Abstract:
Image projectors with increased light intensity and methods for providing brighter images are provided. Image projectors, described herein, can provide the brightness while still providing any or all of compactness, low power consumption, and long lifetime. To increase brightness, sectional mirrors are used to respectively compress the light from two light sources into a single pupil (e.g. an aperture) of an imaging device. The compression can be accomplished by regions (e.g. sections) of the mirror having different angles with respect to the pupil. Relatively little light may be lost in the compression since minima for a light intensity pattern from a light source may occur between the regions that reflect the light.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is related to commonly owned U.S. Pat. No. 7,033,056 entitled “MULTI-LAMP ARRANGEMENT FOR OPTICAL SYSTEMS” by Odd Ragnar Andersen et al et al. (Attorney Docket No. 027467-000200US), filed May 2, 2003, the disclosure of which is incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to image projectors, and more specifically to image projectors having high intensity (brightness) and/or luminosity (total amount of light). Most projection systems today uses ultra high pressure (UHP) lamps, e.g. Mercury arc lamps, with wattage from 120 W-350 W and a lifetime of typical 1500-4000 h. These projectors are compact and portable with brightness level of typical 1000-5000 lumens. Most of these projectors are single lamp solutions. These arc lamp projectors are typically for home or office use where the space is relatively small. 
         [0003]    Projectors used for digital cinema, large venues, and for fixed installations have a typical brightness of 10,000-30,000 μm. These projectors typically use Xenon lamps with wattage range of 2-6 KW. However, a typical lifetime for a Xenon lamp is 500-1500 hours. Accordingly, the tradeoff is that the Xenon lamps have a shorter lifetime but a higher brightness (luminosity). 
         [0004]    Thus, it is desirable to have projectors that use arc lamps to obtain a longer lifetime, that also provide the brightness of the Xenon lamps. Also, it may also be desirable to have Xenon projectors with even more brightness. 
         [0005]    As previously mentioned, most of the image projectors use one lamp. To provide more brightness, image projectors do use multiple lamps. However, these lamps combine light from the multiple lamps in an inefficient manner. Typically, the light collection will be only typical 2 to 2.5 times a single lamp solution. 
         [0006]    It is therefore desirable to multiple lamp systems that provide greater efficiency and brightness. 
       BRIEF SUMMARY 
       [0007]    Embodiments of the present invention provide image projectors with increased light intensity (brightness) relative to known models using multiple light sources. For example, certain embodiments meet the needs for high brightness, while still providing any or all of compactness, low power consumption, and long lifetime. Regarding the increased brightness, embodiments of the present invention advantageously can produce flux levels that are 1.5 times or better than other known systems. This increase can reduce power consumption, material cost, and operating cost. 
         [0008]    To increase brightness, embodiments use mirrors to respectively compress the light from two light sources into a single pupil (e.g. an aperture) of an imaging device. In one aspect, the light from one source is compressed into about half of the pupil. The compression is accomplished by regions (e.g. sections) of the mirror having different angles with respect to the pupil. In one embodiment, relatively little light is lost in the compression since steps, which are between the regions, occur where a light pattern from a light source is at a minimum node. 
         [0009]    According to one exemplary embodiment, an image projection system is provided. Two sources each provide electromagnetic (EM) radiation in opposing directions. A first reflective surface reflects EM radiation from the first source. A second reflective surface reflects EM radiation from the second source. An imager has a pupil that receives the reflected EM radiation. The imager uses the received EM radiation to create an image. 
         [0010]    A first half of the pupil receives reflected EM radiation from the first source, and a second half of the pupil receives reflected EM radiation from the second source. Each reflective surface includes a plurality of regions that are flat in at least one direction. A first region of each reflective surface has a smaller angle relative to a line perpendicular to the pupil than does a second region, which is farther from the pupil than the first region. 
         [0011]    According to one exemplary embodiment, a method of creating an image is provided. Two sources (although more may be used) provide electromagnetic (EM) radiation in opposing directions. A first reflective surface reflects EM radiation from the first source to a first half of a pupil of an imager. A second reflective surface reflects EM radiation from the second source to a second half of the pupil. The imager uses the received EM radiation to create an image with the imager. 
         [0012]    Each reflective surface includes a plurality of regions that are flat in at least one direction, for example, in a direction towards the pupil. A first region of each reflective surface has a smaller angle relative to a line perpendicular to the pupil than does a second region of each reflective surface, where each first region is closer to the pupil than each second region. 
