Projecting device for displaying electrical images

Claim 1

a projecting device comprising: an illumination device for emitting a polarized trichrome light which comprises red, green and blue lights; three modulating devices defined as first, second, and third modulating devices, each of the modulating devices being used for reflecting a polarized monochrome light to modulate it and change its polarization; and a rectangular trichromatic prism comprising a first dichroic mirror, a first polarization beam splitting mirror, a second polarization beam splitting mirror, a third polarization beam splitting mirror, and a first retarder film, the rectangular trichromatic prism having a first diagonal line and a second diagonal line approximately perpendicular to each other, wherein the first dichroic mirror and the third polarization beam splitting mirror are installed inside the rectangular trichromatic prism along the first diagonal line, the first and second polarization beam splitting mirrors are installed inside the rectangular trichromatic prism along the second diagonal line, and the first retarder film is installed inside the rectangular trichromatic prism between the second and the third polarization beam splitting mirrors, wherein the first dichroic mirror transfers the polarized trichrome light into a first polarized monochrome light and a polarized dichrome light, and transmits these two lights separately to the first and second polarization beam splitting mirror, the first polarization beam splitting mirror transmits the first polarized monochrome light to the first modulating device and transmits the modulated light reflected from the first modulating device to the third polarization beam splitting mirror, the second polarization beam splitting mirror separates the polarized dichrome light into second and third polarized monochrome lights which are directly transmitted to the second and third modulating devices, and then transmits the modulated lights reflected from the second and third modulating devices to the third polarization beam splitting mirror through the first retarder film, and the first retarder film changes the polarization of one of the modulated lights reflected from the second and third modulating devices, the modulated lights transmitted from the first and second polarization beam splitting mirrors are synthesized by the third polarization beam splitting mirror to form an output light beam.