Optical: systems and elements – Holographic system or element – Head up display
Reexamination Certificate
2003-11-20
2004-12-28
Assaf, Fayez (Department: 2872)
Optical: systems and elements
Holographic system or element
Head up display
C359S014000, C359S015000, C359S630000, C359S631000, C345S008000
Reexamination Certificate
active
06836347
ABSTRACT:
This application claims benefit of Japanese Patent Application No. 2001-122835 filed in Japan on Apr. 20, 2001, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
The present invention relates to a viewing optical system and an image pickup optical system and also pertains to an apparatus using the viewing optical system and/or the image pickup optical system. More particularly, the present invention relates to an optical system for use in an image display apparatus or the like that can be retained on an observer's head or face and can also be added to a portable telephone or a portable information terminal.
In recent years, image display apparatus, particularly head- or face-mounted image display apparatus, have been developed actively for the purpose of enabling the user to enjoy viewing wide-screen images personally. Meanwhile, portable telephones have recently become widespread, and there have been increasing demands that portable information terminals should display images and character data on a large screen.
Under these circumstances, Japanese Patent Application Unexamined Publication Numbers [hereinafter referred to as “JP(A)”] Hei 7-140414 and Hei 9-171151 propose an optical system using a half-mirror as an oblique mirror for branching an optical path in a prism optical system including a concave mirror having a small amount of decentration.
U.S. Pat. No. 5,093,567 and JP(A) 2000-241751 and 2000-180787 propose an optical system in which a first prism having a triangular configuration and a convex lens action is disposed on the eye side of the optical system, and a second prism is disposed to face the first prism across a small air space. These conventional techniques propose a viewing optical system that folds an optical path without loss of light quantity by making use of a total reflection phenomenon occurring owing to the refractive index difference between glass and air produced by the presence of the small air space between the two prisms.
U.S. Pat. No. 4,874,214 proposes a viewing optical system using a holographic element. In this viewing optical system, holographic elements are used at two places, i.e. on an oblique mirror surface that is a plane surface, and on a spherical substrate surface.
In the above-mentioned JP(A) Hei 7-140414 and Hei 9-171151, an oblique mirror disposed in a prism optical system is formed from a half-mirror. With this arrangement, light emitted from an image display device passes through the half-mirror twice. Therefore, the amount of light reduces to ¼, and thus the displayed image becomes unfavorably dark. In order to prevent this problem, it is necessary to illuminate the image display device by using bright illumination or the like consuming more electric power. In a case where the luminance of the light source cannot be increased owing to power consumption or the capability of the light source device, it becomes impossible to view the displayed image under the bright sun.
In the viewing optical systems proposed in U.S. Pat. No. 5,093,567 and JP(A) 2000-241751 and 2000-180787, it is necessary to adjust the optical axes of the two prisms with respect to each other because a small air space is provided between the prisms. Therefore, the assembly cost increases. Further, it is likely that the optical axes of the two prisms will be displaced from each other when an impact or vibration is applied to an apparatus including the viewing optical system.
The optical system proposed in U.S. Pat. No. 5,093,567 is a relay optical system and hence large in size and heavy in weight. Therefore, it is difficult to use the optical system in a portable telephone or a portable information terminal.
The viewing optical system proposed in U.S. Pat. No. 4,874,214 has a spherical holographic element on a spherical surface. Incidentally, a holographic element has two different kinds of optical power, i.e. an optical power derived from a geometrical configuration, and an optical power based on the diffractive effect of the holographic element. Two different kinds of power obtained when a holographic element is provided on a substrate member having a spherical surface, for example, will be explained below with reference to FIGS.
29
(
a
) and
29
(
b
). As shown in FIG.
29
(
a
), the holographic element has a power based on the difference in density of interference fringes, e.g. the pitch of periodic structures in the holographic element. In addition, the holographic element has an optical power derived from the geometrical configuration thereof, as shown in FIG.
29
(
b
). Regarding the optical power based on the geometrical configuration, the optical powers &PHgr; of a conventional optical refractive lens and conventional reflecting mirrors can be calculated according to the following equations:
Refracting system: &PHgr;=(
n
−1)(1
/R
)
Surface-coated mirror: &PHgr;=2
/R
Back-coated mirror: &PHgr;=2
n/R
where &PHgr;: the optical power based on the geometrical configuration
n: the refractive index of the medium
R: the radius of curvature of the hologram substrate
Accordingly, it will be understood from a comparison of the surface-coated mirror with the back-coated mirror that the back-coated mirror can obtain a given optical power based on the geometrical configuration with a gentler curvature (larger curvature radius R) by 1
than in the case of the surface-coated mirror.
That is, even if the geometrical configuration of a reflection type holographic element is formed with a gentle curvature (large curvature radius R), it is possible to obtain a large optical power based on the geometrical configuration by filling the inside of the holographic element with a medium having a refractive index n, e.g. a glass or plastic material, as in the case of the back-coated mirror.
Thus, aberrations occurring at the hologram surface can be suppressed by employing an arrangement that allows a large optical power to be produced with a gentle curvature (large curvature radius R) in the optical system.
However, in the viewing optical system stated in the above-mentioned U.S. Pat. No. 4,874,214, the space between the plane surface and the spherical surface is not filled with a glass or plastic medium. Therefore, it is necessary to form the geometrical configuration with a reduced curvature radius R in order to ensure the required optical power derived from the geometrical configuration having a spherical shape.
When the geometrical configuration is formed with a reduced curvature radius R, aberrations occurring at this reflecting surface increase, and it becomes difficult to effect favorable image display. Further, because there is no optical surface in the optical path between the image plane and the above-described plane surface, it is difficult to correct distortion favorably.
Further, the hologram surface in U.S. Pat. No. 4,874,214 is a spherical surface. In general, methods of bonding a hologram are divided into-one type in which a film-shaped hologram is bonded to a substrate surface, and another type in which a substrate surface is sprayed with a liquid photopolymer or the like as a hologram recording material. The latter method needs to carry out exposure and development after the spraying process. Considering mass-productivity, it is preferable to adopt the method wherein a film-shaped holographic element is bonded to a substrate because this method allows exposure and development to be performed before the holographic element is bonded to the substrate.
However, film-shaped holograms supplied from manufacturers are, in general, plane holograms. It is not easy to bond a film-type holographic element on a three-dimensional curved surface uniformly.
SUMMARY OF THE INVENTION
The present invention was made to solve the above-described problems with the prior art.
An object of the present invention is to provide a viewing optical system for image display apparatus that allows observation of a bright displayed image favorably corrected for aberrations and is easy to assemble, resistant t
Amanai Takahiro
Takeyama Tetsuhide
Watanabe Masachika
Assaf Fayez
Olympus Corporation
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