Tape core type coated optical fiber

Abstract: A tape core type coated optical fiber (1) containing therein a plurality of single optical fibers (4), which comprisesa housing (17) for housing the tape core type coated optical fiber, the tape core type coated optical fiber branches into a plurality of single fibers inside the housing, the housing comprises a plurality of branches (3) through which each of the single fiber passes.

Description: FIELD OF THE INVENTION The present invention relates generally to an optical fiber, and more particularly to a branching device for a tape core type coated optical fiber whose optical fibres branch out at its end portion. BACKGROUND OF THE INVENTION There has been developed a conventional optical fiber cable as shown in Fig. 1. The conventional optical fiber cable shown in Fig. 1 is provided with a tape core type coated fiber 1, reinforcing members 12, a protective sheath 13, single fibers 4, a branching portion protecting plate 15, a reinforcing housing 17, resin 16, and optical fiber connectors 7. The tape core type coated fiber 1 is adhered to the branching portion protecting plate 15. A similar conventional coated optical fiber five-to-one branching cable was shown at the 1988-Spring National Meeting B-599 of the Institute of Electronics, Information and Communication Engineers of Japan. According to the conventional optical fiber cord shown in Fig. 1, the tape core type coated fiber 1 branching on the branching portion protecting plate 15 is provisionally fixed to the branching portion protecting plate 15 through an adhesive, and then, each of the tape core type coated fiber 1 and the single fibers 4 is coated with the reinforcing sheath 13, an end of the sheath 13 and the connection portion between the tape core type coated fiber 1 and the single fibers 4 are covered with the reinforcing housing 17, and the resin 16 is filled in the reinforcing housing 17. Such an optical fiber cord would cause a drawback that stress is exerted onto the tape core type coated fiber 1 and the single fibers 4 in filling the resin and in hardening the resin to thereby increase undesirable light transmission loss. Further, the conventional optical fiber cord would suffer from a problem that the tape core type coated fiber 1 and the single fibers 4 are subject to stress by thermal expansion of the resin 16 when an environmental temperature varies since they are molded with the resin 16, so that the light transmission loss may increase. Moreover, there would be raised a further problem that the work for fixing the branching portion of the tape core type coated fiber 1 to the protecting plate 15 is fine work and poor in workability and, therefore, the light transmission loss may increase if the setting is not well. There has been a still further problem that since the branching portion has such a basic configuration as described above, it is necessary to provide the protecting plate 15 when the tape core type coated fiber 1 is branched into the single fibers 4, and it is impossible to provide a mere branching portion of the single fibers 4 of the tape core type coated fiber 1. A branching device similar to the above is known from JP-A-58166311. A converting case is employed which directly converts an optical fiber cable to separate optical fibers. Again the optical fibers are directly exposed within the case and the same problems as described above would occur when resin is to be filled within the casing. There is also known from FR-A-2331041 an optical fiber branching device which comprises of a branch housing space for enclosing the cable at one end in which the cable's contituent fibers can branch out, and a plurality of exit tubes through which respective fibers can pass through and exit from. However, this prior art device has a very complicated housing arrangement requiring numerous connector elements which are all fitted together. This means that tight tolerances of the various connector elements are necessary in order to achieve a securely sealed branch unit. This type of branching device is, therefore, rather expensive to manufacture as well as involving intricate assembly work. SUMMARY OF THE INVENTION In view of the above-noted drawbacks and problems accompanying the conventional devices an object of the present invention is to provide a tape core type coated optical fiber cable branching device in which the single fibers branching from the tape core type coated fiber do not directly touch an adhesive or resin, no stress is exerted on the optical fibers in the process of hardening the adhesive or resin, no stress is exerted on the optical fibers even when the resin or the like is thermally expanded in use due to a change in an environmental