GB2358483A

GB2358483A - Image projection system with fibre optic harness

Info

Publication number: GB2358483A
Application number: GB0100379A
Authority: GB
Inventors: Paul Andrew Timson
Original assignee: Schott Fibre Optics UK Ltd
Current assignee: Schott Fibre Optics UK Ltd
Priority date: 2000-01-18
Filing date: 2001-01-08
Publication date: 2001-07-25
Anticipated expiration: 2021-01-08
Also published as: GB2358483B; GB0100379D0; GB0000974D0

Abstract

An image projection system has a fibre optic harness having a common end and a plurality of fibre optic tails 6 emanating therefrom to distribute a primary light source 2 disposed adjacent the common end to each of the light emitting faces 10 of the tails. A frusto-conical element 12 is disposed immediately adjacent the light emitting 10 face of each of the fibre optic tails which effectively reduces a diffuse characteristic and increases the intensity of the light emerging from said light emitting face, and the intensified light is then delivered to an image gate 16 before being magnified by a projection lens 18 and projected onto a suitable projection surface 20 some 1-5m distant from said projection lens. The system is suitable for the discrete projection of a plurality of different or similar images in a number of discrete separate locations.

Description

2358483 Image Projection System This invention concerns the projection of

images onto a projection surface using a fibre optic bundle.

The projection of images from, for example a 35mm slide projector is a well established optical configuration. Fixed, rotating and varying images are all currently projected from a projector essentially consisting of the following components:

1. a high power light source, 2. a reflector, 3. a collimator, 4. a filter, 5. a gate, and 6. a projection lens.

Those skilled in the art will appreciate the wide variety of uses to which modern projectors are often put, including the projection of images for theatrical and entertainment effects. In circumstances where it is desired to project an alternating, moving or varying image, so-called "gobos" can be used to replace the 35mm slide which is position intermediately of the filter and the projection lens in the projector configuration described above.

The function of the lamp, reflector, and collimator is to create an even, but high illuminance light field across the whole of the gate plane. (In practise there is a trade off of evenness with illuminance, as devices which are used to achieve evenness necessarily diminish the illuminance characteristic as a result of losses occurring in the medium which increases the uniformity or evenness of the light.).

An important and required property of the light field at the gate is that it is of sufficiently low. numerical aperture to be efficiently

2 collected and imaged by the projection lens. This is one of the key factors in determining image brightness. The projection lens then transfers the gate to the projection lens image plane, usually a few metres away.

The fundamental disadvantage of such projection systems is their inability to project more than a single image at any particular time.

The use of fibre optic harnesses to provide discrete distributed lighting is also well documented. A common application for fibre optic harnesses is the provision of a multi-spotlight lighting arrangement wherein a high intensity light source is used to illuminate the "common" end of the harness, and by virtue of the physical property of total internal reflection inherent in each of the fibre optic "tails" emanating from the common end, a proportion of the light incident on said common end is distributed within and to the end of each of the tails. The particular arrangement and selection of components applied to the free end of each of the tails is dependent on the particular lighting requirements, but it is known to provide each of the tall ends with a lens of some type to intensify and adequately project and/or focus the light emanating therefrom. Said lenses may be adjustable to allow for the focusing of the light on a particular surface remote from the free end.

An example of a fibre optic lighting system is given In _QK patent Number 1491142 to Schott, which describes the use of a fibre optic harness to provide discrete element lighting for a motorway traffic sign. Specifically, each of the tail ends of the harness is provided with a "cone" which has the effect of intensifying the light emerging from a bare fibre optic tail. The particular means by which this is done is related to the particular selection of materials having particular refractive indices, but briefly the overall effect is to align light rays emerging from the tail free end at highly acute angles 3 more with the longitudinal axis of said tall. The light beam therefore becomes less diffuse and more intense. The cone is manufactured from a first material which constitutes the majority of the body of said cone around its central axis having a first refractive index, and a sheath of a second material having a second refractive index is applied around the first material so that light rays impinging on the interface between the two materials are totally internally reflected by virtue of the difference in refractive indices of the two materials.

