GB2179467A

GB2179467A - Optical fibre cable joint

Info

Publication number: GB2179467A
Application number: GB08520647A
Authority: GB
Inventors: Alan James Brewster
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1985-08-17
Filing date: 1985-08-17
Publication date: 1987-03-04
Also published as: GB8520647D0

Abstract

An optical fibre cable joint uses a rigid, e.g., stainless steel, over-tube (1) with a centrally-located resilient plastics sleeve (2) inside it. Each termination is provided with a stepped extension tube (5) from which the fibre plus its coating 4 projects. To make the joint the terminations are fitted into opposite ends of the over-tube 1 plus sleeve 2 until the stepped portions of the extension tubes (5) abut the ends of the over-tube (1). In this condition the optical fibre ends are close to, or in engagement with, each other, and the fibre ends are firmly gripped by the sleeve (2). <IMAGE>

Description

SPECIFICATION Optical fibre joint This invention relates to a low-loss permanent joint between optical fibres.

To produce a high performance optical connection in laboratory conditions usually calls for the use of precision ferrules, precision alignment, and high temperature curing epoxy resins. Under field conditions, however, dirt, moisture and draughts limit the use of such "wet" jointing especially when it has to be done by semi-skilled technicians. An object of the invention is to enable such connections to be made in the field without suffering under such constraints.

According to the invention, there is provided a joint between two optical fibre cables, in which the end of each of the two cables to be jointed is provided with a stepped extension tube from one end of which the fibre in its primary coating projects, in which the diameter of the extension tube is less at its end from which the fibre projects than in the adjoined region, in which a rigid overtube is provided within which there is a sleeve of a resilient plastics material which is located substantially centrally of the overtube, in which the terminations are each fitted into one end of the overtube until the steps on the extension tubes abut against the respective ends of the overtube, when the termination ends are firmly gripped by the plastics sleeve.

With such an arrangement, there are no blind bores to trap dirt and no epoxy resins or other adhesives to affect the yield.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the combination of a metal overtube and plastics alignment sleeve.

Figure 2 shows the arrangement of one of the terminations used in a connection embodying the invention.

Figure 3 shows the in-line joint assembled before being subjected to compression.

We refer first to Fig. 1, which shows the rigid metal over-tube 1, which in the present case is made of stainless steel and contains a resilient plastics, in this case PTFE, alignment sleeve 2, whose inner bore has a diameter such as to receive the fibre. In the arrangement for which the present arrangement was designed, the fibre is a large core fibre having both primary and secondary coatings. The outer diameter of the primary coated fibre is about 0.5mm.

The alignment sleeve 2, as shown, is shorter than, and centrally located in the over-tube 1, and its ends are bevelled as shown, to facilitate fibre entry from the two ends.

Before a joint is made, each of the two cable ends is prepared so that it is as shown in Fig. 2. The cable end is prepared so that we have the primary coated fibre 4 projecting from the end, with a stepped extension tube 5, also of metal such as stainless steel, fitted over the fibre's secondary coating 6. Between the extension tube 5 and the cable jacket 7 there is a braiding or the like 8 of a material such as Kevlar (Registered Trade Mark). The cable jacket is fitted to a crimp ring 9, whose bore receives the extension tube 5 and the braiding 8. This braiding is then turned back over the crimp ring 9, and a crimp cap 10 fitted over as shown to the trap the braiding.

The extension tube plus fibre end then projects from the end of the crimp cap.

Two such terminations are joined to produce the result shown in Fig. 3, which shows it before compression. It should be noted in passing that all three of the figures are to a different scale, but in the present arrangement, the dimension D1, Fig. 2, is 1 1mum and D2, Fig. 2, is 4mm.

The two terminations are fitted into opposite ends of the over-tube 1 plus sleeve 2, as shown in Fig. 3, and when this is done, the extension tubes 5 and 5' locate in the overtube, comprising the ends of the sleeve 2. As the outside diameter of the sleeve 2 is constrained by the over-tube 1, the bore of the sleeve collapses to increase the grip on the fibre. This takes up any clearance between the fibre and bore, thus producing a low loss joint. The stepped extension tubes then butt on to the end of the over-tube, which ensures that the terminations cannot be pushed too far into the over-tube. This prevents axial compression failure of the fibre in the tube.

In Fig. 3 it will be seen that when the terminations are fitted but before compression, there is a small fibre face separation 12, which allows preload travel 13.

With such an arrangement, the use of the PTFE sleeve alignment ensures that the primary coated fibres are aligned immediately upon preparation to protect them from damage or contamination. Thus this method of jointing, which can conveniently be called a non-fusion splice, is especially suited to damage repair. For factory looming terminations, a "pot and polish" epitaxial ferrule offers long term storage protection from damage and grow out". Grow out is not a problem with the new arrangement, as the two aligned fibres support each other's grow out force.

The poiishing process used in the termination preparation creates a square and flat face, capable of sustaining very high loads applied gradually.

The extension tubes are not symmetrical, as can be seen from Fig. 2, which avoids the risk of these being fitted back-to-front.

