GB2277605A - Holder for fibre optic bundles and a light source - Google Patents

Abstract

A holder holds fused fibre ends 19 of several optical fibre bundles in a close-packed arrangement and a light source 14. Metal ferrules 18 and heat sinks 8 are shown. In one arrangement, the end faces are rectangular and arranged radially of a linear light source 14, and the end faces abut. In an alternative embodiment, the end faces are arranged in a plane in the area of a focal point of an ellipsoidal mirror (32, Fig 5), the light source being located at the other focal point so that the light is reflected onto the end faces (36, Figs. 5, 6), which are hexagonal. <IMAGE>

Description

Improvements Relating to Fibre Optics This invention relates to fibre optics The invention is particularly, although not exclusively, concerned with fibre optic illumination systems.

Fibre optic lighting systems normally consist of a single intense light source, connected to which is a fibre optic harness. The harness consists of one common end termination in which all fibres are tightly packed, polished and held in alignment with the light source. The other end of the harness consists of multiple tails each of which may have focusing lenses and be of lengths up to fifteen metres and of various diameters, depending on the required light distribution. Such an arrangement has advantages in maintenance, safety and intrinsic safety. Typical applications are:- A. High ceiling buildings, stairways etc with poor access.

B. Retail illumination areas with multiple low voltage lighting when lamp failure is unacceptable to company image and expensive in life cycle maintenance costs.

C. Areas requiring intrinsic safety such as mining, munitions etc.

D. Low temperature areas where cold lighting is beneficial.

In the common end fibre optic lighting system the light source consists of typically a low voltage quartz halogen bulb with a semi-ellipsoidal dichroic reflector, or a miniature metal halide discharge lamp in a semi-ellipsoidal reflector, either of which result in a light spot centred on the second focus of the elliposiod. The single terminated end of the fibre optic harness is presented to a point near the second focus such that light from the lamp is effectively launched into the fibres.

In reality the efficiency of this system is surprisingly low due to factors such as imperfect reflector shape and surface finish, finite size of the lamp and beam aberrations due to the lamp envelope, poor packing fraction of fibres within the single end, imperfect fibre parallelism, and many other factors. Many of these factors are exaggerated by the large physical size of reflectors in normal use, which result in poor spot formation at the second focus. These large reflectors are normally used to be compatible with lamp dimensions and, in particular, to allow air cooling to be blown across the common end fibres and across the bulb envelope.

In the art of fibre optic lighting systems, terminated ends of cables which are provided in a harness are normally manufactured using an epoxy resin matrix. Epoxy resins are restricted to operating temperatures between 150 and 2000C maximum. In order not to exceed this temperature when using a high power light source it is -normally necessary to distance the common end from the light source and to introduce an air cooling system and/or to introduce an infra red filter between the lamp/reflector and the common end or harness.

Each system has a custom made harness with lengths and diameters of each tail preset at the manufacturing stage and permanently joined together at a common end facing the light source. Such a harness can be very cumbersome with typically ten to twenty tails, each up to fifteen metres long weighing tens of kilograms. Should damage occur to an individual fibre tail or some changes be required to the configuration of the multipoint lighting system, then the whole harness can often need replacement at considerable cost. Furthermore the installation of a complex and heavy harness can be a difficult task.

One known method of reducing the spacing between fibres in a bundle end is to fuse the fibre ends without the use of a matrix, by a heating and compresing method. The fibre ends are deformed in the process to eliminate to a large extent undesirable spacing between the fibre ends, and the bundle end may be cut and polished to provide an end which is better adapted for receiving light.

The use of fused fibre ends has been confined to specialised areas of application, and is mainly used in the field of temperature sensing. In this common application, a thin bundle of fibres terminated by fusion is inserted into a heated area, for example a furnace, and light sensing apparatus outside the furnace and connected to the other end of the bundle are used to monitor the temperature of the furnace. Although these ends are generally cylindrical in form, and consist of relatively small numbers of fibres, there appears to be no reason why it should not be possible to manufacture fused fibre ends in larger sizes and in a variety of forms.

