Patent Application
20090219491
Not Applicable.
1. The Field of the Invention.
The present disclosure relates generally to visual display devices, and more particularly, but not entirely, to illumination systems for use with display systems and other systems requiring illumination.
2. Description of Related Art
Display devices, such as televisions and image projectors, are increasingly using light modulators employing micro-electro-mechanical (“MEMS”) technology. MEMS-based light modulators are currently available in one-dimensional and two-dimensional varieties. Texas Instruments, for example, introduced a MEMS integrated circuit chip having a two-dimensional array formed from millions of tiny MEMS mirrors disposed on a substrate. Each mirror corresponds to a pixel in an image and electronic signals in the chip cause the mirrors to move and reflect light in different directions to form bright or dark pixels. See, for example, U.S. Pat. No. 4,710,732, which is hereby incorporated herein by this reference. One-dimensional light modulators, typically comprising a linear array of MEMS light modulating structures, may also be used to form a two-dimensional image through the use of appropriate magnifying optics and scanning mirrors. See for example, U.S. Pat. Nos. 5,982,553 and 7,054,051, which are hereby incorporated herein by this reference.
Both one-dimensional and two-dimensional light modulators require a light source to illuminate their light modulating surfaces. In order to accurately display an image using a two-dimensional light modulator, the intensity of the illumination provided by the light source should be uniform across its two-dimensional array of light modulating elements so that the generated pixels on a viewing surface are evenly illuminated. The illumination requirements for a one-dimensional light modulator may be slightly different from that of a two-dimensional light modulator. In particular, it has been found that the best images are formed on a viewing surface when the illumination of the light modulating elements of the one-dimensional light modulator is uniform along a first axis and non-uniform, such as Gaussian, along a second axis.
Halogen incandescent bulbs have been used in the past as light sources for at least two-dimensional light modulators. While halogen bulbs will produce a significant lumen output, they are known to be extremely inefficient in terms of converting electrical power to visible light. Further, due to their inherent inefficiency, halogen bulbs produce excessive heat, which requires the engineering of complex heat removal systems to prevent heat damage to surrounding components. Disadvantageously, halogen bulbs also have a relatively short life span and require frequent replacement. Halogen bulbs have, however, proven unsuitable for use with one-dimensional light modulators.
Coherent light sources, such as lasers, have been used in the past as light sources for illuminating one-dimensional light modulators. But, even coherent light sources also have their drawbacks. For example, achieving high amounts of lumen output from coherent light sources may require large and expensive amplification systems. Further, light beams emitted from coherent light sources typically have a non-uniform intensity distribution, such as a Gaussian distribution, that are generally unsuitable for use with light modulators.
In the past, one well-known method for converting a laser beam having a non-uniform distribution into a beam having a uniform, or top-hat distribution, was accomplished by employing a special type of lens, known as a Powell lens. In fact, Powell lenses are widely known to produce an efficient line pattern that overcomes the limits of Gaussian patterns.
Recent advances in the development of diode lasers have attempted to address the need for expensive amplifiers with coherent light sources. However, while more energy efficient, an individual diode laser does not have sufficient output for use with most image projection systems. To overcome this drawback, multiple diode lasers may be grouped together into an array. However, because of the spatial distribution inherent with diode-laser arrays, it is not always possible to use a single Powell lens in order to convert the Gaussian distributions of the beams emitted from a diode-laser array into a uniform, or top-hat, distribution. Another drawback to the use of a diode-laser array is that the differences in the output of each of the diode lasers may cause irregularities in the intensity of the spatial distribution.
