GB2138593A

GB2138593A - Handling Surplus Lengths of Optical Fibers at Cable Connection Points

Info

Publication number: GB2138593A
Application number: GB08408861A
Authority: GB
Inventors: Masakichi Haraguchi; Toshikazu Nakatani; Yuzo Tokumaru; Toshio Shimizu
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1983-04-23
Filing date: 1984-04-05
Publication date: 1984-10-24
Also published as: AU2716584A; GB8408861D0; JPS59197005A

Abstract

Surplus lengths of optical fibers (20, 20') are handled at a junction region at which optical cables (10, 10') are joined whereby excessively small radii of curvature of the fibers are prevented and numerous cut-and- splice operations can be performed without substantially increasing the losses in the fibers. If a sufficiently long surplus length of each optical fiber is available, each optical fiber is wound around a spacer (11) in a complete loop, preferably, through one and one-quarter turns. If a loop would extend along less than one-half the length of the spacer, the fibers are wound around the spacer in the longitudinal direction thereof through three-fourths of a turn without making a loop in the fibers. <IMAGE>

Description

SPECIFICATION Method for Handling Surplus Lengths of Optical Fibres at Cable Connection Points The present invention relates to a method for handling surplus lengths of optical fibers at ends of optical cables at junction boxes where fibers from different cables are spliced. As is well known in the art, it is usually necessary to provide surplus lengths of optical fibers at junction boxes so that the cables can be spliced more than once if needed. With reference to Fig. 1, a prior art approach for handling the surplus lengths of the optical cables at connectors will be described. A cylindrical surpluslength spacer 1 made of rubber has opposite tapered ends connected through sleeves 5 to support members 4 of optical cables 6 and 6'. Circumferentially extending guide spacers 2, preferably made of metal, are affixed to the spacer 1.A plurality of longitudinally oriented guide grooves 3 are formed in the spacer 2.

Optical fibers 7 and 7' of the cables 6 and 6', respectively, are spliced together at a connector 8, leaving predetermined surplus lengths 9 and 9' of the respective fibers 7 and 7'. These surplus lengths 9 and 9' are coiled in the manner shown in the drawing, and then bent around the spacer 1 as indicated by the chain and broken lines. The surplus lengths 9 and 9' are supported by the guide grooves 3 with a cushioning material disposed between the fibers and the metal of the spacers 2.

In the conventional approach described above, the dimensions of the spacer 1 must be determined so as not excessively to bend the optical fibers 7 and 7'. Accordingly, the spacer 1 typically has a length of 360 mm and a diameter of 60 mm. Hence, the overall dimensions of the junction box are quite large, making it difficult to perform splicing of the optical fibers 7 and 7' in a narrow space.

Further, since the surplus lengths 9 and 9' are coiled and then bent around the spacer 1, bending forces are applied thereto in various directions. This has been found to reduce the reliability of the connection.

Accordingly, it is an object of the present invention to provide a method for handling surplus lengths of optical fibers whereby the above-noted problems are eliminated.

In accordance with the above and other objects of the invention, there is provided a method for handling surplus lengths of optical fibers of optical fiber cables at junction boxes wherein each optical fiber to be connected is wound around a surplus length spacer in the longitudinal direction thereof through one and one-quarter turns with the connecting portion between the two optical fibers as a reference. The direction of winding of the two optical fibers are opposite to one another, that is, one is wound clockwise and the other counterclockwise. If less than one-half turn of length is available for the two fibers, the direction of winding should be reversed.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view, partly in cross-section, illustrating a prior art technique of handling optical fibers at a junction box; Fig. 2 is a cross-sectional view taken through a fiber spacer shown in Fig. 1; Fig. 3 is a cross-sectional view taken along the line Ill-Ill in Fig. 2; and Figs. 4 to 8 are schematic views showing steps in a handling method of the invention.

Referring now to Figs. 2 and 3, a surplus length spacer 11 is disposed between respective ends of optical fiber cables 10 and 10'. As in the conventional case, the spacer 11 is formed of rubber. The central part of the spacer 11 is cylindrically shaped, while the end portions thereof are tapered, forming reduced cross-section openings 1 2 and 1 2' at opposite ends of the spacer 1 A connecting sleeve 14 firmly connects supporting members 1 3 and 1 3' of the cables 1 0 and 10' at the center of the spacer 11.

Ribs 1 5 are formed on the inner surface of the spacer 1 The ribs 1 5 and supports 1 6 through which the supporting members 13 and 13' extend are secured together by screws 17. Spacers 18 are formed integrally with the spacer 11 on the outer surface thereof. A plurality of guide grooves 1 9 are formed longitudinally in each spacer 18.

The optical fibers 20 and 20' are spliced together with a connecting member 21 with surplus lengths of the fibers 20 and 20' being provided. The connecting member 21 and the surplus lengths of the optical fibers 20 and 20' are fitted in the guide grooves 19 in a manner to be described. After the surplus lengths of the optical fibers 20 and 20' have been handled in the manner to be described, a protective sheath 22 is disposed around the guide spacers 1 8. Then, a housing 23 is placed around the spacer 11 with a predetermined gap therebetween. The housing 23 includes two halves and funnelshaped end portions 24 connected to a protective sleeve 26, having a longitudinally extending slit 25 (Fig. 3). Spacers 27 are joined to the protective sleeve 26 with an epoxy resin 28 or the like.The length of the spacer 11 may typically be 130 mm and its diameter 50 mm.

