Patent Application
20080106779
A laser is an optical source that emits a coherent beam of monochromatic light. Lasers can be configured to emit relatively high intensity light, and the light can be emitted in a relatively narrow beam. These characteristics make lasers well suited for many applications, including for use as a video projection light source.
The coherent nature of laser light can cause a phenomenon that is referred to as laser speckle—a field-intensity pattern produced by the mutual interference that can result when a laser beam experiences temporal and/or spatial fluctuations. For example, a coherent laser beam that shines on a non-specular reflecting surface may be at least partially scattered by the surface, especially if variations in the surface are greater than the wavelength of laser light. Coherent light scattered by different elements of the surface can interfere to form a speckle pattern. A speckle pattern is characterized by some areas of the laser light appearing blacked out, with the blacked out pattern appearing to sparkle when there is any relative movement between the surface and the observer.
The inventor herein has recognized that laser speckle may be undesirable for some applications, including video projection. Accordingly, a video projection system including a laser light source and a laser despeckler is disclosed.
A despeckling device can be used to limit the appearance of speckle patterns to an observer. As described below, a despeckling device can rapidly change the speckle pattern. In some embodiments, the speckle pattern can be changed so rapidly that the integration time of the human eye is incapable of detecting the movement in the speckle patterns. In this way, even though a speckle pattern may always be present, the speckle pattern changes at a high enough frequency so that it is less perceptible. Furthermore, the speckle pattern can be changed with a sufficient number of permutations so that the same speckle pattern does not repeat too quickly or too often and thus become more perceptible. In some embodiments, the speckle patterns on the viewing screen may overlap, thereby reducing speckle contrast.
The location of the despeckling device in display device 10 can be selected to help limit the perceptibility of the speckle pattern. It is believed that a despeckling device that is located after an image generating device (e.g., LCD, DLP, etc.) can be more effective than a despeckling device that is located in the illumination path before an image generating device, although such positioning is not necessarily required in all embodiments. In one embodiment, the despeckling device may be positioned at a lens stop A, as shown in
In some embodiments, a despeckling device can be positioned in the illumination path before the image generating device. Such an arrangement can help limit image fuzziness when certain types of despeckling devices are used, such as moving diffusers.
Some despeckling devices may be configured to change the phase and/or polarity of the laser light. As nonlimiting examples, a despeckling device may include a variable phase plate or a variable polarization rotator. Such a variable polarization rotator may include an LCD with no polarizers.
As schematically shown in
The despeckling device described above may decrease the perceptibility of laser speckle to a viewer. For example, since the phase of light traveling through each cell can be altered by rotating the cell, numerous speckle patterns may be generated by rotating the cells in different combinations. For example, a despeckling device with m cells may produce nm combinations, where n equals the phase variations possible for each cell individually, and m equals the total number of cells. As a nonlimiting example, if each cell is configured to produce two different phases, and there is a 3×3 matrix of nine cells, then there are 29=512 combinations. If each cell is configured to produce four different phases and there are nine cells, then there are 49=262,144 combinations. The above are not meant to be limiting, but rather are provided as examples of the large number of variations that are possible even if only nine cells are used. Using more cells exponentially increases the number of possible combinations.
As the states of the various cells are changed, the speckle patterns on the viewing screen also change. If the cells are changed sufficiently fast, the speckle patterns can change rapidly enough to be substantially unperceivable to an observer. In some embodiments, the speckle patterns on the viewing screen may overlap, thereby reducing speckle contrast. Accordingly, a despeckling device may reduce speckle through a reduction of coherence, and/or spatial and/or temporal phase randomization of a laser beam.
It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein.
Inventions embodied in various combinations and subcombinations of features, functions, elements, and/or properties may be claimed in a related application. Such claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to any original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.
This application claims priority to U.S. Provisional Patent Application No. 60/864,123, filed Nov. 2, 2006, the entire contents of which are hereby incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60864123 | Nov 2006 | US |
