GB1567636A - Termination of optical fibre cables - Google Patents

Description

(54) IMPROVEMENTS RELATING TO THE TERMINATION OF OPTICAL FIBRE CABLES (71) We, BOWTHORPE - HELLERMANN LIMITED, a British Company, of Gatwick Road, Crawley, Sussex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns improvements relating to the termination of optical fibre cables comprising a plurality of optical fibres bunched together and generally contained within a sheath of, for example, plastics material. For coupling lengths of optical fibre cables to one another or to optoelectric devices for example, it is necessary to terminate the cables with optical couplings.

The traditional method for terminating optical fibre cables has required the ends of the fibres in a cable to be bonded into a metal ferrule using an epoxy resin adhesive and has required a subsequent polishing stage to clean and face the fibre ends. This method, being unsuited to an in-the-field operation, has been carried out in the factory with a view to providing terminated optical fibre cables of predetermined lengths.

The present invention aims to make use of an improved method of terminating optical fibre cables, intended to enable optical fibre cables to be terminated in-the-field, which is described in an article "Terminations and Connectors for Multi-Mode Fibre Bundles" by T. A. Morgon of Marconi Elliot Avionic Systems Limited which appeared in the journal "Electronic Production" Volume 6 No. 2 March 1977 commencing at page 34 and also forms the subject of the Complete Specification filed with cognated British Patent Applications Nos. 28879/75, 29094/ 75, 45220/75 and 26039/76 (Serial No.

1556046). According to this improved method, the end of an optical fibre bundle to be terminated is threaded into an outer ferrule the internal bore of which tapers inwardly adjacent one end of the ferrule, a glass bead and a so-called driving ferrule having first been threaded by the optical fibre bundle, the bead and the driving ferrule being dimensioned externally to fit into the bore of the outer ferrule. With the driving ferrule urged to drive the glass bead into the tapering part of the bore of the outer ferrule, the assembly is heated by contact with an appropriately shaped heating head so as to soften the glass bead which deforms around the bundle end as it is urged further into the taper within the outer ferrule. The deformation of the bead enhances thermal contact with the fibre ends which soften and, under radial compression from the deforming bead, deform without any substantial fusion between contiguous fibres in the bundle and achieve a higher packing density with the substantial elimination of interstices between the fibres. A stop is provided to limit the insertion of the ferrule into the outer ferrule, and, when it has inserted to its maximum extent, the termination is permitted to cool and the fibre ends projecting from the end of the outer ferrule can be cut back to the ferrule and polished. A ceramic or metal bead of such composition as to perform a function equivalent to that of the glass bead can be used.

Disclosed in the said article and in the aforementioned Complete Specification is a composite ferrule, for use in the termination of an optical fibre cable, comprising a first hollow cylindrical member the bore whereof narrows at or towards one end, a hollow cylindrical bead of thermally deformable material received within the bore of the first member, and a second hollow cylindrical member having a portion thereof received within the end of the first member remote from said one end so as to contain the said bead within the bore of the first member, the arrangement being such as in use, with an optical fibre bundle threaded through said first and second members and through said bead and with said bead subjected to heat; ing, to enable the second member to be urged further into the bore of the first member so as by virtue of the narrowing of the bore of the first member to urge the bead to deform about and compact the optical fibre bundle; in the following, such a com- posite ferrule will be referred to as "a com- posite ferrule as herein defined".

According to the present invention there is provided a tool suitable for use with a composite ferrule (as herein defined) in the termination of an optical fibre cable, said tool comprising a manually operable clamp for the composite ferrule enabling one of said members to be located in the tool whilst relative movement is effected between the two members for deforming the bead, a heating head, and manually-operable means for moving the heating head and the clamp relative to one another so as to engage the heating head with a composite ferrule correctly positioned in the clamp such as to apply heat to the bead in the ferrule, the last mentioned means being such as to engage the heating head with the ferrule under a spring loading enabling further relative movement of the heating head and the clamp such as to urge the second member of the ferrule further into the first member as the bead deforms with heating.

As described fully hereinafter, a preferred form of composite ferrule as herein defined comprises an outer ferrule, a driving ferrule and a fusible bead, all secured in operative relationship for convenience in use by means of a weak and rupturable or a thermallysoftenable adhesive. Also described is a portable hot-forming termination tool for use with composite ferrules as described above, which comprises a manually operable clamp for the composite ferrule enabling one ferrule part to be located in the tool whilst the other ferrule part is moved relative thereto for deforming the fusible bead, a heating head shaped complementary to one end of the composite ferrule, and manuallyoperable means for moving the heating head and the clamp relatively so as to engage an end of a composite ferrule correctly positioned in the clamp with the complementary shaped heating -head under a spring loading enabling further relative movement of the heating head and the clamp as the fusible bead deforms. As wilf be appreciated from the following the invention enables optical fibre cable terminations to be made readily in the field employing the method of the Application above-mentioned.