It is an object of the invention to provide a fibre optic lighting apparatus whereby a significantly greater proportion of the light produced by a source is collected by the fibre optic arrangement, and an improved efficiency is obtained over the prior art.

A further object of the invention is to improve the versatility of such an apparatus and to reduce the cost of replacement in the event of damage to any of the fibre optic bundles.

According to the present invention there is provided an apparatus comprising a holding means and a plurality of fibre optic bundles each having a fused end with an end face, the holding means being adapted to arrange respectively the fused ends and a light source so that the end faces receive light emanating from the source.

The holding means is preferably adapted to arrange the fused ends in a close-packed formation and although the end faces may have a circular outline the fused ends are preferably adapted to inters it to present a substantially continuous light catchment area of end faces to the light source.

The fused fibre ends preferably abut when arranged in the holding means.

Preferably, the end faces receive the majority of the light emanating from the light source.

The said fused ends may be arranged radially of the light source, which is then preferably elongated. The fused fibre ends are generally tapered, which feature allows the fused ends when aranged radially to be positioned as closely as possible to the light source.

Each fused end face preferably extends sustantially along the length of the light emitting portion of the light source. The fused end faces may suitably have a rectangular outline.

Each of said fused ends is preferably independently removable from and fixable in the holding means.

The light source is preferably an arc discharge lamp, which preferably is of the small diameter envelope type.

Alternatively, the light source may be a quartz halogen bulb.

According to a further embodiment of the invention, the fused ends may be arranged to one side of the light source, with a reflector cooperating with the light source to project light onto the end faces of the fibre optic bundles. The end faces are preferably arranged in a plane and are suitably arranged in a substantially circular light catchment formation. The end face may have polygonal outlines, and preferably will have hexagonal outlines.

The invention further provides a holder whereby the fused fibre ends of a plurality of fibre bundles may be held in a close-packed arrangement and in an attitude to receive the majority of light emanating from a light source positioned in the holder.

The holder preferably removably receives each fibre bundle in an individual socket.

The holder is preferably effectively air sealed in use to exclude dust and other airborne matter which would otherwise tend to cause a loss in efficiency and other problems after a period of build-up for example in systems utilising air cooling systems.

In the radial arrangement of fused ends, the holder preferably comprises a ring-shaped central means adapted to receive the fibre bundles, and may include heat-sink devices which may be located above and below the ring-shaped means.

The heat-sink devices may suitably be in the form of finned metal extrusions.

The invention shall now be described by way of example only with reference to the accompanying diagrams, wherein: Fig. 1 shows in perspective view a fibre optic light source arrangement according to the present invention; Fig. 2 shows in vertical section view the arrangement shown in Fig. 1; Fig. 3 shows in horizontal section and to an enlarged scale the arrangement shown in Fig. 1; Fig. 4 is a developed view of the fused fibre bundle end faces shown in Fig. 3; Fig. 5 shows in vertical section a fibre optic light source arrangement according to another embodiment of the invention; Fig. 6 shows a close-packed arrangement of fused fibre bundle ends, being a section along line A-A of Fig. 4; Referring first to Fig. 1, showing an external view of an apparatus of the invention in the form of a holder 2 having eight fibre bundles 4 projecting therefrom.The holder comprises two extruded heat sink sections 6 and 8, which are finned for improved heat dissipation and an intermediate ring portion 10, which accommodates the fibre bundles 4.

The holder 2 is hollow, having a central tubular recess 12. A 50W miniature arc discharge lamp 14 and its fixture 16 are situated inside the recess 12, being axially located with respect to the holder 2.

The intermediate ring portion 10 comprises eight cylindrical orifices or sockets which extend radially through the ring 10 and are equally spaced around its circumference. These orifices accommodate the fibre bundles 4, which are each strengthened adjacent their end portions by a metal ferrule 18. The metal ferrule 18 fits precisely into its intermediate ring aperture to present the end face 22 of the bundle 4 to the light source 14.

