Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
1999-11-18
2001-10-09
Henry, Jon (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S030000, C359S034000, C349S063000, C349S112000, C362S035000
Reexamination Certificate
active
06301026
ABSTRACT:
This application is based on application No. 10-330383 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device for illuminating display elements and the like.
2. Description of the Related Art
Reflective type liquid crystal display is an example of a display element used in display devices. An advantage of reflective type liquid crystal display as a display element is the large aperture efficiency compared to transmission type liquid crystal display. Attention has been particularly focused in recent years on reflective type liquid crystal display comprised of cholesteric liquid crystal display, which have many advantages including a high reflective efficiency, and the capability of being integratedly formed with a driver IC on a silicon substrate. Display devices which use a reflective type liquid crystal display as a display element are used in calculators, projectors, and head-mounted displays and the like, and card calculators and the like do not require special illumination when used in bright areas. However, illumination methods do pose problems for the various display devices which require other illumination.
A projector is the subject of the example described below. It is desirable to illuminate the display element from directly in front to achieve illumination with the greatest efficiency. When an illumination device is disposed directly in front, however, the light reflected from the display element is blocked by the illumination device and cannot be observed. To prevent this obstruction, conventional devices achieve illumination from the front by using a half mirror or polarization beam splitter.
An example of a display device which achieves illumination from the front surface of a display element via an illumination device using a half mirror is shown in FIG.
16
. The light emitted from an illumination lamp
101
is reflected by a reflector
102
, and impinges a half mirror
103
. The light reflected by the half mirror
103
illuminates a reflective type liquid crystal display element
104
. Then, the light is converted to a projection image based on the projection image signals via the reflective type liquid crystal display element
104
, and is transmitted through the half mirror
103
and projected to the pupil of an observer via an enlarging lens
105
. In this device, the illumination device comprises the illumination lamp
101
, the reflector
102
, and the half mirror
103
. This illumination device achieves illumination from the front surface of the reflective type liquid crystal display element
104
without blocking the projection image light.
Display devices which achieve illumination from the front surface of a display element using a half mirror or polarization beam splitter as described in the conventional art have expensive and complex structures, and are neither compact, nor light weight. Since compactness and light weight are important factors, this construction is unsuitable for display devices, particularly head-mounted displays.
SUMMARY OF THE INVENTION
In view of the previously described disadvantages, an object of the present invention is to provide an illumination device suitable for an inexpensive, compact, and light weight display device.
This object is attained by providing an illumination device comprising a light source unit for emitting light; an optical plate which the light from the light source unit enters through a side surface of the plate; and a holographic optical element, which is disposed to face a surface of the optical plate, for deflecting the entering light to form light to illuminate a rectangular region, wherein a principal ray of the light enters the holographic optical element perpendicularly relative to one diagonal of the rectangular region.
In another construction, an illumination device of the present invention comprises a light source unit for emitting light; and a holographic optical element, being planar shaped, which the light emitted from the light source unit enters through a side surface of the holographic optical element, and for deflecting the entering light to form light to illuminate a rectangular region, wherein a principal ray of the light enters the holographic optical element perpendicularly relative to one diagonal of the rectangular region.
A display apparatus of the present invention is provided with a light source unit for emitting light; a hologram optical unit for deflecting the light emitted from the light source unit and enters the hologram optical unit through a side of the hologram optical unit, and emitting the deflected light; and a display element, arranged approximately in parallel, which is illuminated by the deflected light.
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patent: 4807978 (1989-02-01), Grinberg et al.
patent: 5418631 (1995-05-01), Tedesco
patent: 5515184 (1996-05-01), Caulfield et al.
patent: 5650865 (1997-07-01), Smith
patent: 5703667 (1997-12-01), OchiIi
patent: 5729367 (1998-03-01), Smith
patent: 6014192 (2000-01-01), Lehureau et al.
patent: 5-045726 (1993-02-01), None
patent: 9-189809 (1997-07-01), None
Henry Jon
Minolta Co. , Ltd.
Sidney Austin Brown & Wood
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