         [0013]    A better understanding of the nature and advantages of the present invention may be gained with reference to the following detailed description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of an image projector  100  according to an embodiment of the present invention. 
           [0015]      FIG. 2  illustrates a lamp  200  that may be used as a light source and a resulting light intensity pattern according to an embodiment of the present invention. 
           [0016]      FIG. 3  is a schematic diagram of an image projector  300  according to an embodiment of the present invention. 
           [0017]      FIG. 4  is a simulation plot of the light intensity node pattern  410  focused on the stepped mirror  400 , where the mirror steps are matched with the created light intensity node pattern according to an embodiment of the present invention. 
           [0018]      FIG. 5  shows a schematic diagram of part of an image projector according to an embodiment of the present invention. 
           [0019]      FIGS. 6A and 6B  show alternative configurations for lamps of light sources according to embodiments of the present invention. 
           [0020]      FIG. 7  shows a color modulator placed between a lamp and a light integrator according to an embodiment of the present invention. 
           [0021]      FIG. 8A  shows a color wheel with a four color segment configuration (Red, Green, Blue and White) according to an embodiment of the present invention. 
           [0022]      FIG. 8B  shows a color wheel with primary colors (Red, Green, Blue) and secondary colors (Cyan, Magenta and Yellow) according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Embodiments of the present invention provide image projectors with increased light intensity (brightness) relative to known models using multiple light sources. To increase brightness, embodiments use mirrors to respectively compress the light from two light sources into a single pupil (e.g. an aperture) of an imaging device. 
         [0024]    In one embodiment, the light from each light source creates a node intensity light pattern, which is focused on a respective stepped mirror. In one aspect, the light received at a stepped mirror has the same f-number as an entrance pupil of an imager. Each stepped mirror can compress its received light to 50% of the entrance pupil. The light reflected from the stepped mirror will transmit into the optical system and focused on the imager. 
         [0025]      FIG. 1  is a schematic diagram of an image projector  100  according to an embodiment of the present invention. Light from sources  110  is used to create an image, which is then displayed as projected image  190 . Herein, light refers to any electromagnetic (EM) radiation, and not just to visible light. Herein, the two terms light and electromagnetic radiation are used interchangeably. 
         [0026]    In one embodiment, the light sources  110  may include a single lamp or include any arrangement of multiple lamps (including the one shown), which produce light from electricity in any suitable manner known or to be developed. Although it common to use UHP types of lamps for the light sources, embodiments may use any type of light sources, including light emitting diodes (LEDs) and lasers. In another embodiment, the light sources  110  are light emitting sources that do not produce light from electricity, such as from other EM radiation or fields, or thermal energy. 
         [0027]    As shown, light sources  110  provide electromagnetic radiation in opposing directions. Herein, the term “opposing” means that some component of the lights rays from the respective sources  110  are provided in opposite directions. Here, the two opposite directions are up and down. 
         [0028]    In one embodiment, light disperses from an outlet of a light source  110 . The dispersed light is then collected into relay lenses  120 . In one aspect, the relay lenses  120  have a diameter big enough to collect almost all (e.g. greater than 90%, and preferably greater than 955) of the light energy from the lamps  110 , and focus the light onto a respective reflective surface  130 . 
         [0029]    Each reflective surface  130  has a sectional surface, for example, a stepped mirror surface. The surfaces  130  are reflective in that at least part of the surface is reflective. However, not every part of the surface is necessarily reflective. The parts that are reflective reflect almost all of the light, e.g., greater than 90% of the incident light, and preferably greater than 95% of the light. 
         [0030]    The reflective light from the surfaces  130  is received by an imager  140  via a pupil  145 . In one embodiment, the pupil is a simple opening. In another embodiment, the pupil is a transmissive object that allows light to pass through it, although the transmissive object may bend the light. 
         [0031]    The reflective surface  130  includes regions  132  (e.g. sections) that are flat in at least one direction, with steps  136  between the regions  132 . These regions reflect the light form the sources  110  to the pupil  145 . As shown, the regions  132  are flat in a direction from right to left. In other words, a cross section of the surface  130  in a plane that is perpendicular to the pupil has regions that are flat. As user herein, the term “flat” means that as one moves in a particular direction along the surface in the region, a direction of the movement does not change (e.g. curve up or down) on a macroscopic scale, i.e. larger than minor chips in the surface. 
         [0032]    In one embodiment, the regions are curved in a direction perpendicular to the cross section shown, i.e. in the direction out of the paper. In another embodiment, the regions  132  are flat in the direction perpendicular to the cross section. In one aspect, the regions may have steps in this direction perpendicular to the cross section. 
