Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
  • G02B27/102—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources
  • G02B27/1026—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources for use with reflective spatial light modulators
  • G02B27/1033—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources for use with reflective spatial light modulators having a single light modulator for all colour channels
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/14—Beam splitting or combining systems operating by reflection only
  • G02B27/145—Beam splitting or combining systems operating by reflection only having sequential partially reflecting surfaces
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
  • G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
  • H04N9/3111—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying the colours sequentially, e.g. by using sequentially activated light sources
  • H04N9/3117—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying the colours sequentially, e.g. by using sequentially activated light sources by using a sequential colour filter producing two or more colours simultaneously, e.g. by creating scrolling colour bands

Definitions

• 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.
• 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.
• a method and architecture are disclosed that utilize dichroic filters at near normal incidence.
• 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.
• 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;
• FIG. 4 is a diagrammatic side view representation of a color splitting and recombination architecture according to an embodiment of the invention.
• 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
• FIG. 4 is a diagrammatic side view representation of
• 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 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.
• 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.
• the display panel 44 a liquid crystal on silicon (LCoS) panel for example, is in this case of the reflective type.
• 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.
• FIG. 3 illustrates the situation when using dichroic filters at normal incidence to light paths.
• 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.
• 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).
• FIG. 3 shows 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.
• a number of light guides are disposed opposite respective prism scanners.
• 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.
• first reflective polarizer 122 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.
• 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.
• 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.
• 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.
• 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.
• 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).
• the differing color bands are scrolling rapidly enough that the image appears to the human eye to be a full color image.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Devices For Indicating Variable Information By Combining Individual Elements (AREA)
• Video Image Reproduction Devices For Color Tv Systems (AREA)

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• 2004
  • 2004-06-25 TW TW093118409A patent/TW200513680A/zh unknown
  • 2004-06-28 WO PCT/IB2004/051034 patent/WO2005002238A1/en not_active Application Discontinuation
  • 2004-06-28 JP JP2006518427A patent/JP2007528015A/ja active Pending
  • 2004-06-28 CN CNA200480018545XA patent/CN1817048A/zh active Pending
  • 2004-06-28 EP EP04737191A patent/EP1642466A1/en not_active Withdrawn

Non-Patent Citations (1)

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