GB2034513A - Colour image intensifier - Google Patents

Abstract

Full colour images in an image intensifier are obtained with an input fibre optic colour filter array which separates "white" light into three primary colour components. A correspondingly patterned output filter or coloured phosphor pattern affords the full colour display. The differently coloured components of the input are each subdivided into a multiplicity of smaller elemental components for increased resolution of image detail. Figure 1 includes photo cathode 20, phosphor screen 26, fibre faceplates 12, 14 and clusters of coloured fibres 36. Figure 4 (not shown) includes a three colour phosphor layer (50), and Figure 5 (not shown) includes multiplier channel plate (52). Fibre sizes and applications are exemplified. <IMAGE>

Description

SPECIFICATION Colour image intensifier This invention relates to image intensifiers with particular reference to a fibre optic means and method for providing a full colour image intensification system.

Image intensifiers capable of a high degree of image intensification have been developed for night vision and similar low light level applications but provide only monochromatic images (e.g. green black as from a P 20 phosphor). Examples of such systems are disclosed in U.S. Patents Nos.

3,141,105; 3,321,658 and 3,436,142.

In photographic view-finding systems,- surveill ance devices, medical instruments and other appar atuses where colour rendition is essential, the advantages of image intensification have heretofore been denied.

According to the present invention we provide an image intensifier including image-receiving and im age-emitting optical fibre face plates in spaced aligned relationship with each other, said plates each having oppositely disposed light-receiving and light-emitting faces, the light-emitting face of said image-receiving plate and light-receiving face of said image-emitting plate being adjacent, means for supporting said plates in said adjacent positions and for hermetically sealing said space therebetween, a photoreceptor on said light-emitting face of said image-receiving plate, electro-luminescent means on said image-emitting plate, and means for ap plying an electrical potential across said photorecep tor and electro-luminescent means;; a colour filter at said light-receiving face of said image-receiving plate, said filter comprising a multi plicity of juxtapositioned mu Itifibre components each embodying a multiplicity of juxtapositioned elemental optical fibres characterized to be selective ly transmissive principally to only one of three of the primary colours of a full colour image directed thereupon, said multifibre components of said col ourfilter being arranged in juxtapositioned clusters of three of said primary colours for uniform colour mixing with high resolution of image detail being afforded by said elemental fibres; and means against said image-emitting plate for re constructing clusters of colours corresponding to those of said colourfilter for full colour display by said intensifier.

Preferably, said means for reconstructing said clusters of colour for full colour display comprises a second colourfilter of substantially identical con struction to that of said first mentioned filter, said filters being in accurately aligned relationship for coordination of multifibre geometries.

Multi-coloured phosphor within the intensifier may be substituted for the output filter.

Reference is now made to the accompanying drawings, in which: Figure l is an illustration in cross-section of a preferred embodiment of the invention; Figure 2 is a face view on a greatly enlarged scale, of a cluster of coloured multifibre light components, the configuration of which is useful in fabricating the colour filter plates of the image intensifier illustrated in Figure 1; Figure 3 is a fragmentary elevational view of a filter plate formed of interfitted clusters of coloured multifibres of the type illustrated in Figure 2; Figure 4 is a cross-sectional view of a modification of the invention; Figure 5 is another modification of the invention shown in cross-section; and Figure 6 is a diagrammatic illustration, in perspective, of a fibrescope system in which an embodiment of the invention is incorporated for output image intensification and colour display.

Referring more particularly to Figure 1 of the drawings, image intensifier 10, being of the proxim ityfocused type, comprises a pair of spaced imagereceiving and image-emitting faceplates 12 and 14 respectively within envelope 16 which provides an evacuated space 18 for image energy conversion from light-to-electron energy and back to intensified light for final display. Face 20 of plate 12 is provided with photocathode 22 and face 24 of plate 14 is provided with light-emitting phosphor coating 26.

High electrical voltage is provided across space 18 by DC source 28.