The invention will best be understood from consideration of the following detailed description of exemplary embodiments of the invention as illustrated in the accompanying drawings wherein: Figure 1 is a schematic sectional view of a composite ferrule as herein defined; Figure 2A shows a perspective view of a termination tool and Figure 2B shows a close-up view of one end of the tool, and Figures 3A and 3B are schematic illustrations of the principle of operation of the termination tool.

Referring to Figure 1, the form of an exemplary composite ferrule is illustrated schematically therein. As shown, the composite ferrule comprises an outer ferrule 1, an inner or driving ferrule 2, and a glass bead 3. The dimensions and spacings shown in the drawing are exaggerated for the sake of clarity, and it is to be understood that the portion of the driving ferrule 2 forward of its external shoulder 4 is dimensioned to make a close fit within the bore of the outer ferrule 1. Likewise the bead 3 is dimensioned to fit closely within the bore of the outer ferrule and has a length calculated to provide the requisite amount of material in the bead to perform its function. The dimensions of the inner bore of the driving ferrule 2 and the bead 3 will be selected to accommodate a selected optical fibre bundle, and, in order to facilitate the threading of the optical fibre bundle end into the composite ferrule, the bore of the driving ferrule 2 is internally tapered as shown.

The three constituent parts of the composite ferrule can if desired be assembled together and secured in assembled condition by a weak or heat softenable adhesive. This obviates the problems which otherwise would arise in handling such small components as the bead 3 and ensures that the task of threading the optical fibre bundle at the stripped end of an optical fibre cable into the composite ferrule is a single operation only. The tapering lead-in to the bore of the driving ferrule 2 makes the threading operation a simple task, even considering the tendency of the optical fibre ends to splay out from one another when the cable end is bared. Dipping of the bared fibre ends into liquid, methyl ethyl ketone for example, causes them to bunch together and resists the splaying tendency of the fibre ends.

As has previously been described, the composite ferrule of Figure 1 is adapted for use in performance of the method described in cognated British Patent Applications Nos.

28879i75, 29094/75, 45220/75 and'26039, 76 (Serial No. 1556046). With the optical fibre bundle end inserted into and through the composite ferrule so that it shows beyond the tapered left-hand end of the outer ferrul 1 as shown in Figure 1, and with the bead 3 and driving ferrule 2 inserted as far as possible into the outer ferrule 1 without use of undue force, heat is applied to the externally tapering surface of the left-hand end of the outer ferrule 1 so as to soften the glass bead 3. As the bead 3 softens, a pressure is maintained upon it by the driving ferrule 2 which tends to move the bead 3, with deformation of the bead, further into the internally tapered portion of the outer ferrule 1. As the bead 3 is thus advanced and deformed, it develops a radially inward force upon the optical fibre bundle thereby urging the bundle to pack more densely. At the same time, the deformation of the bead 3 enhances thermal coupling to the fibres themselves so that, with correct selection of operating temperatures, the fibres themselves soften. The net result of the radial compression and softening of the fibres is to cause them to deform from their typically circular crosssection towards a more hexagonal crosssection maximizing the packing density of the fibres. The heating of the composite ferrule and the urging of the driving ferrule 2 into the bore of the outer ferrule 1 is terminated when the shoulder 4 of the driving ferrule 2 abuts the right-hand end (as viewed in Figure 1) of the outer ferrule 1.

Figures 2A and 2B show a termination tool according to the invention in perspective view, and Figures 3A and 3B illustrate its operation. The tool simply comprises a gene- rally cylindical, hollow tool body cut away at one end, which houses a manually operable ferrule clamp, and containing in its other end a manually operable cam mechanism which controls the movement, to and fro within the tool body and relative to the clamp, of an electrically-powered heating element. In Figures 2A and 2B, the tool body is designated 10, the ferrule clamp is designated 11 and, as shown most clearly in Figure 2B, comprises a fixed jaw 12 and a moveable jaw 13 operated by a control knob 14 for movement towards and away from the fixed jaw 12, the manual control for the movement of the heating element is the control knob 15, and the head of the heating element can just be seen at 16. It will be understood that the movement of the heating element head 16 is arranged to take place along the axis of the tool body 10 and the clamp jaws 12 and 13 are arranged for holding a composite ferrule aligned with the tool body axis. An optical fibre cable 17 and a composite ferrule 18, of the type shown in Figure 1, fitted to the end of the cable but not yet heat-formed thereto, is shown in Figures 2A and 2B; in Figure 2A the clamping jaws 12 and 13 are closed upon the ferrule 18, and in Figure 2B the jaws are open.

