Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1994-01-14
1997-02-04
Dzierzynski, Paul M.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 28, 359462, G02B 532, G02B 2722, G03B 3516
Patent
active
056004540
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to viewing apparatus particularly, but not exclusively, for providing a viewer with an apparent 3-D image.
BACKGROUND OF THE INVENTION
Stereoscopic apparatus exists in which a pair of nearly identical images are viewed through a binocular optical system to provide the viewer with a perception of a single 3-D image. A disadvantage of such apparatus is the necessity of having to provide such an optical system, usually in the form of a pair of goggles, for use by the viewer.
In effect, such a system provides for viewing a plurality of sets of juxtaposed information and it would be a considerable advantage if this could be achieved without the necessity for the viewer to have to be provided with a pair of goggles.
SUMMARY OF THE INVENTION
According to the present invention, there is provided viewing apparatus comprising a holographic recording (15) of a diffusely illuminated zone (5,9) and means (17, 19) for illuminating the holographic recording (15) from a plurality of different positions such that images (18,20) of the zone (5,9) are reconstructed forming viewing zones (18,20) characterised in that there is provided adjacent the holographic recording (15) a non-projected masking means 14 for effecting spatial modulation of light from the respective positions, the arrangement being such as to provide a plurality of viewing zones (18,20) whereby the said spatial modulation can be seen from a corresponding one of the zones (18,20).
Following is a description, by way of example only and with reference to the accompanying drawings, of one method of carrying the invention into effect.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of one method of recording a diffusing holographic optical element (HOE) for apparatus in accordance with the present invention.
FIG. 2 is a diagrammatic perspective view of another method of recording a diffusing HOE for apparatus in accordance with the present invention.
FIG. 3 is a diagrammatic perspective view of an embodiment of apparatus in accordance with the present invention.
FIG. 4 is a diagrammatic representation of another embodiment of apparatus in accordance with the present invention.
FIG. 5 is an enlarged view of a portion of the apparatus shown in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1 of the drawings, there is shown apparatus for providing a master hologram from which many HOEs can be formed. A beam from a laser 1 is split by a beam splitter 3 into two beams. One of the beams, a reference beam is expanded by a beam expander 2 and reflected at a concave mirror 7 as a parallel (collimated) beam 8 which impinges on a holographic plate 6. The other of the beams is expanded by a beam expander 4 and is directed towards a diffuser 5 which scatters the light towards the holographic plate 6 where it interferes with the reference beam and a hologram of the diffuser is recorded.
In the arrangement shown in FIG. 2 of the drawings the laser 1, the beam splitter 3 and the beam expanders 2 and 4 are provided as in the apparatus shown in FIG. 1 but the collinated beam 8 now becomes a restructuring beam. The master 6 is reversed before being replaced in the beam, this means that the beam is the conjugate of the original reference beam and a real image 9 of the diffuser is formed. A second (unexposed) holographic plate 12 is placed between the plate 6 and an image 9. The plate 12 is provided with a reference beam 11 spreading from a beam expander 10 placed close to the plate 12. The light from the reference beam 11 and the light forming the image of the diffuser interfere and the resulting pattern is recorded by the plate 12 and the HOE is thereby formed.
The plate 12 may be provided as a component in the screen or as a tool for use in the manufacture of additional similar HOEs.
As an alternative to manufacturing such HOEs it is possible to replicate them optically by contact copying. In either process the holographic material should exhibit a good diffraction efficiency
REFERENCES:
patent: 3674331 (1972-07-01), Caulfield
patent: 5011244 (1991-04-01), Smith et al.
Orr Edwina M.
Trayner David J.
Chang Audrey
Dzierzynski Paul M.
McMurry Michael B.
Richmond Holographic Research and Development Ltd
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