GB2205662A

GB2205662A - Hologram production and display using a convergent reference beam

Info

Publication number: GB2205662A
Application number: GB08710044A
Authority: GB
Inventors: Paul Nathan; Oran Muduroglu
Original assignee: HOLOCHIP Ltd
Current assignee: HOLOCHIP Ltd
Priority date: 1987-04-28
Filing date: 1987-04-28
Publication date: 1988-12-14
Also published as: GB8710044D0

Abstract

A reference beam 20 converger and an interference pattern is recorded in a plane 14 inclined with respect to the optical axis of the convergent reference beam 20 such that the point of convergence 18 of the reference beam is offset from the centre of the hologram 14 in a lateral direction by an amount greater than the extent of the hologram itself in the said direction. A hologram viewing device (22 Figs. 2-4) provides for reconstruction of the hologram 14 with a light source (32) being located and arranged so as to correspond to the spatial relationship between the point of convergence 18 and the hologram 14. <IMAGE>

Description

HOLOGRAM PRODUCTION AND DISPLAY The present invention relates to a method of manufacturing a hologram, holograms manufactured by the method and a viewer for displaying such holograms.

Conventionally, the display of holograms has consisted of placing the hologram at a desired location, such as mounting it on a wall, and illuminating the hologram with an appropriate light source. For white light holograms a spot lamp is often used as the light source. More recently, there have been proposals for providing an alternative form of hologram display wherein the hologram is mounted in or on a housing. The proposed viewing devices have the disadvantage of a relatively large volume compared with-the size of the hologram and, more importantly, they require a relatively complex optical system within the housing.

The present invention seeks, inter alia, to mitigate the above disadvantages of previously proposed hologram viewing devices.

According to a first aspect of the present invention there is provided a method of manufacturing a hologram comprising the steps of: providing a reference beam, providing an object beam containing information about an object, arranging for the reference beam to converge, arranging for mutual interference between the object beam and the convergent reference beam so as to produce an interference pattern, and recording the interference pattern in a plane inclined with respect to the optical axis of the convergent reference beam such that the point of convergence of the reference beam is offset from the centre of the hologram in a lateral direction by an amount greater than the extent of the hologram itself in the said direction.

Preferably, convergence of the reference beam is arranged such that the said lateral offset of the point of convergence is greater than the said extent of the hologram by substantially 1 inch (2.54 cm). Preferably, the point of convergence lies in a plane which is parallel to the plane of the hologram and spaced apart therefrom by a distance of substantially 3 inches (7.62 cm).

According to a second aspect of the present invention there is provided a hologram made in accordance with the first aspect of the invention.

According to a third aspect of the present invention there is provided a hologram viewing device for displaying a hologram manufactured in accordance with the first aspect of the invention, comprising; a housing having means for receiving the hologram to be viewed, and a light source; the light source being located and arranged with respect to said means at a position offset in a lateral direction from the centre of the received hologram by an amount greater than the maximum extent of the hologram in the said direction while providing for direct illumination of the received hologram.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which; Figure 1 is a diagram of an optical arrangement for producing holograms, Figure 2 is a vertical section through a basic design of viewing device for viewing holograms produced using the arrangement shown in figure 1, Figure 3 is a vertical section through an modified design of the viewing device shown in figure 2, and Figure 4 is a perspective view of the viewing device shown in figure 3.

It is known to provide a hologram viewing device comprising a housing in which is arranged a light source and optical system for illuminating a hologram received in the viewing aperture of the housing. The known arrangement has the disadvantage of requiring a relatively complex and expensive optical system which is prone to mechanical derangement unless the viewing device is handled with care. One reason for use of the optical system is to locate the light source at a position in which it is out of the direct line of sight of a person viewing a hologram located in the viewing aperture.

The applicants have developed a technique which enables the optical system within the viewing device to be dispensed with. The applicants' invention enables the production of a hologram viewing device beneficially reduced in size and complexity and of greatly reduced sensitivity to mechanical shocks.