1. A joint between two optical fibre cables, in which the end of each of the two cables to be jointed is provided with a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical fibre joint This invention relates to a low-loss permanent joint between optical fibres. To produce a high performance optical connection in laboratory conditions usually calls for the use of precision ferrules, precision alignment, and high temperature curing epoxy resins. Under field conditions, however, dirt, moisture and draughts limit the use of such "wet" jointing especially when it has to be done by semi-skilled technicians. An object of the invention is to enable such connections to be made in the field without suffering under such constraints. According to the invention, there is provided a joint between two optical fibre cables, in which the end of each of the two cables to be jointed is provided with a stepped extension tube from one end of which the fibre in its primary coating projects, in which the diameter of the extension tube is less at its end from which the fibre projects than in the adjoined region, in which a rigid overtube is provided within which there is a sleeve of a resilient plastics material which is located substantially centrally of the overtube, in which the terminations are each fitted into one end of the overtube until the steps on the extension tubes abut against the respective ends of the overtube, when the termination ends are firmly gripped by the plastics sleeve. With such an arrangement, there are no blind bores to trap dirt and no epoxy resins or other adhesives to affect the yield. An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the combination of a metal overtube and plastics alignment sleeve. Figure 2 shows the arrangement of one of the terminations used in a connection embodying the invention. Figure 3 shows the in-line joint assembled before being subjected to compression. We refer first to Fig. 1, which shows the rigid metal over-tube 1, which in the present case is made of stainless steel and contains a resilient plastics, in this case PTFE, alignment sleeve 2, whose inner bore has a diameter such as to receive the fibre. In the arrangement for which the present arrangement was designed, the fibre is a large core fibre having both primary and secondary coatings. The outer diameter of the primary coated fibre is about 0.5mm. The alignment sleeve 2, as shown, is shorter than, and centrally located in the over-tube 1, and its ends are bevelled as shown, to facilitate fibre entry from the two ends. Before a joint is made, each of the two cable ends is prepared so that it is as shown in Fig. 2. The cable end is prepared so that we have the primary coated fibre 4 projecting from the end, with a stepped extension tube 5, also of metal such as stainless steel, fitted over the fibre's secondary coating 6. Between the extension tube 5 and the cable jacket 7 there is a braiding or the like 8 of a material such as Kevlar (Registered Trade Mark). The cable jacket is fitted to a crimp ring 9, whose bore receives the extension tube 5 and the braiding 8. This braiding is then turned back over the crimp ring 9, and a crimp cap 10 fitted over as shown to the trap the braiding. The extension tube plus fibre end then projects from the end of the crimp cap. Two such terminations are joined to produce the result shown in Fig. 3, which shows it before compression. It should be noted in passing that all three of the figures are to a different scale, but in the present arrangement, the dimension D1, Fig. 2, is 1 1mum and D2, Fig. 2, is 4mm. The two terminations are fitted into opposite ends of the over-tube 1 plus sleeve 2, as shown in Fig. 3, and when this is done, the extension tubes 5 and 5' locate in the overtube, comprising the ends of the sleeve 2. As the outside diameter of the sleeve 2 is constrained by the over-tube 1, the bore of the sleeve collapses to increase the grip on the fibre. This takes up any clearance between the fibre and bore, thus producing a low loss joint. The stepped extension tubes then butt on to the end of the over-tube, which ensures that the terminations cannot be pushed too far into the over-tube. This prevents axial compression failure of the fibre in the tube. In Fig. 3 it will be seen that when the terminations are fitted but before compression, there is a small fibre face separation 12, which allows preload travel 13. With such an arrangement, the use of the PTFE sleeve alignment ensures that the primary coated fibres are aligned immediately upon preparation to protect them from damage or contamination. Thus this method of jointing, which can conveniently be called a non-fusion splice, is especially suited to damage repair. For factory looming terminations, a "pot and polish" epitaxial ferrule offers long term storage protection from damage and grow out". Grow out is not a problem with the new arrangement, as the two aligned fibres support each other's grow out force. The poiishing process used in the termination preparation creates a square and flat face, capable of sustaining very high loads applied gradually. The extension tubes are not symmetrical, as can be seen from Fig. 2, which avoids the risk of these being fitted back-to-front. CLAIMS

1. A joint between two optical fibre cables, in which the end of each of the two cables to be jointed is provided with a stepped extension tube from one end of which the fibre in its primary coating projects, in which the diameter of the extension tube is less at its end from which the fibre projects than in the adjoined region, in which a rigid overtube is provided within which there is a sleeve of a resilient plastics material which is located substantially centrally of the overtube, in which the terminations are each fitted into one end of the overtube until the steps on the extension tubes abut against the respective ends of the overtube, when the termination ends are firmly gripped by the plastics sleeve.

2. A joint as claimed in claim 1, in which the plastics sleeve is of PTFE and the overtube and the extension tubes are of stainless steel.

3. A joint as claimed in claim 1 or 2, in which the ends of the plastics sleeve are bevelled, to facilitate entry of the fibre ends.

4. A joint as claimed in claim 1, 2 or 3, in which the fibre has a primary and a secondary coating, the secondary coating being removed from the portion of the fibres which project from the respective extension tube.

5. A joint between two optical fibre cables, substantially as described with reference to the accompanying drawings.