Optics: image projectors – Plural projection paths with single light source
Patent
1989-11-15
1991-07-02
Miller, Stanley D.
Optics: image projectors
Plural projection paths with single light source
350337, 353 31, 353 81, 353 84, G02F 1133, G03B 2114, G03B 2128
Patent
active
050281216
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a projection device with a light source and an arrangement for generating a white parallel light beam, with at least one dichroic prism which is provided on three of its sides with liquid crystal light valve arrangements allocated to three different color image separations, and with an objective through which the color image separations generated by the light valve arrangements can be projected in common onto a canvas.
Such a projection device for projecting color images without the use of a cathode ray tube is described in S. Morozumi et al., SID 86 DIGEST (1986), pages 375 ff. The liquid crystal light valve arrangements allocated to the color image separations are arranged on three face sides of a dichroic prism, the projection objective being arranged on the fourth face side. The white parallel light beam coming from the light source is deflected with the aid of a mirror arrangement with two dichroic mirrors in such a way that it passes over the light valve arrangements into the interior of the dichroic prism and from there to the projection objective.
Proceeding from this state of the art, underlying the invention is the problem of creating a projection device which makes it possible to achieve a higher light yield and/or image resolution.
This problem is solved according to the invention by the means that two dichroic color divider cubes with reflectively operating light valve arrangements are provided which are coupled in each case with one of the outputs of a polarizing beam divider allocated to the various polarization directions, through which, on the one hand the white light beam is divisible onto the two color divider cubes and through which, on the other hand, the light which returns to the color divider cubes of the activated image points is leadable into the objective.
Expedient formations and further developments of the invention are characterized in the subclaims.
In the following the invention is explained in detail with the aid of the drawing.
FIG. 1 shows a projection device according to the invention in a schematic perspective view;
FIG. 2 a view corresponding to FIG. 1, in which the dielectric coatings of the various optical components are shaded;
FIG. 3 the beam divider cube of the device of the invention in an enlarged representation to illustrate the various polarization directions;
FIG. 4 a cross section through one of the liquid crystal light valves of the projection device;
FIG. 5 a schematic plan view of a liquid crystal matrix display which is used as light valve;
FIG. 6 the first color divider cube of the projection device, in a perspective view;
FIG. 7 the second color divider cube in a perspective view to illustrate the differing orientations of the dichroic color divider layers;
FIG. 8 a second form of execution of the beam divider cube and
FIG. 9 a third form of execution of the beam divider cube.
The electro-optical projection device represented in FIG. 1 has a light source 1 delivering white light, to which there are allocated a reflector 2 and collimator lens 3 in order to generate a white parallel light beam bundle, which is schematically illustrated in FIG. 1 by its center line 4. The light beam 4 is deflected with the aid of a deflecting mirror 5. The deflected light beam 6 acts upon a light valve unit 7. In the light valve unit 7, in correspondence to the images to be projected, the white light beam bundle 6 is influenced in the manner discussed further below in its color distribution and intensity distribution in such a way that with the aid of an objective 8 a projection image is formed on a canvas (not represented in the drawing). The central axis of the light leaving the light valve unit 7 is provided in FIG. 2 with the reference number 9.
The light valve unit 7 contains a polarizing beam divider cube 10, the upper side 11 of which serves as light inlet for the light beam 6 and the side 12 of which, facing to the right in FIGS. 1, 2 and 3, serves as light outlet. The beam divider cube 10 is a MacNeille prism, the vaporized-on polarizing
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"Practical Methods of Making and Using Multilayer Filters", Mary Banning, urnal of the Optical Society of America, vol. 37, No. 10, Oct. 1947, pp. 792-797.
"LCD Full-Color Video Projector", Shinji Morozume et al., SID 86 Digest, pp. 375-378.
Baur Gunter
Pickelmann Lutz
Seibel Jorg
Fraunhofer-Gesellschaft Zur Forderung der Angewandten Forschung
Gross Anita Pellman
Miller Stanley D.
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