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United States Patent (19) 11 Patent Number: 6,072,635 Hashizume Et Al

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United States Patent (19) 11 Patent Number: 6,072,635 Hashizume Et Al US006072635A United States Patent (19) 11 Patent Number: 6,072,635 Hashizume et al. (45) Date of Patent: Jun. 6, 2000 54) DICHROIC PRISM AND PROJECTION FOREIGN PATENT DOCUMENTS DISPLAY APPARATUS 7-294.845 11/1995 Japan. 75 Inventors: Toshiaki Hashizume, Okaya; Akitaka Primary Examiner Ricky Mack Yajima, Tatsuno-machi, both of Japan Attorney, Agent, or Firm-Oliff & Berridge, PLC 73 Assignee: Seiko Epson Corporation, Tokyo, 57 ABSTRACT Japan The invention provides a dichroic prism capable of reducing displacements of projection pixels of colors caused by 21 Appl. No.: 09/112,132 chromatic aberration of magnification. A dichroic prism is formed in the shape of a quadrangular prism as a whole by 22 Filed: Jul. 9, 1998 joining four rectangular prisms together. A red reflecting 30 Foreign Application Priority Data dichroic plane and a blue reflecting dichroic plane intersect to form Substantially an X shape along junction Surfaces of Jul. 15, 1997 JP Japan .................................... 9-1900OS the prisms. The red reflecting dichroic plane is convex shaped by partly changing the thickness of an adhesive layer 51 Int. Cl." ............................ G02B 27/12: G02B 27/14 for connecting the rectangular prisms together. Accordingly, 52 U.S. Cl. ............................................. 359/640; 359/634 Since a red beam can be guided to a projection optical System 58 Field of Search ..................................... 359/634, 637, while being enlarged, it is possible to reduce a projection 359/640 image of the red beam to be projected onto a projection plane Via the projection optical System. This makes it 56) References Cited possible to reduce relative displacements of projection pix U.S. PATENT DOCUMENTS els of color beams caused by chromatic aberration of mag nification. 5,098,183 3/1992 Sonehara et al. ......................... 353/31 5,221,998 6/1993 Sugahara ................................. 359/831 18 Claims, 11 Drawing Sheets U.S. Patent Jun. 6, 2000 Sheet 1 of 11 6,072,635 U.S. Patent Jun. 6, 2000 Sheet 2 of 11 6,072,635 g U.S. Patent Jun. 6, 2000 Sheet 3 of 11 6,072,635 100 FIG.4 U.S. Patent Jun. 6, 2000 Sheet 4 of 11 6,072,635 U.S. Patent Jun. 6, 2000 Sheet S of 11 6,072,635 U.S. Patent Jun. 6, 2000 Sheet 6 of 11 6,072,635 U.S. Patent Jun. 6, 2000 Sheet 7 of 11 6,072,635 00|| i |9 U.S. Patent Jun. 6, 2000 Sheet 8 of 11 6,072,635 WEISSMOId0NO1OHTOJd<!-- 9| 8 U.S. Patent Jun. 6, 2000 Sheet 9 of 11 6,072,635 ÆissMºldoNO.1,0,- 009|| |||'0|| U.S. Patent Jun. 6, 2000 Sheet 10 of 11 6,072,635 PROJECTION PROJECTION PROJECTION IMAGE B' IMAGE G IMAGER 7 - 100 FIG. 12 U.S. Patent Jun. 6, 2000 Sheet 11 of 11 6,072,635 PROJECTION PIXEL -- -- d FIG.13A PROJECTION PIXEL PROJECTION PIXEL FIG.13C 6,072,635 1 2 DICHROIC PRISM AND PROJECTION largest, and the areas of the projection images of the colors DISPLAY APPARATUS relatively differ from one another. In the industry associated with projection display BACKGROUND OF THE INVENTION apparatuses, efforts have been made to increase the defini 1. Field of Invention tion of a light valve formed of a liquid crystal panel and the The present invention relates to a projection display like by increasing the number of pixels of the light valve. apparatus that Separates light emitted from a light Source There has been a tendency to reduce the area of each pixel into color beams of at least two colors, modulates these color with this increase of definition, which lowers the permitted beams via light valves formed of liquid crystal panels limit of the above-described pixel displacement d1 and according to image information, Synthesizes the modulated decreases the tolerance for chromatic aberration of magni color beams again, and projects and displays the Synthesized fication. Therefore, there is a need to reduce the influence of beams onto a projection plane via a projection optical chromatic aberration of magnification on a projection image System. More particularly, the present invention relates to a by correcting chromatic aberration of magnification, in order dichroic prism capable of correcting relative displacements to obtain a high-resolution and high-quality projection of projection pixels of the colors caused by chromatic 15 image. aberration of magnification. 