To the extent thus far described, intensifier 10 having faceplates 12 and 14 each constructed of a great multiplicity of fused optical fibres 12a and 14a is of conventional design requiring no further description. Those interested in details of image intensifiers of this type may, however, refer to U.S.

Patents Nos. 3,141,105; 3,321,658; and 3,436,142.

In making intensifier 10 adaptable to producing intensified full colour renditions of coloured images directed thereinto, additional fibre optic faceplates 30 and 32 are provided, preferably but not necessarily, within envelope 16.

Plates 30 and 32, being of identical geometrical patterning and carefully identically aligned along axis 34 of intensifier 10, are each formed of a great number of tightly interfitted and preferably fused, cemented or otherwise connected together multifibres 36 (Figures 1,2 and 3), i.e. each multifibre 36 consists of a multiplicity of individual tightly juxtapositioned light-conducting fibres 38 (Figure 2).

Multifibres 36 are preferably assembled in clusters of three as illustrated by the triangular T-formation of Figure 2.

In each triangular cluster of multifibres 36, there is provided one multifibre 36 formed of coloured fibres 38 adapted to transmit substantially only one of the primary colours, i.e. blue, green (or yellow) and red, another multifibre 36 being constructed of fibres 38 adapted to transmit substantially only one other primary colour and a third multifibre adapted to transmit substantially only the remaining third primary colour. The letters R, G and B, representing the colours red, green, and blue, indicate a coloured multifibre arrangement which, when assembled into a faceplate structure such as is illustrated in Figure 2, provides an integration suitable for producing colour mixing (producing full colour images) according to the invention.

Fibres 38 may be formed of red, green (or yellow) and blue glasses or plastics materials and integrated as multifibres 36 by any well-known technique. U.S.

Patents Nos. 2,992,516; 3,188,188; 3,119,678 and 3,837,824 illustrate the making of glass multifibres, for example.

Since the coloured fibre groups (multifibres 36) must, for optimum performance, be in a strict 1 - 1 geometrical correspondence at input and output ends of intensifier 10, a relatively large multifibre group size (e.g. 25 -150 micron) is preferred.

Elemental fibres 38 for providing monochromatic images of high resolution within each colour dot (multifibre 36) are, however, preferably held to within 5 -10 microns in diameter.

A desirable proximity focused intensifier (e.g.

intensifier 10) may comprise vacuum tight faceplates 12 and 14formed of 5 - 10 micron clear glass fibres, the usual photocathode or photoreceptor (e.g. of cadmium sulfide, cadmium selenide or selenium), electroluminescent coating 26 (e.g. of "white" light phosphor or zinc sulfide activated with copper or manganese) and input and output colour plates 30 and 32 as described above.

In Figure 6, intensifier 10 is illustrated in use as a colour image display device where, for example, an image of an object 40 focused on one end 42 of a fibre bundle (fibrescope) 44 and transmitted to emitting and 46 of bundle 44 may be imaged by lens 48 (Figures 1 and 6) upon receiving face 30 of intensifier 10 for intensification and full colour display at emitting face 32 of the intensifier.

Another application for which intensifiers of the present type may be used is in conjunction with a reflex view finder for motion picture or still cameras.

This would permit binocular viewing of the view finder image without the usual constraints on head or eye position. Moreover, the image would be bright even with the taking lens stopped down or in low light level photographic conditions. It has the further advantage of not letting light back through the reflex view finder system where such unwanted light might fog the film.

Other applications include low light Ivel surveillance or search systems for which monochromatic image intensifiers have been used, i.e. military, police, marine, border patrol, etc. This invention would add a minimum of space and cost to the device in such applications.

A modification of the invention is illustrated in Figure 4 wherein a multi-component (3-colour) phosphor layer 50 is substituted for coating 26 of Figure 1.

