WO2005002238A1

WO2005002238A1 - Color recombination for projektion display systems

Info

Publication number: WO2005002238A1
Application number: PCT/IB2004/051034
Authority: WO
Inventors: Peter Johannes Michiel Janssen
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2003-06-30
Filing date: 2004-06-28
Publication date: 2005-01-06
Also published as: EP1642466A1; CN1817048A; TW200513680A; JP2007528015A

Abstract

A method for combining more than one light beam into a single beam for a display device includes reflecting the light beams (202, 204, 206) off a first reflective polarizer (122), and then reflecting them off dichroic filters (132, 134, 136) at substantially normal respective angles of incidence to combine them into a combined light beam (210). In another aspect of the invention, a display system includes a first dichroic filter (132) capable of substantially totally reflecting a first color light beam (202) at substantially normal angles of incidence and capable of substantially totally transmitting second and third color light beams (204, 206) at substantially normal angles of incidence; a second dichroic filter (134), superposed over the first dichroic filter (132), capable of substantially totally reflecting a second color light beam (204) at substantially normal angles of incidence, and capable of substantially totally transmitting the third color light beams (206) at substantially normal angles of incidence; and a third dichroic filter (136), superposed over the first and second dichroic filters (132, 134), capable of substantially totally reflecting the third color light beam (206) at substantially normal angles of incidence. The first, second and third colors are all different from one another, and the first, second, and third colors are all different from one another, and the first, second, and third dichroic filters (132, 134, 136) are all non-parallel to one another.

