WO2005074299A1

WO2005074299A1 - Color splitting for producing differing width bands for a scrolling display projector

Info

Publication number: WO2005074299A1
Application number: PCT/IB2005/050297
Authority: WO
Inventors: Peter J. Janssen
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2004-01-30
Filing date: 2005-01-25
Publication date: 2005-08-11

Abstract

A scrolling color display projector includes a light source, at least a first light condenser disposed for producing at least a first light beam from the light source, a first, color-selective mirror disposed to intercept and reflect a first color component of the light of the first light beam, a second mirror disposed to intercept and reflect light of the first light beam that has passed through the first mirror, and first and second light guides disposed to receive and carry light reflected from the first and second mirrors, respectively.

Description

COLOR SPLITTING FOR PRODUCING DIFFERING WIDTH BANDS FOR A SCROLLING DISPLAY PROJECTOR

This invention relates to light engines for projection display systems, and more particularly relates to a compact light engine employing light guides which is particularly suitable for use in a single panel scrolling color projection display system. A single panel scrolling color projection display system is characterized by a single light modulator panel such as a liquid crystal display (LCD) panel having a raster of individual picture elements or pixels, which panel is illuminated by horizontally elongated red, green and blue illumination bars or stripes. The stripes are continuously scrolled vertically across the panel while the illuminated rows of pixels are synchronously addressed with display information corresponding to the color of the then incident stripe. See, for example, United States Patent 5,410,370, "Single panel color projection video display improved scanning" issued to P. Janssen (the present applicant) on March 25, 1994, and United States Patent 5,416,514, "Single panel color projection video display having control circuitry for synchronizing the color illumination system with reading/writing of the light valve" issued to P. Janssen et al. on May 16, 1995. Such single panel systems are to be distinguished from the more conventional three- panel systems, in which separate red, green and blue beams each fully illuminate and are modulated by a separate light modulator panel. The modulated beams are then superimposed on a display screen to produce a full color display. See, for example, United States Patent 5,917,561, "Liquid-crystal image projecting apparatus having a color purity correction filter" issued to Hatanaka on June 29, 1999. Light engines for both single-panel and three-panel color projection display systems commonly utilize high intensity arc lamps to provide the level of intensity needed for a bright display, as well as dichroic filters to split the lamp light into red, green and blue components for modulation, and then to recombine the modulated components for projection display. In both the single panel and the three panel systems of the prior art, the desire for high light efficiency has dictated that the optical path lengths of the red, green and blue beams are approximately equal. Otherwise, those beams which must travel farther from the light source to the display panel have a greater etendue (angular extent), and some of light from those beams is lost. See, for example, US patent Bl 4,864,390, "Display System with Equal Path Lengths", issued to McKechnie et al. on September 5, 1989. Unfortunately, such systems, while efficient in terms of light utilization, require multiple relays of relatively high optical quality to create equivalent images for the three colors. In addition, thorough integration (mixing) of light in the preceding light collection stages is necessary. The large number of optical components contributes significantly to the size and overall cost of the system. The illumination architecture for a presently used light engine 1 for a scrolling color projector is shown schematically in Fig. 1. White light from source S is split into a blue component B and a green/red component G R by dichroic element 2. The B component is directed by lens 3 and mirror 4 to prism scanner 5. The G/R component is passed by dichroic element 2 through lens 6 to dichroic element 7, which splits the G/R component into a green component G and a red component R. The G component is reflected by element 7 to prism scanner 8, while the red component is passed through dichroic element 7 to prism scanner 9. The scanned R, G, B components are then directed to recombination dichroic elements 10 and 11 by mirror 12 and relay lenses 13 through 17. Relay lenses 13 through 17 are designed to limit the light expansion over the long recombination path from the prism scanners 5, 8 and 9 to the output lens 18. Consequently, light that is telecentric at the prism scanners 5, 8 and 9 is not telecentric at the recombination dichroic elements 10 and 11. As a result, color shifting is introduced over the scan (from the top to the bottom of the display) unless (expensive) shaded dichroics are used. Some of the problems associated with such a design can be averted by first splitting white light into primary colors and then using light guides to direct them to band-scrolling mechanism. For example, copending US patent application SN 10/161,753, attorney docket No. US-020171 (ID 702699), filed 4 June 2002, by the same applicant and assigned to the same assignee as this application, and incorporated herein by reference, discloses a projection display system that employs loss-less etendue-preserving light guides, enabling a compact arrangement through the use of unequal path lengths for the separate light beams, while eliminating the need for many high quality optical lenses, and preserving the light efficiency of the equal path length designs of the prior art. Copending US patent application SN 10/161,798, attorney docket No. US-020170 (ID 702697), also filed 4 June 2002 by the same applicant and assigned to the same assignee as this application, and incorporated herein by reference, shows how light guides can be made without loss of etendue of the guided light beam, regardless of changes in direction of the guided light beam or intersection of the guided light beam with other beams. For a better quality picture using a scrolling color projector, it may be advantageous to have one or more of the color bands wider than the others. Accordingly, in one aspect of the invention a scrolling color display projector includes a light source, at least a first light condenser disposed for producing at least a first light beam from the light source, a first, color- selective mirror disposed to intercept and reflect a first color component of the light of the first light beam, a second mirror disposed to intercept and reflect light of the first light beam that has passed through the first mirror, and first and second light guides disposed to receive and carry light reflected from the first and second mirrors, respectively. This application shows a simple, compact design that can accomplish this. For this purpose, light collection optics for a scrolling color illumination system are used that are a variation of those disclosed in copending US patent application SN 60/474,819, attorney docket No. US-030127 (ID 703568), filed 30 May 2003 by the same applicant and assigned to the same assignee as this application, and incorporated herein by reference. In the currently disclosed embodiment(s), color-splitting is incorporated into the light collection optics, in such a way that color bands of unequal width are produced that can be carried by light guides of unequal width to the band-scrolling mechanism. Referring now to Fig. 2, two orthogonally arranged ellipsoidal reflectors 21, 23 receive light from a light source 25 with back mirror 27. The light source 25 is centered on the common focus of the two reflectors 21, 23. It should be appreciated that other environments may use a single mirror, or more than two mirrors. Using fewer mirrors can reduce the complexity of the design, but using more mirrors can allow greater amounts of high- intensity light to be combined into a thin light cone. The two ellipsoidal reflectors 21, 23 focus respective light cones into light guides 28, 29, 30 after reflection by color selective (for example, dichroic) mirrors 31, 33, 35, 31', 33', 35'. For example, blue light from the light cone from a first reflector 21 is reflected by a blue- selective mirror 31 and focused into a rectangular "blue" light guide 28. Red and green components of the light passes through the blue-selective mirror 31. The red component is reflected by a red-selective mirror 33 into a "red" light guide 29. The green component passes through the blue-selective mirror 31 and is reflected by a final mirror 35 into a "green" light guide 30. Similarly, the second reflector 23 utilizes similar mirrors 31', 33', 35' to direct the various color components into their respective light guides 28, 29, 30. Notice that Fig. 3 illustrates how each color component from the different mirrors is combined and turned 90 degrees so that the light from both mirrors is now traveling together in the same direction through its respective light guide. If Fig. 2 is considered a "top view" then the light guides, for example the "red" light guide shown in Fig. 3, carry the light "down." Fig. 4 illustrates a polarizing stack 37 and half-wave plate 39 polarization recovery assembly that converts all the light in light guide to the same direction of polarization, doubling the stripe aspect ratio in the process. Fig. 5 illustrates how the unequally sized light guides carry their respective colors to the (for example) rotating prisms that cause the color bands to scroll across a liquid crystal, e.g. LCoS, panel. In other environments rotating drums or other scrolling mechanisms could be used. In this embodiment the width of the red color band is enlarged, to achieve a better looking final picture. Other embodiments, variations of embodiments, and equivalents, as well as other aspects, objects, and advantages of the invention, will be apparent to those skilled in the art and can be obtained from a study of the drawings, the disclosure, and the appended claims. For example, a preferred embodiment of the invention uses an ellipsoidal mirror for condensing (i.e., collecting, focusing, etc.) the light from a high-intensity lamp. Various light condenser configurations are illustrated in Fig. 6, for example. However, mirrors of other shapes, and other light-condensing methods, could be used as well. As a further example, in preferred embodiments the three different light components are carried the three separate and/or individual light guides. However, the invention could also be practiced by putting one color component into a light guide of a first size, and the other color components together into another light guide of a second size. There, more than three components could be routed in more than three respective light guides.

