Branch device for multi-core optical fiber

Abstract: In a branch device for a multi-core optical fiber (1), a branch portion protector (10) which includes a spindle-shaped protector (11) and a perforated member (12) which are integrally formed with each other is provided between the end portion of the multi-core optical fiber (1) and the single-core optical fiber protection tubes (15) so that no excessive force is exerted on the branching-out single-core optical fibers (2) and the optical loss is stable.

Description: The present invention relates to an optical fibre cable branch device having a multi-fibre optical cable which may be in the form, for example, of a tape, cord or cable constituted a by plurality of single optical fibres collected together and branching therefrom. Figs. 1A and 1B illustrate an example of the branch portion of a conventional multi-fibre optical tape. Fig. 1A illustrates a configuration of a multi-branch tube used to form the branch portion and Fig. 1B illustrates the configuration of the branch portion. A multi-branch tube 31 is constituted by an optical fibre fixing portion 32 which receives and fixes a multi-fibre optical tape 1, a plurality of single optical fibre protection tubes 33 which are disposed on the side opposite to the optical fibre fixing portion 32 so that branched single optical fibres 2 are passed therethrough respectively, and a branch portion accommodation space 34 which is formed between the optical fibre fixing portion 32 and the single optical fibre protection tubes 33, those portions 32, 33 and 34 being formed integrally with each other. As shown in Fig. 1B, the multi-fibre optical tape 1 is fixed in the vicinity of an end portion thereof in the optical fibre fixing portion 32 of the multi-branch tube 31, and the single optical fibres 2 branched from the optical multi-fibre tape 1 are inserted through and protected by the single optical fibre protection tubes 33 of the multi-branch tube 31. Thus, the branch portion is formed. Figs. 2A and 2B illustrate another example of the branch portion of a conventional multi-fibre optical tape. Fig. 2A illustrates the configuration of a multi-branch tube used to form the branch portion and Fig. 2B illustrates the configuration of the branch portion. This example is different from the example of Fig. 1A in that a multi-branch tube 31 has no portion for fixing a multi-fibre optical tape 1 and a protection tube 35 for protecting the multi-fibre optical tape 1 is integrally formed. Accordingly, the tape 1 inserted into the protection tube 35 is not fixed thereto. The foregoing conventional branch portion of the multi-fibre optical tape 1 attempts to provide a simple solution to the problem of how to make the multi-fibre optical tape 1 branch into a plurality of the single optical fibres 2, and the branch portion is designed in consideration of the arrangement of the single optical fibre protection tubes 33 so that no force is exerted on the single optical fibres 2 in the respective single optical fibre protection tubes 33. The branch portion is however ineffective in protecting the branching out single optical fibres 2 in the branch portion accommodation space 34 between the end portion of the optical fibre tape 1 and the single optical fibre protection tubes 33. There is therefore a problem in that when resin or the like is poured into the branch portion accommodation space 34 so as to fix the single optical fibres 2, force is exerted on the single optical fibres 2 and may cause an increased optical loss. Further, if no resin is poured into the space 34, the increase of optical loss is similarly caused because of the lack of stability of the optical fibres 2 in the branch portion accommodation space 34. FR-A-2534700 also discloses an optical fibre cable branch device which additionally includes a branch portion protector arranged between an end portion of a multi-fibre optical cable and single optical fibre protection tubes, the branch portion protector including a perforated member having a plurality of insertion holes formed at the same circumference. A substantially spindle-shaped protector extends coaxially from the perforated member and the branching single optical fibres are passed along an outer surface of the protector and passed through the insertion holes of the perforated member and thence through the single fibre protection tubes. This arrangement provides only a partial solution to the fibre stability problem referred to. In accordance with the present invention, there is provided an optical fibre cable branch device comprising a multi-fibre optical cable, a plurality of single optical fibres branching out from said multi-fibre optical cable, a plurality of single optical fibre protection tubes, and a branch portion protector arranged between an end portion of said multi-fibre optical cable and said single optical fibre protection tubes, said branch portion protector including a perforated member having a plurality of insertion holes formed at the same circumference, and a substantially spindle-shaped protector formed integrally with said perforated member and disposed coaxially with said perforated member, said single optical fibres branching out from said multi-fibre optical cable passing over said spindle-shaped protector along an outer surface thereof and through said insertion holes of the perforated member and thence through the single optical fibre protection tubes