Description

COLOR RECOMBINATION FOR PROJEKTION DISPLAY SYSTEMS

This invention relates to color display systems, and more particularly, to color recombination for projection displays, such as scrolling color projection televisions for example. Modern projection systems, for example liquid crystal (LC) projection systems, commonly use filters to split light from a lamp into number of colors. The different colored light beams can be used to form single color components of an image which are later combined to form a full color image. Commonly, the splitting and recombination parts of a system are highly symmetrical, each consisting of orthogonal branches with typically 45 degree dichroic filters, as described in U.S. Pat. No. 5,548,347 to Melnik and Janssen for example. This architecture typically requires a large volume. Furthermore, transmission and reflection of dichroic filters have a dispersion that increases strongly with increasing angle of incidence, causing color bleeding. Additional filters that can be used to prevent color bleeding can cause loss of efficiency. It would be advantageous to achieve a more compact design, with high-efficiency and good color purity. Accordingly, a method and architecture are disclosed that utilize dichroic filters at near normal incidence. In a method for combining a light beams into a single beam for a display device according to a first aspect of invention, a plurality of light beams are reflected off a first reflective polarizer, and are subsequently combined into a combined light beam by reflecting them off a plurality of dichroic filters at substantially normal respective angles of incidence. In another aspect of the invention, a display system includes a first dichroic filter capable of substantially totally reflecting a first color light beam at substantially normal angles of incidence and capable of substantially totally transmitting second and third color light beams at substantially normal angles of incidence; a second dichroic filter, superposed over the first dichroic filter, capable of substantially totally reflecting the second color light beam at substantially normal angles of incidence, and capable of substantially totally transmitting the third color light beam at substantially normal angles of incidence; and a third dichroic filter, superposed over the first and second dichroic filters, capable of substantially totally reflecting the third color light beam at substantially normal angles of incidence. The first, second, and third colors are all different from one another, and the first, second, and third dichroic filters are all non-parallel to one another. Features of the invention can be better understood with reference to the drawing figures, in which certain features may be repositioned to better explain their functions and certain dimensions may be exaggerated for clarity, and in which: FIG. 1 is a diagrammatic side view representation of a color splitting and recombination architecture that uses orthogonal branches coupled through dichroic filters that are tilted 45 degrees; FIG. 2 illustrates transmittance of light through a dichroic filter at 45 degree incidence, as a function of wavelength; FIG. 3 illustrates transmittance of light through a dichroic filter at normal incidence, as a function of wavelength; and FIG. 4 is a diagrammatic side view representation of a color splitting and recombination architecture according to an embodiment of the invention. In FIG. 1 a white light beam 2 from a lamp (not shown), incorporating first, second, and third colors, encounters a first dichroic filter 4. A first color beam 6 of the first color is reflected to a first mirror 8 and thence through a first scanning prism 10 and first collimating lens 12 arrangement. The first color beam 6 then passes through a second dichroic filter 14 that transmits nearly all of the first color, through a second collimating lens 16, reflects off a third dichroic filter 18 that reflects nearly all of the first color, passes through a third collimating lens 20, and finally to a reflective polarizer 22. A multi-color light beam 24 of the remaining second and third colors (the first color having been removed by the first dichroic filter 4) encounters a fourth dichroic filter 26 that reflects nearly all of the second color light and transmits nearly all of the third color light. A second color beam 28 of the second color passes through a second scanning prism 30 and fourth collimating lens 32 arrangement, encounters the second dichroic filter 14 which reflects nearly all of the second color light, passes through the second collimating lens 16, reflects off the third dichroic filter 18 that reflects nearly all of the second color light, passes through the third collimating lens 20, and finally to the reflective polarizer 22. After passing through the fourth dichroic filter 26, a third color beam 34 of the third color (the second color having been removed by the fourth dichroic filter 26) passes through a third scanning prism 36 and fifth collimating lens 38 arrangement, reflects off a mirror 40, passes through a sixth collimating lens 41, encounters the third dichroic filter 18 which transmits nearly all the third color light, passes through the third collimating lens 20, and finally to the reflective polarizer 22. It can be seen that upon leaving the third dichroic filter 18, the three different colored light components have been reunited into a recombined beam 42. The recombined beam 42 passes through the reflective polarizer 22 and onto a display panel 44. However, since the architecture shown in FIG. 1 is for a scrolling color projection device, the three scanning prisms 10, 30, 36 have been rotating in a coordinated manner during operation of the device so that the recombined beam 42 comprises multiple bands of alternating first, second, and third color light scrolling across the surface of the display panel 44. The scrolling is accomplished fast enough that the human eye will see the resulting image on (or rather, reflected from) the panel as though it were a full color image, and so for practical display purposes it is a full color image. The display panel 44, a liquid crystal on silicon (LCoS) panel for example, is in this case of the reflective type. Accordingly, the image reflects off the display panel 44, then off the reflective polarizer 22, through a post polarizer 46, and finally through a projection lens 48 so that the image can be projected onto a screen (not shown). FIG. 2 illustrates why color bleeding can be caused when using dichroic filters at non-normal incidence to light paths (in this case, at 45 degree incidence), such as in an arrangement like that of FIG. 1. Conversely, FIG. 3 illustrates the situation when using dichroic filters at normal incidence to light paths. In each case, theta refers to the cone angle of the light beam encountering the dichroic filter. That is, since light beams are not perfectly coherent, and certainly an image being displayed is not of a point source, light from different portions of a light beam arrives at angles of incidence that vary somewhat. The total variation within the beam is called the "cone angle" of the beam. It can be seen from FIG. 2 that the transmittance or reflectance of a particular wavelength can be highly dependent on the exact angle of incidence centered around 45 degrees (FIG. 2 shows examples ranging 12 degrees on either side of 45). However, it can be seen from FIG. 3 that the transmittance/reflectance varies much less due to exact angle of incidence centered about normal incidence. Accordingly, there is a sizable improvement that includes reduction of color bleeding, when an image beam can be kept as near to normal incidence as possible when encountering a dichroic filter. FIG. 3 shows the preferred results that are available when angles of incidence are kept within 12 degrees of normal incidence for example. In the embodiment of the invention illustrated in FIG. 4, a number of light guides are disposed opposite respective prism scanners. In this embodiment, there are first, second, and third light guides 102, 104, 106 disposed opposite respective first, second, and third prism scanners 112, 114, 116. The first, second, and third prism scanners 112, 114, 116 are disposed on one side of a first lens 120. On the other side of the first lens 120 is a first reflective polarizer 122. On one side of the first reflective polarizer 122 are, in order, a quarter wave plate 124, a second lens 126, and first, second, and third dichroic filters 132, 134, 136. On the other side of the first reflective polarizer 122 is a second reflective polarizer 140 disposed between a reflective display panel 144, which in this embodiment is a reflective LCoS panel 144, and a post polarizer 146 and projection lens 148. In this embodiment, the dichroic filters are kept close to normal incidence with respect to the light beams carrying the different color components of the image. A number of color components of light (three in the illustrated embodiment, for example blue, green, and red) are generated, either individually (by laser, LED, or filtered light for example), or by separating color components from a lamp or other white light source (not shown), as in the illustrated embodiment. The three components of this embodiment are delivered via light guides 102, 104, 106 that cause the component beams to exit at precise protected angles (the illustrated embodiment has the three components parallel for simplicity, but this is not essential; other angle arrangements can be used). The functions of the various components of this embodiment are now discussed. In operation, the different color component light beams are passed through the prism scanners 112, 114, 116 to cause different colored first, second, and third scanning beams 202, 204, 206 (similar to the manner described above with reference to FIG. 1) which in the illustrated embodiment pass through the first lens 120 to reorient the respective colored scanning beams 202, 204, 206. Other embodiments might use separate lenses or other structures (light guides, etc.) for collimation and/or reorientation, or this could be accomplished later in the light path, etc. The different colored scanning beams 202, 204, 206 then reflect off the first reflective polarizer 122, through the quarter wave plate 144, then (in this embodiment) through the secondary lens 126, and toward the first, second, and third dichroic filters 132, 134, 136. The first dichroic filter 132 is such that light of the color of the first scanning beam 202 will be reflected from it at normal incidence, while light of the colors of the second and third scanning beams 204, 206 will pass through it. The second dichroic filter 134 is such that light of the color of the third scanning beam 206 will be reflected from it at normal incidence, while light of the color of the second scanning beam 204 will pass through it. The third dichroic filter 136 is such that light of the color of the second scanning beam 204 will be reflected from it at normal incidence. Accordingly, all three scanning beams 202, 204, 206 are reflected back through the secondary lens 126, through the quarter wave plate 124 a second time, and thence back to the first reflective polarizer 122. Of course, in other embodiments the order of the different color beams 202, 204, 206 and the dichroic filters 132, 134, 136 can be switched as desired, providing the characteristics of transmission and reflection for the dichroic filters 132, 134, 136 are properly set. The double pass through the quarter wave plate causes a change in polarization direction that allows the scanning beams 202, 204, 206 to pass through the first reflective polarizer 122 instead of being reflected. They continue onto the second reflective polarizer 140 where they are reflected onto the reflective display panel 144. Preferably, as shown in the illustrated embodiment, the filters 132, 134, 136 are slightly tilted with respect to one another (since the different color components are arriving from somewhat different angles) as necessary for all the reflected collimated color beams to be parallel to a common axis. Accordingly, the reflected collimated color beams effectively form a single collimated beam 210 comprising a number of different color bands that scroll across the reflective display panel 144. Additionally, preferably the light guides 102, 104, 106, the prism scanners 1 12, 114, 1 16, and the first lens 120 are oriented and configured so that they reach the dichroic filters 132, 134, 136 at as close to normal incidence as possible. The reflective display panel 144 is modulated to create the image in coordination with the different color bands that are scrolling across its surface. The collimated beam 210 is therefore reflected off the reflective display panel 144, after which it is, for practical display purposes as explained above with reference to FIG. 1, a full color image (though actually comprising a sequence of different colored bands). The image passes through the second reflective polarizer 140, the polarization direction having been changed by the reflection of the reflective display panel 144. The image continues through the post polarizer 146 and into the projection lens 148, by which it is projected onto a screen for example (not shown). As explained above, the differing color bands are scrolling rapidly enough that the image appears to the human eye to be a full color image. Many variations other than those already mentioned can be made in practicing the invention. For example, instead of reflecting display panel, a transmissive display panel could be used, in which case the scrolling light would pass through the transmissive panel to reach the projection lens. Countless other variations to the disclosed embodiments can also be made by those skilled in the art while practicing the claimed invention from a study of the drawings, the disclosure, and the appended claims.

