Optics: image projectors – Reflector
Reexamination Certificate
2001-11-05
2004-10-19
Dowling, William C. (Department: 2851)
Optics: image projectors
Reflector
C353S038000
Reexamination Certificate
active
06805450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector for projecting and displaying an image.
2. Description of Related Art
In a projector, image light representing an image is formed from illumination light using an electrooptic device, and an image is displayed by projecting the image light. As the electrooptic device, an optical modulation device (emitting direction control-type optical modulation device) for modulating the illumination light according to the image information (image signal) and emitting the image light representing the image, is used. As an example of the optical modulation device, a micro-mirror-type optical modulation device, such as a Digital Micro-mirror Device (registered trademark of Texas Instruments, Inc.; hereinafter, referred to as “DMD”) can be given.
The DMD has a plurality of micro-mirrors corresponding to a plurality of pixels constituting the image. The inclination of the micro-mirrors varies with image information, and the micro-mirrors reflect light according to the inclination thereof. Of the light reflected by the micro-mirrors, the light reflected in a predetermined direction is used as the image light. That is, the DMD is an electrooptic device of a type which controls the direction of reflection of light so as to form image light.
FIG. 13
is a schematic plan view showing a construction of a principal part of a conventional projector using a micro-mirror-type optical modulation device. A projector
5000
includes an illuminating optical system
100
E, a micro-mirror-type optical modulation device
200
, and a projection lens
300
.
The illuminating optical system
100
E includes a light source
110
, a first condenser lens
120
, a color wheel
130
, a light-transmitting rod
180
A, and a second condenser lens
190
.
The light emitted from the light source
110
passes through the first condenser lens
120
, the color wheel
130
, the light-transmitting rod
180
A, and the second condenser lens
190
to enter the micro-mirror-type optical modulation device
200
. The light entered the micro-mirror-type optical modulation device
200
is modulated according to an image signal given to the micro-mirror-type optical modulation device
200
. The light modulated by the micro-mirror-type optical modulation device
200
is projected as light representing an image (image light) via the projection lens
300
, whereby an image is displayed.
There may be many cases where illuminance distribution of the light emitted from the light source
110
is not uniform. When such light is used as illumination light, there may be many cases where the brightness of the displayed image is not uniform according to the illuminance distribution of the illumination light. However, an image displayed by a projector may preferably have uniform brightness and be bright. Thus, in order to solve the problem, the light-transmitting rod
180
A has been often used as in the illuminating optical system
100
E. The light-transmitting rod
180
A is an optical element having the function of emitting light whose illuminance distribution is uniform even if the illuminance distribution of incident light is not uniform.
The light-transmitting rod
180
A is, however, an optical element in which light entered from an incident-side side surface
180
AI of the light-transmitting rod
180
A passes through the light-transmitting rod
180
A while being repeatedly reflected by the inner surface of the light-transmitting rod
180
A, thereby producing a uniform illuminance distribution of light emitted from a side surface
180
AO on the side of an emitting surface. Therefore, in order to produce a uniform illuminance distribution of the light emitted from the light-transmitting rod
180
A, the light entered the light-transmitting rod
180
A must be reflected many times by the inner surface of the light-transmitting rod
180
A. That is, the light-transmitting rod
180
A requires a length according to the illuminance distribution of the light emitted from the light source
110
, and the longer length is more preferable. Consequently, in a projector which utilizes an illuminating optical system using a light-transmitting rod, the length of an optical path of the illuminating optical system (physical length of the optical path between a light source and a micro-mirror-type optical modulation device) is generally elongated, causing a problem in that a reduction in size of the device is difficult.
Incidentally, the brightness of the image displayed by the projector greatly depends on the illuminance of an illumination region to which the light emitted from the illuminating optical system is applied. That is, in illuminating optical systems each emitting the same amount of illumination light, the illuminance increases in the illuminating optical system having a small area of the illumination region to which the illumination light is applied, whereby the image displayed by the projector is brightened. Therefore, the illuminating optical system of the projector may preferably have high illumination efficiency to a light application surface of the electrooptic device. However, when an optical modulation device (emitting direction control-type optical modulation device), such as the DMD, is used as an electrooptic device for the projector, there is a problem in that illumination efficiency of the illuminating optical system is decreased by the positional relationship between the illuminating optical system and the optical modulation device. In addition, this problem also occurs in optical modulation devices for controlling the direction of emission of illumination light applied to a light application surface (including a plurality of pixels) according to image information (for each pixel) to thereby emit image light representing an image.
SUMMARY OF THE INVENTION
It is one aspect of this invention to provide a technique for achieving a reduction in size of a projector using an optical modulation device (emitting direction control-type optical modulation device) for controlling a direction of emission of illumination light applied to a light application surface for each pixel according to image information to thereby emit image light representing an image, by shortening a length of an optical path (physical length of an optical path between a light source and the emitting direction control-type optical modulation device) of an illuminating optical system as compared to that of a conventional illuminating optical system. In addition, it is a second object of this invention to provide a technique for achieving an increase in illumination efficiency of the illuminating optical system.
In order to solve at least a part of the above-described problems, in accordance with the first aspect of the present invention, there is provided a projector, that may include an illuminating optical system for emitting illumination light, an optical modulation device for modulating the illumination light emitted from the illuminating optical system, and a projection optical system for projecting light emitted from the optical modulation device, wherein the optical modulation device is an emitting direction control-type optical modulation device for controlling a direction of emission of illumination light applied to a light application surface of the optical modulation device according to a given image signal to modulate the illumination light, thereby emitting image light representing an image.
The illuminating optical system may include a light source, a first lens array having a plurality of first small lenses for dividing light emitted from the light source into a plurality of partial light beam fluxes, and a second lens array having a plurality of second small lenses corresponding to the plurality of first small lenses.
The plurality of partial light beam fluxes divided by the first lens array are applied onto the entire light application surface of the optical modulation device via the second lens array, respectively. That is, the first lens array and the second lens array
Nishida Kazuhiro
Ushiyama Tomiyoshi
Dowling William C.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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