GB2236866A

GB2236866A - Protecting optical fibre splice

Info

Publication number: GB2236866A
Application number: GB8923192A
Authority: GB
Inventors: Raymond Charles Foss
Original assignee: Bowthorpe Hellerman Ltd
Current assignee: Bowthorpe Hellerman Ltd
Priority date: 1989-10-14
Filing date: 1989-10-14
Publication date: 1991-04-17
Anticipated expiration: 2009-10-14
Also published as: GB8923192D0; GB2236866B

Abstract

An optical fibre splice comprises a hollow tube of semi-rigid polymeric material 1 slid over the splice 2 between two optical fibres. A material 5 may be applied to one or both ends of the tube 1 and drawn in by capillary attraction. <IMAGE>

Description

OPTICAL FIBRE SPLICE PROTECTION This invention relates to the protection of an optical fibre fusion splice.

Glass fibres are drawn down in diameter during manufacturing to a very small diameter, typically 125 microns, and an external thin coating of polymer is deposited onto the drawn glass fibre surface. The combination of pure drawn glass and the external polymer coating provides a fibre that is durable when subjected to normal handling and can therefore bend to relatively small radii, typically down to a few centimetres, without damage.

In forming a fusion weld between two optical fibres, the outer coating of polymer is removed over an end portion of each fibre to expose the glass, prior to cleaning with a solvent and loading into a fusion machine.

Once the external polymer coating has been stripped, the fibre is more prone to damage, thus breaking.

This is particularly true of the small zone over the fusion weld where the mechanical properties are inferior to those of the drawn glass.

Splice protectors are applied to such fusion splices to provide a rigid external covering to the delicate fibres avoiding any bending of the fibre for a distance of approximately 15mm on each side of the fusion weld.

There are various known techniques for protecting optical glass fibre fusion welds. They include (a) hollow metal tubes or channel shaped protectors providing a local environment to reduce impact or stress on the fused glass fibres, (b) heatshrink sleeves recovered onto the fibres and having an inner liner which melts and encapsulates the fused glass fibres, and (c) fold-over splice protectors which are hinged and have an eg. adhesive backing to keep them closed.

These conventional techniques have various disadvantages. For example, the hollow metal tubes or channel shaped protectors are expensive to manufacture both in materials and production prrocesses. In addition, metallic components within a cable splicing closure can be detected underground, which is not acceptable for data transmission in military applications.

The heatshrink sleeves recovered onto an inner liner encapsulant require a heat source to recover the external sleeve. This is not always easy to achieve in inaccessible places in external environments, e.g. along a railway line or power distribution line, where a power source cannot be obtained from a service vehicle. Also, heatshrink sleeves are recovered onto both an inner liner and a metal strength member: this is expensive and allows easy detection underground in military applications. The fold-over splice protector is very short in length requiring it to be used in conjunction with a specific type of fusion splicing machine to ensure that the fusion weld is central of the splice protector. This reduces operator's flexibility.In addition, fold-over splice protectors have an adhesive backing to keep the two halfs together, which is prone to opening in hot and humid environments over prolonged periods of time.

In accordance with this invention, there is provided an optical fibre splice having a protective sleeve disposed over it, the sleeve comprising a hollow tube of polymeric material. Preferably the polymeric material of the tube is semi-rigid, e.g. rigid polyethylene or PVC. Typically the length of the sleeve is 40mm. The hollow tube has a small bore slightly greater than the maximum fibre diameter, typically 0.15mm to 1.0mum. The external diameter of the tube or sleeve is typically 3mm to 5mm, allowing approximately 2mm wall thickness providing an optimal stiffness to protect the fibre.

Preferably the fibre is fixed in position, with the fusion weld approximately mid-way along the sleeve, using a sealant either at one or both ends of the splice protector sleeve, or along its length by applying a viscous liquid sealant silicon to one or each end and allowing the liquid to draw itself along the length of the sleeve bore by capillary attraction. For the sealant, cyanoacrylate, a silicon-based substance or a cross-linked acrylate polymer may be used.

