Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1998-06-11
2001-12-25
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
C359S630000, C359S631000, C359S729000
Reexamination Certificate
active
06333820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display apparatus and, more particularly, to a head- or face-mounted image display apparatus which is retained on a user's head or face to project an image into an observer's eyeball.
2. Description of the Related Art
In recent years, head- or face-mounted display apparatuses have been developed for the purpose of enabling the user to enjoy a wide-screen image personally.
In such circumstances, Japanese Patent Application Unexamined Publication (KOKAI) Nos. 7-333551 (1995) and 8-234137 (1996) propose an ocular optical system which leads to a position of an observer's eyeball an image formed by an image display device comprising a liquid crystal display (hereinafter called “LCD”). This ocular optical system is constructed by a decentered optical system made of a medium which is surrounded by three optical surfaces and has a refractive index larger than 1, wherein light rays emitted from the LCD enter the decentered optical system from a third surface, are totally reflected on a first surface inside, are reflected on a second surface forming a concave mirror, and exits through the first surface to the outside of the decentered optical system, thereby leading an image of the image display device to the observer's eyeball without forming an intermediate image.
Japanese Patent Application Unexamined Publication (KOKAI) Nos. 7-333551 (1995) and 8-234137 (1996) each employ a transmission-type LCD as the LCD constructing the image display apparatus. On the other hand, Japanese Patent Application Unexamined Publication (KOKAI) No.7-72446 (1995) proposes a face-mounted image display apparatus in which a reflection-type LCD is used as an image display device.
FIG. 42
of the present application shows an optical system of the image display apparatus, in which light rays from a lamp light source
55
are made parallel rays by a collimator optical system
56
, and part of the light rays (s-polarized light) are reflected by a polarization beam splitter
57
to illuminate a reflection-type LCD
58
from its front side. An image displayed on the reflection-type LCD
58
is projected by an optical system
59
onto a screen
52
, and the projection image is observed by an observer through an ocular optical system
53
.
In addition to the reflection-type LCD as the reflection-type image display device, an image display device called DMD (digital micro device) has also been proposed. This device has a structure shown in FIGS.
43
(
a
) and
43
(
b
). That is, FIG.
43
(
a
) shows a plane view and FIG.
43
(
b
) shows a structure of each element. In this structure, micro mirrors
60
corresponding to respective picture elements are arranged two-dimensionally. By tilting a mirror
60
′ at a designated position about its diagonal axis, light rays incident on the mirror
60
′ from a fixed direction are reflected in a direction different from the reflecting direction of the mirrors which are not tilted, thereby displaying a two-dimensional image. Each of the mirrors
60
is supported via hinges
63
at a pair of diagonally opposite corners by posts
62
set up on a substrate
61
. Each of the mirrors
60
is rotatable about its diagonal axis between the hinges
63
by an electrostatic force generated by applying a voltage to one of a pair of electrodes
64
provided behind the mirrors
60
on the substrate
61
(IEEE Spectrum, Vol. 30, No. 11 pp. 27-31).
When a decentered optical system is employed as an optical system of an image display apparatus, there are the advantages that the whole apparatus can be made small and lightweight, keeping high optical performance (field angle, resolving power, etc.), and that the image display apparatus can display a bright image. Up to now, however, it has been intended to use only a transmission-type LCD as the image device for use with the decentered optical system. Therefore, each of the decentred optical systems disclosed in Japanese Patent Application Unexamined Publication (KOKAI) Nos. 7-333551 (1995) and 8-234137 (1996) has been constructed only as a telecentric optical system in which the position of an entrance pupil is set at an infinity point.
Further, the transmission-type LCD as an image display device has a lower vignetting factor of the picture element compared to the reflection-type LCD, and black matrices between the picture elements are conspicuously observed. Therefore, it is necessary to use a low pass filter (which cuts high spatial frequencies and passes low spatial frequencies) or the like so that the black matrices will not be conspicuously observed. On the other hand, in the reflection-type LCD, it is possible to make the vignetting factor of the picture elements higher, and the aforesaid problem is small. However, as disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 7-72446 (1995), when a non-decentered optical system is used to observe an image, illumination must be made through an optical element such as a beam splitter. This is contrary to the requirement of miniaturization and weight reduction, and there remains a problem that a displayed image is dark.
SUMMARY OF THE INVENTION
The present invention has been made in view of these situations of the conventional techniques. An object of the present invention is to provide a decentered optical system which is constructed as a non-telecentric optical system in which the position of its entrance pupil is set at a finite point. A further object of the present invention is to provide a compact, lightweight and bright image display apparatus which has high optical performance by using a decentered optical system and a reflection-type image display device, such as a reflection-type LCD and a DMD.
To attain the aforesaid objects, an image display apparatus of the present invention comprises an image display device, and an ocular optical system which leads an image formed by the image display device to an eye point of an observer without forming an intermediate image so that the image can be observed as a virtual image, the ocular optical system comprising a decentered optical system having at least one decentered back-coated reflecting surface, and the decentered optical system being a non-telecentric optical system. In this case, it is preferable that the image display device is a reflection-type image display device which displays an image by reflection of illumination light, and that an illumination means for forming the illumination light is arranged outside an optical path between the reflection-type image display device and the eye point of the observer.
Further, it is preferable that the illumination means is arranged such that an incident angle of the illumination light with respect to a display surface of the reflection-type image display device equals approximately to an exit angle of a principal ray in display light which exits from the reflection-type image display device.
It is also preferable that the illumination means is arranged at a position which is approximately conjugate with a position of an entrance pupil of the decentered optical system.
It is also preferable that at least one reflecting surface of the decentered optical system is a rotationally asymmetric surface having no axis of rotational symmetry in nor outside the surface. In this case, it is preferable that the rotationally asymmetric surface is a plane-symmetry three-dimensional surface having only one plane of symmetry.
It is also preferable that the illumination means is arranged at a position in at least one of a first space between the display surface of the reflection-type image display device and a surface of the decentered optical system on which the display light will be incident, and a second space surrounding the first space, the position being outside the optical path so that the display light is not blocked. Furthermore, it is preferable that the illumination means is arranged at a position such that the display surface of the reflection-type image d
Hayakawa Kazuhito
Takahashi Koichi
Togino Takayoshi
Epps Georgia
Lucas Michael A.
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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