One previous attempt to transform a non-uniform intensity distribution of a beam emitted from a laser into a beam with a uniform intensity distribution is disclosed in U.S. Pat. No. 4,744,615 (granted May 17, 1988 to Fan et al.). Fan et al. discloses directing a coherent laser beam having a non-uniform spatial intensity distribution into a light tunnel to thereby produce a beam having a substantially uniform spatial intensity distribution. The light tunnel of the Fan et al. device includes a polygonal cross-section such that the image produced at the exit of the light tunnel will have a substantially uniform intensity distribution in two-dimensions. While the Fan et al. device is suitable for its intended purpose of illuminating a mask for the fabrication of microcircuits as disclosed therein; it is not suitable for illuminating a one-dimensional light modulator. In particular, the Fan et al. device cannot generate a line image with a substantially uniform distribution along a first axis and a non-uniform distribution along a second axis, as is necessary for the most effective use of one-dimensional light modulators.
Thus, there exists a need for an optical system that is able to efficiently convert the non-uniform distribution of laser beams generated by a diode-laser array into a uniform distribution along a first axis and a non-uniform distribution along a second axis, especially when such diode-laser arrays are used to illuminate one-dimensional light modulators. The features and advantages of this disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the disclosure without undue experimentation. The features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and upon payment of the necessary fee.
The features and advantages of the disclosure will become apparent from a consideration of the subsequent detailed description presented in connection with the accompanying drawings in which:
For the purposes of promoting an understanding of the principles in accordance with the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the disclosure as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the disclosure claimed.
It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Further, as used herein, the terms “comprising,” “including,” “containing,” “having,” “characterized by,” and grammatical equivalents thereof are inclusive or open-ended terms that do not exclude additional, unrecited elements or method steps.
Applicants have discovered an illumination system for transforming an image generated by an array of coherent light sources with a non-uniform intensity distribution into an image having a uniform distribution, or top-hat distribution, along a first axis, and a non-uniform intensity distribution along a second axis. The present disclosure may be particularly adapted for use with one-dimensional light modulators that require a line image of light with a uniform intensity distribution over the long dimension of the array of light modulating elements on the light modulator.
The present disclosure may further preserve a Gaussian intensity distribution in an axis orthogonal to the long dimension of the one-dimensional array of light modulating elements on the light modulator. It will be appreciated by those having ordinary skill in the art that the preservation of the non-uniform, or Gaussian, intensity distribution along this orthogonal axis helps to achieve narrower line widths (i.e., improved image resolution in the orthogonal direction) since Gaussian beams focus to smaller spot sizes as compared to the spot sizes achieved with uniform-intensity beams. The present disclosure is further unique in that it may be aligned to maintain the polarization state of the original laser beams.
Referring now to
Each of the light sources 100 may emit a light beam 101 that is the same wavelength as the light beams 101 emitted by the other light sources 100. That is, the light beams 101 may all be of the same color, such as red, green or blue. It will be appreciated that the light sources 100 may be grouped into an array to generate the necessary output suitable for use with the optical system 10. Each of the beams 101 may be generated from an array of diode emitters or just a single emitter.
Novalux, Inc. currently manufactures diode laser platforms suitable for use with the present disclosure. However, the present disclosure may be used with single laser beams such as those taught in U.S. Pat. No. 6,763,042, which is hereby incorporated by reference in its entirety. It should be further noted that the present disclosure may include only one of the light sources 100 and beams 101.
As mentioned, each of the beams 101 may be generated from one of the light sources 100. The beams 101 may each have a divergence a, which is not explicitly shown in
In an embodiment of the present disclosure, reflective mirrors (not explicitly shown) may reduce the spatial distances and angular separations between the beams 101 emitted from the light sources 100. These mirrors may be operable to direct the beams 101 into a set of injector optics 102. It will be noted that the multiple beams 101 together form an apparent object with a height of H just prior to entering the set of injector optics 102. Furthermore, because the beams 101 are lasers, they may have a relatively small divergence a (typically, 0<α<0.01 radians, although much greater values of a are permissible).