Referring now to Figs. 4 to 8, the method of the invention of handling the surplus lengths of the optical fibers 20 and 20' will now be described.

Fig. 4 illustrates the state in which the first splice between the fibers 20 and 20' has been completed. The fiber 20, with reference to the connector 21 as a starting point, is wrapped longitudinally around phe spacer 11 in the longitudinal direction, running in the counterclockwise direction, through one and one-quarter turns, forming a complete loop. Similarly, the fiber 20' of the cable 10' extends from the connector 21 around the spacer 11, running in the clockwise direction, through one and one-quarter turns before reaching the end of the cable 10', forming a complete loop.

The fibers 20 and 20' are, of course, attached to the spacer 11 to be supported thereby.

When the ends of the fibers 20 and 20' are subsequently cut from the connector 21 and then respliced, as illustrated in Fig. 5, approximately one-quarter turn of each of the fibers 20 and 20' is lost in the process. Hence, the surplus lengths of the fibers 20 and 20' are insufficient to pass entirely around the spacer 11 and only one full turn of each is available Nevertheless, they are still wound around the spacer 11 in the longitudinal direction and form complete loops.

As subsequent cutting and splicing of the fibers 20 and 20' are performed, the available surplus lengths thereof are successively depleted, as illustrated in Fig. 6 and 7. In the state shown in Fig. 7, the surplus lengths of the fibers 20 and 20' is only about one-half turn, although they still form complete loops. If further cutting and splicing of the fibers 20 and 20' is to be done, the radii of curvature of the fibers 20 and 20' would be so small that the losses in the fibers would be excessive.

This problem can be avoided by using the embodiment illustrated in Fig. 8. In this embodiment, the directions of winding of the fibers 20 and 20' have been reversed. Each is wound by approximately three-fourths of a turn around the spacer 11 with the fiber 20' being wound in the counterclockwise direction and the fiber 20 in the clockwise direction. In this case, complete loops are not formed.

Hence, a fifth splicing operation can be performed without greatly increasing the radii of curvature of the fibers.

The Table below shows measurements made on two different cable samples of a four-channel optical fiber cable in which a series of five cut-and-splice operations was performed: TABLE

Number of Times of Splicing Cable Loss Fiber Loss Per Fiber (dBm) Sample Filament No. No. 1 sot. 2nd. 3rd. 4th. 5th. Min. Max. Aver.

1 0.03 0.02 0.06 0.09 0.10 0.02 0.10 0.06 No. 1 2 0.06 0.06 0.08 0.03 0.08 0.03 0.08 0.06 3 0.08 0.10 0.09 0.15 0.10 0.08 0.15 0.10 4 0.03 0.06 0.13 0.09 0.05 0.03 0.13 0.07 1 0.07 0.08 0.05 0.11 0.10 0.05 0.11 0.08 No.2 2 0.06 0.04 0.06 0.04 0.04 0.04 0.06 0.05 3 0.04 O.tO 0.16 0.11 0.10 0.04 0.16 0.10 4 0.08 0.09 0.07 0.09 0.09 0.07 0.09 0.08 From the Table abdve, it can readily be ascertained that there is little change in the loss in the cable in the first embodiment of the invention for the first through fourth splices and the second embodiment of the invention for the fifth spliCe. Further, vibration and heat cycle tests were performed, but no change in the loss in the cable was found.

According to the invention described above, since surplus lengths of the optical fibers are handled by winding them in the longitudinal direction of the spacer, both the length and the diameter of the spacer can be reduced from what was required with the prior art approach. Accordingly, the space needed for mounting the connector apparatus can be reduced, and hence splicing of the optical fibers can be performed in a narrower space than previously. Further, the invention is advantageous in that the radii of curvature of the optical fibers are prevented from being so small that the losses in the fibers are significantly increased. Still further, the invention is advantageous in that a large number of cutand-splice operations can be performed without significantly increasing the losses in the fibers.

Claims

1. A method for handling surplus lengths of optical fibers of optical fiber cables at a junction region between optical cables to be connected together, said optical fiber cables having supporting means joined together inside of a surplus length holding spacer having tapered ends, comprising the steps of: if surplus lengths of said optical fibers are as long as one-half turn in the longitudinal direction around said spacer, winding said optical fibers around said spacers in the longitudinal direction and with opposite directions of winding, forming complete loops, and connecting said fibers together at a substantially center position along an outer surface of said spacer; and if said surplus lengths of said fibers are less than one-half turn in the longitudinal direction around said spacer, reversing the direction of winding of said fibers around said spacer and connecting said fibers at said substantially center portion along said side of the said spacer without forming complete loops.

2. The method as claimed in claim 1, wherein the first recited step comprises winding each of said fibers around said spacer in the longitudinal direction thereof through substantially one and onequarter turns.

3. The method of claim 1, wherein the second recited step comprises winding each of said fibers around said spacer in the longitudinal direction thereof through substantially three-fourths of a turn without forming a complete loop.

4. A method for handling surplus lengths of optical fibers of optical fiber cables substantially as hereinbefore described with reference to and as shown in Figures 4 to 8 of the accompanying drawings.