The present invention includes the production of holograms in accordance with the optical arrangement illustrated in figure 1. An object beam 10 and reference beam 12 are generated in conventional manner, that is with object beam 10 containing information concerning the object and beam 12 being collimated. The object and reference beams 10, 12 mutuaily interfere so as to produce an interference pattern which is recorded, for example, on a photographic plate 14. Plate 14 is subsequently processed so as to fix the recorded interference pattern and thus form the hologram.

The arrangement illustrated in figure 1 differs from the conventional arrangement by introduction of an optical component 16 in the path of reference beam 12, prior to mutual interference between the object and reference beams.10, 12. Optical component 16, which may be in the form of a converging lens, has the function of causing the reference beam 12 to converge towards a point of convergence 18. As will readily be appreciated from figure 1, photographic plate 14 is inclined with respect to the optical axis of the convergent portion 20 of reference beam 12. This inclination is such that the point of convergence 18 is offset from the centre of the hologram 14 in a lateral direction by an amount greater than the lateral extent of the hologram itself in the relevant direction. The point of convergence 18 does, of course, lie in a plane parallel to the plane of plate 14.In the preferred arrangement this plane is spaced apart from the plane of the plate by a distance of approximately 3 inches (7.62 cm) and the point of convergence 18 is laterally (upwardly) displaced by a distance of approximately 1 inch (2.54 cm). These distances are indicated in figure 1 by references X and Y, respectively. The ratio of Y to X, which is 1 to 3, is preferably maintained even if the above values of X and Y are varied.

Holograms produced in accordance with the above described arrangement will typically be image plane, full aperture, white light holograms. That is, object beam 10 will in fact be diffuse light originating from a pre-formed "master" hologram. However, the principle can be applied to the production of other forms of holograms, for example, production of so-called "rainbow" transmission holograms. Adaptation of the arrangement, where necessary, to generate different forms of hologram is within the normal skills of a person versed in the art of holography and is thus not described in detail herein.

Reconstruction of the hologram produced in accordance with the arrangement shown in figure 1 is achieved by locating a light source with substantially the same spatial relationship to the hologram as established by the point of convergence 18. The specified spatial relationship is conveniently maintained in a housing of the form shown in figure 2.

This is indicated by inclusion of the X and Y references in figure 2.

Figure 2 is a diagrammatical vertical section through a hologram viewing device 22. The viewing device 22 comprises a housing 24 fabricated, for example, from a moulded plastics material. Housing 24 has a viewing aperture 26 and means for receiving a hologram to be viewed. The means for receiving the hologram comprise a slot 28, provided in the upper surface of the housing adjacent the viewing aperture 26, and a guide arrangement 30. Guide arranagement 30 is provided within the housing and extends beneath slot 28 so as to guide the edges of a received hologram. Guide arrangement 30 may be in the form of channels or rails.

A compact light source such as a tungsten-halogen bulb 32 is located in the upper portion of the rear wall of the viewing device. Housing 24 is configured and dimensioned such that the spatial relationship between light source 32 and the hologram receiving means 28, 30 closely corresponds to the spatial relationship between the point of convergence 18 and the photographic plate 14 as shown in figure 1. It will be appreciated that light source 32 is not in the direct line of sight of a person viewing a hologram through viewing aperture 26.

That is, the normal position for viewing the reconstructed hologram is to view the hologram in a direction perpendicular to the plane of the hologram.

The simplicity of the viewing device illustrated in figure 2 is immediately apparent, particularly when contrasted with the optical systems included in previously known hologram viewing devices. It will be recognised by those skilled in the art that the hologram reconstructed using the viewing device shown in figure 2 may suffer from colour dispersion which may be more noticable under certain viewing conditions. This is, however, unlikely to be of significance in many of the commercial applications of the viewing device made available by the simplicity and robustness of the viewing device of the present invention. It is envisaged that the viewing device of the present invention will be used in a wide range of new commercial applications, one example of which may well be bar-top display units.