Although the word "cone" is used above to describe the element reducing the diffuse characteristic of the light emitted from the free end of the fibre optic tall, it is to be mentioned that the geometric shape of the element is more frusto-conical than conical, and has two substantially planar faces one smaller than the other, the smaller face being position proximate the light emitting end of the fibre optic tail.

However, the invention described in the abovementioned patent deals only with the provision of a number of discrete lights in a motorway traffic sign, and not with the projection of images.

US3829857 to Allan and others describes a further use of a fibre optic harness to illuminate certain elements of a motorway matrix sign to provide a meaningful sign to a road user. 1n particular, a plurality of fibre optic harnesses with tails emanating therefrom are used with each of the tails being installed in regions within the matrix sign. The tails of any one or more of the common ends of the harnesses are fed to a number of different regions so that illumination of any one of the common ends results in the illumination of a number of different regions to provide a meaningful sign. Behind each region, there are disposed the light emitting faces of a number of different tails, and therefore to ensure a collimated light output from one or more of these tails, an optical 4 unit consisting of a cylindrical housing and having a converging lens at one end thereof is provided. The tails are fed into the alternate end of the housing until abutting a fibre optic clad rod, the free end of which is disposed just at the focal point of the converging lens so that light emerging therefrom in any direction is aligned into a focussed beam by the lens. By means of the clad rod, off-axis cones of light emanating from the off-axis light guides are integrated into an axis cone of light emanating from the lens. This document is exclusively related to the provision of matrix motorway signs and makes no mention of image projection and the need therein for specific light characteristics.

It is the object of the invention to provide an image projection system incorporating a fibre optic harness.

According to the invention there is provided an image projection system comprising a light source for directing light onto a fibre optic harness common end, said harness having a plurality of fibre optic tails emanating therefrom and having free light-emitting end faces, said ends being provided with means for reducing a diffuse characteristic of light emerging from said end faces, said diffuse characteristic reduction means having a further light emitting face, characterised in that an image gate for retaining an image and a projection lens are disposed in front of the light emitting face of the means for reducing said diffuse characteristic of the light, and in that one, other or both of said image gate and projection lens are positioned fixedly with relation to the light emitting face of the diffuse characteristic reducing means.

Preferably the diffuse characteristic reducing means includes a substantially solid block having end faces substantially perpendicular to the axis of the block and side walls, a first of said end faces being disposed proximate or adjacent the free light- emitting face of a fibre optic tail and allowing for transmission of light along the length of said block from the first end face to the second end face, the side walls substantially preventing escape of light therethrough by virtue of a coating, their varying crosssectional shape along the length of the block or by virtue of the material from which the block is made.

Preferably the diffuse characteristic reducing means is a tapering cone.

Preferably the diffuse characteristic reduction means is a fibre optic clad rod.

Preferably the dimensions of said cone are 20mm long with the diameter of the smaller face being 1.5mm and that of the larger being 4mm.

Alternatively the cone dimensions can be scaled up for larger fibre diameters, and cones having dimensions of 40mm in length, and having diameters of the smaller surface more proximate the image plane of 3mm and of the larger surface more proximate the object plane of 8mm are considered.

Preferably both image gate and projection lens maintained in a fixed relationship with respect to the light emitting face of the diffuse characteristic reducing means.

In general the use of fibre optic harness for the projection of images onto a remote projection screen has never heretofore been considered, and the benefits of such a system are instantly appreciable.

6 The cones described in the abovementioned Schott patent are ideal for use in the image projection system herein described as they match the gate requirements by providing a narrow angle emission with excellent spatial uniformity across the output (gate) face. A single element lens, typically of 10-30mm diameter depending on focal length and image size required, projects the gate object onto the image surface. Images as small as 20mm or as large as 500mm can usefully be produced.

A specific embodiment of the abovementioned invention is now provided by way of example with reference to the following diagrams wherein:

Figure 1 shows schematically an image projection system according to the present invention.

