GB2373591A

GB2373591A - Optic fibre spliced joint with time dependent coating

Info

Publication number: GB2373591A
Application number: GB0106758A
Authority: GB
Inventors: Christopher Mark Hardingham
Original assignee: Marconi Caswell Ltd; Marconi Applied Technologies Ltd
Current assignee: Marconi Caswell Ltd; Teledyne UK Ltd
Priority date: 2001-03-19
Filing date: 2001-03-19
Publication date: 2002-09-25
Also published as: WO2002075397A2; AU2002242845A1; GB0106758D0; WO2002075397A3

Abstract

A method of identifying a spliced joint 6,8 in an optical fibre 7,9 by including on or adjacent the joint 6,8 a time-dependent dye or coating, the visual characteristics of which vary over time. An optic fibre amplifier is also disclosed. The invention also discloses a spliced joint 6,8 in an optical fibre 7,9 which has on or adjacent the joint 6,8 a time-dependent dye or coating, the visual characteristics of which vary over time.

Description

OPTICAL FIBRE AMPLIFIER

The present invention relates to an optical fibre amplifier, that is a light signal amplifier which does not need to convert the light signal to an electrical signal for amplification purposes. The invention also relates to improvements in methods of manufacturing such amplifiers.

As is known, when using optical fibre for data transmission or telecommunications, there is unavoidable loss of light occurring inside the optical fibre because a gradual attenuation of the signal takes place along the path of the optical fibre. It is therefore necessary when the optical signal has to be transmitted for long distances to use one or more optical fibre amplifiers which are spaced along the length of the optical fibre at determined distances. In this way, the signal being transmitted along the fibre is boosted periodically to avoid the signal being degraded to such an extent that signal transmission strength is reduced to a level below which it is impossible to capture the data at the destination.

The optical fibre amplifier includes a number of components which must be joined optically both to each other and to the main data transmission optical fibre and this is achieved by a technique of fusing the glass fibres together which is known as splicing.

In order to optically join components together, each component has, for each light input or output, a so-called pigtail, which consists of length of optical fibre typically about 1 m long. The end of this pigtail is joined to, for example, the main optical fibre or a pigtail of another component in a splicing machine, which is a well-known technique.

There are two reasons why it is necessary for the pigtail to be quite long. The first is that the fused joints may not be optically efficient enough when the fully assembled product is tested. With the long pigtail, it is possible to cut out a defective joint, sacrificing about 15 cm of fibre, and then splice the two cables together again. It is possible to do this several times to obtain an efficient joint. Secondly, it is also necessary for a free length of fibre to be available, since once a component has been secured in the casing, it is necessary to move its pigtail and the fibre to which it is to be joined outside the casing and into an adjacent splicing machine.

Since there are a number of components in the amplifier, there is a large number of optical fibres which must be neatly stored in the amplifier case without any sharp bends which would damage the fibre and reduce the efficiency of light transmission. To achieve this, the casing contains one or more drums or annular walls around which spare optical fibre is wound. Typically, six or more different fibres may be wound round each drum in the completely assembled amplifier. In practice, it is possible to test the amplifier properly only when it is fully assembled. If at that stage, the test reveals a deficiency in a particular joint, it is necessary to first locate and then remove the pigtail manually to enable the faulty splice to be cut out and the two fibres rejoined.

The present invention seeks to provide a method of more readily identifying joints visually which testing has indicated are deficient.

According to the present invention there is provided a method of identifying a spliced joint in an optical fibre by including on or adjacent the joint, a time-dependent dye or

coating, the visual characteristics of which vary over time.

The present invention also provides a spliced joint in an optical fibre which has on or adjacent the joint a time-dependent dye or coating, the visual characteristics of which vary over time.

In this way, by keeping a check on the sequence in which the various spliced joints are made, it will be easier to visually locate a particular joint for correction.

The present invention will now be described by way of example, with reference to the accompanying drawing in which : Figure 1 shows a schematic view of an amplifier, and Figure 2 shows a plan view of a casing for the amplifier.