         [0033]    The regions  132  advantageously have different angles relative to the line  142 . For example, a region farther from the pupil  145  has an angle that is larger than the angle for a region closer to the pupil  145 . In this manner, a region  132   a  farther from the pupil  145  can be situated higher than a top edge of the pupil  145 , but still reflect light into the pupil  145 . Also, a region closer to the pupil  145  can reflect light into a different location within the pupil  145  than region  132  does, without reflecting light into the lower half of the pupil  145 . 
         [0034]    In one embodiment, the angle for each region increases as the distance to the pupil becomes shorter. For instance, the region closest to the pupil may have a 45° with the line  142 . The region would thus reflect light horizontal to line  142 . The angle for the farthest respective region may have the largest angle and reflect light to the lowest or highest point on the pupil. The angle larger than 45° allows the region to be located below the lowest point of the pupil  145 , but still reflect light into the pupil  145 . In one aspect, almost all of the reflected light can be received by the pupil  145  and still have a relatively homogeneous light distribution. 
         [0035]    Such embodiments have advantages over other arrangements or structures. For example, as shown, the height of the pupil  145  is smaller than the total height of the two surfaces  130  combined. If the surface  130  had a single flat region having one angle (e.g. 45 degrees), then the light incident on the far edges of the surface  130  would not reflect into the pupil  145 . Although it may be possible to use a different angle than 45° to reflect light from the outer edges of single surfaces in this inferior arrangement, an uneven brightness in the image would result. 
         [0036]    After light is received by the pupil  145 , the imager  140  uses the light to create an image, e.g. by modulating different parts (potentially for different colors or wavelengths) corresponding to different pixels of an image. The modulated light (i.e. the image) is then sent to a projection lens  150 , which is configured to project the image onto an external surface to create the projected image  190 . 
         [0037]    In some embodiments, more than two light sources may be used. For example, two other light sources may provide light in a perpendicular direction to the light sources shown. These light sources may be directly above and below the reflective surfaces  130 . In this embodiment, two other reflective surfaces would also be used. 
         [0038]      FIG. 2  illustrates a lamp  200  that may be used as a light source and a resulting light intensity pattern  250  according to an embodiment of the present invention. As depicted, the lamp  200  is an arc lamp, although other lamps may be used in other embodiments of the invention. Types of arc lamps include ultra-high performance or ultra-high pressure (UHP) lamps (e.g. containing Mercury), as well as other lamps that have a short arc gap. Exemplary arc-gaps are from 0.7 mm-1.5 mm with a wattage of between 120-500 W. 
         [0039]    Electrodes  210  produce electric discharges (arcs)  220 . These arcs  220  emit light rays  240 . Typically, these light rays  240  are emitted generally in all directions. A reflector  230  is used to focus the rays  240  to provide a more concentrated beam of light. Given that the arc  220  is not a perfect point of light, the rays  240  reflected from the reflector  240  will travel different distances and a diffraction (intensity) node pattern  250  results. Thus, different points will have different intensities. 
         [0040]    In some embodiments, other node patterns may be created via other mechanisms. For example, a node pattern may be created from a uniform pattern, which has already been compressed. This new node pattern may then be compressed again to create the light at pupil  145 . In this manner, a multi-level compression mechanism may be achieved. In one embodiment, each light source could include reflective light surfaces  230  to perform a first level of compression, or compression for any subsequent or prior level of compression. 
         [0041]    Embodiments account for this resulting intensity node pattern to achieve greater efficiency. In one embodiment, the flat regions  132  are aligned with the high intensity nodes so that an optimal amount of light is reflected into pupil  145 . 
         [0042]      FIG. 3  is a schematic diagram of an image projector  300  according to an embodiment of the present invention. In this embodiment, each light source described in  FIG. 1  is composed of two lamps  305 . Thus, in general, the illumination for image projector  300  includes four lamps; however, each light source may be made of any number of lamps. 
         [0043]    Each lamp  305  is positioned to transmit light into respective light guides  308  (also called an integrator) that are each optically connected to a collective light guide  312 . The optical connection may be accomplished in any number of ways, e.g., via methods described in the Andersen patent, referenced above. 
         [0044]    As shown, the two lamps  305  of each light source are in parallel configuration, which allows the lamps to be rotated around its own axis. In other embodiments, the lamps are in other configurations. In one embodiment, the lamp  305  needs to burn and emit light in a horizontal direction within about +/−20 degrees from normal because a vertical burning direction would reduce lamp lifetime significant, e.g., due to burn back of the electrodes. 
