Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-08-24
2002-07-16
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
C359S637000, C359S631000, C359S633000
Reexamination Certificate
active
06421184
ABSTRACT:
This application claims benefit of Japanese Application No. 2000-254052 filed in Japan on Aug. 24, 2000, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical path splitting element and an image display apparatus using the same. More particularly, the present invention relates to an optical path splitting element for splitting a light beam from a single object into two optical paths. The present invention also relates to a head- or face-mounted image display apparatus using such an optical path splitting element.
2. Discussion of Related Art
There has heretofore been known an optical path splitting element for leading an image displayed by a single display device to both eyes of an observer, as disclosed in Japanese Patent Application Unexamined Publication No. [hereinafter referred to as “JP(A)”] 9-181999. This splitting element uses a single prism to split a light beam from the displayed image into two optical paths extending in different directions.
In an image display apparatus using the above-described splitting element, however, when the image display device is reduced in size, it is necessary to shorten the focal length of the optical system while ensuring the required eye relief. Therefore, it is difficult to construct a viewing optical system of wide field angle.
There has also been proposed an image display device using a half-mirror to split an optical path as disclosed in JP(A) 9-061748.
In the above-described conventional optical path splitting element that splits the light beam into two optical paths extending in different directions, the size of the optical path splitting element becomes unfavorably large. Accordingly, an image display apparatus using the optical path splitting element becomes undesirably large in size and heavy in weight. The above-described conventional method of splitting an optical path by using a half-mirror suffers from the problem that because the light quantity is halved for each optical path, the image for observation becomes dark.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described problems with the prior art.
Accordingly, an object of the present invention is to provide a compact optical path splitting element having a reduced number of components and also provide an image display apparatus using the optical path splitting element. More specifically, the present invention provides an optical path splitting element having at least two split axial principal rays each extending from the center of an object to the center of an image. The optical path splitting element uses a three-dimensional optical system in which bent segments forming each of the axial principal rays lie in at least two planes, thereby making the optical path splitting element compact in size. At the same time, a power is given to the optical path splitting element to reduce the number of components thereof.
To attain the above-described object, the present invention provides an optical path splitting element for splitting a light beam from a single object into two optical paths. The optical paths in the optical path splitting element are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a straight line passing through the center of the object. The optical path splitting element has at least two pairs of reflecting surfaces in the optical paths. When a pair of reflecting surfaces closest to the object side of the optical path splitting element among the at least two pairs of reflecting surfaces are defined as a left first reflecting surface and a right first reflecting surface, respectively, and a pair of reflecting surfaces closest to the exit side of the optical path splitting element among the at least two pairs of reflecting surfaces are defined as a left final reflecting surface and a right final reflecting surface, respectively, the optical paths in the optical path splitting element are arranged so that the entering optical axis of an axial principal ray incident on the left first reflecting surface and the exiting optical axis of the axial principal ray exiting from the left final reflecting surface are not coplanar with each other, and the entering optical axis of an axial principal ray incident on the right first reflecting surface and the exiting optical axis of the axial principal ray exiting from the right final reflecting surface are not coplanar with each other. At least one pair of the at least two pairs of reflecting surfaces are formed from rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
In addition, the present invention provides an image display apparatus including an optical path splitting element for splitting a light beam from a single object into two optical paths. The optical paths in the optical path splitting element are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a straight line passing through the center of the object. The optical path splitting element has at least two pairs of reflecting surfaces in the optical paths. When a pair of reflecting surfaces closest to the object side of the optical path splitting element among the at least two pairs of reflecting surfaces are defined as a left first reflecting surface and a right first reflecting surface, respectively, and a pair of reflecting surfaces closest to the exit side of the optical path splitting element among the at least two pairs of reflecting surfaces are defined as a left final reflecting surface and a right final reflecting surface, respectively, the optical paths in the optical path splitting element are arranged so that the entering optical axis of an axial principal ray incident on the left first reflecting surface and the exiting optical axis of the axial principal ray exiting from the left final reflecting surface are not coplanar with each other, and the entering optical axis of an axial principal ray incident on the right first reflecting surface and the exiting optical axis of the axial principal ray exiting from the right final reflecting surface are not coplanar with each other. At least one pair of the at least two pairs of reflecting surfaces are formed from rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations. The image display apparatus further includes an image display device placed at the position of the object. The left and right eyeballs of an observer are placed at left and right exit pupils formed in the left and right optical paths exiting the optical path splitting element, thereby allowing observation of an image displayed by the image display device.
The reasons for adopting the above-described arrangements in the present invention, together with the functions thereof, will be described below.
FIG. 1
is a perspective view schematically showing the surfaces and optical axes of a viewing optical system of an image display apparatus according to Example 1 (described later). The viewing optical system includes an optical path splitting element
10
and a pair of ocular optical systems
20
L and
20
R (left and right). The optical path splitting element
10
is formed from a decentered prism. The viewing optical system has a single image display device
1
common to left and right optical systems. A display light beam from the image display device
1
is split into left and right beams through the optical path splitting element
10
. The beams are passed through the left and right ocular optical systems
20
L and
20
R to project enlarged images of the image display device
1
into the left and right eyeballs of an observer. In Example 1, the optical path splitting element
10
has a first surface
11
as a common entrance surface (refracting surface) through which left and right axial principal rays
2
L and
2
R emanating from the image display device
1
at an angle to each other enter the opti
Mack Ricky
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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