Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2000-01-07
2001-01-30
Gray, David M. (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S081000, C353S099000, C348S771000
Reexamination Certificate
active
06179424
ABSTRACT:
This application is based on application No. H11-008671 filed in Japan on Jan. 18, 1999, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical system for a projector, and particularly to such an optical system for a projector as incorporates a reflection-type spatial light modulator, such as a digital mirror device™ (or DMD™ for short, manufactured by Texas Instruments Incorporated; hereinafter referred to simply as a digital mirror device or DMD), that is provided with a large number of variable-reflection-angle mirror elements that can vary the reflection angle of the light incident thereon in accordance with a video signal so that only the light corresponding to the video signal will be reflected toward a projection optical system.
2. Description of the Prior Art
In recent years, as higher and higher resolution is desired in images in general, also in the field of projectors, development of techniques has been sought that achieve a substantial increase in the number of pixels without making the optical system larger. One attempt to meet such needs is the development of a projector employing a DMD.
A DMD is produced by forming a large number of minute rectangular high-reflectance mirror elements, of which the inclination is variable in accordance with a video signal, on a silicon memory chip by a process as used to manufacture a semiconductor device. A projector employing such a DMD, by varying the inclination of those mirror elements, controls the direction in which it reflects the illumination light incident thereon in such a way as to converge only the desired parts of the reflected light on a screen and thereby project a desired image thereon.
In accordance with a video signal, the individual mirror elements of a DMD, when in an on state, reflect light toward a projection optical system and, when in an off state, change their inclination to reflect light in a different direction so that the light will not enter the projection optical system. However, owing to restrictions imposed on the design of a projector, the light reflected from the mirror elements when they are in an off state is shone on a side-wall portion of a prism constituting a prism system disposed between the DMD and the projection optical system, and therefore there is a possibility of this light being further reflected therefrom so as to enter the projection optical system.
In particular, when the prism is surrounded by a medium, such as air, having a small refractive index, most of the above-mentioned light shone on the side-wall portion of the prism is reflected from the inner surface of the side-wall portion of the prism, and this greatly increases the amount of such secondary-reflection light. This secondary-reflection light (unnecessary, or stray, light), when it enters the projection optical system, may cause another image (a ghost) separate from the normal image to appear on the screen.
One way to prevent such entry of secondary-reflection light into the projection optical system is to form the side-wall portion of the prism into a diffusive surface that diffuses the light incident thereon. Another way is to paint the outer surface of the side-wall portion of the prism black, or to vapor-deposit on that surface a light-absorbing dielectric film, or to affix to that surface a member having a bottom surface so shaped as to absorb light so that this bottom surface will absorb light and convert it into heat.
The method of absorbing light and converting it into heat by the use of a member having a bottom surface so shaped as to absorb light is adopted, for example, in the projector-oriented optical system disclosed in Japanese Laid-Open Patent Application H9-96867. In this optical system, a heat-dissipating member having a comb-tooth-shaped bottom surface is arranged so as to face a side wall of a prism, with a shock-absorbing pad in between, in such a way that this bottom surface is kept in close contact with the shock-absorbing pad. In this optical system, the recessed portions of the comb-tooth-shaped bottom surface absorb light and convert it into heat, and the heat-dissipating member as a whole dissipates the resulting heat.
However, even if light is diffused, it is inevitable that part of the diffused light will enter the projection optical system. It is practically impossible to form a black thin film that completely absorbs the light incident thereon, and therefore, even if a black thin film is applied, some light, left unabsorbed, may enter the projection optical system. It is difficult to produce a member having so intricate a shape as to absorb completely the light incident thereon, and therefore it is inevitable that part of the incident light will be reflected or diffused in the vicinity of the protruding portions of the comb-tooth-shaped bottom surface of this member.
SUMMARY AND WORKING PRINCIPLE OF THE INVENTION
An object of the present invention is to provide a projector-oriented optical system in which entry of unnecessary light into a projection optical system is prevented more strictly than ever.
To achieve the above object, according to one aspect of the present invention, an optical apparatus is provided with: a reflection-type spatial light modulator having a plurality of minute variable-reflection-angle mirrors that individually deflect the light incident thereon in one of two different directions, namely in a first direction or in a second direction, in accordance with a signal fed in; an optical system to which the light deflected in the first direction by the modulator is directed; a prism disposed between the modulator and the optical system so as to direct the light deflected in the first direction by the modulator to the optical system and direct the light deflected in the second direction by the modulator to a side face of the prism; and a light-expelling member having a polyhedral shape and disposed with an entrance face thereof kept in close contact with the side face of the prism. The light-expelling member is so designed that the light deflected in the second direction by the modulator enters the light-expelling member through the entrance face thereof and exits from the light-expelling member through a face thereof other than the entrance face.
In this optical apparatus, preferably, the light-expelling member has a second flat face opposite to the entrance face and is so designed that the entrance face and the second flat face approach each other according as the distance to the modulator decreases, and that the angle &thgr; formed between the two lines lying where the entrance face and the second flat face respectively cut the plane that includes both a normal to the entrance face and the optical axis of the optical system fulfills the condition
&thgr;≧1/2[sin
−1
(
n
1
2
)−sin
−1
{(
n
1
2
) sin &agr;
1
}]
where n
1
represents the refractive index of the prism, n
2
represents the refractive index of the light-expelling member, and &agr;
1
represents the minimum angle of incidence of light incident on the entrance face.
According to another aspect of the present invention, a projector is provided with: an illumination optical system that includes a light source and that emits the illumination light generated by the light source; a reflection-type spatial light modulator having a plurality of minute variable-reflection-angle mirrors that individually deflect the illumination light emitted from the illumination optical system in one of two different directions, namely in a first direction or in a second direction, in accordance with a signal fed in; a projection optical system to which the light deflected in the first direction by the modulator is directed; a prism disposed between the modulator and the optical system so as to direct the illumination light emitted from the illumination optical system to the modulator, direct the light deflected in the first direction by the modulator to the optical system, and dir
Blackman Rochelle
Gray David M.
Minolta Co. , Ltd.
Sidley & Austin
LandOfFree
Optical system for a 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 Optical system for a projector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical system for a projector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2533414