         [0045]    The lamps  305  have a focus point close to the light guides  308 . In one embodiment, the light guide are solid and act as an integrator of the light. In one aspect, the surface of the light guides  308  at which the focus point is located is anti-reflection (AR) coated to reduce the level of back reflection in the transition between air and the surface (e.g. the glass of the light guide). 
         [0046]    The light in the integrator  308  is reflected by an angled mirror surface (e.g. 45°) coated directly on the light integrator. The light is then reflected again in the solid light integrator on an angled (e.g. 45°) mirror coated surface on another end of the solid light integrator. The exit side of the light integrator  308  is AR coated to achieve maximum light transmission in the transition between glass and air. 
         [0047]    The light travels from the solid light integrator  308  to the collection light integrator  312 . In one embodiment, the collection light integrator is of a hollow type, e.g., where 4 pieces of surface mirrors are glued together and form a hollow light tunnel. In one aspect, the cross section of the collecting light integrator  312  has similar format as the final image. As user herein the term “format” refers to an aspect ration of the sides of the image, for example, 16:9, 4:3, etc. In another aspect, the entrance cross section of the integrator  312  is twice the length of the exit cross section of the solid light integrators  308 . 
         [0048]    In one embodiment, the collecting light integrator  312  has a length such that the light is uniformly integrated by multiple reflections from the collecting light integrator mirror surfaces. Ideally, the exit cross section of the collecting light integrator  312  should be free of chips from the mirror surface or any dust from the edge that will be focused into the imager  340 . Any dust or chips on this cross section will be visible on a focused image from the projector  300 . 
         [0049]    The light are then collected into relay lenses  320  with diameter big enough to collect all (or almost all) of the light energy from the lamps  305 , and focus the light intensity node pattern from the light integrators onto the reflective surfaces  330  (e.g. a stepped mirror surface). The light intensity node pattern on the surfaces  330  is a virtual mapping of the light spots from the light integrators  308  entrance. In one embodiment, the solid light integrators  308  for the depicted parallel position lamp have a same cross section and length to beneficially create a node pattern with well defined maximums and minimums. In one aspect, if the integrators do not have a same cross section the node pattern may be destroyed. 
         [0050]      FIG. 4  is a simulation plot of the light intensity node pattern  410  focused on the stepped mirror  400 , where the mirror steps are matched with the created light intensity node pattern according to an embodiment of the present invention. As shown, the node patterns shows peaks as one moves from left to right. The highest peak shown roughly corresponds to the center of the mirror. Additionally, peaks can be seen as one moves up and down from a middle of the mirror. 
         [0051]    In one aspect, the flat regions  432  are located at or near the peaks, and the steps  436  are located at or near the minimums of the node pattern. This configuration is able to reflect almost all of the light. For example, in one embodiment, about 90%-95%. In one embodiment, the steps are not reflective, for instance, because very little light is received by them. 
         [0052]    Therefore, referring back to  FIG. 3 , each stepped mirror surface  330  compresses the illumination of the entrance pupil to about 50% from each stepped mirror unit. Thus, by designing a stepped mirror  330  where each mirror surface has a dimension and an angle matched to reflect the light intensity node pattern into the pupil  345 , all (or almost all) of the light energy from a light source illuminates approximately 50% of the pupil  345 . 
         [0053]    As shown, the pupil  345  is a lens that is attached to a total internal reflection (TIR) prism  348  where the surface of the lens is AR coated and the lens is glued, aligned and fixed in x-y-z position to the TIR prism  348 . In one embodiment, the TIR prism  348  is a 2 glass block component where there is air gap between the glass substrates of typical 5-25 micron meter. The light is reflected in the TIR surface and illuminates the digital micromirror device (DMD)  342  from Texas Instrument, US, or other imaging device. 
         [0054]    A DMD is a mirror device that consists of a pixel matrix of mirror tilted, e.g., +/−12 degrees to obtain an On/Off state. The DMD reflects the light into the projection lens when the DMD is ON position. In one embodiment, to avoid any reflections into the projection lens, the DMD reflects the light in a dump light area of the optical engine when the DMD is in Off position. Such reflection can reduce the contrast of the projected image. 
         [0055]    Compression of light from a light source by a stepped mirror is now further described, particularly with regard to the location of the steps. 
         [0056]      FIG. 5  shows a schematic diagram of part of an image projector according to an embodiment of the present invention. Two lamps  505  are shown in one illumination axis. The stepped mirror  530  compresses the illumination from the lamps  505  to only illuminate 50% of the entrance pupil  545  of an imager. In one aspect, such compression can effectively double the light intensity for the area of the pupil  545 . 
