GB2206976A

GB2206976A - Optical fibre cable

Info

Publication number: GB2206976A
Application number: GB08716362A
Authority: GB
Inventors: Melvin Murray Ramsay; James Garrard Titchmarsh
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1987-07-10
Filing date: 1987-07-10
Publication date: 1989-01-18
Anticipated expiration: 2007-07-10
Also published as: GB8716362D0; GB2206976B

Abstract

An optical fibre cable comprises a sheath 11 containing an optical fibre 13 supported in a filler material, e.g. an elastomeric filler, 14. The cable has a longitudinal split 15 at least in the filler, whereby the fibre 13 may be exposed thus allowing the insertion of one or more non-intrusive taps. <IMAGE>

Description

OPTICAL FIBRE CABLE This invention relates to optical fibre cables and in particular to a cable construction whereby coupling of a tap to the cable is facilitated.

Fibre optic transmission systems are finding increasing use for the handling of large volumes of data and/or voice traffic. The capability of optical systems to handle large volumes of traffic is of particular value in applications such as the connection of a plurality of data terminals to a control computer or to the interconnection of plurality of active systems. The full potential of optical transmission systems in such.

applications has however not yet been exploited.

Conventional systems comprise a number of stations to which optical cables are connected. Such. systems cannot be expanded or modified without considerable recabling of the optical connections. In an attempt to overcome this disadvantage it has been suggested that, e.g. in an office environment, a system of permanent optical wiring may be provided so that terminal stations may be coupled at will to various points of this wiring system.

However, difficulties have been experienced in coupling the terminal stations to the optical fibres. Present couplers are both costly and involve intrusion into (i.e.

cutting and reconnection) the optical fibre system.

The object of the present invention is to minimise or to overcome this disadvantage.

Our copending application No. (M.M.

Ramsay - J. Lees 32-22) of even date describes and claims a non intrusive tap for coupling to an optical fibre cable, the tap having means for inducing locai microbending of the fibre whereby coupling between bound and radiating modes in the fibre is effected.

Sne present invention is concerned with a cable structure adapted to receive such a tap.

According to the invention there is provided an optical fibre cable, including an optical fibre supported within a body of filler material in a protective sheath, there being a longitudinal split at least in the filler whereby the optical fibre may be expose5 to allow application of a tap thereto.

An embodiment of the invention will now be described with reference to the accompanying drawings in which Fig. 1 is z cross-sectional view of an optical ire cable construction adapter to facilitate insertion of an optical tap; and Figs. 2 an S are respectively cross-sectioned and longitudinal sectional views of the cable of Fig. 1 fitted with a tap.

Referring to Fig. 1, the cable comprises an outer sheath 11 in which a number of strength members 12 are disposed and within which an optical fibre 13 is supported with a filling 1 of an elastomer. The elastomer filling 14 has a longitudinal split 15 extending to the fibre 13 at the axis of the cable whereby, by cutting a selected portion of the sheath 11, the sheath and the elastomer filling 14 may be pushed apart to expose the fibre so as to allow the insertion of 2 tap 21 (Figs. 2 and 3) whereby a terminal station may be coupled to that region cf the cable. As the tap 21 is inserted in the cable the surfaces of the split elastomer guide the tap to the fibre 13. This makes insertion of the tap a relatively simple operation that can be performed by unskilled persons.Typically, the cable is of circular cross section with the fibre 13 disposed along the axis.

As can be seen from Figs. 2 and 3 the tap 21 comprises a mating pair of transparent plastics members 21a, 21b which together form an assembly of wedge shaped cross section, the apex of the wedge defining a cylindrical tubular cavity in which the fibre 13 is located in a self-aligning relationship with the tap 21.

The tap 21 couples to the fibre 13 by applying a stress thereto so as to induce microbending whereby coupling between bound and radiating modes is effected. This allows light to be radiated from the fibre and directed into a terminal station (not shown) via an output port 22 of the tap. The construction and operation of the tap are more fully described in our aforementioned copending application.

The cable of Fig. 1 may be manufactured by extruding the elastomeric filler 14 on to the fibre via an extruder the head of which is provided with a web whereby the longitudinal split is formed. The split is held open until the extruded material has cooled sufficiently to ensure that the split does not reseal.

The protective sheath 11 is then extruded over the assembly. The line along which the sheath may be cut to expose the split in the underlying elastomer may be indicated by a longitudinal groove or by a longitudinal strip 17 of plastics material, e.g. of a different colour from that of the sheath, applied to the sheath via a small 'piggy back' extruder. Access to the fibre 13 is provided by removal of an appropriate length of the strip 17 and cutting of the underlying sheath to expose the split. In an alternative embodiment the sheath 11 also has a longitudinal split in register with the split in the elastomer. The split in the sheath may be covered with an adhesive plastics strip, a length of which is removed to allow insertion of a tap.

The cable construction described herein may be used in a variety of applications but is of particular application in a 'wired office' environment. In such a system a network of cabling is provide, Terminal stations can be coupled at will to various points of the cable network simply by insertion of a tap into the cable. Other applications include local area telephone cable where the tap insertion facility is again of particular advantage.

Claims

CLAIMS:

1. An optical fibre cable, including an optical fibre supported within a body of filler'material in a protective sheath, there being a longitudinal split at least in the filler whereby the optical fibre may be exposed to allow application of a tap thereto.

2. An optical fibre cable as claimed in claim 1, wherein the fibre is supported by an elastomeric filler within the sheath.

3. An optical fibre cable as claimed in claim 1 or 2, wherein a removable plastics strip is applied longitudinally to the sheath and in register with the split in the filler.

4. An optical fibre cable as claimed in claim lor 2, wnerein the sheath has a longitudinal cut in register with the split in the filler, said cut being sealed with an adhesive tap.

5. An optical fibre cable substantially as described herein with reference to and as shown in the accompanying drawings

6. An optical transmissions system provided with one or more cables as claimed in any one of claims 1 to Amendments to the claims Amendments to the claims have been filed as follows

7. An optical fibre cable, including an optical fibre supported within a body of elastomeric filler material contained within a protective outer sheath, the cable being of circular cross-section with the fibre disposed at the centre of the circle, wherein the elastomeric filler has a longitudal radial split whereby the elastomer may be displaced to expose the fibre to allow insertion of a tap, the split surfaces of the elastomeric material providing a guide for alignment of the tap with the fibre.