Preferably, the tungsten-halogen bulb has a low power rating, about five watts being practical, and housing 24 is provided with a bulb cooling system. The bulb cooling system may consist of apertures 34 located beneath the bulb 32 and apertures 36 located above bulb 32. Apertures 36 are preferably provided by slats arranged to prevent distracting emission of light from the housing. Bulb 32 is preferably arranged with its filament end-on towards viewing aperture 26 and, if necessary, a simple pin-hole screen may be located in front of the bulb, as illustrated by phantom lines 38.

The configuration of the housing shown in figure 2 may be considered ungainly, particularly because of the sloping upper surface and relative height of the rear of the housing. Additionally, vertical orientation of the hologram may not provide a convenient viewing position with the device placed at the desired height.

Figures 3 and 4 illustrate a modified design of the housing shown in figure 2. The modified form of housing mitigates or avoids the described disadvantages of the design shown in figure 2. Figure 3 in particular is useful in emphasising location of the light source with respect to the line of sight of a person viewing the hologram. Figure 3 includes the X and Y references. The viewing device shown in figures 3 and 4 is intended to display a hologram to a person looking down from above and in front of the viewing device 22. Thus, light source 32 will not be in the normal direct line of sight of the person viewing the hologram.

It will be readily apparent to those skilled in the art that various modifications of the described and illustrated embodiments may be made without departing from the scope of the appended claims.

Claims

Claims:

1. A method of manufacturing a hologram comprising the steps'of: providing a reference beam, providing an object beam containing information about an object, arranging for the reference beam to converge, arranging for mutual interference between the object beam and the convergent reference beam so as to produce an interference pattern, and recording the interference pattern in a plane inclined with respect to the optical axis of the convergent reference beam such that the point of convergence of the reference beam is offset from the centre of the hologram in a lateral direction by an amount greater than the extent of the hologram itself in the said direction.

2. A method as claimed in claim 1, wherein the step of arranging for the reference beam to converge comprises arranging for convergence of the reference beam such that the said lateral offset of the point ofconvergence is greater than the said extent of the hologram by a first distance and such that the point of convergence lies in a plane which is parallel to the said inclined plane and spaced apart therefrom by a second distance, the ratio of the first distance to the second distance being substantially 1 to 3.

3. A method as claimed in claim 1 wherein the step of arranging for the reference beam to converge comprises arranging for convergence of the reference beam such that the said lateral offset of the point of convergence is greater than the said extent of the hologram by substantially one inch (2.54 cm).

4. A method as claimed in claim 1 or 3 wherein the step of arranging for the reference beam to converge comprises arranging for convergence of the reference beam such that the point of convergence lies in a plane which is parallel to the said inclined plane and spaced apart therefrom by a distance of substantially three inches (7.62 cm).

5. A hologram manufactured in accordance with any of claims 1 to 4.

6. A hologram viewing device for displaying a hologram of the type claimed in claim 5, comprising: a housing having means for receiving the hologram to be viewed. and a light source; the light source being located and arranged with respect to said means at a position offset in a lateral direction from the centre of the received hologram by an amount greater than the maximum extent of the hologram in the said direction while providing for direct illumination of the received hologram.

7. A hologram viewing device as claimed in claim 6, wherein the ratio of the said lateral offset to the distance between respective parallel planes defined by the means for receiving the hologram and the light source is 1 to 3.

8. A hologram viewing device as claimed in claim 6, wherein said lateral offset is substantially one inch (2.54 cm).

9. A hologram viewing device as claimed in claim 6 or 8, wherein the means for receiving the hologram and the light source define respective planes which are parallel and spaced apart by substantially three inches (7.62 cm).

10. A hologram viewing device as claimed in any of claims 6 to 9, wherein the housing has an upper surface which is substantially horizontal.

11. A hologram viewing device as claimed in any of claims 6 to 10, wherein the light source is a tungsten-halogen bulb.

12. A hologram viewing device as claimed in any of claims 6 to 11, further comprising a pin-hole screen located between the light source and the means for receiving the hologram to be viewed.

13. A method of manufacturing a hologram, substantially as hereinbefore described with reference to and as illustrated in figure 1 of the accompanying drawings.

14. A hologram viewing device substantially as hereinbefore described with reference to and as illustrated in figure 2 or figures 3 and 4 of the accompanying drawings.