The bundle ends 19 are removably fixable within the holder by means of catch counterparts 20. This is a considerable improvement over the common end termination, since in the event of damage to one of the fibre-optic bundles 4, that bundle can be individually replaced rather than the complete set, as would be necessary were all the fibres permanently set in a common end.

The arrangement of bundle ends is shown in detail in Figs. 3 and 4. Each bundle 4 is terminated by fusing. One process which may be suitably used entails fusing at around 7000 C in a furnace using a mould of an appropriate form for the duration of half an hour and under the continual application of compression pressure. The mould may be in in the form of two interengaging counterparts, which are compressed by spring means during the fusing process. In the embodiment shown in Figures 1 to 4, the bundle ends are fused to produce tapered ends 24 having end faces 22 which are rectangular.

The bundle end faces are approximately 10mm x 3mm, with an approximate 20% reduction in area compared with the main bundle cross-sectional area being obtained by the fusing thereof.

Fig. 3 shows all eight bundle ends 19 fixed within the holder, and in it can be seen that the bundle end faces 22 are closely presented to the light source 14, aiding the efficient collection of light therefrom. Further, the bundle ends inter fist to provide a substantially continuous collection surface surrounding the elongate light source 14.

The end faces 22 are contiguous and abutting to minimise the spacing between the end faces.

The combination of close presentation of the end faces 22 and the substantial continuity of light-collecting surface enables a highly effective collection of the light produced by the source 14, although it will be appreciated that either of these alone will produce an improvement. The combination is enabled by the development according to the invention of bundle ends which are fused to a desired form, generally without a circular bundle end, to inters it and allow the close-packing of the end faces to build up a light collection surface or surfaces of a desired form. This interfitment may be achieved in any configuration, although the use of identical ends is desirable to allow for cost-effective mass production and simple replacement.

Since the source 14 in the embodiment described thus far is linear, the use of rectangular bundle ends 8 therein is suitable to enable most of the light produced to be collected by the end faces, the majority of the light being emitted radially from the axis of the source.

The reader may refer to the developed view of the bundle end faces 22 and the light source 14, of Fig. 4 to appreciate the features of the invention descibed above. The fused fibre bundle ends 19 are held in the holder precisely so that the rectangular end faces 22 abut contiguously and surround the light-producing discharge between the electrodes 24 of the lamp. As a conventional two-envelope discharge lamp is of undesirably large diameter, the arc discharge lamp 14 is of a miniature design to allow the desired close-presentation of the end faces 22 thereto.

A further significant feature of the apparatus is that the holder need not embody air cooling means, but sufficient cooling can be provided in the use of the heat sink portions 6 and 8, as the fused fibre ends can withstand temperatures of up to 4000C. The close presentation of the end faces 22 to the source 14 would also not be possible without this heatresistant characteristic of the fused bundle ends.

It has been found in practice that an arrangement of ten fibre bundles 4 around a primary light source is preferred to the abovementioned arrangement utilising eight such bundles 4, although of course any configuration as desired may be adopted.

A further embodiment of the invention is shown in Figs. 5 and 6. The arrangement shown is akin to the prior art light collection arrangements for fibre-optic illumination systems, in that it comprises a light source 30 positioned at a focus of a semi-ellipsoidal reflector 32. The light-collecting fibre bundle ends 34 are positioned at the second focus of the reflector.

In the prior-art arrangement, however, the bundle ends are commonly terminated in an epoxy matrix thus a) spacing the fibre ends apart, b) rendering the individual bundles permanently fixed within the common end, and c) preventing the close-presentation of the end faces to the light source.

The invention alleviates these disadvantages by providing bundle ends which are fused to form fused end blocks 34 which are for example in the form of a hexagonal prism. The bundle ends 34 are therefore closely-packable and interfitting as shown in Fig. 6, with the end faces 36 in a planar formation.

The fibre ends within the fused bundle ends 34 are themselves closely-packed, as is known in the prior art, by the fusing process.