Preferably the polymeric material of the sleeve is transparent or semi-transparent and the liquid sealant is coloured so that easy identification can be made by the operator to see how far the liquid has travelled along the sleeve bore in the narrow annular space between the fibre and the sleeve. The liquid sealant when cured or dried acts as a buffer replacing the original polymer coating which has been stripped from the end portions of the spliced fibres. Also in accordance with this invention there is provided a method of installing a protective sleeve over an optical fibre splice, comprising sliding a protective sleeve of polymeric material along one fibre fusion welding two optical fibres, and sliding the polymeric sleeve over the weld.An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a section through an optical fibre splice provided with a splice protector sleeve in accordance with the invention; Figure 2 is a plan view of a splice storage tray; Figure 3 is a section through the tray on the line 'V-V' of Figure 2; and Figure 4 is a plan view of a splice storage tray with a number of splices in position, each splice being provided with a protector sleeve in accordance with this invention.

Referring to Figure 1, a splice protector sleeve 1 is disposed over a fusion weld 2 between two glass fibres 3A, 3B. The polymer coating 4 of each fibre has been removed from an end portion of each fibre before they are welded together, but sealant 5 fills the small annular space between the fibres and the sleeve and replaces the polymer coating over these end lengths.

Figures 2 and 3 show a fibre/splice storage tray having a flat base with a series of parallel ridges between which the splice protector sleeves 1 are disposed, the individual fibres being shown at 6. Figure 4 shows the tray when filled with a plurality of splices 1 and their fibres and an elastic strap 7 fitted across the tray to hold the splices and fibres in position.

The splice protector sleeve 1 comprises a semirigid polymeric material, e.g. rigid polyethylene or PVC. The sleeve may be drawn during extrusion down to the required small bore diameter, of e.g. 0.15mm to 1.00mm. The extrusion is then cut to length, e.g. 40mm.

The splice protector sleeve is fitted by sliding it onto one glass fibre, then fusion welding the two fibres together and then sliding the sleeve back until it is centrally disposed over the weld. Then the sealant is applied to one or both ends of the sleeve, and is drawn in to fill the annular space between the fibres and sleeve by capillary attraction.

The sealant is then allowed to cure or dry. The sealant may comprise cyanoacrylate, a silicon-based substance or a crosslinked acrylate polymer.

Claims

1) An optical fibre splice having a protective sleeve disposed over it, the sleeve comprising a hollow tube of rigid or semi rigid polymeric material.

2) An optical fibre splice as claimed in claim 1, in which the bore of the hollow tube is slightly greater than the maximum optical fibre diameter.

3) An optical fibre splice as claimed in claim 2 in which the bore of the hollow tube is 0.15mm to l.Omm.

4) An optical fibre splice as claimed in any preceding claim in which the external diameter of the sleeve is 3mm - 5mm.

5) An optical fibre splice as claimed in any preceding claim in which the sleeve is positioned mid-way over a fusion weld between the two fibres.

6) An optical fibre splice as claimed in any preceding claim in which a sealant is applied to one or both ends of the sleeve.

7) An optical fibre splice as claimed in claim 6 in which the sealant is silicon based.

8) An optical fibre splice as claimed in claim 6 in which the sealant is a cross-linked polymer.

9) An optical fibre splice as claimed in any one of claims 6 to 8, in which the sealant is coloured.

10! An optical fibre splice as claimed in any preceding claim in which the polymeric material of the sleeve is transparent or semi-transparent.

11) A method of installing a protective sleeve over an optical fibre splice, comprising sliding a protective sleeve of polymeric material along one fibre, fusion welding two optical fibres, and sliding the polymeric sleeve over the weld.

12) A method as claimed in claim 11, in which a viscous liquid sealant is applied to one or both ends of the sleeve, and allowed to draw itself along the length of the sleeve bore by capilliary action.

13) An optical fibre splice substantially as herein described with reference to the accompanying drawings.

14) A method of installing a protective sleeve over an optical fibre splice, the method being as claimed in claim 11 and substantially as herein described.