Referring to Figure 1 there is shown an image projection system comprising a light source having a fibre optic harness common end mounted therein to allow for projection of light onto said common end within the source 2. Said harness is provided with a plurality of fibre optic tails 6 emanating from the common end, each of which is ideally provided with a light emitting end 8 having a light emitting face 10. To each tail 6, or to as many tails from which it is desired to project images, there is applied a tapering cone 12 which reduces the diffuse characteristic of light which would conventionally emerge from the face 10. Light emerging from the face 14 is therefore on average substantially parallel with the longitudinal axis of said tapering cone and of said light emitting end 8 so that the majority of light emerging therefrom is incident on the image (such as a transparency) retained within the image gate 16.

Thereafter, a projection lens 18 is fixedly disposed in front of the cone (with relation to its distance from the light emitting face 14 of 7 the cone, and more specifically with relation to the image gate 16) to allow for a focused, sharp and intense image to be projected by the lens 18 onto a projection surface 20 which may be typically of the order of 1- 5m distant from said lens.

The projection of micro-images can be used in combination with light source colour changes, interruption by dimming discs, sequencing of fibre optic tails and the like to give flowing colour effects, and other techniques which are well established in the fibre optic lighting art.

Other applications for the present invention are numerous, and include the projection of multi-image corporate logos onto walls, corridors, and floors, etc., advertisement and promotional image projection (e.g. onto shop, public house, and retail facility counters), provision of arrows for route direction on floors of large premises, projection of composite images, (e.g. writing words, composing a picture from several images), and pseudo movement by overlaying projected images combined with sequenced harness/light source interruption.

In summary therefore an image projection system is described wherein a fibre optic harness having a common end and a plurality of fibre optic tails emanating therefrom is used to distribute a primary light source disposed adjacent the common end to each of the light emitting faces of the tails. A frusto-conical element is disposed immediately adjacent the light emitting face of each of the fibre optic tails which effectively reduces a diffuse characteristic and increases the intensity of the light emerging from said light emitting face, and the intensified light is then delivered to an image gate before being magnified by a projection lens and projected onto a suitable projection surface some 1-5m distant from said projection lens. The system is suitable for the discrete projection of a plurality

8 of different or similar images in a number of discrete separate locations.

9

Claims

1. An image projection system comprising a light source for directing light onto a fibre optic harness common end, said harness having a plurality of fibre optic tails emanating therefrom and having free lightemitting end faces, said ends being provided with means for reducing a diffuse characteristic of light emerging from said end faces, said diffuse characteristic reduction means having a further light emitting face, wherein an image gate for retaining an image and a projection lens are disposed in front of the light emitting face of the means for reducing said diffuse characteristic of the light, and in that one, other or both of said image gate and projection lens are positioned fixedly with relation to the light emitting face of the diffuse characteristic reducing means.

2. An image projection system according to claim 1 wherein the diffuse characteristic reducing means includes a substantially solid block having end faces substantially perpendicular to the axis of the block and side walls, a first of said end faces being disposed proximate or adjacent the free light-emitting face of a fibre optic tail and allowing for transmission of light along the length of said block from the first end face to the second end face, the side walls substantially preventing escape of light therethrough by virtue of a coating, their varying crosssectional shape along the length of the block or by virtue of the material from which the block is made.

3. An image projection system according to claim 1 or 2 wherein the diffuse characteristic reducing means is a tapering cone.

4. An image projection system according to claim 1 or 2 wherein the diffuse characteristic reduction means is a fibre optic clad rod.

5. An image projection system according to claim 4 wherein the rod is cylindrical.

6. An image projection system according to claim 3 wherein the dimensions of said cone are 20mm long with the diameter of the smaller face being 1. 5mm and that of the larger being 4mm, said smaller face being disposed adjacent the light emitting face of said fibre optic tall.

7. An image projection system according to claim 3 wherein the dimensions of said cone are between 20-40min long with the diameter of the smaller face being between 1.5-3mm and that of the larger being between 4-8mm, said smaller face being disposed adjacent the light emitting face of said fibre optic tall.

8. An image projection system according to any preceding claim wherein both image gate and pro)ection lens maintained in a fixed relationship with respect to the light emitting face of the diffuse characteristic reducing means.

9. An image pro)ection system substantially as hereinbefore described with reference to the accompanying drawing.