The ends 34 may be held in place at the focus in an orifice of complementary shape, each end being individually removable therefrom by slotting. This embodiment of the invention therefore also has the advantage over the prior art of the bundles being individually replaceable.

Since the light is focused onto a circular region at the second focus of the reflector, an even more efficient collection of light might be achieved by producing for example for each hexagonal fused end face 38, six ends fused to form end-faces 40 which are partially hexagonal and partially curved, so that the combination may interf it, as indicated by the spaced lines in Fig. 6, to present a planar surface of circular outline. This alternative interfitment complements the shape of the collection area into which light is launched by the light source/mirror arrangement, but a disadvantage is that the fused ends 30 and 40 are not identical, but rather are of two forms and therefore not fully interchangeable. It will however be appreciated that as more hexagonal bundle ends 36 are utilised in the light collection surface, the outline thereof will approach the circular in any case.

It is to -be mentioned that the above-described embodiments are not the only arrangements considered according to the invention, for example one might also utilise a light source in conjunction with a hemispherical mirror, and an opposing hemispherical arrangement of fused fibre bundle end faces.

Where the fibre bundle ends are adapted to inters it so as to produce a substantially continuous light catchment area which may be presented to a light source, it is contemplated that not only may the end faces inters it to produce a planar surface, but alternatively individual fused ends may protrude to a greater extent than others.

Claims (23)

1. An apparatus comprising a holding means and a plurality of fibre optic bundles each having a fused end with an end face, the holding means being adapted to arrange respectively the fused ends and a light source so that the end faces receive light emanating from the source.

2. An apparatus according to claim 1 wherein the holding means is adapted to arrange the fused ends in a close-packed formation.

3. An apparatus according to claim 1 or 2, wherein the fused ends are adapted to inters it to present a substantially continuous area of end faces to the light source when arranged in the holding means.

4. An apparatus according to any of claims 1 to 3, wherein the fused fibre ends abut when arranged in the holding means.

5. An apparatus according to any of claims 1 to 4 wherein the fused ends are arranged radially of the light source.

6. The apparatus according to claim 5, wherein the light sourse is elongated.

7. An apparatus according to claim 6, wherein each fixed end face extends substantially along the light-emitting portion of the light source.

8. An apparatus according to claims 6 or 7, wherein the light source is an arc discharge lamp.

9. An apparatus according to claim 8, wherein the arc discharge lamp is of the small diameter envelope type.

10. An apparatus according to any of claims 1 to 4 wherein the fused fibre ends are arranged are arranged to one side of the light source, with a reflector co-operating with the light source to project light onto the end faces of the fibre of the fibre optic bundles.

11. An apparatus according to claim 10 wherein the end faces are arranged in a plane.

12. An apparatus according to claim 10 or 11 wherein the end faces are arranged in a subtantially circular light catchment formation.

13. An apparatus according to any of claims 1 to 12, wherein the end faces have polygonal outlines.

14. An apparatus according to claim 13, wherein the end faces have rectangular outlines.

15. An apparatus according to claim 13, wherein the end faces have hexagonal outlines.

16. An apparatus according to any of claims 1 to 7 or 10 to 15, wherein the light source is a quartz-halogen bulb.

17. A holder whereby the fused fibre ends of a plurality of fibre bundles may be held in a close-packed arrangement to receive the majority of light emanating from a light source positioned in the holder.

18. A holder according to claim 18 wherein the holder removably receives each fibre bundle in an individual socket.

19. A holder according to claim 17 or 18 which is effectively air sealed in use to exclude dust and other airborne matter.

20. A holder according to any of claims 17 to 19 comprising a ring-shaped central means adapted to receive the fibre bundles in a radial arrangement.

21. A holder according to claim 20 further comprising heatsink devices located above and below the ring-shaped means.

22. A holder according to claim 21 wherein the said heat sink devices are in the form of fixed metal extensions.

23. An apparatus according to any of claims 1 to 16, wherein the said end faces receive the majorty of the light emanating from the source.