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Projection system and mirror elements for improved contrast ratio in spatial light modulators
| Details |
Inventors: Ilkov, Fedor A.; Patel, Satyadev R.; Richards, Peter W.; Stockton, John K.;
Assignee: Reflectivity, Inc. (Sunnyvale, CA)
Primary Examiner: Dowling; William
Assistant Examiner:
Attorney, Agent or Firm: Muir; Gregory R.
In order to minimize light diffraction along the direction of switching and more particularly light diffraction into the acceptance cone of the projection optics, in the present invention, mirrors are provided which are not rectangular. Also, in order to minimize the cost of the illumination optics and the size of the display unit of the present invention, the light source is placed orthogonal to the rows (or columns) of the array, and/or the light source is placed orthogonal to a side of the frame defining the active area of the array. The incident light beam, though orthogonal to the sides of the active area, are not however, orthogonal to any substantial portion of sides of the individual mirrors in the array. Orthogonal sides cause incident light to diffract along the direction of mirror switching, and result in light `leakage` into the on-state even if the mirror is in the off-state. This light diffraction decreases the contrast ratio of the mirror. The mirrors of the present invention result in an improved contrast ratio, and the arrangement of the light source to mirror array in the present invention results in a more compact system. |
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DETAILED DESCRIPTION In order to minimize light diffraction along the direction of switching and more particularly light diffraction into the acceptance cone of the projection optics, in the present invention, mirrors are provided which are not rectangular ("rectangular" as used herein including square mirrors).
Diffraction as referred to herein, denotes the scattering of light off of a periodic structure, where the light is not necessarily monochromatic or phase coherent Also, in order to minimize the cost of the illumination optics and the size of the display unit of the present invention, the light source is placed orthogonal to the rows (or columns) of the array, and/or the light source is placed orthogonal to a side of the frame defining the active area of the array.
The incident light beam, though orthogonal to the rows (or columns) and/or side of the active area, should not, however, be orthogonal to sides of the individual mirrors in the array.
Orthogonal sides cause incident light to diffract along the direction of mirror switching, and result in light `leakage` into the on-state even if the mirror is in the off-state.
This light diffraction decreases the contrast ratio of the mirror.
The present invention optimizes the contrast ratio of the mirror array so that when mirrors are in their off-state they send minimal light to the spatial region where light is directed when mirrors are in their on-state.
More specifically, the present invention comprises a particularly located light source and incident light beam and particularly designed mirrors in the array, which minimizes light diffracted into the acceptance cone of the projection (or viewing) optics, so as to provide an improved contrast ratio.
The arrangement/design of the present invention also minimizes non-reflective areas in the array, by allowing for a tight fit of mirrors and a large fill factor with low diffraction from the off to the on-state, even when the array is illuminated along the axes of mirror periodicity.
Namely, the design optimizes contrast ratio through angular sides non-parallel to the mirror's axis of rotation and optimizes fill factor through hinges that require a relatively small amount of area and allow neighboring mirrors to tile together with little wasted non-reflective area
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MEMS 
