Optical: systems and elements – Stereoscopic – Stereo-viewers
Reexamination Certificate
2001-05-07
2003-04-08
Chang, Audrey (Department: 2872)
Optical: systems and elements
Stereoscopic
Stereo-viewers
C359S464000, C359S462000, C345S009000, C348S051000, C348S052000
Reexamination Certificate
active
06545803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a display device which displays an output, such as characters or image information, from an output device such as a computer, a television (TV), a video player, an optical disc drive, a TV phone, a TV or computer game and the like, and more particularly, the present invention relates to a virtual screen (VS) display device which enlarges and displays an image in space as an observed image while a background behind the VS display device can be simultaneously observed. The VS display device can be a VS stereoscopic display device and is applicable to a head-up display (HUD), a head mount display (HMD), a projector type color image display device, a liquid crystal projector, a portable display and other display devices.
2. Description of Related Art
Conventional virtual screen display devices are known in which an image displayed on a cathode ray tube (CRT), a liquid crystal display element (LCD) or another image display is enlarged and displayed in space as an observed image, rather than a displayed image as displayed on the CRT or LCD or the like, by using a hologram combiner or another combiner and such that a background located behind or on the rear side of the combiner can be simultaneously observed or seen while viewing an image displayed on the virtual screen display device. Also, a display device for enlarging and projecting a three-dimensional image is known.
For example, a display system described in Japanese Patent Application Laid-open Publication No. 1-147421/1989 uses a volume phase hologram or the like as a light flux combining element to polarize only a light flux having a specified wavelength and project the specified wavelength light flux toward an observer. The observer can observe the displayed information and another person's face in the same field of view while the displayed information can not be viewed or read by the other person.
A display device described in Japanese Patent Application Laid-open Publication No. 8-201722/1996 is provided with an optical filter including a plurality of surface-splitting filter portions having different transmission wavelengths and a hologram combiner which displays virtual images of a plurality of display images which are transmitted through the filter portions of the optical filter in a different position or substantially the same position as that seen by an observer.
A three-dimensional image projecting device described in Japanese Patent Application Laid-open Publication No. 9-243961/1997 is provided with a projecting lens for enlarging and projecting a three-dimensional image, a first concave mirror forming an enlarged virtual image of the image output from the projecting lens and a second concave mirror forming a real image of an image output from the projecting lens. It is further described that in the three-dimensional image projecting device, first and second holograms are used instead of first and second concave mirrors such that the virtual image of the projecting lens is positioned at the center of curvature of the second concave mirror and such that the first and second holograms are arranged to be connected to each other.
In JP 1-147421/1989, since a volume phase diffraction grating is used as the combiner, a substantially plane surface must serve in the same manner as a spherical surface. Therefore, a display light flux is directed toward the observer's eyes even when the combiner is arranged vertically. However, the display has a disadvantage in that the display can be performed only within a specified wavelength.
In JP 8-201722/1996 described above, an optical filter similar to a display information color filter is divided into a plurality of regions, but the image divided into regions on the optical filter can be displayed at substantially the same position by laminating or exposing multiple layers of the hologram combiner for each wavelength. Therefore, a full-color display is possible. On the other hand, since the image displayed on an LCD or CRT is displayed as a virtual image as it is, the LCD or CRT must be enlarged while maintaining high resolution which results in significantly increased cost. Furthermore, a broad, uniform and highly luminous light source is necessary for such an apparatus for proper viewing of the virtual image. Such a light source is technically complicated and significantly increases the cost of the apparatus.
In JP 9-243961 described above, although the structure is applied to a three-dimensional image projecting device, a field optical element may include a concave mirror or a reflective hologram, i.e., an optical system of a so-called VS (virtual screen) display device. In this device, two components of the concave mirror or the hologram are used to enlarge an observation view region. Specifically, the optical system includes the first concave mirror for forming the enlarged virtual image of the projecting lens and the second concave mirror for forming the real image of the projecting lens, and the observation view region is enlarged by locating the virtual image of the projecting lens in the curvature center of the second concave mirror. However, in this device, a projected object is enlarged about 1.94 times while the observation view field is enlarged twice or about 2.0 times. Therefore, a distinguishing effect cannot be obtained and the image is not easily viewable. Strangely, the magnitude of the projecting lens is not expressly described in this reference, although the projecting lens actually has a size of an exit pupil. Therefore, it is uncertain how much or to what degree the observation view region is enlarged as compared with the related devices described above. Even assuming that an F number of the projecting lens is set to F=1.4, a focal distance f is 300 mm, then the observation view region is 429 mm when the diameter of the exit pupil is 214 mm. Although this is a good value, such level can be realized without using two concave mirrors as described later in the preferred embodiments of the present invention. Moreover, the use of two concave mirrors and locating the virtual image of the optical projecting element formed by the first concave mirror in the curvature center of the second concave mirror excessively restricts the freedom in designing an optical system layout. This means that the possibility of developing various applications is remarkably reduced.
In another related device, conventional projection type color image display devices using a liquid crystal panel are known to use either a three-plate system or a single-plate system. In the three-plate system, three liquid crystal panels are used, and three color component images, i.e., red, green and blue images of a color image to be displayed are displayed on the individual liquid crystal panels. These three liquid crystal panels are separately irradiated with red, green and blue lights, and the red, green and blue lights transmitted through the liquid crystal panels are focused by a common image forming lens to synthetically form an image on a screen, and thereby a color image is displayed.
In the single-plate system, one liquid crystal panel (single-plate liquid crystal panel) is used. Red, green and blue component images are simultaneously displayed on the single-plate liquid crystal panel. The red component image is irradiated with a red light, the green component image is irradiated with a green light and the blue component image is irradiated with a blue light. The red, green and blue light for irradiation is obtained from a single white light source and by using a color separator as described below. Light fluxes transmitted through the single-plate liquid crystal panel are focused by a common image forming lens to form an image on a screen, and thereby a color image is displayed.
In the three-plate system, since the red, green and blue component images are separately displayed on the three liquid crystal panels, each component image can be displayed with a high picture element density
Momose Akira
Obu Makoto
Sakuma Nobuo
Chang Audrey
Greenberg & Traurig, LLP
Manak Joseph M.
Ricoh & Company, Ltd.
Rzucidlo Eugene C.
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