Fiber identification in an optical fiber overhead cable

Abstract: An optical fiber composite overhead ground wire in which a plurality of optical fibers (1-6) are wound together on a tension member (32) to form an optical unit. A plurality of such optical units are disposed in a spacer (21) around which ground wires are wound. The optical fibers within a unit are identified by color and possibly winding order. Each tension member is also identified from other tension members so each optical fiber can be uniquely identified.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to identifying the optical fibers of an optical fiber overhead cable made of a ground wire and the optical fibers of the kind as defined in the preamble of claim 1. Such a cable is shown in Fig. 4. Background of the Invention An optical fiber overhead cable is shown in Fig. 1 and comprises optical fiber units 20 (each made of one or more optical fibers). A grooved spacer 21 made of aluminum or plastic contains the optical units 21. The spacer is contained in an aluminum tube 22. Aluminum wires or aluminum-coated steel wires 23 are wound on the aluminum tube 22. For example, six optical fibers of an optical fiber overhead cable are included in each of two optical fiber units and are laid on a central tension member 30 as shown in Figs. 2, 3 and 4. Each of the twelve resultant optical fibers is conventionally identified by one of the three following methods. (1) Twelve different colors 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are provided on the twelve optical fibers, as shown in Fig. 2, for identification. This is an all-color differentiation system. (2) The two optical fiber units are identified by the difference between colors 2 and 3 of fibers contained respectively therein, as shown in Fig. 3. The remaining optical fibers of each of the optical fiber units are identified by counting to the direction of 1 to 2 and 1 to 3. This is a tracer system. (3) The mutually-corresponding optical fibers of the two optical fiber units are provided with the same colors l through 6 and the two units are identified by tapes or sheaths 31 having different colors and wound or fitted on the units, as shown in Fig. 4. This is the unit color differentiation system. In the all-color differentiation system, it is easy to identify the optical fibers but twelve colors are needed, thus increasing the cost. In the tracer system, only four colors are needed for all the optical fibers and therefore this system yields a lower cost. However, it is inefficient to identify and count the optical fibers in field work because the diameter of each of the optical fibers is as small as 0.25 to 0.9 mm and the same color 4 is used for a large number of optical fibers. In the unit colour differentiation system, it is not inefficient to identify the optical fibres because the optical fibre units are identified by the different colours and the optical fibres of each of the units are then identified by different colours. However, since the tapes or sheaths 31 having the different colours are provided, the number of manufacturing steps and the cost of the cable are increased. Although the unit colour differentiation system is adopted for most of optical fibre overhead cables and also in the type of cable disclosed in DE-A-3 200 760 and DE-A-2 302 662, the system has the above-mentioned problems which increase the number of manufacturing steps and the cost of the cable. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical fibre overhead cable in which the separate fibres in multiple units can be easily identified and yet be inexpensive. According to the present invention, this object is achieved by an optical fibre overhead cable comprising the features set out in claim 1. Preferred embodiments of the invention are claimed in the dependent claims. Thus, central tension members indispensable to the constitution of optical fibre units are provided with identification means in order to solve the problems of the unit colour differentiation system. Since the central tension members is indispensable to the construction of the optical fibre units, they may easily be provided with identification means for identifying the units. The process of manufacturing an optical fiber overhead cable is simplified and the cost thereof is reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of an optical fiber composite overhead ground wire. Fig. 2 shows a view for explaining an all-color differentiation system for identifying each of optical fibers. Fig. 3 shows a view for explaining a tracer system for identifying each of optical fibers. Fig. 4 shows a view for explaining a unit color differentiation system for identifying each of optical fibers. Fig. 5 shows a sectional view of an optical unit of an optical fiber overhead cable which is an embodiment of the present invention. Fig. 6 shows an enlarged sectional view of a part of the cable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 5 shows a sectional view of part of an embodiment of the present invention, which is an optical fiber overhead cable having a grooved spacer. Fig. 6 shows an enlarged sectional view of each of the optical fiber units of the cable. Shown in Figs. 5 and 6 are two optical fiber units 20 whose optical fibers have the same sequence of six colors. Both optical units 20 are placed in respective grooves of a grooved aluminum spacer 21. The tube 22 and electrical wires 23 of Fig. 1 surround the spacer 21. The six optical fibers in in each unit have six mutually different colors 1 through 6 in this embodiment. However, generally, they do not need to have completely mutually different colors. The two central tension members 32 are differentiated from each other by identification means. These colors are provided by, for example, colored FRP. According to the present invention, simple identification means are provided for central tension members indispensable to the constitution of optical fiber units, so as to enable the identification of each of the optical fiber units and that of each of optical fibers.

Claims: An optical fibre overhead cable, comprising: two or more optical fibre units (20); and a plurality of ground wires (23) provided externally to said units, each of said optical fibre units (20) comprising: a tension member (32); and a plurality of optical fibres (25) wound around said tension member; and includes first identifying means to distinguish each optical fibre from any other optical fibre within said plurality of optical fibres, characterised in that , each of said tension members (32) associated with a respective optical fibre unit (20) includes second identifying means to distinguish said each tension member from any other of said tension members to enable the identification of each of said optical fibre units. An optical fibre overhead cable as recited in claim 1, wherein said second identifying means are visual identifying means. An optical fibre overhead cable as recited in claim 2, wherein said first identifying means are the same as said second identifying means. An optical fibre overhead cable as recited in claim 1, wherein said first identifying means includes a different colour surface on each of said plurality of optical fibres (25). An optical fibre overhead cable as recited in claim 1, further comprising: a spacer (21) in which said optical units are disposed; and a tube (22), on which said plurality of ground wires are wound around.

Inventors: NISHIYAMA SATOSHI C O YOKOHAMA, NISHIYAMA, SATOSHI C/O YOKOHAMA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1987
Main classification: G02B6
IPC codes: H01B7, H01B11, G02B6