temperature, and the light transmission loss does not increase, as well as avoiding any complicated and expensive means for branching. The foregoing and other objects have been achieved by the provision of a tape core type coated optical fiber cable branching device comprising the features set out in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a conventional optical fiber cable; Fig. 2 is a sectional view of an optical fiber branching portion according to a first embodiment of the present invention; Fig. 3 is a view showing an optical fiber branching portion according to a second embodiment of the invention; Fig. 4A is a view showing a multi-branch pipe for forming the branching portion of Fig. 2; Figs. 4B and 4C are cross sectional views showing two arrangements of a configuration of a multi branch pipe; Fig. 5A is a plan view of a multi-branch pipe arrangement different from that of Fig. 4A; Fig. 5B is a side view of the multi-branch pipe arrangement shown in Fig. 5B; Fig. 6 is a view showing a multi-branch pipe for forming branching portion of Fig. 3; Fig. 7 is a sectional view showing an optical fiber cord applied to the present invention; and Fig. 8 is a sectional view showing another optical fiber cord applied to the present invention. Fig. 9 is a sectional view showing another arrangement of the optical fiber cord according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The branching portion of the tape core type coated optical fiber of the present invention will now be described with reference to accompanying drawings. Fig. 2 shows a first embodiment of a branching portion of a tape core type coated optical fiber (hereinafter simply referred to an "optical fiber branching portion") A. The optical fiber branching portion shown in Fig. 2 is provided with a tape core type coated fiber 1, a fixing portion 2 for fixing the tape core type coated fiber 1, a branch housing space 3, a single fiber 4, a single-fiber protecting sheath 5, an optical connector 7, and a multi-branch pipe B. Fig. 3 shows a second embodiment of a branching portion of a tape core type coated optical fiber according to the present invention, in which the tape core type coated fiber 1 is not fixed by the fixing portion instead the fiber 1 is housed in a protecting member 6 such as a tube or the like. Referring to Figs. 4 through 6, the above-mentioned multi-branch pipe B will be described. Fig. 4A is a principle view of the multi-branch pipe B employed in the first embodiment shown in Fig. 2, which pipe comprises the single-fiber protecting sheath 5, the tape core type coated fiber fixing portion 2, and the branch housing space 3. Figs. 4B and 4C are cross sectional views showing arrangements of the configuration of single-fiber protecting sheath 5. That is, four protecting sheaths 5 form in a line in the arrangement of Fig. 4B, and in two lines and two columns in the arrangement of Fig. 4C. Figs. 5A and 5B show an example of a method of assembling the multi-branch pipe B arranged such that tubes 9 are inserted into a porous box 8 opened at its one side and a cover 10 is provided for covering the open side of the porous box 8. Figs. 5A and 5B are a plan view and a side view of the example, respectively. Fig. 6 is a sectional view showing the multi-branch pipe B employed in the second embodiment shown in Fig. 3, in which there is provided the tape core type coated fiber protecting member 6, a branch housing space 3, and a single-fiber protecting sheath 5. Fig. 7 is a sectional view showing an example of an optical fiber cord applied to a branching portion of a tape core type coated fiber according to the present invention. The optical fiber cord shown in Fig. 7 has a configuration in which each of a tape core type coated fiber 1 and single fibers 4 is coated with a protecting sheath 13 containing therein a reinforcing member 12. An end of the protecting sheath 13 together with the multi-branch pipe B is contained in the reinforcing housing 17 filled with a resin 16. Although the reinforcing housing 17 is pipe-like in Fig. 7, it is applicable to facilitate assembling of the inside by such a configuration that the reinforcing housing 17 is replaced by an one-side opening lunch box type reinforcing box 18 provided with a cover 10 as shown in Fig. 8. The tape core type coated fiber branching portion A shown in Fig. 2 is configured such that the tape core type coated fiber 1 branched at its forward end into single fibers is inserted from the tape core type coated fiber fixing portion 2 of the multi-branch pipe B shown in Fig. 4A into the protecting sheath 5 of the branching single fibers 4, and the tape core type coated fiber 1 is fixed at the tape core type coated fiber fixing portion 