Patent Application
20080095203
Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
In describing embodiments of the present invention, the following terminology will be used.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an emitter” includes reference to one or more of such emitters.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.
As used herein, the term “about” means that dimensions, sizes, formulations, parameters, shapes and other quantities and characteristics are not and need not be exact, but may be approximated and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill in the art.
Numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 to 10” should be interpreted to include not only the explicitly recited values of about 1 to 10, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4, and sub-ranges such as 1-2, 2-5, and 5-9, etc.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
It has been recognized that a projection system can provide improved performance by using a plurality of means for emitting light to cooperatively form an image. A means for non-mechanically perturbing the plurality of means for emitting light to disrupt waveform uniformity can help to reduce speckle in the image.
For example,
As laser light tends to be coherent, coupled to the laser light emitters are perturbation modulators 104 for non-mechanically perturbing the light emitters. The perturbation modulators vary an input to the light emitters to disrupt wavefront uniformity across the array of laser light emitters 102. This helps to reduce speckle in the image 108 by reducing the coherence of the emitted light. For example, the perturbation modulators can be electrical circuits that produce a chaotic signal. The chaotic signal can be used to vary an electrical input to the light emitter, such as a drive current. As another example, the perturbation modulators can be optical feedback systems that feedback a portion of the optical output of the light emitters back into the light emitters.
One advantage of the system 100 is that the intensity of individual laser light emitters 102 can be reduced relative to a system that uses a single laser light emitter without sacrificing brightness in the image. For example, an array of N×N laser light emitters emitting incoherently with respect to each other can provide a brightness increase of N2 relative to a system using a single laser light emitter for the same image size. This can help to reduce the risk of eye injury. In addition to the N2 brightness increase, individual laser light emitters need not be scanned as rapidly, or over as wide an angular range, since each laser light emitter can form a portion of the image. The laser light emitters can be modulated to form pixels of the image, for example, by varying the brightness (intensity), color (wavelength), or both. For example, a laser light emitter may be simultaneously modulated and scanned across a region to provide varying illumination for different points on a screen corresponding to a desired brightness, color, or both for pixels at the different points.
For example,
Each patch may correspond to one pixel or may correspond to multiple pixels of the image. For example, a 1280×760 pixel image may be formed using an array of 1280×760 light emitters, a total of 972,800 light emitters. While this is a large number of laser light emitters, multiple light emitters may be formed on a common substrate using semiconductor processing techniques. For example, large arrays of laser light emitters may be formed using vertical cavity surface emitting lasers (VCSELs) fabricated on a common substrate.
Alternately, the patches may correspond to several pixels of the image. For example, a patch may be N×M pixels. For example, a patch may include 4 pixels (arranged in a 2×2 square), 4 pixels (arranged in a 1×4 row), 12 pixels (arranged as a 3×4 rectangle), 100 pixels (arranged in a 100×100 square), etc.
Different mappings of pixels to patches may be used, and the mapping need not be constant. A multi-resolution projection system may use a variable number of pixels per patch, depending on the resolution being projected. For example, an array of 100 by 100 light emitters may be switched between resolution modes of 1024×768, 1280×720, 1920×1080, and 1600×1200 by varying the patch size so that N varies between about 10 to about 20 and M varies between about 7 to about 12. For some resolution modes, it may be helpful to use only some of the light emitters in the array. It should also be appreciated that not all patches need be the same size in pixels. Depending on the particular application for which the projection system is intended, different combinations of resolution and number of light emitters may be used.
By including laser light emitters for each of the additive primary colors, color images can be provided. For example, as illustrated in
In another embodiment, the laser light emitters may be ultraviolet sources that interact with an ultraviolet-fluorescent screen to produce the image. For example, a screen may include material which emits different wavelengths of visible light in response to different wavelengths of ultraviolet illumination to allow multiple colors to be produced. It will be appreciated that ultraviolet light emitters may be used advantageously in a rear projection system, since the risk of eye damage due to the ultraviolet radiation is reduced.
Returning to
A chaotic signal generator can be provided by a chaotic system for which an electrical output is produced, where the output is unpredictable. Residual time coherence of the emitted light can be shorter than the refresh time for the image, for example, in excess of 80 Hz to reduce speckle perception by the viewer. This unpredictability can be caused by the combination of high system sensitivity to initial conditions and a bounded output. Some chaotic systems include a non-linear or piecewise linear element within a feedback path. Various ways of producing a chaotic system can be used, including for example, coupled nonlinear L-C oscillators, non-linear feedback oscillators, and the like.
In addition to helping to disrupt the wavefront uniformity of the individual light emitters, the perturbation modulators 104 can also help to reduce interference that may occur between overlapping portions of adjacent patches in the image. Overlap may intentionally be included, for example, to provide smoothing of pixilation in the projected image. Overlap may unintentionally be included, for example, due to alignment errors in the optical system. Adjacent light emitters, if coherent, may cause constructive or destructive interference, resulting in visible artifacts or interference patterns. By including the perturbation modulators, this helps avoid these effects.
A method for reducing speckle in an image projected by an array of laser light emitters will now be described in conjunction with the flowchart of
The method may also include the step of non-mechanically perturbing 604 an input to the plurality of light emitters to a degree sufficient to disrupt waveform uniformity to reduce speckle in the image. For example, perturbing an input can be performed by modulating a drive current of the laser light emitters using a chaotic signal. As another example, perturbing an input can be providing feedback of optical output from the light emitters.
Summarizing and reiterating to some extent, the disclosed techniques can help to provide increased image brightness in a projection system by using an array of laser light emitters to cooperatively project the image. Because multiple light emitters are used, brightness of the image can be increased without increasing the brightness of individual emitted laser beams. To help reduce speckle, coherence of the emitted laser light can be reduced using chaotic circuits to modulate drive current of the laser light emitters. The high directionality provided by the laser light emitters can also help to simplify overall design and improve efficiency of the projector system, since fewer or simpler lenses may be used. Because many low power laser light emitters can be used, overall power efficiency and reliability of the projector may also be improved.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
