GB2088578A

GB2088578A - Splicing two overlapping optical fibres

Info

Publication number: GB2088578A
Application number: GB8029097A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1980-09-09
Filing date: 1980-09-09
Publication date: 1982-06-09

Abstract

A method of splicing together two optical fibres 1,2 useful in the field needing a minimum of (unsophisticated) equipment is required. The method consists of overlapping the end lengths of the two fibres so that they lie parallel and in contact with each other and fusing the fibres together at a mid point 37 along the overlapping end lengths, simultaneously forming a controlled kink at the point of fusion. Preferably the kink is controlled to give each end length two bends, each of between 0 DEG and 90 DEG and the two bends being of opposite sense. The splice may be coated in a low refractive index coating to minimise external radiation loss and may be strengthened by encapsulation in a metal coating or by securing the two fibre ends 38,39 with adhesive. <IMAGE>

Description

SPECIFICATION Improvements in or relating to optical fibre splicing The invention relates to optical fibre splicing.

It is possible to identify two types of circumstances which demand the creation of an optical fibre junction, namely the splicing together of fibres and the creation of a coupler.

In general, only a small fraction of light transmitted by an optical fibre is required to be tapped via a coupler whereas in most applications a splice must be capable of transmitting as much light as possible.

In addition to the requirement for low attenuation, it is generally desirable that a splice is also rugged and has a long field life.

Known methods used in splicing include the joining of fibres by an adhesive and also by using heat fusion. Disadvantages involved in the use of adhesives include the need to index-match the fibres and the adhesive and also a tendency for the splice to deteriorate with time, particularly in a harsh environment. In addition, the mechanical stability of suitable adhesives is also highly temperature dependent.

In the laboratory, splicing methods giving low attenuation, but requiring sophisticated techniques are acceptable, whereas, "in the field", there is a requirement for a quick and unsophisticated method with perhaps less stringent constraints on signal attenuation.

Known methods used to splice together two optical fibres require precise axial and lateral alignment of the two fibre ends, light coupling efficiency at the splice being particularly sensitive to relative lateral displacement. As optical fibres in common use are of very small diameter, exact alignment is therefore a precision exercise requiring, usually, a microscope and micromanipulators.

In known methods the splice is also dependent on the fibre ends being properly prepared, end preparation being an inconsistent process.

An object of the invention is to provide a means of splicing together optical fibres which does not demand precision techniques and can be conveniently used outside the laboratory.

According to the present invention there is provided a method of splicing together a first and a second optical fibre including: overlapping an end length ofthefirstfibre in contact along its length with an end length of the second fibre and fusing together the fibres at a mid-point along the overlapping end lengths, simultaneously forming a controlled kink at the point of fusion.

The fibres may be fused by passing the overlapping end lengths through an electric discharge between two pointed rod electrodes or by passing them through a microtorch flame.

The resulting splice may be covered in a lowrefractive index coating in order to reduce external radiation losses and may be strengthened by, for example, applying an adhesive between the overlapping end lengths away from the point of fusion, or by encapsulation in, for instance, a metal envelope.

The splice may be produced by mounting the two fibres in a spring-loaded clamp arrangement so that the fibres are clamped at two positions along their overlapping end lengths with the mid-point lying between the clamping positions. The geometry of the kink may then be controlled by controlling the relative positions of the two clamping positions.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which Figure 1 is a schematic elevation, not to scale, showing end lengths of two optical fibres clamped in a clamping apparatus in order to be spliced. x and z axes are indicated in the diagram for reference.

Figure 2 is a schematic elevation of the arrangement of Figure 1 as seen in the direction indicated by arrow 'A' in Figure 1 and withy and z directions indicated.

Figure 3 shows the optical fibres of Figure 1 after splicing.

In Figure 1 and Figure 2 end lengths of an optical fibre, 1, and of an optical fibre, 2, are shown clamped in a clamping apparatus, 3, in order to be spliced.

The fibres are 125 cm diameter, step-index fibres with silica core and cladding.

Fibres 1 and 2 are in contact along their end lengths and are held in place by clamp elements 4 and 5. Element 4 is mounted on a vertical rod, 6, which is slidably mounted inside a vertical sleeve, 7, the rod, 6 being adjustable in the z direction by course-adjustment screw, 8, and a fine-adjustment screw, 9. Sleeve 7 is slidabley mounted inside a horizontal casing, 10, such that it can move along the casing in they direction under the influence of a course-adjustment screw, 11, and a fine-adjustment screw, 12. Casing 10 is slidably mounted by a mounting, 13, on a rail, 14, which is supported by supports 17 and 18 on a firm base-plate, 19.

Mounting 13 is movable on rail 14 in the x direction under the influence of a course-adjustment screw 15.

Clamping element 5 is mounted on rail 14 by a fixed vertical support rod, 20.

Clamp element, 4, as shown in more detail in Figure 2, comprises a supporting shell, 28, containing wedges 29 and 30 held in place by sprung supports 31 and 32 respectively and movable by adjusters 33 and 34 respectively which are movable in the directions shown by arrows 35 and 36 respectively. Optical fibres 1 and 2 are held firmly in position by the spring-supported wedges 29 and 30.

Clamp element 5 is of the same construction.

The clamping apparatus, 3, is prepared prior to inserting the fibres 1 and 2 for splicing by setting the position of clamp element 4 by means of the screw adjustments to give a geometry which has been predetermined as optimum for the type of fibre being used.

With fibres 1 and 2 clamped in place, a microtorch (not shown in the drawings) is introduced from the direction indicated by arrow B in Figure 2 so that its flame traverses a mid-point, 37, of the clamped fibres (as shown in Figure 1) in order to fuse them together at this point.

