The present invention may best be understood through the following description with reference to the accompanying drawings, in which:
Referring to
The separating mirror 52 and the second reflecting mirror 54 are positioned along a light output path of the polarizer 51. The separating mirror 52 is adapted to separate the polarized white light beam Ws of three primary colors R, G, B from the polarizer 51 into two sets of light beams, a polarized monochromatic light beam containing a single primary color and a polarized bichromatic light beam containing the other two primary colors. Preferably, the polarized monochromatic light beam contains the green color G, and the polarized bichromatic light beam contains the red and blue colors R, B. The monochromatic light beam Gs is reflected by the first reflecting mirror 53 positioned above the separating mirror 52, and the bichromatic light beam (Rs, Bs) is reflected by the second reflecting mirror 54 positioned on the left side of the separating mirror 52.
The first polarization separator 56, the second polarization separator 57 and the color separator 58 are combined together as an L-shaped prism module by cementing. The first polarization separator 56 is adapted to transmit or reflect the incident monochromatic light beam according to the polarization state (P-polarization or S-polarization) thereof. The second polarization separator 57, which is positioned right below the first polarization separator 56 and proximate to the projection lens 59, is adapted to transmit and/or reflect the incident bichromatic light beam according to the polarization states (P-polarization or S-polarization) of the two constitute primary colors thereof. The color separator 58 is positioned on the right side of the second polarization separator 57, and is adapted to reflect one constitute primary color light of the incident bichromatic light beam and transmit the other constitute primary color light. Each of the first and second polarization separators 56, 57 is in the form of a PBS that is formed by cementing the bottom sides of two conventional isosceles right-angle prisms. The color separator 58 is in the form of a dichroic prism that is also formed by cementing the bottom sides of two conventional isosceles right-angle prisms.
The image modulation device 60 is adapted to modulate the incident polarized light into a polarized light having a reversed polarization and carrying an image signal. The image modulation device 60 is composed of a first reflective liquid crystal panel 60G, a second reflective liquid crystal panel 60B and a third reflective liquid crystal panel 60R. The first reflective liquid crystal panel 60G is arranged on one side of the first polarization separator 56, and the second and third reflective liquid crystal panels 60B, 60R are arranged on two respective sides of the color separator 58. The projection lens 59 is disposed on one side of the second polarization separator 57 for projecting the modulated and transformed light beam from the image modulation device 60 onto the screen for display.
The half-wave plate 55 is disposed between the first and second polarization separators 56, 57 for transforming the polarization of the incident light beam. The first converging lens 61 is arranged between the first reflecting mirror 53 and the first polarization separator 56, and the second converging lens 62 is arranged between the second reflecting mirror 54 and the second polarization separator 57. The employment of the two converging lenses 61, 62 is to converge the incident light beam and thus improve the light utility efficiency.
The bichromatic light beam (Rs, Bs) output by the separating mirror 52 is sequentially reflected by the second reflecting mirror 54, converged by the second converging lens 62 and incident into the second polarization separator 57. The second polarization separator 57 is also in the form of a PBS for transmitting P-polarized light and reflecting S-polarized light. Therefore, the bichromatic light beam (Rs, Bs) is reflected by the second polarization separator 57 into the color separator 58. The color separator 58, in the form of a bichromatic prism, is adapted to reflect blue light and transmit red light. Accordingly, the blue light Bs in the bichromatic light beam (Rs, Bs) is reflected by the color separator 58 to the second reflective liquid crystal panel 60B, while the red light Rs in the bichromatic light beam (Rs, Bs) is transmitted through the color separator 58 into the third reflective liquid crystal panel 60R. Consequently, the blue light Bs is transformed and modulated into a blue light beam Bp carrying blue image signal by the second reflective liquid crystal panel 60B, and the red light Rs is transformed and modulated into a red light beam Rp carrying red image signal by the third reflective liquid crystal panel 60R. The blue light beam Bp and red light beam Rp are then reflected back to the color separator 58 by the respective second and third reflective liquid crystal panels 60B, 60R. The color separator 58 respectively reflects and transmits the blue light beam Bp and red light beam Rp back into the second polarization separator 57. Further, the second polarization separator 57 transmits the incident blue and red light beams Bp, Rp from the color separator 58 to the projection lens 59, and reflects the incident green light beam Gs from the half-wave plate 55 to the projection lens 59. Finally, the projection lens 59 combines and projects the three primary color lights Bp, Rp, Gs carrying corresponding image signals onto the screen for image display.
In the second embodiment, the L-shaped prism module, consisting of the first polarization separator 56, the second polarization separator 57 and the color separator 58, is composed of five cemented isosceles right-angle prisms, not six isosceles right-angle prisms of the same size as in the first embodiment of
Referring to
As described above, in the liquid crystal projection system of the present invention, the bichromatic light beam (preferably containing the red and blue lights R, B) is incident into the second polarization separator 57 and the color separator 58, 58′ in an S-polarization state, and the monochromatic light beam (preferably containing the green light G) is incident into the first and second polarization separators 56, 57 also in an S-polarization state. This is because that the utility efficiency of the S polarization light in a PBS is 99 percent, while the P polarization light is only 90 percent. The remaining unutilized 10 percent will cause the color phase shift problem due to light interference. Accordingly, making the three primary color lights of the incident white light enter the PBSs in an S-polarization state may increase the utility efficiency of the incident white light, effectively decrease the likelihood that color phase shift occurs and thus improve the image contrast, whereby the projection image performance is increased. Further, the liquid crystal projection system achieves the light polarization and separation functions by employing two polarization separators 56, 57 and one color separator 58, 58′ that are cemented together as an L-shaped prism module. Within the L-shaped prism module, no additional optical elements are arranged therebetween except for a half-wave plate 55, which decreases the system cost and increases the system reliability. This L-shaped prism module may be composed of six conventional isosceles right-angle prisms of the same size, or four conventional isosceles right-angle prisms of the same size plus one larger-sized conventional isosceles right-angle prism, or four conventional isosceles right-angle prisms of the same size plus two smaller-sized conventional isosceles right-angle prisms. Therefore, the liquid crystal projection system of the present invention also has the advantages of simple manufacture, easy assembly and low cost.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Date | Country | Kind |
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095129213 | Aug 2006 | TW | national |