Claims

CLAIMS:

1. A scrolling color display projector, comprising: a light source; at least a first light condenser disposed for producing at least a first light beam from the light source; a first, color-selective mirror disposed to intercept and reflect a first color component of the light of the first light beam; a second mirror disposed to intercept and reflect light of the first light beam that has passed through the first mirror; first and second light guides disposed to receive and carry light reflected from the first and second mirrors, respectively.

2. The scrolling color display projector of claim 1, including: a third, color-selective mirror disposed to intercept and reflect light of the first light beam that has passed through the first mirror, the second mirror being disposed to intercept and reflect light of the first light beam that has passed through both the first and third mirrors; and a third light guide disposed to receive and carry light reflected from the third mirror.

3. The scrolling color display projector of claim 1, the first light condenser including a first ellipsoidal or partial-ellipsoidal reflector positioned to receive light from the light source and focus it into the first light beam.

4. The scrolling color display projector of claim 2, including: a second light condenser disposed for producing at least a second light beam from the light source; a fourth, color-selective mirror disposed to intercept and reflect the first color component of the light of the second light beam; a fifth mirror disposed to intercept and reflect light of the second light beam that has passed through the fourth mirror; and a sixth, color-selective mirror disposed to intercept and reflect light of the second light beam that has passed through the fourth and fifth mirrors, the first light guide being disposed to receive and carry light reflected from the fourth mirror as well as from the first mirror, the second light guide being disposed to receive and carry light reflected from the sixth mirror as well as from the second mirror, and the third light guide being disposed to carry light reflected from the fifth, as well as from the third mirror.

5. The scrolling color display projector of claim 2, including: a fourth, color-selective mirror disposed to intercept and reflect light of the first light beam that has passed through the first and third mirrors, the second mirror being disposed to intercept and reflect light of the first light beam that has passed through all of the first, third, and fourth mirrors; and a fourth light guide disposed to receive and carry light reflected from the fourth mirror.

6. The scrolling color display projector of claim 1, including a polarization recovery assembly in at least one of the first and second light guides, for converting light to a single direction of polarization while doubling the width of the light beam in said at least one of the first and second light guides.