Although not readily visible from the Figures, the clamping jaws 12 and 13 are formed to mate with the shoulder 4 of the driving ferrule 2 and locate the driving ferrule whilst permitting the outer ferrule 1 to move back on to the driving ferrule 2 under the action of the heating head 16 and as the glass bead 3 softens.

Figures 3A and 3B illustrate the internal arrangement of the terminating tool of Figures 2A and 2B. As shown, the heating head 16 is mounted in a schematically-shown slider 20 supported between a loading spring 21 at one end and return springs 22 at i other end, and moveable axially of the tool body 10 under control of the cam 23 which is arranged to be turned by control knob 15.

An electrically powered heating element 24 is associated with the heating head 16. In the position of the cam 23 as shown in Figure 3A, the slider 20 is urged, by virtue of the compression of loading spring 21 by cam 23, towards the right-hand side as shown in the drawing so as to contact the forward end of the composite ferrule 18 clamped in the schematically-shown jaws 12 and 13 with a complementary-shaped recess in the head 16. In this position, the heat from the head 16 is transferred to the ferrule 18 for softening the bead 3 therein, and the loading spring 21 maintains a force on the outer ferrule 1 tending to move it back on the inner ferrule 2 as the bead 3 softens. The process is complete when the rearward (right-hand) end of the outer ferrule 1 abuts the shoulder 4 of the driving ferrule 2.

Return of the cam 23 to its position shown in Figure 3B unloads unloading spring 21 and permits the slider 20 to be returned by the return springs 22 to a position whereat the heating head 16 is remote from the ferrule. The heating element can be arranged to switch on and off in response to operation of the control knob 15 for example, or can be independently switched, or can be made automatically operating in dependence upon the position of the slider 20 for example.

After the operation on the composite ferrule with the terminating tool, it is adviseable to crimp the outer ferrule 1 to the driving ferrule 2 to secure the two parts together.

Having fixed the composite ferrule to the optical fibre cable end as described above and using the termination tool of Figures 2A, 2B, 3A and 3B the termination thus made must be finished on a polishing tool which might for example simply comprise a tool body housing an electric motor in its lower part and a polishing, disc, arranged to be rotated by the motor, in its upper part. A clamping arrangement might be provided to enable the ferrule to be held vertically to the polishing disc and moved for example between coarse and fine polishing areas spaced radially from one another on the disc. A reservoir might be provided for wetting fluid for the disc, the internal construction of the polishing tool being such as to ensure that the fluid cannot get to the motor.

