Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-12-02
2001-12-04
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S629000, C359S833000, C353S081000
Reexamination Certificate
active
06327092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cross dichroic prism and an optical system having the same, and is suitable, for example, as color separating means and/or color combining means for use in a color liquid crystal projector, a three-plate CCD camera or the like.
2. Related Background Art
A cross dichroic prism P as shown in
FIGS. 13 and 14
of the accompanying drawings has heretofore been used as the color separating means or color combining means of a color liquid crystal projector.
The cross dichroic prism P, as shown in
FIG. 13
, comprises four rectangular prisms
1
,
2
,
3
and
4
of triangle poles cemented together so that the apex angles of those prisms may intersect with one another. A dichroic surface (film) is provided on the joined surface of each prism. The dichroic surface intersects with other surface at 90°.
The cross dichroic prism according to the prior art comprises four rectangular prisms cemented together as previously described and therefore suffers from the problem that it is bulky and heavy. Particularly in a liquid crystal projector using a liquid crystal panel provided with a microlens for condensing light for each pixel, a light beam emerging from the liquid crystal panel is great in angle of divergence due to the action of the microlens, and it has been necessary to make the cross dichroic prism provided between the liquid crystal panel and a projection lens considerably large.
SUMMARY OF THE INVENTION
The present invention has as its object the provision of a compact cross dichroic prism and an optical system using the same.
The cross dichroic prism according to a first aspect of the invention is a cross dichroic prism in which four square pillar prisms, of which the total of the angles including the prism ridge lines is 360°, are joined together with the prism ridge lines thereof made coincident with one another, and prism sides forming the respective prism ridge lines are joined together so that the joined surface thereof may become two planes intersecting with each other. Dichroic film is provided on the joined surface. When the lengths of perpendiculars from a point on the prism ridge line to the non-joined surfaces of the respective square pillar prisms are defined as L1, L2, L3 and L4,
L1≠L2=L3=L4
is satisfied.
The term “square pillar” is not limited to a square shape but includes the meaning of “prismatic shape”.
A second aspect of the invention is characterized in that in the first aspect of the invention a set of square pillar prisms of two opposedly disposed square pillar prisms of the four square pillar prisms are equal in the area of the non-joined surface thereof to each other and the other set of square pillar prisms differ in the area of the non-joined surface thereof from each other.
A third aspect of the invention is characterized in that, in the first or second aspects of the invention, two of the four square pillar prisms are isosceles square pillar prisms of which the two sides are equal and the other two are square pillar prisms of which the sides differ in length from one another.
The optical. system according to a fourth aspect of the invention is characterized by the cross dichroic prism of any one of the first to third aspects of the invention.
The projection apparatus according to a fifth aspect of the invention is characterized in that, by the utilization of the cross dichroic prism of any one of the first to third aspects of the invention, a plurality of image lights differing in color from one another are projected by a projection optical system.
The cross dichroic prism according to a sixth aspect of the invention is characterized in that one of a set of opposed light transmitting surfaces is made smaller than the other.
The cross dichroic prism according to a seventh aspect of the invention is characterized by providing another set of light transmitting surfaces which are opposed to each other and have the same light transimitting area.
The cross prism of an eighth aspect of the invention is characterized in that one of a set of opposed light transmitting surfaces is made smaller than the other.
A ninth aspect of the invention is characterized in that in the eighth aspect of the invention there is provided another set of light transmitting surfaces which have the same size and are opposed to each other.
A tenth aspect of the invention is characterized in that in the eighth aspect of the invention half-transmitting films crossing each other are supplied to the interior of the prism.
An eleventh aspect of the invention is characterized in that in the eighth aspect of the invention dichroic films crossing each other are supplied to the interior of the prism.
The optical system of a twelfth aspect of the invention is a light combining optical system having the cross dichroic prism of the sixth aspect of the invention, characterized in that three divergent lights to be combined are caused to enter the prism from the one small light passing surface and light passing surfaces on the opposite sides of the light passing surface.
The optical system of a thirteenth aspect of the invention is a light combining optical system having the cross prism of any one of the ninth to eleventh aspects of the invention, characterized in that three divergent lights to be combined are caused to enter the prism from the one small light passing surface and light passing surfaces on the opposite sides of the light passing surface.
The optical system of a fourteenth aspect of the invention is a light separating optical system having the cross dichroic prism of the sixth aspect of the invention, characterized in that a convergent light to be separated is caused to enter the prism from the other large light passing surface.
The optical system of a fifteenth aspect of the invention is a light separating optical system having the cross prism of any one of the ninth to eleventh aspects of the invention, characterized in that a convergent light to be separated is caused to enter the prism from the other large light passing surface.
A sixteenth aspect of the invention is a projection apparatus characterized by utilization of a prism according to any one of the sixth to eleventh aspects of the invention, a plurality of image lights differing in color from one another are projected by a projection optical system.
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patent: 0 945 749 (1999-09-01), None
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patent: 2-220040 (1990-09-01), None
Canon Kabushiki Kaisha
Epps Georgia
Fitzpatrick ,Cella, Harper & Scinto
Seyrafi Saeed
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