Referring to Figure 1, there is shown in schematic form, an optical fibre amplifier utilising two pump lasers 1 and 2. The components in the amplifier can be conveniently divided into three groups 3, 4 and 5. Group 3 consists of optical components including two dichroic couplers, two active optical fibre coils and directional couplers, group 4 consists of opto-electronic components and group 5 consists of electronic control circuitry. The opto-electronic components in group 4 are optically connected by means of spliced joints to the optical fibres in group 3 and electrically to the control circuitry in group 5. The amplifier is connected through a spliced joint 6 to the main data

transmission input fibre 7 and through a splicing joint 8 to an output optical fibre 9. The remaining components in group 3 are connected optically by means of further spliced joints indicated by crosses 10.

The component parts of the amplifier are mounted in the amplifier casing and their optical or electrical leads are connected, as required, in a particular sequence in accordance with a strict procedure. Typically, each of the pig tails and optical fibres to be joined together are colour-coded to ensure that the correct connections are made.

The colour coding typically is on paper or plastic tags attached to the fibres. These tags are inconvenient and get in the way of assembling the components, particularly at the stage of coiling the optical fibres into the casing and are removed by the assembler as soon as possible.

Since there are a number of components in the amplifier, there is a large number of optical fibres, some of considerable length, which must be neatly stored in the amplifier case without any sharp bends which would damage the fibre and reduce the efficiency of light transmission. To achieve this, the casing contains typically two drums 10,11 or annular walls around which spare optical fibre is wound. Typically, six or more different fibres may be wound round each drum in the completely assembled amplifier.

In practice, it is possible to test the amplifier properly only when it is fully assembled.

If at that stage, the test reveals a deficiency in a particular joint, it is necessary to first locate and then remove the pigtail manually to enable the faulty splice to be cut out and the two fibres rejoined.

The optical fibre 9 consists of a central silica core of about seven microns diameter surrounded by sleeve of about 120 microns. The sleeve is encased by an outer coating of a polymer resin which both protects the silica core and sleeve from damage and also assists in giving a degree of flexibility to the fibre. The overall diameter of the polymer coating is of the order of 250 to 400 microns. In order to prepare the fibre for splicing, some of the polymer coating must be removed from the ends of each of the two fibres to be joined. The coating can be removed by chemical dipping, mechanical stripping or heating to melt a portion of the coating. The two ends are then placed in a splicing machine for fusing together.

After splicing, the bare silica portion is coated with a material that protects the silica in the same manner as the polymer but is visually distinct so that it is possible to easily spot the presence of a splice even on the very fine fibre. The material used is a timedependent dye or paint so that it fades or otherwise changes colour, for example, over a 24-hour period. Since all of the splicing of the fibres is carried out in a laid down, predetermined sequence, which lasts typically for several hours, it is possible to see from the colour of the material surrounding a splice the particular place in the sequence in which the splicing has been carried out. Therefore, if the testing indicates that a particular splice is inadequate, the position of that splice in the predetermined sequence is known. Knowing its position in the sequence and knowing the total degree of colour variation which has taken place since the sequence was started, it is possible to determine quite simply by visual inspection which of the many splices has the particular colour variation indicative of that position in the sequence. The person repairing the splice can then easily remove that splice from the casing.

A further advantage of each splice being indicated by a different colour from the main outer coating polymer, is that it is possible for the person assembling the amplifier to keep each splice in a straight path as the fibre is being laid up in the casing. This has the advantage of increasing the reliability of the amplifier since it is known that having a splice stored in a coil increases the stress on the splice joint since it is forced into a curve. This can lead to premature failure of the splice.

Claims

CLAIMS 1. A method of identifying a spliced joint in an optical fibre by including on or adjacent the joint, a time-dependent dye or coating, the visual characteristics of which vary over time.
2. A method of splicing optical fibre, including the step of coating fibre on or adjacent the joint with a time-dependent dye or coating, the visual characteristics of which vary over time.
3. A spliced joint in an optical fibre which has on or adjacent the joint a timedependent dye or coating, the visual characteristics of which vary over time.
4. A method of identifying a spliced joint in an optical fibre substantially as described herein with reference to, and as illustrated in, the accompanying drawings.
5. A method of splicing optical fibre substantially as described herein with reference to, and as illustrated in, the accompanying drawings.
6. A spliced joint in an optical fibre, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.
7. Optical fibre including a spliced joint as claimed in claim 3 or 6.
8. An optical fibre amplifier including optical fibre as claimed in claim 7.
9. An optical communications system including optical fibre as claimed in claim 7.