The set of injector optics 102 may comprise lenses 102A, 102B, 102C and 102D. It will be appreciated that the overall purpose of the injector optics 102 may be to reduce the size of the object of height H formed by the beams 101 to a new image having a lesser height of h. Furthermore, the injector optics 102 may increase the divergence of the beams 101 from α to α′, which is also not explicitly shown in
In an embodiment of the present disclosure, the injector optics 102 may reduce the image size of the beams 101 between about 5 and about 50 times. In an embodiment of the present disclosure, the injector optics 102 may reduce the image size of the beams 101 between about 18 and about 22 times. In an embodiment of the present disclosure, the injector optics 102 may reduce the image size of the beams 101 approximately by about 20 times. That is,
The injector optics 102 may be collectively referred herein as an “optical reducer” since the injector optics 102 are operable to reduce the size of the apparent object of the beams 101.
At the same time the object height H is reduced to an image height h, the injector optics 102 increase the divergence α of the beams 101 to divergence α′. In an embodiment of the present disclosure, the divergence is increased between about 5 and about 50 times. In an embodiment of the present disclosure, the divergence is increased between about 18 and about 22 times. In another embodiment of the present disclosure, the divergence is increased between about 5 times to about 30 times. In yet another embodiment of the present disclosure, the divergence is increased about 20 times. That is,
α=20×α
Turning now to the optics 102A, 102B, 102C, and 102D, each will now be described pursuant to an embodiment of the present disclosure. Optic 102A may comprise a spherical or cylindrical optic having a clear aperture such that it can transmit all of the light from an object of height H. Optic 102B may comprise a spherical or cylindrical optic having a clear aperture such that it can transmit all of the light transmitted by optic 102A. Optic 102C may comprise a spherical or cylindrical optic having a clear aperture such that it can transmit all of the light transmitted through optics 102A and 102B. Optics 102A, 102B, and 102C may cause the beams 101 of apparent object size H to be collimated such that the chief rays of each of the beams 101 passes through a common focal point. In an embodiment of the present disclosure, the beams 101 are also collimated such that a common pupil is formed in the focal plane of the system consisting of optics 102A, 102B, and 102C.
In an embodiment of the present disclosure, the optic 102D may comprise a spherical or cylindrical optic having a different focal length than optics 102A, 102B, and 102C. The focal point of optic 102D may be placed at approximately the same position of the focal point of the system consisting of optics 102A, 102B, and 102C, wherein a reduction in size of the apparent object of height H formed by the beams 101 is reduced to an image having a height of h upon exiting the injector optics 102. The optic 102D now finishes the injection of the light beams 101 into the light tunnel 103. It will be appreciated by one having ordinary skill in the art that the divergence of the beams 101 in the system will increase by the same factor with which the height of the object is reduced as determined by the equation H/h.
The light tunnel 103 may comprise two opposing sides having walls 103A and 103B, respectively, and extend along a Z-axis. The walls 103A and 103B may be substantially parallel to each other and include a reflective coating on their inner surfaces. The walls 103A and 103B may be orthogonal to a Y-axis and parallel to an X-axis. The light tunnel 103 may have a hollow interior passageway with a light entrance at one end and a light exit at the other end. The walls 103A and 103B may extend from the light entrance to the light exit. In addition, the remaining two sides of the light tunnel 103, the sides orthogonal to the X-axis and parallel to the Y-axis, may be left open or constructed from a material that will not interact with light, such as clear glass or a material with a light absorbing capability.
The light tunnel 103 operates to convert the non-uniform distribution of the beams 101 into a beam with a uniform distribution along a Y-axis and a non-uniform distribution along an X-axis. This may be accomplished as the beams 101 are repeatedly reflected between the inner surfaces of the walls 103A and 103B. It will be appreciated by those having ordinary skill in the art that the greater the increase in divergence of the beams 101 as caused by the injector optics 102, the more numerous such multiple internal reflections are for a given propagation distance within the light tunnel 103. Further, without the increased divergence imparted to the beams 101 by the optics 102, or, without substantially increasing the length of the light tunnel 103, the light tunnel 103 would be less effective in converting the non-uniform distribution to a uniform distribution along the Y-axis of the beams 101.
