Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2002-04-25
2004-06-29
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S632000
Reexamination Certificate
active
06757107
ABSTRACT:
This application claims benefit of Japanese Application No. 2001-127806 filed in Japan on Apr. 25, 2001, 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 and 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 on a single display device to both eyes of an observer, as disclosed in Japanese Patent Application Unexamined Publication Number (hereinafter referred to as “JP(A)”) Hei 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) Hei 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 the image for observation becomes unfavorably dark because the light quantity is halved for each optical path.
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 at least two optical paths. The optical path splitting element has a prism member formed from a medium having a refractive index (n) larger than 1 (n>1). The prism member has an entrance surface through which the light beam from the object enters the prism member. The prism member further has at least one reflecting surface reflecting the light beam within the prism member, and an exit surface through which the light beam exits the prism member. Moreover, the prism member has at least one rotationally asymmetric surface. At least one optical functional surface of the prism member is a discontinuous surface formed from at least two surfaces adjacent to each other. The other optical functional surfaces of the prism member are common to the at least two optical paths.
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 at least two optical paths. The optical path splitting element has a prism member formed from a medium having a refractive index (n) larger than 1 (n>1). The prism member has an entrance surface through which the light beam from the object enters the prism member. The prism member further has at least one reflecting surface reflecting the light beam within the prism member, and an exit surface through which the light beam exits the prism member. Moreover, the prism member has at least one rotationally asymmetric surface. At least one optical functional surface of the prism member is a discontinuous surface formed from at least two surfaces adjacent to each other. The other optical functional surfaces of the prism member are common to the at least two optical paths. The image display apparatus further includes an image display device disposed at the position of the object, and an ocular optical system having at least a positive power to project the at least two optical paths split by the optical path splitting element near an eyeball of an observer.
In this case, it is desirable that the ocular optical system should have at least one rotationally asymmetric surface.
The reasons for adopting the above-described arrangements in the present invention, together with the functions thereof, will be described below.
The present invention features an optical path splitting element that splits a light beam from an object into at least two light beams and allows the light beams to exit at a desired angle and with a desired optical axis separation while performing aberration correction appropriately.
It is known that an optical system that is compact and has minimal aberrations can be constructed by using a decentered prism as an optical element.
A specific example of such an optical apparatus is shown in JP(A) 2000-221440. That is, an optical apparatus has a relay optical system for forming an observation image as a relay image and an ocular optical system for forming an exit pupil to lead the relay image to an observer. The relay optical system has a decentered prism formed from a medium having a refractive index (n) larger than 1 (n>1). The decentered prism has an entrance surface through which a light beam from an image display device enters the decentered prism. The decentered prism further has at least one reflecting surface reflecting the light beam within the decentered prism, and an exit surface through which the light beam exits the decentered prism. The at least one reflecting surface has a curved surface configuration that gives a power to the light beam. The curved surface configuration is a rotationally asymmetric surface configuration that corrects aberrations due to decentration. The ocular optical system comprises a concave mirror. The concave mirror has a rotationally asymmetric curved surface configuration that gives a power to the light beam upon reflection and corrects aberrations due to decentration.
A refracting optical element such as a lens is provided with a power by giving a curvature to an interface surface thereof. Accordingly, when rays are refracted at the interface surface of the lens, chromatic aberration unavoidably occurs according to chromatic dispersion characteristics of the refracting optical element. Consequently, the common practice is to add another refracting optical element for the purpose of correcting the chromatic aberration.
Meanwhile, a reflecting optical element such as a mirror or a prism produces no chromatic aberration in theory even when a reflecting surface thereof is provided with a power, and need not add another optical element only for the purpose of correcting chromatic aberration. Accordingly, an optical system using a reflecting optical element allows the number of constituent optical elements to be reduced from the viewpoint of chromatic aberration correction in comparison to an optical system using a refracting optical element.
At the same time, a reflecting optical system using a reflect
Dang Hung Xuan
Olympus Corporation
Pillsbury & Winthrop LLP
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