Patent Document 1 discloses a projection-type display device that is provided with three DMDs. FIG. 1 is a schematic perspective view showing the principal parts of the projection-type display device disclosed in Patent Document 1.
Referring to FIG. 1, projection-type display device 1000 is equipped with lighting optical system 100, light color separation optical system 200, three DMDs 300R, 300G, and 300B, three Total Internal Reflection (TIR) prisms 400R, 400G, and 400B, cross-dichroic prism 500, and projection lens 600.Lighting optical system 100 is provided with light source 110, first lens array 120, second lens array 130, polarization conversion optical system 140, and superposing lens 150. The light beam from light source 110 is separated into a plurality of component light beams by first lens array 120. Each component light beam is irradiated into polarization conversion optical system 140 via second lens array 130. Polarization conversion optical system 140 arranges the polarized light of each component light beam into p-polarized light. Superposing lens 150 superposes each component light beam (p-polarized light) that is emitted from polarization conversion optical system 140 upon the image-forming surfaces of DMDs 300R, 300G, and 300B, respectively.
Light color separation optical system 200 is provided with cross-dichroic prism 210, dichroic mirror 220, reflecting mirrors 230 and 240, and condenser lenses 250 and 260. Cross-dichroic prism 210 color-separates the light beam from lighting optical system 100 into a red component light beam and a light beam that contains the blue component and the green component. The red component light beam is irradiated upon DMD 300R via reflecting mirrors 230 and 240, condenser lenses 250 and 260, and TIR prism 400R.
The light beam that contains the blue component and the green component is irradiated upon dichroic mirror 220 by way of reflecting mirror 230 and condenser lens 250. Dichroic mirror 220 transmits light of the blue component and reflects light of the green component. The light beam of the green component that is reflected by dichroic mirror 220 is irradiated into DMD 300G by way of TIR prism 400G. The light beam of the blue component that is transmitted through dichroic mirror 220 is irradiated into DMD 300B by way of TIR prism 400B.
The red image beam from DMD 300R is irradiated into the first incident surface of cross-dichroic prism 500 by way of TIR prism 400R. The green image beam from DMD 300G is irradiated into the second incident surface of cross-dichroic prism 500 by way of TIR prism 400G. The blue image beam from DMD 300B is irradiated into the third incident surface of cross-dichroic prism 500 by way of TIR prism 400B. Half-wave plate 700 is provided on the surface of TIR prism 400G that is opposite the second incident surface of cross-dichroic prism 500.
Cross-dichroic prism 500 includes red light reflecting surface 506 and blue light reflecting surface 508 that are provided so as to intersect each other. Red light reflecting surface 506 has the characteristic of reflecting the red light component and transmitting the colored light whose wavelength is shorter than that of the red light component. Blue light reflecting surface 508 has the characteristic of reflecting the blue light component and transmitting the colored light whose wavelength is longer than that of blue light. The red image beam that is incident from the first surface is reflected by red light reflecting surface and emitted in the direction of projection lens 600. The green image beam that is incident from the second incident surface is transmitted through both red light reflecting surface 506 and blue light reflecting surface 508 and emitted in the direction of projection lens 600 without undergoing alteration. The blue image beam that is incident from the third incident surface is reflected by blue light reflecting surface 508 and emitted in the direction of projection lens 600. In this way, cross-dichroic prism 500 emits toward projection lens 600 a combined image beam in which the red image beam, green image beam and blue image beam have been color-combined.Projection lens 600 projects the combined image beam from cross-dichroic prism 500 upon a screen.
DMDs 300R, 300G, and 300B are of the same construction. FIG. 2 gives a schematic representation of the relation between the image-forming surface of a DMD and incident light. As shown in FIG. 2, image-forming surface 302 is composed of a plurality of micromirrors 304 arranged in matrix form. Micromirror 304 is quadrilateral in shape and is configured to rotate at a predetermined angle with the diagonal line that joins the lower left vertex and the upper right vertex as axis of rotation 304c. The angle that is formed between incident ray IR and rotational axis 304c is 90 degrees, and the angle that is formed between incident ray IR and the horizontal direction h (the row direction) of image-forming surface 302 when viewed from the direction perpendicular to image-forming surface 302 is approximately 45 degrees (the limit of the direction of incidence).
In the projection-type display device shown in FIG. 1, DMDs 300R, 300G, and 300B are arranged to enclose the side surfaces of cross-dichroic prism 500. Due to the above-described limit of the direction of incidence, DMDs 300R, 300G, and 300B are arranged inclined such that long sides of the image-forming surfaces intersect the plane that contains the center light ray of each of the red light beam, green light beam and blue light beam at approximately 45 degrees.