Patent Application
20060268417
Disclosed embodiments relate to optical projection systems, and more particularly to an optical device for homogenizing multiple light sources.
Many types of optical projection systems have been developed that use an illumination source to project an image. These optical projection systems are capable of providing high resolution and high contrast images having an excellent color gamut. One of the key criteria that distinguish various projection systems is the brightness of the image. High image brightness is an important differentiating factor in the marketplace. High projector flux output enables high image brightness, which enables viewers to clearly see the projected image, even in venues having a high ambient light level, and enables projection of very large images.
The brightness of a projected image is limited by the light source luminance (lumens per emitting area per solid angle). High output flux levels are especially difficult to achieve with optical devices that have a relatively small area because they in turn require use of light sources having very small etendue or area-solid angle product.
Xenon and metal halide arc lamps are light sources with very high luminance, but may be unacceptable for many projection system applications because of the short lifetimes (generally less than 2000 hours), high power requirements, and safety concerns. A few arc lamps, such as high-pressure mercury lamps, have longer lifetimes (between 6000 and 8000 hours) and a smaller etendue, but do not provide a high total flux. One technique that may be used to increase the brightness of a projected image is to use larger light sources, but larger lamps mean greater arc or larger etendue, which does not efficiently couple to smaller area optical components such as digital micromirror devices (DMDs). Another technique involves combining multiple light beams from multiple lamps within an integrating rod, as disclosed in U.S. Pat. No. 6,545,814 to Bartlett et al. However, orientation of the lamps not only physically increase the size of the package, the lamps are also tilt-sensitive because of fundamental arc electrode limitations thereby constraining efficient operation to one fixed orientation.
Described are optical devices for homogenizing multiple light sources for an optical projection system. The disclosed optical devices are operable to homogenize multiple light sources with minimum package dimension and with the freedom from light source orientation constraints. The disclosed optical devices further disclose small etendue to enable efficient coupling to DMDs. One embodiment of the optical device includes at least two light sources having first and second optic axes and a light refraction element for substantially aligning the first and second optic axes of the two light with each other. In another embodiment, an aperture may be located between the at least two light sources and the light refraction element wherein the aperture substantially reflects the at least two light sources and the light source's reflectors substantially recollects the rejected light. In yet another embodiment, the at least two lights are substantially combined and confined within a housing that may be solid, hollow, or partially solid and partially hollow.
The presently disclosed embodiment combines multiple light sources 102 along with optical devices 104, thereby allowing an optical projection system to meet the lumens high brightness requirement.
In general,
As illustrated, light beams 202 from the two light sources 204 and their respective reflectors 205 are projected toward a housing 210 through an aperture 208 at their own respective optic axes 203. For example, the optic axis of the light beam 202a from the top light source 204a passes through the aperture 208 substantially along a first direction 203a, while the optic axis of the light beam 202b from the bottom light source 204b passes through the aperture 208 substantially along a second direction 203b. Most of the light 202 that is projected toward the aperture 208 passes through an opening 206 on the aperture 208. In one embodiment, each light source reflector 205 has a diameter of about 40 mm, while the aperture opening 206 is about 10 mm. The aperture 208 also reflects light beams 214 back into the light source reflectors 205, which then reflect the light beams 212 back again toward the aperture 208. The aperture opening 206 then passes at least some of these reflected light beams 212 from the light source reflectors 205. Although the aperture 208 appears to be detached from the housing 210, the two may be formed from a single unit. The aperture 208 may also be a separate unit masked or formed over the housing 210. Additionally, the aperture 208 may also be placed very close to, or on the same plane as the housing's 210 input face. In another embodiment, an aperture 208 may not be necessary, and the light beams 202 from the two light source reflectors 205 may be focused directly into the housing 210 without any loss of light.
After passing through the aperture opening 206, the light beams 202 are transmitted through a light refraction element 216 such as a prism within the housing 210. The prism 216 may also be positioned outside of the housing 210. Although the light beams 202 are illustrated as being focused on the aperture opening 206, the light beams 202 from the two light source reflectors 205 may also be focused at the entrance of the housing 210. In particular, the light beams 202 from the two light source reflectors 205 are focused at an input face of the prism 216. The aperture opening 206 may be larger than as shown to allow the converging ray bundles of light beams 202 to get to the input face of the prism 216. In a specific embodiment, the light refraction element 216 is a 45-45-90 prism. The beams of light 202 are once-refracted 218 when they enter the light refraction element 216 and twice refracted 220 when they exit the light refraction element 216. The twice-refracted beams of light 220 will then travel through the housing 210 and exit as homogenized light 228. In addition, the housing 210 may be solid 222 or hollow 224 with a coating 226. These and other elements described herein will be discussed in further detail.
Referring now to
A modulator (not shown) may then be configured in the optical projection system to receive the substantially homogenized and aligned mixed light beams 228. The mixed light beams 228 are subsequently modulated by the modulator, transmitted to a projection lens (not shown), and eventually onto an image plane (not shown). Additionally, the mixed light beams 228 may also be processed by a DMD on a digital light projection (DLP) board before being transmitted to a projection lens. The features and functions of spatial light modulators (SLMs) and DMDs are further described in a commonly owned U.S. Pat. No. 6,643,069 entitled “SLM-based color projection display having multiple SLM's and multiple projection lenses,” Ser. No. 09/940,978, filed Aug. 28, 2001, which is incorporated herein by reference in its entirety for all purposes.
It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character thereof. For example, multiple color wheels or color filters may be positioned at various locations including the output of each light source 204 to filter specific wavelengths and colors of light. Additionally, the color wheels or color filters may also be positioned at the output of the housing 210 to filter the homogenized mixed light 228. Furthermore, positioning of the light sources 204 requires modeling or experimental testing to determine the optimum spacing between the light sources 204. One advantage of the presently disclosed embodiment over that of Bartlett is that the light sources 204 may be placed closer together thereby minimizing the size of the package. Furthermore, the presently disclosed embodiments are not constrained by tilt-sensitive arc lamps. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and ranges of equivalents thereof are intended to be embraced therein.
Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. § 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” the claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a characterization of the invention(s) set forth in the claims found herein. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty claimed in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this disclosure, and the claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification, but should not be constrained by the headings set forth herein.