Furthermore, the Gaussian profile of the beams 101 along their X-axis, which is orthogonal to the Y-axis, remains substantially unchanged by the light tunnel 103 due to the fact that the light tunnel 103 is constructed such that its width in the direction of the X-axis is always greater than that of the Gaussian distribution of the beams 101, so that the corresponding sides of the light tunnel 103 never interact with the beams 101 in the X-axis. For this reason, the sides of the light tunnel 103 adjacent the sides 103A and 103B may be left open or constructed from a material that does not interact with light, such as glass or a light absorbing material. In an embodiment of the present disclosure, sides parallel to the Y-axis are present on the light tunnel 103, but they do not interact meaningfully with the beams 101.
Referring now to
In an embodiment of the present disclosure, the walls 103E and 103F may be omitted entirely and the sides of the internal passageway may be left open. It will be appreciated however, that even though the walls 103E and 103F do not interact with light passing through the light tunnel 103, that it is convenient to use walls 103E and 103F to maintain the proper spacing between, and to support the walls 103A and 103B.
Still referring to
Referring now to FIGS. 1 and 5A-5C, in order to cause a relatively uniform image in the Y-axis suitable for use with a one-dimensional light modulator, each beam 101 may need to be internally reflected between the walls 103A and 103B (in the Y-axis) at least five (5) times in the light tunnel 103. More than five (5) reflections inside of the light tunnel 103 is typically not required to achieve a uniform distribution, i.e., the distribution is completely uniform within five (5) reflections as the beams 101 propagate through the tunnel 103. Increasing the divergence will cause the beams 101 to reflect more often, thereby causing the length of the light tunnel 103 needed to achieve a uniform distribution to be relatively short. If the divergence of the beams 101 were smaller or “slower,” the length of the light tunnel 103 would need to be increased. As mentioned, the light tunnel 103 need not have sides to reflect a beam in the X-axis and, therefore, the light tunnel 103 may consist of just two parallel mirrors.
It will be appreciated that other light-mixing devices can also be utilized with the present disclosure. For example, a light rod constructed of a transmissive material such as glass or plastic with similar dimensions may also be utilized. Thus, it will be appreciated that any light-mixing device operable to generate a uniform distribution from a non-uniform beam, such as a beam with a Gaussian distribution, falls within the scope of the present disclosure.
With sufficient length of the light tunnel 103 for a given divergence α′ of the beams 101, the output of the light tunnel will be uniform in intensity along an axis (hereafter referred to as the “Y-axis”) that is normal to both of the internal reflective surfaces of walls 103A and 103B. Thus, any faithful image of the output of the light tunnel 103 will also exhibit a uniform intensity distribution along this same Y-axis.
The light from each individual beam of beams 101 will be uniformly distributed along the Y-axis at the output of the light tunnel 103, so that any image of this output will cause light from each individual beam to be uniformly distributed over the entire image. Consequently, it is convenient to treat the output plane of the light tunnel 103 as an object O for the remaining optics 104 of the illumination system.
Referring now primarily to just
Along the axis perpendicular to the Y-axis (hereafter referred to as the “X-axis”), the imaging optics 104 cause an image P, not explicitly shown in
Furthermore, it should be noted that, as drawn in
Still referring primarily to
Referring now to
In an embodiment of the present disclosure, the light modulation device 200 may modulate light via diffraction. In particular, a first group of the ribbons 204 may comprise alternate rows of the ribbons. The ribbons 204 of the first group may be collectively driven by a single digital-to-analog controller (“DAC”) such that a common bias voltage may be applied to each of them at the same time. For this reason, the ribbons 204A of the first group are sometimes referred to as “bias ribbons.” A second group of ribbons 204 may comprise those alternate rows of ribbons 204 that are not part of the first group. Each of the ribbons 204B of the second group may be individually addressable or controllable by its own dedicated DAC device such that a variable bias voltage may be independently applied to each of them. For this reason, the ribbons 204 of the second group are sometimes referred to as “active ribbons.”