2. Description of Related Art SUMMARY OF THE INVENTION A well-known type of projection display apparatus In view of the above problems, an object of the present includes a light Source, a color Separation device that Sepa invention is to provide a dichroic prism that can reduce rates a light beam emitted from the light Source into color displacements of projection pixels of colors caused by beams of three colors, three light valves for modulating the chromatic aberration of magnification. Another object of the Separated color beams according to image information, a present invention is to provide a projection display apparatus dichroic prism Serving as a color Synthesizing device that in which the dichroic prism is incorporated. synthesizes the color beams modulated by the three light In order to achieve the above objects, the present inven Valves, and a projection optical System for enlarging and 25 tion provides a dichroic prism that is formed by joining four projecting the beams Synthesized by the dichroic prism onto prisms of a triangular cross-section, and is provided with a projection plane. first and Second dichroic planes interSecting So as to form The dichroic prism is disclosed in, for example, Japanese approximately an X shape along joint Surfaces of the prisms Unexamined Patent Publication No. 7-294845. As shown in and having different reflectance characteristics, wherein at FIG. 11, a dichroic prism 1000 disclosed in this publication least the first dichroic plane of the first and second dichroic is shaped like a quadrangular prism as a whole by bonding planes is either concave or convex. four rectangular prisms 11, 12, 13, and 14 having a cross In Such a dichroic prism of the present invention, the Section shaped like a rectangular isosceles triangle. In this reflection state of a color beam to be reflected from the first dichroic prism 1000, red reflecting dichroic planes 1500 and 35 dichroic plane varies depending on the degree of concavity 1500 and blue reflecting dichroic planes 1600 and 1600 or convexity of the first dichroic plane. Therefore, it is diagonally extend along the junction Surfaces of the prisms possible to either enlarge or reduce the color beam. Since the 11-14 so that they form a flat red reflecting dichroic plane magnification of a projection image of a desired color beam and a flat blue reflecting dichroic plane, respectively. A layer can be adjusted through the use of the dichroic prism of the of an adhesive 1800, which is formed between the junction 40 present invention as a color Synthesizing device in the Surfaces to join the rectangular prisms 11-14, is 10 um to 20 projection display apparatus, the areas of projection images tim thick. of colors can be made almost equal. That is, it is possible to Such a dichroic prism 1000 is used as a color synthesizing correct chromatic aberration of magnification, and to device in a projection display apparatus. In this case, color thereby reduce relative displacements of projection pixels of beams R, G, and B from liquid crystal light valves 925R, 45 the color beams. Accordingly, the use of the dichroic prism 925G, and 925B, which are placed to oppose three sides of of the present invention as a color Synthesizing device in the the dichroic prism 1000, are synthesized by the pair of projection display apparatus makes it possible to prevent dichroic planes 1500 and 1600, and the synthesized beams degradation of a projection image due to chromatic aberra are emitted from the other side of the dichroic prism 1000 tion of magnification. toward a projection optical System. 50 There has been a trend in the industry associated with Since the influence of chromatic aberration of magnifi projection display apparatuses to increase the definition of cation on images of the colors, which are projected and the light valve in order to obtain a projection image with displayed via the projection optical System, increases with higher resolution. In this case, the permitted limit of pixel the distance from the center, displacements of the projection displacements is lowered, and the tolerance for chromatic images of the colors become large. For example, as shown 55 aberration of magnification is decreased. Since the dichroic in FIG. 12, the areas of color projection imageS projected on prism of the present invention can, as mentioned above, a projection plane 100, a blue projection image B', a green correct chromatic aberration of magnification and thereby projection image G', and a red projection image R", increase reduce relative displacements of pixels of the colors, it is in this order. In terms of projection pixels, projection pixels particularly Suitable for a color Synthesizing device to be b, g, and r of the colors are not in complete alignment, as 60 employed in a projection display apparatus that projects a shown in FIGS. 13(A)-13(C), and there is a pixel displace high-resolution and high-quality image through the use of a ment d1. While the pixel displacement d1 hardly affects high-definition light valve. display quality when it is Small (d1sd), it degrades the It is preferable that the first dichroic plane be inclined quality of a projection image when it exceeds the permitted Symmetrically with respect to a line of interSection of the limit (dsd1=d2).
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