Claims

CLAIMS:

1. A method for combining a plurality of light beams into a single beam for a display device, comprising: reflecting a plurality of light beams (202, 204, 206) off a first reflective polarizer (122); and subsequently combining the plurality of light beams (202, 204, 206) into a combined light beam (210) by reflecting them off a plurality of dichroic filters (132, 134, 136) at substantially normal respective angles of incidence.

2. The method of claim 1, the plurality of light beams (202, 204, 206) comprising at least first, second, and third light beams (202, 204, 206).

3. The method of claim 1, the plurality of light beams (202, 204, 206) comprising at least a first color beam (202), a second color beam (204), and a third color beam (206), all three colors differing from one another.

4. The method of claim 3, including shining the combined light beam (210) onto a display panel (144).

5. The method of claim 4, including changing the directions of the first, second, and third color beams in a cyclic manner such that the combined light beam (210) shining on the display panel (144) comprises a series of different colored bands of light scrolling across its surface.

6. The method of claim 5, including passing the combined beam through the first reflective polarizer (122).

7. The method of claim 6, including reflecting the combined beam off a second reflective polarizer (140).

8. The method of claim 7, including reflecting the combined beam of the display panel (144).

9. The method of claim 5, including passing the first, second, and third color beams twice through a quarter wave plate (124).

10. The method of claim 4, further passing the first, second, and third color beams through respective rotating prisms such that the combined light beam (210) shining on the display panel (144) comprises a series of different colored bands of light scrolling across its surface.

11. A display system, comprising: a first dichroic filter (132) capable of substantially totally reflecting a first color light beam (202) at substantially normal angles of incidence and capable of substantially totally transmitting second and third color light beams (204, 206) at substantially normal angles of incidence; a second dichroic filter (134), superposed over the first dichroic filter (132), capable of substantially totally reflecting the second color light beam (204) at substantially normal angles of incidence, and capable of substantially totally transmitting the third color light beam (206) at substantially normal angles of incidence; and a third dichroic filter (136), superposed over the first and second dichroic filters (132, 134), capable of substantially totally reflecting the third color light beam (206) at substantially normal angles of incidence, wherein the first, second, and third colors are all different from one another, and the first, second, and third dichroic filters (132, 134, 136) are all non-parallel to one another.

12. The system of claim 11, including a first reflective polarizer (122) disposed opposite the first, second, and third dichroic filters (132, 134, 136), such that lines substantially perpendicular to the first, second, and third dichroic filters (132, 134, 136) pass through the first reflective polarizer (122).

13. The display system of claim 12, including a second reflective polarizer (140) disposed on an opposite side of the first reflective polarizer (122) from the first, second, and third dichroic filters (132, 134, 136), such that said lines pass through the second reflective polarizer (140).

14. The display system of claim 12, including a quarter wave plate (124) disposed between the first reflective polarizer (122) and the first, second, and third dichroic filters (132, 134, 136).