respectively, a branch portion protection tube being disposed around the end portion of the multi-fibre optical cable and the branch portion protector, characterised in that the section of the branch portion protection tube around the end portion of the multi-fibre optical cable and the spindle-shaped protector is filled with resin, and in that the branch portion protection tube is fitted around the spindle-shaped protector in such a manner as to prevent the resin extending into the respective end portions of the single optical fibre protection tubes adjacent to the branch portion protector. With the arrangement of the invention, no excessive bending force or the like is exerted on the branching-out single optical fibres. Further, the branching-out single optical fibres and the spindle-shaped protector are fixed to each other with resin or the like, so that it is possible to obtain a branch portion which is more stable with reduced optical loss. Increased stability and reduction in optical loss may be achieved if a plurality of longitudinal grooves are formed in the outer surface of the spindle-shaped protector so as to accommodate the branching-out single optical fibres therein. With reference to the accompanying drawings:- Figs. 1A, 1B, 2A and 2B are views for explaining the conventional branch devices; Fig. 3 is a longitudinal sectional view showing a specific example of the optical fibre cable branch device of the present invention; Figs. 4A and 4B are for explaining a branch portion protector in the device of Fig. 3; and Figs. 5 and 6 are longitudinal sectional views showing other specific examples of the optical fibre cable branch device of the present invention. Fig. 3 is a longitudinal sectional view showing an embodiment of the optical fibre cable branch device of the present invention. Figs 4A and 4B show the configuration of the branch portion protector constituted by a spindle-shaped protector and a perforated member formed integrally with the spindle-shaped protector according to the present invention. Specifically, Fig. 4A is a longitudinal sectional view and Fig. 4B is a side view in the direction of the arrows X - X of Fig. 4A. As shown in figures 3 and 4, in the branch device of the present invention, a branch portion protector 10 is arranged between an end portion of a multi-fibre optical cable 1 such as a multi-fibre optical tape, a multi-fibre optical cord, or the like, and single optical fibre protection tubes 15 for protecting single optical fibres 2 which branch out from the optical cable 1 and are inserted through the protection tubes 15. The branch portion protector 10 is constituted by a substantially spindle-shaped protector 11 and a perforated member 12 integrally formed with each other, as shown in Figs. 4A and 4B. The perforated member 12 has pairs of two kinds of large and small insertion holes 13 and 14 formed on the same circumference, each pair having the small insertion hole 13 and the large insertion hole 14 which communicate with each other axially. The substantially spindle-shaped protector 11 is disposed coaxially with the perforated member 12 and has a plurality of grooves 11a formed in the outer surface thereof, if necessary, so as to accommodate therein the branching-out single optical fibres 2. In the perforated member 12, the small insertion holes 13 are provided to insert the single optical fibres 2 therethrough and the large insertion holes 14 are provided to insert the respective ends of the single optical fibre protection tubes 15 therein, where they are fixed. The plurality of single optical fibres 2 branching out from the multi-fibre optical cable 1 are respectively led into the small insertion holes 13 of the perforated member 12 along the outer surface of the spindle-shaped protector 11 of the branch portion protector 10 or along the grooves 11a of the outer surface of the spindle-shaped protector 11, and respectively inserted through the single optical fibre protection tubes 15 fixed in the respective large insertion holes 14. A protection tube 17 is provided so as to envelop the vicinity of the end portion of the multi-fibre optical cable 1 and the spindle-shaped protector 11 of the branch portion protector 10. The inside of the protection tube 17 is filled with resin 20 so that the single optical fibres 2 and the spindle-shaped protector 11 are fixed. The resin used may be formal resin, UV-setting resin, one-component or two-component resin, or the like. In this case, a heat-shrinkable tube may be used as the protection tube such that the inside thereof is filled with heat-fusible adhesive. Further, an external protection tube 19 is provided outside the protection tube 17. The multi-fibre optical cable 1 is inserted through a protection tube 16 for protection thereof, and one end of the external protection tube 19 is located over a portion of the protection tube 16 and fixed thereat. A rubber boot 18 is attached onto the other end of the external protection tube 19 so as to protect the single optical fibre protection tubes 15. Fig. 5 is a longitudinal sectional view showing another embodiment of the optical fibre cable branch device of the present invention. This embodiment shows the case where fibrous anti-tensile bodies 23 and external coatings 21 and 22 are provided over the single optical fibre protection tubes 15 and the multi-fibre optical cable protection tube 16 so as to reinforce them. In this case, the fibrous anti-tensile