Color separation and synthesis systems, color separation systems and color synthesis systems, illumination optical systems, projection optical systems, and projection display devices using these systems

#The present invention relates to separation and/or synthesis systems of light beams according to polarization and wavelength characteristics of the light beams. Additionally, the present invention relates to projection display devices that use such systems in their illumination optical systems and/or their projection optical systems and that use light beams that are modulated with image information by display elements for magnified projection, and especially relates to such projection display devices that use reflection-type display elements with polarization changing properties, such as some liquid crystal display elements.

#In recent years, the projector market has been growing rapidly, along with the use of personal computers. Liquid crystal display elements of the transmission-type and the reflection-type, and DMD display elements which include micromirrors in an orderly array, are known as light valves that modulate light in order to produce image light signals. In particular, an image display device of the reflection-type is suitable to create very small picture elements with high efficiency, and therefore it has gained attention as an image display device for producing a high quality image.

#Various projection display devices have been developed that use reflection-type display elements and polarization properties of light beams. For instance, projection display devices that illuminate reflection-type display elements with polarization changes after color separation of the light beams according to wavelengths from a light source by an illumination optical system with a projection optical system that use four polarization-sensitive beam splitters, generally known as a COLORQUAD™, and that project imaging light beams from the reflection-type display elements, are known. FIG. 26 and FIG. 27 are cross-sectional diagrams of prior art Example 1 and prior art Example 2 of such devices. In FIG. 26 and FIG. 27, light beam channels corresponding to each of the three primary colors of light are shown as straight lines, and short intersecting lines and the black round shapes shown on these lines indicating the paths of the three light beams indicate one of two polarization states (S polarized light or P polarized light) of each of the light beams at particular locations in the projection display devices. In the following descriptions, the short intersecting lines are called the first polarization state and the black round shapes are called the second polarization state of the light beams.

#The present invention will become more fully understood from the detailed description given below and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, wherein:

#FIG. 1 is a cross-sectional schematic diagram of the color separation and synthesis system of Embodiment 1 of the present invention;

#FIG. 2 is a cross-sectional schematic diagram of the color separation and synthesis system of Embodiment 2 of the present invention;

#Color separation and synthesis systems, color separation systems, as well as color synthesis systems, that relate to preferred embodiments of illumination optical systems, projection optical systems and projection-type display devices of the present invention that use such systems will be described with reference to FIGS. 1-28.

#In particular, color separation and synthesis systems will first be described with reference to FIGS. 1-16. More specifically, Embodiments 1-4 of the color separation and synthesis systems that pertain to a first mode of the color separation and synthesis systems will first be described with reference to FIGS. 1-4, respectively, then Embodiments 5-14 of the color separation and synthesis systems that pertain to a second mode of the color separation and synthesis system will be described with reference to FIGS. 5-14, respectively, and then Embodiments 15 and 16 of the color separation and synthesis systems that pertain to a third mode of the color separation and synthesis system will be described with reference to FIGS. 15 and 16, respectively. Additionally, FIG. 20, more fully described below, is a cross-sectional schematic diagram of a projection display device that may use color separation and synthesis systems of the present invention as one part of the illumination optical system of a projection display device. The term “systems” will be used in the following descriptions to refer generally to the color separation and synthesis systems, color separation systems, color synthesis systems, illumination optical systems, projection optical system, and even to projection display devices that include these systems, of the present inventions and characteristics of the various embodiments of the present invention described herein extend to all the systems disclosed herein to which the embodiments described herein are useful.

#FIG. 1 is a cross-sectional schematic diagram of Embodiment 1 of the color separation and synthesis; systems of the present invention. As shown as 1a in FIG. 1, Embodiment 1 of the color separation and synthesis system of the present invention includes a wavelength-splitting element, which, is a dichroic mirror 10a in FIG. 1, that reflects or transmits portions of an incident light beam according to the wavelength of the light and at least one polarization-transforming element, which is a half-wave plate 11a in FIG. 1, that changes the direction of polarization of linearly polarized light of one wavelength and that is arranged adjacent and at least nearly parallel to the wavelength-splitting element. The phrase “arranged adjacent and at least nearly parallel” includes states of the polarization-transforming element and the wavelength-splitting element being superimposed or where they abut one another in a parallel or nearly parallel relationship. The phrase “nearly parallel” encompasses slight variations from parallelism that to at least a first approximation provide the same effects as an exact parallel relationship would provide. A small separation of the polarization-transforming element and the wavelength-splitting element is allowed based on considerations of manufacture. However, the systems will tend to become too large if the separation is too large.