splicing together the fibre ends which have been stripped of their cladding. The plastics material is preferably cured by exposure to ultra-violet light. According to a further aspect, the invention provides a method of joining optical fibre cable, comprising separating out from each cable at least one optical fibre tube containing one or more plastics clad optical fibres, exposing the fibre or fibres, and splicing at least one such pair of optical fibres using the method in accordance with the invention described above, and finally reconstituting the cable. One way of performing the method of the invention, using a mould embodying the invention, will now be described by way of example only, with reference to the accompanying schematic drawings, of which ; Figure 1 is a perspective view of a plastics mould embodying the invention, and Figure 2 is a corresponding perspective view to an enlarged scale of a portion only of the mould of Figure 1, in its open configuration. Figures 1 and 2 is formed of a clear flexible material. It is laminar, and is formed with a straight, uniform-section bore 12 parallel to its upper planar surface and communicating with that surface through a planar cut 11 normal to the surface. In the closed configuration illustrated in Figure 1 the bore 12 is cylindrical. The mould 10 is flexible, and is capable of being flexed along a central portion 16 adjacent to the longitudinal bore 12, as shown in Figure 2. In its open configuration, the side walls 14, 15 of the cut 11 are separated, and the bore 12 is broadened, allowing access from the exterior to the interior of the bore. The cross-section of the interior of the mould is thus cylindrical in its closed configuration shown in Figure 1, but key-hole-shaped in its open configuration shown in Figure 2. The use of this mould in the splicing of optical fibres will now be described. The optical fibres to be spliced may have any number of cladding layers over a glass core, but for the purposes of this description it is assumed that only a primary plastics cladding layer or coating remains on each optical fibre. A length of 25mm at the end of each fibre is stripped mechanically of its primary cladding, to leave exposed the bare glass core which comprises at least two layers of glass of different refractive indices. These exposed ends are cleaned ultrasonically in agitated solvent, and are then each cleaved in a cleaver, the primary coating being gripped in a clamp. The exposed ends are cleaved to leave a specific length of bare glass core still exposed. The end face must be controlled to lie within one degree of the plane perpendicular to the fibre axis. The exposed fibre ends are cleaned in an ultrasonic cleaning tank with clean solvent, ensuring that the fibre does not touch the container. The cleaned, cleaved fibre ends are then transferred to a conventional fusion machine in which they are clamped by their primary coatings, ensuring that the exposed ends do not come into contact with anything. The fusion machine is then operated to fuse together the exposed ends, splicing the fibres together. The steps of stripping the primary coating, cleaning the bare fibre, cleaving the fibre end, cleaning the end once again and transferring the fibre end to the fusion machine, may be performed simultaneously on both optical fibres, or alternatively may be performed in sequence. After cleaning the mould of Figure 1 thoroughly with a solvent and blowing dry with an air duster, the spliced optical fibres are removed from the fusion machine and are located on a moulding jig (now shown) associated with the mould 10. The mould 10 is opened, and the spliced portion of the optical fibre is located within the bore 12 using a clean spatula, arranging the spliced portion with its primary cladding layer removed to lie centrally of the mould 10. A slight tension is applied to the fibre, to ensure that it is straight. A U-V curable coating material, compatible with the fibre cladding, is applied drop-wise using a syringe onto the spliced portion of the optical fibre, allowing the coating material to flow into the mould by capillary action. The gap between the spliced portion of the optical fibre stripped of its primary cladding and the inner wall of the bore 12 is completely filled by the coating material, the dimensions of the gap being controlled to ensure that this occurs. However, the presence of any air bubbles or voids should be checked, and remedied by careful application of further coating material. The coating material is allowed to flow over the surface of the mould 10, as shown in Figure 1 at 13, ensuring an air-tight seal. The region 13 of application of the coating material is slightly longer than the length of fibre whose glass core is exposed, some of the coating material being allowed to flow over the primary cladding layer. The mould 10 is then closed, to assume the configuration shown in Figure 1, causing the surplus material to be expelled from the interior of the mould onto the surface 13. In the closed configuration, the internal surface of the bore 12 is complementary to the surface of the primary cladding of the optical fibres, so that closing the mould has the effect of driving the excess material from the surface of the primary cladding, and reconstituting the exposed glass core with the coating material with a matching external diameter. A high intensity beam from an ultra-violet lamp is passed up and down the moulded area 13 for a period of time to cure the material. The excess material is then removed from the surface 13 of the mould 10 with a clean spatula, and the surface of the mould 10 is cleaned with solvent. The mould 10 is then opened, and the spliced optical fibres are removed from the mould, tested for any voids in the reconstituted layer, removed from the moulding jig and proof tested by applying a predetermined tension sufficient to extend the optical fibre length by a specific percentage. This technique may be used in the jointing of optical fibre cable, for example submarine cable. In such cable, the individual clad optical fibres are usually accommodated in flexible tubes. In order to join two such cables, the unit tubes are separated, and unit cutters are used to expose a length of optical fibre from each unit. The first section of each unit is then clamped to a jig, and then the ends of the optical fibres are cut to leave a specific length projecting from their corresponding units. The individual pairs of optical fibres are then spliced using the method described above, leaving them with their outer diameter reconstituted by means of the a coating material. A predetermined length of split unit tubing is then fitted over the spliced fibre, ensuring that the separation between the unit tubes is adjusted to give the correct amount of fibre overfeed. A length of heat shrink tubing, previously passed over the unit tube, is then placed evenly over the jointed area and shrunk down to hold the longitudinally-split tube and unit ends in place. This provides a nominally uniform diameter joint across the cable unit.

Claims: A mould for reconstituting an outer plastics cladding layer on a splice region which comprises stripped, spliced ends of optical fibres, said mould having a planar surface portion and a bore of uniform cross-section substantially parallel to said surface portion for accommodating the splice region, characterised in that the mould comprises a flexible unitary plastics body (10); the entire length of the bore (12) communicates with the planar surface portion by means of a longitudinal slot (13); and the portions of the flexible body (10) adjacent the slot can be flexed so as to widen the longitudinal slot (13) and to broaden the bore (12) for access to its interior. A mould according to Claim 1, and characterised in that it consists of a plastics lamina. A mould according to Claim 2, and further characterised in that the bore (12) extends through the entire length of the lamina. A mould according to Claim 2 or 3, and further characterised in that the longitudinal slot (13) is normal to the planar portion of the surface. A mould according to Claim 2, 3 or 4 and further characterised in that the bore (12) is cylindrical when the mould is in its closed configuration. A method of splicing optical fibres having a glass core and at least one plastics cladding layer using a mould according to Claims 1 to 5, said method comprising: stripping the or each cladding layer from the fibre ends, fusion splicing the bare fibre ends, placing the resulting splice region in the bore (12) of the mould (10), and filling the gap between the bare splice region and the inner wall of the bore (12) with a curable plastics material, by applying the plastics material drop-wise over the splice region; the dimensions of the gap having been chosen in relation to the viscosity of the plastics material so that the plastics is distributed around the spliced ends by surface tension effects; closing the flexible mould (10) so that the bore walls close together and assume an internal shape complementary to that of the cladding layer or layers whereby to expel the surplus plastics material, curing the plastics material remaining within the mould, and opening the mould by flexure. A method according to Claim 6, and further characterised in that the plastics material is cured by exposure to ultra-violet light.

Inventors: JUNG, ROGER ERWIN, SMOKER, JOHN VICTOR
Applicants: TELEPHONE CABLES LIMITED
Application year: 1990
Main classification: G02B6
IPC codes: G02B6, C03C25