By such means, the output multi-colourfaceplace 32 of Figure 1 may be eliminated. All other parts of intensifier 10a of Figure 4 being substantially identical to corresponding parts of intensifier 10 of Figure 10 have been given like reference numerals.

It is required that the geometrical patterning of the multi-colour phosphor layer 50 be coordinated to the geometrical structure of input faceplate 30 similarly to the above-discussed coordination of the faceplate 32 geometry with that of plate 30. To this end, input faceplate 30 may be used to transfer its intrinsic geometry by copying means (e.g. photographic methods) to the phosphor "dot" pattern using photoresist methods to deposit the "dot" pattern. The expression "dot" is meant to be descriptive of a shape corresponding to the cross sectional shape of a multifibre 36 of input plate 30.

Those interested in photog raphic-photoresist methods for forming various configurations of phos phor coatings may refer to U.S. Patents Nos.

3,139,340; 3,255,003; and 3,360,450.

The still further modification of the invention which is illustrated in Figure 5 includes the addition of an electron multiplier channel plate 52 intermediately of photocathode 22 and phosphor coating 26.

This is also adaptable to the structure of Figures 1 and 4 and is energized by potential V2 (Figure 5) for increased intensification of images produced at the emitting end 54 of intensifier 1 Ob.

Those interested in the details of channel plate electron multipliers may refer to U.S. Patents Nos.

3,867,183; 3,979,621; 3,979,637; and 4,031,423.

It should be appreciated that there are various other modifications and/or adaptations of the precise forms of the invention here shown and that the foregoing illustrations are not to be interpreted as restrictive of the invention beyond that necessitated by the following claims.

Claims (7)

1. An image intensifier including image receiving and image-emitting optical fibre face plates in spaced aligned relationship with each other, said plates each having oppositely disposed light-receiving and light-emitting faces, the lightemitting face of said image-receiving plate and light-receiving face of said image-emitting plate being adjacent, means for supporting said plates in said adjacent positions and for hermetically sealing said space therebetween, a photoreceptor on said light-emitting face of said image-receiving plate, electro-luminescent means on said image-emitting plate, and means for applying an electrical potential across said photoreceptor and electro-luminescent means;; a colour filter at said light-receiving face of said image-receiving plate, said filter comprising a multiplicity of juxtapositioned multifibre components each embodying a multiplicity of juxtapositioned elemental optical fibres characterized to be selective ly transmissive principally to only one of three of the primary colours of a full colour image directed thereupon, said mutifibre components of said colour filter being arranged in juxtapositioned clusters of three of said primary colours for uniform colour mixing with high resolution of image detail being afforded by said elemental fibres; and means against said image-emitting plate for reconstructing clusters of colours corresponding to those of said colour filter for full colour display by said intensifier.

2. An image intensifier according to claim 1 wherein said multifibre components are of a generally square cross-sectional shape and each of said clusters comprises the T-formation of three of said components, each having differently coloured elemental fibres.

3. An image intensifier according to claim 1 or 2 wherein a cross-sectional dimension of each of said multifibre components is within a range of from approximately 25 to 150 microns and said elemental fibres thereof are of from approximately 5 to 10 microns in diameter.

4. An image intensifier according to any of claims 1 to 3 wherein said means for reconstructing said clusters of colour for full colour display comprises a second colour filter of substantially identical construction to that of said first mentioned filter, said filters being in accurately aligned relationship for coordination of multifibre geometries.

5. An image intensifier according to any of claims 1 to 3 wherein said means for reconstructing said clusters of colour for full colour display comprises said electro-luminescent layer being formed of multi-component phosphors, said phosphors being preselected and arranged to exhibit, when activated, a luminescence corresponding in colour, geometrical position, shape and size to that of said colour filter.

6. An image intensifier according to any of claims 1 to 5 including a multichannel electron multiplier plate intermediately of said photoreceptor and electro-luminescent means.

7. An image intensifier substantially as herein described with reference to and as shown in the accompanying drawings.