WHAT WE CLAIM IS: 1. A tool suitable for use with a compo

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. outer ferrule 1 so as to soften the glass bead 3. As the bead 3 softens, a pressure is maintained upon it by the driving ferrule 2 which tends to move the bead 3, with deformation of the bead, further into the internally tapered portion of the outer ferrule 1. As the bead 3 is thus advanced and deformed, it develops a radially inward force upon the optical fibre bundle thereby urging the bundle to pack more densely. At the same time, the deformation of the bead 3 enhances thermal coupling to the fibres themselves so that, with correct selection of operating temperatures, the fibres themselves soften. The net result of the radial compression and softening of the fibres is to cause them to deform from their typically circular crosssection towards a more hexagonal crosssection maximizing the packing density of the fibres. The heating of the composite ferrule and the urging of the driving ferrule 2 into the bore of the outer ferrule 1 is terminated when the shoulder 4 of the driving ferrule 2 abuts the right-hand end (as viewed in Figure 1) of the outer ferrule 1. Figures 2A and 2B show a termination tool according to the invention in perspective view, and Figures 3A and 3B illustrate its operation. The tool simply comprises a gene- rally cylindical, hollow tool body cut away at one end, which houses a manually operable ferrule clamp, and containing in its other end a manually operable cam mechanism which controls the movement, to and fro within the tool body and relative to the clamp, of an electrically-powered heating element. In Figures 2A and 2B, the tool body is designated 10, the ferrule clamp is designated 11 and, as shown most clearly in Figure 2B, comprises a fixed jaw 12 and a moveable jaw 13 operated by a control knob 14 for movement towards and away from the fixed jaw 12, the manual control for the movement of the heating element is the control knob 15, and the head of the heating element can just be seen at 16. It will be understood that the movement of the heating element head 16 is arranged to take place along the axis of the tool body 10 and the clamp jaws 12 and 13 are arranged for holding a composite ferrule aligned with the tool body axis. An optical fibre cable 17 and a composite ferrule 18, of the type shown in Figure 1, fitted to the end of the cable but not yet heat-formed thereto, is shown in Figures 2A and 2B; in Figure 2A the clamping jaws 12 and 13 are closed upon the ferrule 18, and in Figure 2B the jaws are open. Although not readily visible from the Figures, the clamping jaws 12 and 13 are formed to mate with the shoulder 4 of the driving ferrule 2 and locate the driving ferrule whilst permitting the outer ferrule 1 to move back on to the driving ferrule 2 under the action of the heating head 16 and as the glass bead 3 softens. Figures 3A and 3B illustrate the internal arrangement of the terminating tool of Figures 2A and 2B. As shown, the heating head 16 is mounted in a schematically-shown slider 20 supported between a loading spring 21 at one end and return springs 22 at i other end, and moveable axially of the tool body 10 under control of the cam 23 which is arranged to be turned by control knob 15. An electrically powered heating element 24 is associated with the heating head 16. In the position of the cam 23 as shown in Figure 3A, the slider 20 is urged, by virtue of the compression of loading spring 21 by cam 23, towards the right-hand side as shown in the drawing so as to contact the forward end of the composite ferrule 18 clamped in the schematically-shown jaws 12 and 13 with a complementary-shaped recess in the head 16. In this position, the heat from the head 16 is transferred to the ferrule 18 for softening the bead 3 therein, and the loading spring 21 maintains a force on the outer ferrule 1 tending to move it back on the inner ferrule 2 as the bead 3 softens. The process is complete when the rearward (right-hand) end of the outer ferrule 1 abuts the shoulder 4 of the driving ferrule 2. Return of the cam 23 to its position shown in Figure 3B unloads unloading spring 21 and permits the slider 20 to be returned by the return springs 22 to a position whereat the heating head 16 is remote from the ferrule. The heating element can be arranged to switch on and off in response to operation of the control knob 15 for example, or can be independently switched, or can be made automatically operating in dependence upon the position of the slider 20 for example. After the operation on the composite ferrule with the terminating tool, it is adviseable to crimp the outer ferrule 1 to the driving ferrule 2 to secure the two parts together. Having fixed the composite ferrule to the optical fibre cable end as described above and using the termination tool of Figures 2A, 2B, 3A and 3B the termination thus made must be finished on a polishing tool which might for example simply comprise a tool body housing an electric motor in its lower part and a polishing, disc, arranged to be rotated by the motor, in its upper part. A clamping arrangement might be provided to enable the ferrule to be held vertically to the polishing disc and moved for example between coarse and fine polishing areas spaced radially from one another on the disc. A reservoir might be provided for wetting fluid for the disc, the internal construction of the polishing tool being such as to ensure that the fluid cannot get to the motor. WHAT WE CLAIM IS:

1. A tool suitable for use with a compo

site ferrule (as herein defined) in the termination of an optical fibre cable, said tool com- prising a manually operable clamp for the composite ferrule enabling one of the said members thereof to be located in the tool whilst relative movement is effected between the two said members for deforming the bead of the composite ferrule, a heating head, and manually operable means for moving the heating head and the clamp relative to one another so as to engage the heating head with a composite ferrule correctly positioned in the clamp such as to apply heat to the bead in the ferrule, the last mentioned means being such as to engage the heating head with the ferrule under a spring loading enabling further relative movement of the heating head and the clamp such as to urge the second member of the ferrule further into the first member as the bead deforms with heating.

2. A tool as claimed in claim 1 wherein the clamp is arranged to locate the said sec- ond member of the composite ferrule in the tool whilst the heating head is moved towards and engaged with the first member of the composite ferrule under said spring loading which tends to urge the first member of the ferrule back on to the second member as the bead deforms.

3. A tool as claimed in claim 2 wherein the heating head is mounted upon a slider mounted for movement towards and away from the clamp under the action of forward and return springs the action whereof is controlled by a manually operable cam arranged to determine the loading of the forward spring such that in one position of the cam the forward spring is compressed and urges the slider to move towards the clamp and in another position of the cam the forward spring is relatively relaxed and can be overcome by the action of the return spring.

4. A tool, for use in the termination of optical fibre cables by means of a composite ferrule substantially as herein described with reference to Figure 1 of the accompanying drawings, substantially as herein described with reference to Figures 2A, 2B, 3A and 3B of the accompanying drawings.

5. An optical fibre cable when terminated with a composite ferrule as herein defined by means of a tool as claimed in any of claims 1 to 4.