bodies 23 are led into the space between the protection tube 17 and the external protection tube 19, and the inside of the external protection tube 19 is filled with resin so that the fibrous anti-tensile bodies 23 are fixed therein. As a result, a branch portion durable to tensile force is obtained. Fig. 6 is a longitudinal sectional view showing a third embodiment of the multi-fibre optical cable branch device of the present invention. In this specific example, similarly to the specific example of Fig. 5, the single optical fibre protection tubes 15 and the multi-fibre optical cable protection tube 16 are reinforced by the fibrous anti-tensile bodies 23 and the external coatings 21 and 22. In this case, the fibrous anti-tensile bodies 23 are led onto the protection tube 17, and then a layer of a heat-shrinkable tube 24 or a heat-shrinkable tube 24 having a heat-fusible adhesive 25 in the inside thereof is provided over the protection tube 17 so as to fix the fibrous anti-tensile bodies 23 on the protection tube 17. As a result, similarly to the embodiment of Fig. 5, a branch portion durable to tensile force is obtained. Further, it is not necessary to wait until the resin is hardened because no resin is poured into the inside, unlike the embodiment of Fig. 5. Accordingly, the working time is shortened. As described above, in the multi-fibre optical cable branch device of the present invention, the branch portion protector constituted by the spindle-shaped protector and the perforated member which are integrally formed with each other is provided between the end portion of the multi-fibre optical cable and the single optical fibre protection tubes so that no excessive force is exerted on the branching-out single optical fibres and the optical loss is stable. Therefore, the multi-fibre optical cable branch device of the present invention is exceedingly effective when it is used as a branch device for a fibre optical tape or the like which is introduced into a fibre optical cable to reduce the diameter thereof.

Claims: An optical fibre cable branch device comprising: a multi-fibre optical cable (1), a plurality of single optical fibres (2) branching out from said multi-fibre optical cable (1), a plurality of single optical fibre protection tubes (15), and a branch portion protector (10) arranged between an end portion of said multi-fibre optical cable (1) and said single optical fibre protection tubes (15), said branch portion protector including a perforated member (12) having a plurality of insertion holes (13, 14) formed at the same circumference, and a substantially spindle-shaped protector (11) formed integrally with said perforated member and disposed coaxially with said perforated member, said single optical fibres branching out from said multi-fibre optical cable passing over said spindle-shaped protector along an outer surface thereof and through said insertion holes (13, 14) of the perforated member (12) and thence through the single optical fibre protection tubes (15) respectively, a branch portion protection tube (17) being disposed around the end portion of the multi-fibre optical cable (1) and the branch portion protector (10), characterised in that the section of the branch portion protection tube (17) around the end portion of the multi-fibre optical cable (1) and the spindle-shaped protector (11) is filled with resin (20), and in that the branch portion protection tube (17) is fitted around the spindle-shaped protector (11) in such a manner as to prevent the resin (20) extending into the respective end portions of the single optical fibre protection tubes (15) adjacent to the branch portion protector (10). A branch device as claimed in Claim 1, wherein a plurality of longitudinal grooves (11a) are formed on the outer surface of said spindle-shaped protector (11) to accommodate said single optical fibres (2) respectively. A branch device as claimed in Claim 1 or Claim 2, wherein said resin (20) filling said branch portion protection tube is selected from a group comprising formal resin, UV-setting resin, one-component resin and two-component resin. A branch device as claimed in any one of Claims 1 to 3, wherein said branch portion protection tube (17) is a heat-shrinkable tube and the filling resin (20) is heat-fusible. A branch device as claimed in any one of Claims 1 to 3, wherein said single optical fibre protection tubes (15) and a multi-fibre optical cable protection tube (16) are reinforced with fibrous anti-tensile bodies (23) and external coatings (21, 22), said fibrous anti-tensile bodies extend into a portion between the branch portion protection tube (17) and an external protection tube (19) and said portion is filled with resin (20) so that said fibrous anti-tensile bodies are fixed therein. A branch device as claimed in any one of Claims 1 to 3, further comprising a heat-shrinkable tube (24) provided outside of fibrous anti-tensile bodies (23) and external coatings tubes (21, 22), and said fibrous anti-tensile bodies extend between said heat-shrinkable tube and said branch portion protection tube (17) so as to be fixed on said branch portion protection tube. A branch device as claimed in Claim 6, wherein said heat-shrinkable tube (24) has a heat-fusible adhesive (25) provided in the inside thereof.

Inventors: OHKURA TOSHIHIKO C O YOKOHAMA, OHKURA, TOSHIHIKO, C/O YOKOHAMA WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: G02B6
IPC codes: G02B6, H02G15