Optics: image projectors – Unitary plural refracting surfaces
Reexamination Certificate
2001-01-26
2003-08-05
Dowling, William (Department: 2851)
Optics: image projectors
Unitary plural refracting surfaces
C353S028000, C353S098000
Reexamination Certificate
active
06601958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector.
2. Description of Related Art
In recent years, attention has been focused on a projector (namely, a liquid crystal projector) employing a reflection type liquid crystal device. In such a reflection type liquid crystal device, a structure, such as a transistor, for driving a liquid crystal is incorporated under a reflection mirror. Consequently, the pixel density of the device can be enhanced. Therefore, the reflection type liquid crystal device has an advantage in that a higher-resolution and clearer projection image can be realized, as compared with the case of using a transmission type liquid crystal device.
Further, there has been proposed the use of an integrator optical system or a polarization conversion illumination system in a projector employing an electro-optical device, such as a liquid crystal device, so as to realize a bright projection image, which is free from display unevenness, and to reduce the size of the entire projector (see Japanese Unexamined Patent Application Publication Nos. 8-34127 and 10-232430). In the integrator optical system, a light beam coming from a light source is divided by a light beam dividing optical element into a plurality of light beams to thereby form a plurality of light source images, which are regarded as pseudo light sources. Then, light beams from a plurality of light source images are superposed on a liquid crystal panel. Consequently, light beams having uniform intensity distribution can be obtained. Further, in the polarization conversion illumination system, the illumination light beam is first separated into a plurality of light beams and then undergo the polarization conversion. Then, the light beams are superposed on the liquid crystal device. Consequently, illumination light beams whose polarization directions are uniform can be obtained.
Thus, it is considered that a higher-resolution and brighter projection image, which is free from display unevenness, can be realized by the use of the integrator optical system or the polarization conversion illumination system in combination with the reflection type liquid crystal device that is employed in the projector.
SUMMARY OF THE INVENTION
In the case of using a reflection type liquid crystal device, which utilizes a polarization mode as a display mode, in a projector, generally, a polarization beam splitter for spatially separating light beams, which are respectively in different polarization states, is used. This beam splitter has polarization separation characteristics that largely depend on an incidence angle of a beam. Practically, the polarization separation characteristics of this beam splitter have incidence-angle dependency according to which the polarization separation performance extremely lowers when the incidence angle of light becomes larger in a plane perpendicular to a plane of incidence defined in such a way as to include a substantially center axis of incident light and a normal to the polarization separation film of the beam splitter. Further, in the integrator optical system and the polarization conversion illumination system, optical processes performed therein inevitably result in increase in the incidence angle.
Thus, in the case of using the combination of the integrator optical system and the polarization conversion illumination system in the projector that employs the reflection type liquid crystal device, the incidence angle of light impinging upon the polarization beam splitter is increased. Thus, such a projector has problems in that the polarization separation performance of the polarization beam splitter is degraded, and that the light utilization efficiency thereof is lowered.
The present invention is accomplished in view of at least the aforementioned problems. One object of the present invention is to provide a projector that can at least realize a bright projection image with high light utilization efficiency by using the combination of a reflection type liquid crystal device and an integrator system or a polarization conversion illumination system.
According to an exemplary embodiment of the present invention, there is provided a projector which may include: an illumination device including a light beam dividing optical element for dividing a light beam into a plurality of sub light beams and for forming a plurality of light source images from the plurality of sub light beams; an electro-optical device for modulating an illumination light beams emitted by the illumination device; a projection lens for projecting light beams modulated by the electro-optical device; and a polarization separation film for selecting a light beam of a predetermined polarization component included in the illumination light beam emit the selected light beam of the predetermined polarization component to the electro-optical device, and for selecting a light beam of a predetermined polarization component from the light beams modulated by the electro-optical device to emit the selected light beam of a predetermined polarization component to the projection lens. The light beam dividing optical element is a rod-like light guide having an incidence end surface, an exit end surface, and at least four reflective surfaces. Assuming that an incident plane is a plane defined by a center axis of the illumination light beam and a normal to the polarization separation film, that a direction parallel to the incident plane and perpendicular to the illumination optical axis is the X-direction and a direction perpendicular to the incident plane is the Y-direction, that a length of the incidence end surface in the X-direction is MX and a length of the incidence end surface in the Y-direction is MY, that placement intervals of the plurality of light source images in the X-direction is SX and placement intervals of the plurality of light source images in the Y-direction is SY, then the lengths MX and MY and the intervals SX and SY meet the following condition:
SY/SX<MY/MX.
The polarization separation performance of a practical polarization separation film has large dependency on the incidence angle of each incident light beam. Especially, when the incidence angle of each of the light beams increases in the Y-direction that is perpendicular to the incident surface, the polarization separation performance is extremely degraded. However, the projector of this exemplary embodiment of the present invention satisfies the condition
SY/SX<MY/MX.
Thus, a range of incidence angles in Y-direction of a light beam impinging on the incident surface can be narrowed. Consequently, the polarization separation performance of the polarization separation film can be enhanced. Thus, a bright projection image having a high contrast ratio can be realized.
Further, in the case that a color separation optical system for separating an illumination light beam from the illumination device into a plurality of color light beams is added to the constituent elements of this projector, and that a plurality of the electro-optical devices for modulating the color light beams separated by the color separation optical system are provided in this projector, a high-resolution color display can be realized.
Preferably, in the projector of this exemplary embodiment, the distance between a pair of the reflection surfaces opposed to each other in the Y-direction of the light guide gradually increases toward the exit end surface from the incidence end surface. With such a configuration, the placement interval in the Y-direction of a plurality of the light source can easily be decreased. Thus, a range of the incidence angle in Y-direction of a light beam impinging on the polarization separation surface can be narrowed. Moreover, the polarization separation performance of the polarization separation film can be enhanced. Furthermore, a space, in which a plurality of images of the light source are formed, can be reduced. Consequently, the area of the polarization separation film can be reduced. Reduction in the size and weight of t
Dowling William
Seiko Epson Corporation
LandOfFree
Projector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Projector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Projector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3102480