GB2198859A

GB2198859A - Optical fibre assembly of robust construction

Info

Publication number: GB2198859A
Application number: GB08727187A
Authority: GB
Inventors: Martin Alexander Haley
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1986-12-13
Filing date: 1987-11-20
Publication date: 1988-06-22
Anticipated expiration: 2007-11-20
Also published as: GB2198859B; GB8727187D0; GB8629842D0

Abstract

An optical fibre assembly is made by inserting a tube 4 of deformable polymeric material e.g. polytetrafluoroethylene, into an outer metal sleeve 10. The outer sleeve is then mechanically deformed, e.g. swaged down, to produce elongation and contraction of its width, thereby compressing the tube 4. At least one optical fibre 1, which may be lubricated, is then inserted in at least one bore 3 through the tube 4 which supports it along its length. Electrical wires optionally extend alongside the fibre(s). <IMAGE>

Description

OPTICAL F B RE ASSEMBLIES AND ThEIR MANTFACTURE This invention relates to optical fibre assemblies and to methods of manufacture of optical fibre assemblies.

Optical fibres are being increasingly used as a communication medium and for conveying optical radiation to sensors, such as in pyrometry apparatus.

Optical fibres have several advantages. They can, for example, be lighter and more compact that the equivalent coaxial electrical cable needed to carry the same information. They are also immune from electrical interference and have safety advantages, because damage to an optical cable will not lead to sparking as is possible with electrical cables.

Optical fibre cables, however, do have a disadvantage in that they can be more susceptible to damage because of the relatively fragile nature of glass materials used in their construction.

It is an object of the present invention to provide a method of making an optical fibre assembly of robust construction that is protected from damage.

According to one aspect of the present invention there is provided a method of making an optical fibre assembly comprising the steps of providing an outer metal sleeve, inserting a filling of deformable polymeric material within said sleeve, subjecting the outer sleeve to mechanical deformation such as to produce elongation of the outer sleeve along its length and contraction of its width thereby to compress the filling in the outer sleeve and prevent subsequent displacement between the outer sleeve and the filling, and supporting an optical fibre by said filling to extend along the outer sleeve.

The or each optical fibre is preferably inserted in the filling after the step of deforming the outer sleeve. The mechanical deformation may be carried out by swaging. The mechanical deformation is preferably arranged such as to produce no substantial elongation of the filling.

According to another aspect of the present invention there is provided an optical fibre assembly made by a method according to the above one aspect of the invention.

According to a further aspect of the present invention there is provided an optical fibre assembly comprising an outer metal sleeve deformed about a compressed filling of a deformable polymeric material within the sleeve and an optical fibre extending along the outer sleeve supported by the filling.

The filling is preferably a tube with a solid wall having one or more bores extending along its length through which extend the or each optical fibre. The or each bore preferably supports a single fibre only. The filling may be of polytetrafluoreothylene. The or each optical fibre may have a lubricating layer on its surface such as of polytetrafluoroethylene. The assembly may include an electrical wire extending alongside the or each fibre which is broken when the fibre is damaged.

An optical fibre cable assembly and its method of manufacture, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional side-elevation of a part of the cable assembly; Figure 2 is a transverse section through the cable along the line II - II, to a larger scale.

Figures 3 illustrate two steps in the manufacture of the and 4 cable; and Figure 5 is a transverse section through a modified cable.

The optical fibre assembly includes a single optical fibre 1 that extends axially, centrally along the length of the assembly. The fibre 1 is of conventional construction being of glass and with an external diameter of about 100 - 300 micron.

The fibre 1 may be coated on its outer surface with a lubricating layer 2 of polytetrafluoreothylene, although other lubricants could be used. The lubricating layer 2 enables the fibre 1 to slide freely along the bore 3 of a filling 4. The filling 4 is in the form of a capillary tube with a solid continuous wall of polymeric material such as polytetrafluoroethylene. The bore 3 of the tube 4 is just large enough to accommodate the fibre 1 as a relatively loose fit.

The filling tube 4 extends axially, as a tight fit along the bore 9 of an outer metal sleeve 10 of external diameter about 6mm and an internal diameter of about 4mm. The tight fit of the filling tube 4 in the sleeve 10 prevents relative displacement between the tube and sleeve.