The bias and active ribbons may be sub-divided into separately controllable picture elements referred to herein as “pixel elements.” Each pixel element contains, at a minimum, a bias ribbon and an active ribbon. When the reflective surfaces of the bias and active ribbons of a pixel element are co-planar, incident light directed onto the pixel element is reflected. By blocking the reflected light from a pixel element, a dark spot is produced on the viewing surface at a corresponding display pixel. When the reflective surfaces of the bias and active ribbons of a pixel element are not co-planar, incident light may be both diffracted and reflected off of the pixel element. By separating the diffracted light from the reflected light, the diffracted light produces a bright spot on the corresponding display pixel.
The intensity of the light produced on the viewing surface by a given pixel element may be controlled by varying the separation between the reflective surfaces of its active and bias ribbons. Typically, this is accomplished by varying the voltage applied to the active ribbon while holding the bias ribbon at a common bias voltage. It has been previously determined that the maximum light intensity output for a pixel element may occur in a diffraction based system when the distance between the reflective surfaces its active and bias ribbons is λ/4, where λ is the wavelength of the light incident on the pixel element. The minimum light intensity output for a pixel element may occur when the reflective surfaces of its active and bias ribbons are co-planar. Intermediate light intensities may be output from the pixel element by varying the separation between the reflective surfaces of the active and bias ribbons between co-planar and λ/4.
It will be appreciated that although a limited number of ribbons 204 are depicted for the light modulation device 200 for purposes of convenience and clarity, that the light modulation device 200 may include a column of several hundred or thousand ribbons 204 extending along the Y-axis. In this manner, the ribbons 204 may form several hundred or thousand pixel elements. It will be further appreciated that the light modulation device 200 is best suited for display systems that employ a line-scan architecture. Display systems that employ a line-scan architecture typically scan an entire column, or row, of pixels across a viewing surface using a single scanning mirror.
Still referring to
Still primarily referring to
The optical system 10 shown in
It will be appreciated that the use of a light tunnel, with two open or non-light interactive sides, as described herein, e.g., light tunnel 103 represented in FIGS. 1 and 5A-5C, also provides another benefit relating to the polarization of the light. In particular, the use of a four-sided light tunnel, i.e., a tunnel whose four-side walls all interact with a light beam, fails to maintain the polarization of the light passing through it. For example, when a light tunnel with four (4) reflective sides is used by a LCOS-based projector, additional optical devices are utilized in an attempt to restore the linear polarization lost through the use of the four-sided light tunnel. Thus, an unexpected result to the use of a light tunnel with only two light reflective sides as described herein is that it may maintain the linear polarization of the incoming light beams.
Those having ordinary skill in the relevant art will appreciate the advantages provided by the features of the present disclosure. For example, it is a feature of the present disclosure to provide a system for converting the non-uniform distribution from a plurality of laser beams into a uniform distribution along a first axis of each of the laser beams and a non-uniform distribution along a second axis of the laser beams. Another feature of the present disclosure is a display system that is able to utilize multiple semiconductor lasers as a light source for a one-dimensional light modulator, such that light from each laser will uniformly illuminate an array of light modulating structures.
In the foregoing Detailed Description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.
It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present disclosure and the appended claims are intended to cover such modifications and arrangements. Thus, while the present disclosure has been shown in the drawings and described above with particularity and detail, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made without departing from the principles and concepts set forth herein.
This application claims the benefit of U.S. Provisional Application No. 60/999,622 filed Oct. 18, 2007, which is hereby incorporated by reference herein in its entirety, including but not limited to those portions that specifically appear hereinafter, this incorporation by reference being made with the following exception: In the event that any portion of the above-referenced provisional application is inconsistent with this application, this application supersedes said above-referenced provisional application.
| Number | Date | Country | |
|---|---|---|---|
| 60999622 | Oct 2007 | US |