         [0057]    As shown, the solid rays  517  correspond to peaks in a light intensity node pattern provided from collective light guide  512 . The mirrors  532  are located so that the solid rays  517  (i.e. the peaks) are reflected to the pupil  545 . The dashed rays  519  signify any light rays that are at the minimums in the node pattern. The rays  519  are incident on the stepped mirror at steps  536 , which do not reflect the rays  519  to the pupil  545 . However, as few of the rays  519  exist, the stepped mirror  530  can accomplish compressing most of the illumination to half (half A as shown) of the pupil  545 . 
         [0058]    The steps  519  occur so that different mirror regions  532  can have their angle with line  542  adjusted to appropriate values in order to compress the illumination to half A of the pupil  545 . Ideally, the change from one mirror to another is as short as possible. Accordingly, in one embodiment, a step has a surface with an orientation within a range of 90 degrees from perpendicular to the received EM radiation to parallel to the EM radiation with the surface facing away from the pupil  545 . In other words, the step  536  is horizontal, vertical (face to the left), or somewhere in between. 
         [0059]    Additionally, in one embodiment, the mirrors  532  may be curved in a direction perpendicular (i.e. transverse—out of the paper) to the cross section shown. In another embodiment, there are different mirror sections in the transverse direction. These embodiments may provide a greater illumination as follows. 
         [0060]    As shown, the central ray  517   a  is transformed into the ray  521   a  that is received by the pupil  545 . The ray  517   a  occurs at the greatest height of the relay lens  520  (i.e. from top to bottom of the relay lens  520 ). However, the ray  521   a  occurs at a point between the middle  547  and the narrow end  549  of the pupil lens  545 . Thus, the height at this point may be less than the height of the relay lends  520  at its middle. Accordingly, embodiments compress the ray  517   a  in the vertical direction (i.e. in direction into/out of the paper). 
         [0061]    To compress the illumination in this direction, a similar mechanism as the compression in the other direction (as described above) may be used. For example, a greater angle from a plane perpendicular to the cross-section shown may be used for regions of a mirror that correspond to the top and the bottom of the relay lens  520 . As another example, mirror regions that are above a central plane perpendicular to the pupil are tilted so that an angle between a respective region and the central plane is less than 90 degrees. The central plane cuts the pupil in half. The central plane would be a horizontal plane, i.e. in the same plane as the cross-section shown. This titled mirror region would reflect the light with a component in a downward direction so that the light would be compressed. Similarly, a mirror region below the central plane would reflect light upwards. 
         [0062]    As mentioned above, different lamp configurations may be used as a light source. Examples of other configurations are as follows. 
         [0063]      FIGS. 6A and 6B  show alternative configurations for lamps of light sources according to an embodiment of the present invention. In  FIG. 6A , the lamps  605  provide light in opposing directions into light guides  608 , which are also in opposing directions. These light guides then transmit the light into a collective light guide  612 . In  FIG. 6B , the lamps provide light in perpendicular directions to the light guides  608 , which are also perpendicular to each other. These light guides also then transmit the light into a collective light guide  612 . In other embodiments, different configurations may be combined to provide light sources with more than two lamps, e.g. combining these two configurations so that 3 lamps are used. 
         [0064]    Embodiments also provide modulation of different colors of the light sources. 
         [0065]      FIG. 7  shows a color modulator  725  placed between a lamp  705  and a light integrator  708  according to an embodiment of the present invention. In one aspect, the color modulator  725  is close or at a focus point of the reflector of the lamp. The color modulators  725  operate to filter certain wavelengths (or colors) of a light source. Such operation is further described in the Andersen patent, referenced above. In one embodiment, each lamp  705  has its own color modulator, which are synchronized to each other during operation. 
         [0066]      FIG. 8A  shows a color wheel with 4 segments, shows here by Red, Green, Blue and White, according to an embodiment of the present invention. The sequence of the colors can vary, and are not be limited strictly to combinations or ordering of R,G,B; W or R,G,B. 
         [0067]      FIG. 8B  shows a color wheel with primary colors (R,G,B) and secondary colors (Cyan, Magenta and Yellow) according to an embodiment of the present invention. The sequence of the color can be any and are not limited to use of Cyan, Magenta and Yellow as the specific secondary colors. 
         [0068]    The description above has been focused on single display systems; however, embodiments may also be used with multiple display systems, or in non display solutions. 
         [0069]    The above description of exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.