Opposite ends 20 and 30 of the assembly may be terminated by metal ferrules (not shown) welded to both the inner and outer sleeves so as to retain the filling 4 in the assembly. Various other arrangements could be used for sealing the filling 4 in the assembly and the fibre 1 in the filling.

The assembly provides a high degree of protection to the fibre 1. The outer metal sleeve and the continuous filling make the assembly stiff to bend and limit its radius of curvature, thereby protecting the fibre from damage and transmission loss that can otherwise be caused by small radius curves.

The fibre 1 will also be protected from crushing because of the extra strength provided by the thickness of the filling.

Because the filling 4 is of a thermally-insulative material, the fibre 1 will be protected from the effects of high temperature and rapid temperature changes. The effects of localised high temperatures on the assembly are also reduced by making the outer sleeve of a metal or other heat conducting material which helps dissipate the heat over a longer length of the cable assembly.

The assembly is manufactured in the manner shown in Figures 3 and 4 by first threading the polymeric tube 4 into the outer sleeve 10 (Pigure 3) and then swaging down the outer sleeve 10 slightly in a swaging machine 50 (Figure 4) to reduce its diameter, thereby producing some elongation of the outer sleeve. This results in slight compression of the solid filling 4 to ensure that there is no subsequent differential displacement between the outer sleeve 10 and the filling. Other mechanical deformation processes, such as drawing, could alternatively be used to reduce the diameter of the outer sleeve. The swaging process is selected to be sufficient to produce compression of the filling 4 without producing any significant elongation of the filling. The fibre 1, is then threaded along the bore 3 of the filling 4.

Alternatively, the fibre could be threaded along the inner sleeve prior to swaging, although this could make some fibres prone to damage during the swaging process.

The assembly is now complete and its ends 20 and 30 are capped by the ferrules (not shown).

More than one fibre could be incorporated in the cable. These could either extend along the same bore in the filling or each have their own respective bore, as shown in Figure 5. The cable shown in Figure 5 has four fibres 41 to 44 each of which extend along a respective bore 51 to 54. The bores 51 to 54 are equally disposed around the filling 40 in the outer sleeve 60 of the cable.

An electrical wire may extend within the assembly alongside the fibres to check the status of the fibres. Any damage to the fibres, which also breaks the wire, will be indicated by an increase in electrical resistance.

Claims

1. A method of making an optical fibre assembly comprising the steps of providing an outer metal sleeve, inserting a filling of deformable polymeric material within said sleeve, subjecting the outer sleeve to mechanical deformation such as to produce elongation of the outer sleeve along its length and contraction of its width thereby to compress the filling in the outer sleeve and prevent subsequent displacement between the outer sleeve and the filling, and supporting an optical fibre by said filling to extend along the outer sleeve.

2. A method according to Claim 1, wherein the or each optical fibre is inserted in said filling after the step of deforming the outer sleeve.

3. A method according to Claim 1 or 2, wherein the mechanical deformation is carried out by swaging.

4. A method according to any one of the preceding claims, wherein the mechanical deformation is arranged such as to produce no substantial elongation of the filling.

5. A method substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

6. A method substantially as hereinbefore described with reference to Figures 1 to 4 as modified by Figure 5 of the accompanying drawings.

7. An optical fibre assembly made by a method according to any one of the preceding claims.

8. An optical fibre assembly comprising an outer metal sleeve deformed about a compressed filling of a deformable polymeric material within the sleeve and an optical fibre extending along the outer sleeve supported by the filling.

9. An optical fibre assembly according to Claim 7 or 8, wherein the filling is a tube with a solid wall having one or more bores extending along its length through which extend the or each optical fibre.

10. An optical fibre assembly according to Claim 9, wherein the or each bore supports a single fibre only.

11. An optical fibre assembly according to any one of Claims 7 to 10, wherein the filling is of polytetrafluoroethylene.

12. An optical fibre assembly according to any one of Claims 7 to 11, wherein the or each said optical fibre has a lubricating layer on its surface.

13. An optical fibre assembly according to Claim 12, wherein the said lubricating layer is of polytetrafluorethylene.

14. An optical fibre assembly according to any one of Claim 7 to 13, wherein the assembly includes an electrical wire extending alongside the or each fibre which is broken when the fibre is damaged.

15. An optical fibre assembly substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

16. An optical fibre assembly substantially as hereinbefore described with reference to Figures 1 to 4 as modified by Figure 5 of the accompanying drawings.