Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-12-20
2002-10-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S618000, C359S628000, C359S619000
Reexamination Certificate
active
06462881
ABSTRACT:
This application claims the benefit of Japanese Application No. Hei 11-362681 filed in Japan on Dec. 21, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to image display apparatus and, more particularly, to a head- or face-mounted image display apparatus that can be retained on the observer's head or face.
Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 11-125791 is publicly known as a head- or face-mounted image display apparatus using a reflection type image display device, e.g. a reflection type liquid crystal display device (reflective LCD). The publication [JP(A) Hei 11-125791] proposes an optical system including a light source on the assumption that it uses a reflection type image display device. In the proposed optical system, however, no measure is taken to eliminate ghost light.
Let us explain ghost light by using a specific example of image display apparatus shown in FIG.
13
.
FIG. 13
is a diagram showing an optical path in an image display apparatus using two decentered prisms
10
and
20
and a reflective LCD
3
.
FIG. 13
shows the path of normal viewing light from a light source
5
to an eye E. In this example, the decentered prism
10
has four optical surfaces
11
to
14
, and the decentered prism
20
has three optical surfaces
21
to
23
. Light from the light source
5
enters the decentered prism
10
through a half-mirror surface provided on a surface
13
of the prism
10
. Light rays refracted by the surface
13
are internally reflected by a surface
12
and then refracted by a surface
11
to illuminate the reflective LCD
3
. Light reflected from the reflective LCD
3
enters the decentered prism
10
through the surface
11
. The incident light is internally reflected successively by the surfaces
12
and
13
and exits the prism while being refracted through a surface
14
. Then, the light enters the decentered prism
20
while being refracted through a surface
21
. The incident light is totally reflected by a surface
23
and then internally reflected by a surface
22
. The reflected light exits the prism
20
while being refracted through the surface
23
and reaches the eye E. Thus, the image displayed on the reflective LCD
3
is observed as an enlarged image.
However, as shown in
FIG. 14
, light from the light source
5
is partly reflected by the half-mirror surface on the surface
13
to reach the inner wall of a housing
6
. Reflected light from the inner wall of the housing
6
does not travel along the path of normal viewing light shown in FIG.
13
. For example, reflected light from the inner wall of the housing
6
passes through the prism
10
while being refracted through the surfaces
13
and
14
and enters the prism
20
while being refracted through the surface
21
. The incident light is totally reflected by the surface
23
and then internally reflected by the surface
22
. The reflected light exits the prism
20
while being refracted through the surface
23
and reaches the eye E. In this way, ghost light
7
occurs.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described problems associated with the prior art. An object of the present invention is to prevent the occurrence of ghost light in a viewing optical system using a reflection type image display device and a decentered prism. More specifically, in the viewing optical system, an illumination system and a viewing system share an optical path, and a half-mirror is used as a surface through which light from a light source enters the decentered prism. The reflection type image display device is illuminated with an approximately telecentric light beam. The present invention prevents the occurrence of ghost light which would otherwise be caused by light reflected from the half-mirror and further reflected from the inner wall of the housing of the apparatus or the like.
To attain the above-described object, the present invention provides an image display apparatus including a light source for illumination and a reflection type image display device adapted to display an image by reflecting a light beam from the light source. The image display apparatus further includes a viewing optical system for leading the image displayed by the reflection type image display device to an observer.
The viewing optical system has at least a first prism having at least a part thereof interposed in an optical path between the light source and the reflection type image display device.
The light source and the reflection type image display device are so positioned that an illuminating light beam from the light source is applied to the display surface of the reflection type image display device after passing through at least a part of the first prism.
The first prism has a first prism entrance surface through which an image display light beam reflected from the reflection type image display device enters the first prism. The first prism further has at least one first prism first reflecting surface for reflecting the light beam entering the first prism and a first prism exit surface through which the light beam entering the first prism exits. At least one of the first prism entrance surface, the first prism exit surface and the first prism first reflecting surface has a curved surface configuration that gives a power to a light beam.
A harmful light eliminating member is provided in an illuminating light path extending from the light source to the reflection type image display device in the vicinity of the light source to eliminate harmful light resulting from branching off a part of the light beam emitted from the light source from the illuminating light path when it passes through the first prism.
In this case, it is desirable that the viewing optical system should have at least a first prism that passes the illuminating light path between the light source and the reflection type image display device and a first optical element disposed on the observer side of the first prism apart from it. The first optical element should preferably have at least one first optical element first reflecting surface, which has a rotationally asymmetric curved surface configuration that gives a power to a light beam and corrects rotationally asymmetric aberrations due to decentration.
It is desirable that the first optical element should be a second prism having a second prism entrance surface through which the image light beam exiting the first prism enters the second prism. The second prism further has a second prism first reflecting surface for reflecting the light beam in the second prism and a second prism exit surface through which the light beam exits the second prism. It is desirable that at least one of the second prism entrance surface and the second prism exit surface should have a curved surface configuration that gives a power to a light beam.
The arrangement may be such that the first prism has at least one first prism second reflecting surface in the optical path between the first prism entrance surface and the first prism first reflecting surface. The first prism second reflecting surface has a rotationally asymmetric curved surface configuration that gives a power to a light beam and corrects rotationally asymmetric aberrations due to decentration.
The reasons for adopting the above-described arrangements in the present invention, together with the functions thereof, will be described below.
The image display apparatus according to the present invention includes a viewing optical system that has at least a first prism having at least a part thereof interposed in an optical path between a light source for illumination and a reflection type image display device. The light source and the reflection type image display device are so positioned that an illuminating light beam from the light source is applied to the display surface of the reflection type image display device after passing through at least a part of the first prism. In other words, a reflection type image display device, e.g. a reflective LCD, and a l
Epps Georgia
Olympus Optical Co,. Ltd.
Thompson Timothy J.
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