GB2201805A - Holographic display means having a baffle plate - Google Patents

Abstract

In a holographic display device as disclosed in the patent publication GB 2 178 866 A, there is provided a baffle plate 20 between the light source 18 and the reflector 14, and an aperture 22 formed in baffle plate defines the beam of light 16 which illuminates the reflector and hence on reflection the desired area of the hologram 10. <IMAGE>

Description

HOLOGRAPHIC DISPLAY MEANS This invention relates to holographic display means, that is to say to means arranged to display images of three dimensional objects by means of illuminated holograms, which images portray in life-like manner the real objects used in producing the holograms, and give the impression to a viewer that the object whose image is portrayed in the display is really present. For example, with such displays, the image is seen to move in a realistic way when the viewer moves his observation position relative to the object portrayed in the display means.

In my co-pending patent application No. 86 17300 (published as GB 2 178 866 A), I have disclosed and claimed various forms of compact holographic display devices. The reader's attention is hereby directed to the disclosure of that copending application.

It has been discovered during the further development of those devices, that light reflected on to the hologram by the reflecting means has included (in addition to the desired, designed light beam emanating in the desired way from the light source) other spurious, diffused and reflected light emanating from parts of the display device which inadvertently and disadvantageously have acted as additional sources of light. Furthermore, light from outside the display device has reached the reflecting means via, for example, ventilation louvres or passages which have been provided for cooling the light source.

Such spurious light reaching the reflecting means, and thence the hologram, has either blurred the displayed holographic image, or otherwise, by virtue of the spurious multiple sources has produced a plurality of secondary, unwanted holographic images displaced from the 'design' image.

The present invention seeks to provide a means for enhancing the holographic display by improving its resolution and eliminating the unwanted secondary images.

According to one feature of the present invent ion, in a holographic display means as defined in the claims of my copending patent application 86 17300, there are provided light baffling means arranged to prevent the emission of light to the reflecting means except through a predetermined aperture of size, shape and position such as to provide a predetermined light beam for illuminating the reflecting means and thence a predeterminded area of the hologram.

If desired, the light baffling means may include to the rear of the light source a light reflecting means for increasing the light which originates at the source and passes through the said aperture to the reflecting means.

Other features of the present invention will appear from the description that follows hereafter, and from the claims appended at the end of that description.

One holographic display device according to the present invention will now be described by way of example and with reference to the accompanying diagrammatic drawings.

In those drawings: Figure 1 shows a vertical cross sectional view taken centrally through a light source incorporated in the device, on the section indicated in Figure 2 at I-I; and Figure 2 shows a horizontal cross sectional view taken through the said light source, on the section indicated in Figure 1 at II-II.

Referring now to the drawings, in the device there shown, a reflection hologram 10 carried on a support (not shown) is illuminated over a predetermined area by a 'design' light beam 12 of predetermined shape and size. That beam is produced by a curved reflector 14 which is positioned to reflect to the hologram a 'design' light beam 16 which emanates from a 'design' light source 18. The light beam 16 is defined by a front baffle plate 20 positioned between the light source 18 and the reflector 14, and in which is formed an aperture 22 of predetermined shape and size sufficient to closely define the desired light beam 16, 12.

A lower baffle plate 24 prevents light from the source reaching the hologram 10 directly.

Preferably, upper, rear and end baffle plates 26, 28 and 30 are provided to limit the unwanted emission of light from the source in directions other than that of the aperture 22.

The various baffle plates have to be designed to withstand the intense heat emitted by the light source, and to enable the passage of cooling air over the light source. They must also have as far as possible non-reflecting surfaces, so that they cannot act as spurious light sources reflecting spurious light through the aperture 22 towards the reflector 14.

The reflector shown is curved in both the vertical and the horizontal directions, and may be curved either parabolically, spherically or in a combination of the two types, in either or both such directions.

If desired, a concave reflector 32 may be disposed adjacent the rear side of the light source, so as to improve the intensity of the light beam 16 reaching the reflector 14 from the source 18. If desired, that reflector may be positionedrrelative to the light source such that the reflected image of the source (as seen looking at the reflector and the source through the aperture) is displaced from but closely adjacent the source.

Alternatively, if desired the rear reflector may comprise a planar reflector.

