GB2072875A - Light guide junction and shaped reflector - Google Patents

Abstract

A light guide junction in which a more intense centre portion of a signal light emitted by a source light guide 3 is transmitted to some of a number of distribution guides 2 whilst a less intense outer portion is transmitted to the remainder of the distribution guides, the transmission being by way of a light intensity modifer e.g. a specially shaped reflector 4 which diffuses the more intense signal light and concentrates the less intense portion. A shaped reflector 4 comprises a central convex portion 9 and an outer annular concave portion 10 surrounding the portion 9. <IMAGE>

Description

SPECIFICATION Light guide junction This invention relates to light guide junctions where a light signal from a source light guide is to be accepted by a plurality of distribution light guides for distribution to remote sites.

Such distribution can be achieved by having the distribution light guides branching at spaced junctions from the source light guide. It is found, however, that there is a cumulative loss in intensity of the light signal at successive junctions; this arrangement is therefore inefficient.

An alternative is to effect distribution at one junction region with means arranged to disperse the signal from the source light guide to a plurality of distribution light guides at that junction region.

Even this arrangement has a disadvantage in that the intensity of signal light received by the distribution guides is not necessarily uniform due to the non-uniformity of the signal light emitted by the source light guide.

In practice it is found the light signal emitted by a light guide is more intense near its centre than its edges.

It is an object of the present invention to provide such a light guide junction which overcomes at least some of the problems of the known light guide junctions described above.

According to one aspect of the invention, there is provided a light guide Junction for distributing a signal from a source light guide to a plurality of distribution light guides, which Junction includes location means for positioning a light emitting surface of the source guide in light signal communication with light accepting surfaces of the distribution guides, light intensity modifying means positioned so that a more intense centre portion of the source light signal is incident upon a first region thereof and is transmitted to the light accepting surfaces of some distribution light guides, and so that a less intense outer portion of the source light signal is incident upon a second region thereof and is transmitted to the light accepting surface of other distribution light guides.

Preferably, the more intense portion of the source light signal is diffused on to the light accepting surfaces of said some distribution light guides, and the less intense portion is concentrated on to the light accepting surfaces of said other distribution light guides and the light intensity modifying means conveniently comprise a reflecting means.

Advantageously, the source light guide is surrounded by two concentric series of distribution light guides and the first region of the reflecting means is of concave form and the second region is an annular of convex form surrounding said first region, said first region diffusing the source light signal on to the inner series of distribution light guides and said second region concentrating the source light signal on to the outer series.

The ratio between the amount of light falling on the first region and the second region of the light intensity modifying means is preferably approximately equal to the ratio between the number of distribution light guides which receive light from said first region and the number of those distribution light guides which receive light from said second region; this assists uniform distribution of the signal light to the distribution guides.

According to another aspect of this invention, there is provided a reflector for use in a light guide junction which reflector includes a central portion of convex form, and an annular portion contiguous with the central portion, of generally concave form.

One embodiment of the invention is described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic, not necessarily to scale, side view of a junction, Figure 2 is a plan view, to a smaller scale, Figure 3 shows graphically the approximate light intensity variation across the diameter of a light guide, Figure 4 is a perspective view of a light intensity modifying mirror, and Figure 5 is an axial cross-section of the mirror giving suitable dimensions.

In the Figures, a light guide junction includes a housing 1 for accepting and locating a bundle of light guides including eighteen distribution light guides 2, and a single source light guide 3. The housing also locates light intensity modifying means in the form of a mirror 4.

The source light guide 3 lies co-axially with a longitudinal axis X-X and has a signal light emitting face 5 transverse to that axis. The eighteen distribution light guides lie parallel to the source light guide 1 and are arranged around it in two distinct concentric rings, an inner ring 6 having six guides and an cuter ring 7 having twelve guides. Each distribution light guide 2 has a signal light accepting face 8 which lies co-planar with the other light accepting faces and with the light emitting face 5.

The mirror 4 is positioned co-axially with the axis X-X and is spaced from that plane including the faces 5 and 8. It has an inner reflecting surface 9 formed as a surface of revolution by a convex arc, the surface being generated and of such an area that it accepts about 1/3 of the light from the emitting face 5 and reflects it in the form of an annular divergent beam 11 on to the six accepting faces 8 of the inner ring 6, i.e. the surface 9 diffuses the signal light incident thereupon.

The mirror has an outer reflecting surface 10 formed as a surface of revolution by a concave arc, the surface being generated and of such an area that it accepts about 2/3 of the light from the emitting face 5 and reflects it in the form of a convergent annular beam 1 2 on to the twelve accepting faces 8 of the outer ring 7, i.e. the surface 10 concentrates the signal light incident thereupon.

Referring to Figure 5, the surface 9 may have an arc radius rax of 3.503 mm. formed from an annular locus Y, and a radius rx of 0.33 mm., whilst the surface 10 may have an arc radius rax of 3.491 mm. formed from an annular locus Z, and an inner radius corresponding to that of the surface 9 (ray) and an outer radius of 1.997 mm.

The mirror may thus be about 4 mm. in diameter.

It will of course be understood that these typical dimensions may be varied as necessary to suit the size and number of light guides in the arrangement.

As is shown with particular reference to Figure 3, the more intense signal light emitted by the central region of the face 5 is selectively diffused on to the inner ring; since that ring has six guides of the eighteen total, approx. 1/3 of the emitted light is diffused upon them, whilst the less intense signal light emitted by the annular outer region of the face 5 is selectively concentrated on to the outer ring; since that ring has twelve guides of the eighteen total, approx. 2/3 of the emitted light is concentrated upon them.

This arrangement ensures that the eighteen distribution guides receive generally equal signal density.

n an alternative junction, where the source light guide is positioned opposite the distribution guides, the mirror 4 may be replaced by a lens through which the emitted signal light passes.

Claims (7)

1. A light guide Junction for distributing a signal from a source light guide to a plurality of distribution light guides, which Junction includes location means for positioning a light emitting surface of the source guide in light signal communication with light accepting surfaces of the distribution guides, light intensity modifying means positioned so that a more intense centre portion of the source light signal is incident upon a first region thereof and is transmitted to the light accepting surfaces of some distribution light guides, and so that a less intense outer portion of the source light signal is incident upon a second region thereof and is transmitted to the light accepting surface of other distribution light guides.

2. A light guide junction as claimed in claim 1, wherein the more intense portion of the source light signal is diffused on to the light accepting surfaces of said some distribution light guides, and the less intense portion is concentrated on to the light accepting surfaces of said other distribution light guides.

3. A light guide junction as claimed in claim 1 or claim 2, wherein the light intensity modifying means comprise a reflecting means.

4. A light guide junction as claimed in claim 3, wherein the source light guide is surrounded by two concentric series of distribution light guides and the first region of the reflecting means is of concave form and the second region is an annulus of convex form surrounding said first region, said first region diffusing the source light signal on to the inner series of distribution light guides and said second region concentrating the source light signal on to the outer series.

5. A light guide junction according to any of the preceding claims, wherein the ratio between the amount of light falling on the first region and the second region of the light intensity modifying means is approximately equal to the ratio between the number of distribution light guides which receive light from said first region and the number of those distribution light guides which receive light from said second region.

6. A reflector for use in a light guide junction according to any of claims 1 to 5, which reflector includes a central portion of convex form, and an annular portion contiguous with the central portion, of generally concave form.

7. A light guide junction, substantially as hereinbefore described, with reference to, and as illustrated in, any of the accompanying drawings.