Figure 3 shows fibres 1 and 2 after fusion and on completion of the splice. The geometry assumed by the fibres during fusion has been so as to create a kink in the region of point 37 such that the displacement, h, is of the order of the diameter of the fibre.

Initial experimental results with this geometry has produced a splice with good light coupling efficiency.

If a force is applied to the fused fibres in the direction shown by arrows 40 and 41 the forces acting at the kink are not purely tensile, there being a shear element present. The kink therefore presents a weakness. In orderto alleviate the problem quicksetting epoxy adhesive is applied at end points 38 and 39. The adhesive is pulled by capillary action between fibres 1 and 2 at either side of the fusion point, 37, and sets to produce a rigid structure.

Having spliced together two fibres with the clamping apparatus set up according to the predetermined optimum geometry, they may be removed and a second similar pair of fibres inserted for splicing with a minimum of difficulty and without there being any need for readjustment of the clamp element, 4.

The method described above is particularly advantageous as there is no need for an operator using the clamping apparatus to perform a complex programme of set procedures or use special viewing aids in conjunction with micro-manipulators in order to accomplish a splice as is necessary in prior art methods.

Splicing according to the above-directed method is therefore an unsophisticated process requiring simple and portable apparatus. The apparatus is particularly convenient for use "in the field" as it provides a clamp with a geometry preset according to the type of fibre to be spliced which allows splicing without the necessity for a skilled operator.

The invention is not confined to the details outlined in the above-described embodiment, variations within the scope of the invention being apparent to those skilled in the art. The fusion device may, for instance, be an electric arc discharge instead of a microtorch. Greater control of the fusion parameters are possible using the electrical method and less skill of an operator is required, but at the cost of more bulky apparatus.

A more complex apparatus may include a motor drive for the microtorch flame so that traversal of the flame across the fibres may be automatically controlled.

Other configurations of the kink in the spliced fibres are possible. The radius of curvature of the bends in a double-bend configuration may, for instance, be varied, or height, h, may be varied or both.

A less complex apparatus may include two fixed clamp elements as opposed to one fixed and one adjustable clamp element, the two fixed elements being disposed with an optimum geometry for use with a specified type of optical fibre.

CLAIMS (Filed 24Aug. 1981) 1. A method of splicing together a first and a second optical fibre including overlapping an end length of the first fibre in contact along its length with an end length of the second fibre and fusing together the fibres at a mid point along the overlapping end lengths, simultaneously forming a controlled kink at the point of fusion.

2. A method of splicing together a first and a second optical fibre as claimed in Claim 1 which additionally includes the step of securing the ends of both fibres to the splice by application of adhesive between the end of the first fibre and its point of contact with the second fibre and between the end of the second fibre and its point of contact with the first fibre.

3. A method of splicing together a first and a second optical fibre as claimed in either of the previous claims wherein the splice is additionally encapsulated in a low refractive index coating.

4. A method of splicing together a first and a second optical fibre as claimed in any of Ciaims 1 to 3 additionally including the step of encapsulating the splice in a metal coating.

5. A method of splicing together a first and a second optical fibre as claimed in any previous claim wherein the kink is such as to give each end length two bends, each of between 0 and 90 and the two bends being of opposite sense.

6. A method of splicing together a first and a second optical fibre as claimed in Claim 5 wherein the two bends in each fibre are dispersed from each other by one fibre diameter.

7. A spliced pair of optical fibres spliced together by a method as claimed in any previous claim.

8. A method of splicing together a first and a second optical fibre substantially as herein described with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the fibres during fusion has been so as to create a kink in the region of point 37 such that the displacement, h, is of the order of the diameter of the fibre. Initial experimental results with this geometry has produced a splice with good light coupling efficiency. If a force is applied to the fused fibres in the direction shown by arrows 40 and 41 the forces acting at the kink are not purely tensile, there being a shear element present. The kink therefore presents a weakness. In orderto alleviate the problem quicksetting epoxy adhesive is applied at end points 38 and 39. The adhesive is pulled by capillary action between fibres 1 and 2 at either side of the fusion point, 37, and sets to produce a rigid structure. Having spliced together two fibres with the clamping apparatus set up according to the predetermined optimum geometry, they may be removed and a second similar pair of fibres inserted for splicing with a minimum of difficulty and without there being any need for readjustment of the clamp element, 4. The method described above is particularly advantageous as there is no need for an operator using the clamping apparatus to perform a complex programme of set procedures or use special viewing aids in conjunction with micro-manipulators in order to accomplish a splice as is necessary in prior art methods. Splicing according to the above-directed method is therefore an unsophisticated process requiring simple and portable apparatus. The apparatus is particularly convenient for use "in the field" as it provides a clamp with a geometry preset according to the type of fibre to be spliced which allows splicing without the necessity for a skilled operator. The invention is not confined to the details outlined in the above-described embodiment, variations within the scope of the invention being apparent to those skilled in the art. The fusion device may, for instance, be an electric arc discharge instead of a microtorch. Greater control of the fusion parameters are possible using the electrical method and less skill of an operator is required, but at the cost of more bulky apparatus. A more complex apparatus may include a motor drive for the microtorch flame so that traversal of the flame across the fibres may be automatically controlled. Other configurations of the kink in the spliced fibres are possible. The radius of curvature of the bends in a double-bend configuration may, for instance, be varied, or height, h, may be varied or both. A less complex apparatus may include two fixed clamp elements as opposed to one fixed and one adjustable clamp element, the two fixed elements being disposed with an optimum geometry for use with a specified type of optical fibre. CLAIMS (Filed 24Aug. 1981)

1. A method of splicing together a first and a second optical fibre including overlapping an end length of the first fibre in contact along its length with an end length of the second fibre and fusing together the fibres at a mid point along the overlapping end lengths, simultaneously forming a controlled kink at the point of fusion.