Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reissue Patent
1999-08-10
2001-05-08
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S631000, C359S630000
Reissue Patent
active
RE037169
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an ocular optical system, and more particularly to an ocular optical system intended for use with a head- or face-mounted image display device which is mounted on the head or face of the user to project images into the user's eyeballs.
In recent years, helmet or goggle-type of head-mounted or face-mounted image display devices have been developed for virtual reality purposes or with a view to allowing individuals to enjoy wide-screen viewing.
For instance, JP-A-2-297516 discloses an optical system made up of a 2D display device
11
for displaying images, an objective collimating lens
12
and a parallel transparent plate
13
having off-axis paraboloidal mirrors on both its ends, as shown in FIG.
6
. Light beams leaving the 2D display device
11
for displaying images are converted by the objective collimating lens
12
into parallel beams, which are then subjected to first transmission through a parallel surface of the parallel transparent plate
13
, reflection at the first paraboloidal mirror, some total reflections within the parallel transparent plate
13
, reflection at the second paraboloidal mirror and second transmission through the parallel surface of the parallel transparent plate
13
(8 reflections and 2 transmissions), whereby an intermediate image is formed on a point F for projection into an observer's eyeball
14
.
U.S. Pat. No. 4,026,641 discloses an optical system wherein, as shown in
FIG. 7
, a image of an image display element
11
is converted by a transmission optical element
15
into a curved object image, which is in turn projected from a toric surface
16
into an observer's eyeball
14
.
A problem associated with an image display device of the type wherein an image thereof is relayed as shown in
FIG. 6
is, however, that it needs not only an ocular optical system, but also a relay optical system, resulting in increases in the size and weight of the whole optical system as well as an increase in the amount of extension of the whole optical system from a person's head or face. Therefore it is not fit for a head-mounted or face-mounted image display device.
The optical system for forming parallel beams as an intermediate image as well as the optical system for projecting an intermediate image into an eyeball produce some considerable aberrations because only the paraboloidal mirrors that have power.
The ocular optical system composed of a concave mirror, as shown in
FIG. 7
, also produces some considerable aberrations and so is detrimental to image quality, even though the concave mirror is defined by a toric surface as shown in FIG.
7
.
To correct for field curvature occurring at the ocular optical system, therefore, it is required to use the transmission optical element
15
such as a fiber plate. Even by use of the transmission optical system
15
and toric surface
16
, however, it is impossible to make adequate correction for coma, and other aberrations.
SUMMARY OF THE INVENTION
In view of such problems associated with the prior art as mentioned above, an object of the present invention is to provide an ocular optical system designed to form no intermediate image, especially, an ocular optical system which is compact and light in weight with well corrected aberrations, and so is best suited for use on a head- or face-mounted image display device.
To achieve the aforesaid object, the present invention provides an ocular optical system comprising at least three juxtaposed optical surfaces, characterized in that at least two optical surfaces of said at least three optical surfaces are defined by curved surfaces which are concave on a pupil position side of said optical system and at least four reflections occur between said curved surfaces.
In this case, it is desired that a space defined by said at least three surfaces be filled with a transparent medium having a refractive index greater than 1.
It is also desired that an image display element be located on an object surface of said ocular optical system, and that a display surface of said image display element be directed to a side opposite to said pupil position.
An account will now be given of why the aforesaid arrangement is used in the present invention and how it works.
The present invention is concerned with an optical system layout needed for locating an ocular optics system in a compact manner. In other words, making the ocular optical system is important for making, for instance, an image display device on which it is used thin. By making the display device thin, it is possible to reduce the moment of inertia even at the same weight because the center of gravity comes close to the center of an observer's head. In short, the ability of the display device to follow the movement of the observer's head is much improved.
According to the present invention, therefore, there is provided an ocular optical system designed to project an image of an image display element directly into an observer's eyeball without recourse to any relay optical system.
According to the present invention, the ocular optical system can successfully be made thin by allowing light rays to reciprocate therein, thereby defining a turn-back optics path.
It should here be noted that only by use of a turn-back optics path it is impossible to achieve a wide-enough viewing angle. For this reason, it is essentially important that at least two reflecting surfaces are defined by curved surfaces concave on the pupil position side of the optical system, and that light rays reflect between the curved surfaces while a light beam converges simultaneously with repeated reflection within the ocular optical system.
In other words, reflecting surfaces of concave mirrors, convex mirrors or the like are more reduced than refracting surfaces having the same power in terms of the quantity of aberrations generated, and do not give rise to chromatic aberration at all. The use of three or more reflecting surfaces having power enables the power to be so dispersed that projection can be achieved with more reduced aberrations if the power is on the same level. By properly locating concave and convex mirrors at proper intervals it is additionally possible to keep aberrations in a good state because field curvature, spherical aberration and other aberrations generated at the reflecting surfaces of those concave and convex mirrors can be offset with one another.
If there is provided a turn-back optics path allowing at least four reflections to occur between those mirrors, it is then possible to make the optical system compact and thin.
If two of at least three optical surfaces are located with their concave surfaces directed to the observer's eyeball located on the pupil position side of the optical system, it is then possible to obtain, with reduced coma, an observed image which has high resolution yet is clear over its whole length and breadth.
If the space defined by the aforesaid three surfaces is filled with a medium having a refractive index greater than 1, it is then possible to construct the reflecting surfaces of back-surface mirrors, and hence, reduce the occurrence of coma and spherical aberration. This is because back-tracing light rays from the pupil converge upon being transmitted through the second transmitting surface (a second transmitting surface as counted from the image display element side) whereby the diversion of light rays within the optical system is more reduced as compared with an optical system defined by surface mirrors when making sure of the same viewing angle, so that it is possible to reduce aberrations generated at the reflecting surfaces and, at the same time, to make the optical system compact without giving rise to any shading of light rays.
When the ocular optical system of this invention is used with an image display device, it is desired that the image display element be located on the object surface of the ocular optics system with its display surface located on the opposite side of the pupil posi
Mack Ricky
Olympus Optical Co,. Ltd.
Pillsbury Madison & Sutro LLP
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