2, so that the branching portion A can be assembled without giving excessive force to the single fibers 4. Further, the branching portion A shown in Fig. 3 can be housed in the branching portion housing space 3 without fixing the tape core type coated fiber 1 at the branching portion A as shown in Fig. 6. Thus, the freedom of the tape core type coated fiber increases and the light transmission loss can sufficiently be minimized. Further, the optical fiber cord branching portion shown in Fig. 7 has a configuration in which the tape core type coated fiber branch portions made as described above are coated with the respective sheaths 13 and the reinforcing housing 17, and then the resin 16 is filled in the reinforcing housing 17. Accordingly, the resin 16 never directly touches the single fibers 4. The optical fiber cord branching portion shown in Fig. 8 is similar in advantage to that shown in Fig. 7. Fig. 9 shows another arrangement of the optical fiber cord branching portion according to the invention. This arrangement is similar to the arrangement shown in Fig. 7. However, in this arrangement, the reinforcing housing 17 is not filled with a resin. Instead, the branching portion of the optical fiber cord, an end part of the tape and an end part of each of the sheath 13 are fixedly covered with a heat-shrinkable tubing 19. This arrangement is advantageous in that the manufacturing time is shortened relative to the case in which a resin is filled in the housing 17. A heat-melting adhesion may be applied to the inner periphery of the heat-shrinkable tubing 19 thereby firmly fixing the branching portion, end part of the tape and end part of the sheath to one another. In the above-described embodiments, the multi-branch pipe has four branches. However, the invention is not limited thereto or thereby. That is, the multi-branch pipe may have a plurality of branches other than four. As described above, according to the present invention, the single fibers branching from an end of the tape core type coated fiber never touch directly the adhesive or resin, so that stress is never exerted onto the optical fibers in the process of hardening the resin or adhesive, and the light transmission loss never increases in the manufacturing process.

Claims: A tape core type coated optical fibre cable branching device, said cable (1) containing a plurality of constituent single optical fibres (4), the device comprising: protection means (2,3,5,6) for enclosing said cable at one end wherein the cable's constituent fibres can branch out inside said protection means, said protection means comprising a corresponding plurality of exit tubes (B) through which respective fibres can freely pass to leave the protection means, the protection means being encased in resin or encased by a heat shrinkable tube containing a heat melting type adhesive. The device of claim 1, wherein said cable is fixed to said protection means at one end thereof. The device of claim 1, wherein said protection means includes a pipe (6) projecting therefrom through which the cable freely passes. The device of claim 1, wherein said protection means comprises a box (8) having holes for said plurality of exit tubes (9). The device of claim 4, wherein said box (8) is provided with a cover (10). The device of claim 3, wherein said pipe means (6) contains therein a reinforcing means (12,13) associated with an optical tape core type cable end housed within the protection means. The device of claims 1 and 6, wherein each of said tubes (5) is covered by reinforcing means (12) associated with fibres housed within the protection means. The device of claim 1, wherein said protection means (2, 3, 5, 6) is accommodated within a housing (17). The device of claim 8, wherein said protection means is held within the housing by filling the housing with said resin. The device of claims 8 or 9, wherein said housing is provided with a cover (10). The device of claims 8 or 9, wherein said housing is one-side opening lunch box type (18). The device of claim 1, wherein an optical fibre connector (7) is disposed at the outside end of each exit tube. The device of claims 8 or 9, wherein said housing means comprises four branches and wherein said four branches of said housing means extend in a common plane or extend in two parallel planes.

Inventors: HIRAO KOUJI C O YOKOHAMA WORKS, KASHIHARA KOUJI C O YOKOHAMA W, OKURA TOSHIHIKO C O YOKOHAMA W, WATANABE TETSUAKI C O YOKOHAMA, HIRAO, KOUJI C/O YOKOHAMA WORKS OF SUMITOMO, KASHIHARA, KOUJI C/O YOKOHAMA WORKS OF SUMITOMO, OKURA, TOSHIHIKO C/O YOKOHAMA WORKS OF SUMITOMO, WATANABE, TETSUAKI C/O YOKOHAMA WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1989
Main classification: G02B6
IPC codes: G02B6, H01B7