The light source 18 may be positioned as shown forwards of the plane of the hologram 10, or alternatively, it may be positioned in the same plane as the hologram, or to the rear of that plane, the baffle plates being correspondingly modified.

The size and shape of the aperture 22 (determined by the relative sizes and positions of the light source 18, the front baffle plate 20 and its aperture 22, the reflector 14, and the hologram 10) are such as to provide the desired illumination of the hologram by light emanating from only the aperture 22.

The front baffle plate 20 may be planar as shown, or of any other desired shape.

The present specification shall be taken as incorporating the disclosure of my two earlier co-pending patent applications Nos. 87 02535 (filed 5th February 1987) and 87 02633 (filed 6th February 1987) from which the present application claims priority; and for the sake of convenience the disclosure of the first of those two applications is reproduced in the following two pages of text and the sheet '2/2' of the drawings.

When illuminating concave or convex hologram sections or a 360" cylindrical hologram using the system described in the above-mentioned patent application 86 17300, a concave or convex baffle and aperture or a 3600 cylindrical baffle and aperture may be used to prevent unwanted direct, diffused or reflected light reaching the hologram surface from the light source filament or support or the reference beam reflector.

HOLOGRAM DISPLAY MEANS This invention relates to the illumination of a hologram as described in Patent Application ???????????? When illuminating a hologram using the previously disclosed systems identified above:spurious,diffused,reflected light from the illumination source can cause problems,with various components in the structure of the system acting as sources for this unwanted light to reach a hologram plate.This can cause blurring and multiple reference sources producing a duplicity of two or more images simultaneously.

This invention seeks to limit these effects.

According to the present invention a light source shines through an aperture to minimise the effects of spurious,iffused,reflected light.

A specific embodiment will now be described by way of example with reference to the accompanying drawings.

Figure 1 shows schematically a system containing an aperture in cross-section taken on the vertical plane.

Figure 2 shows schematically a cross-section of figure 1 taken on a horizontal plane.

Referring to the drawings,a means for displaying or reconstructing a hologram.

In figure 1,a vertical cross-section,a light source 1 radiates light 2 from or through an aperture 6,which can be of any required shape onto a reflector 3,which is curved in its horizontal and vertical directions either spherically or parabolically or a combination of the two, types of curvature.Light 4 is reflected from reflector 3 onto a hologram 5.

Baffles 7,12 and optional baffles 8 can be used to enclose the light source,thereby excluding spurious,diffused;reflected light from the hologram surface.Resolution will thereby noticaply improve from a system lacking such a baffling system.

A concave reflector 9 can also be introduced into the system if required.

This system is particularly suited to display or reconstruction of reflection type holograms 10.

Figure 2 shows a horizontal cross-section of figure 1.

Such baffling will also prevent external light sources from degrading the quality of a reconstructed hologram.

If required the light source can be positioned in frontssbehind or in the plane of the hologram plate,with relevant adustments being made to the baffles to prevent unwanted light hitting the hologram plate-apart from through a suitably designed aperture.

The size and shape of the aperture will normally be determined by three factors,1.Distance of the light source behind the hologram plate(if any)2.Degree of radiated beamspread required to reach the extremities of the illuminating reflector.3.The size and shape of the area to be illuminated.

Claims (6)

1. Holographic display means as defined in co-pending patent application 86 17300, wherein there are provided light baffling means arranged to prevent the emission of light to the reflecting means except through a predetermined aperture of size, shape and position such as to provide a predetermined light beam for illuminating the reflecting means and thence a predeterminded area of the hologram.

2. Holographic display means according to claim 1, wherein the light baffling means include to the rear of the light source a light reflecting means for increasing the light which originates at the source and which passes through the said aperture.

3. Holographic display means according to claim 2, wherein the said rear reflecting means comprises a concave reflecting means.

4. Holographic display means according to claim 3, wherein the rear reflecting means is positioned in relation to the light source so that the reflected image of the source as seen looking at the source and rear reflecting means through the aperture is displaced from but closely adjacent the source.

5. Holographic display means comprising any operable combination of the features disclosed herein, other than as claimed in any preceding claim.

6. Holographic display means substantially as hereinbefore described with reference to and as illustrated by the accompanying diagrammatic drawings.