Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
2000-01-03
2001-02-13
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Diffraction
From grating
C359S290000, C359S291000
Reexamination Certificate
active
06188519
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to spatial light modulators that are based on micromechanically-actuated, diffractive mirror structures. A prior-art device in this category, the “Flat Diffraction Grating Light Valve” (U.S. Pat. No. 5,841,579), comprises two interdigitated groups of parallel ribbon reflectors, wherein one group is fixed and the other is electrostatically actuated to control the ribbons' surface heights. The device is dynamically controlled to function alternately as a plane mirror (with the ribbons' reflective surfaces all coplanar) or as a diffraction grating (with the movable ribbon surfaces recessed relative to the fixed ribbons). The device functions as a pixel element in a spatial light modulator that has applications to image displays and printing systems.
Advantages of the grating light valve are that it can operate under high illumination levels and at very high (e.g., megahertz-level) switching rates, and it can be used with broadband illumination. It is especially well adapted for display applications, although it could have potential limitations for applications such as high-resolution printing and maskless lithography that require smaller pixels and more precise control of the image illumination levels. The lithographically defined gaps between ribbons can limit efficiency and contrast, and performance could also be compromised by non-planarity of the elongated ribbon elements.
SUMMARY OF THE INVENTION
This invention is an improved light-modulating pixel device termed a “bigrating light valve” (BLV) comprising a movable reflective surface in which an array of subapertures is formed, wherein a fixed reflective surface fills each subaperture. Illuminating radiation reflects off of the pixel, and the movable surface is electrostatically actuated to control the phase distribution of the reflected radiation across the pixel. Like the grating light valve, the device functions essentially as a plane mirror if the fixed and movable surfaces are coplanar, and it functions as a diffracting element when the movable surface is positionally displaced from the fixed element. But unlike the grating light valve, each pixel comprises a single movable element, and the fixed reflectors in each pixel form a two-dimensional grating (i.e., “bigrating”), rather than a linear grating. The movable element is inherently resistant to torsional bending or distortion that would affect planarity.
The BLV is preferably manufactured by a method in which the gaps between movable and fixed reflectors are defined by a sacrificial film; hence the gap size and dimensional accuracy are not limited by lithographic patterning capabilities. This method would make it possible to make very small pixels that would be useful for applications such as high-resolution printing and maskless lithography. Also, the manufacturing process provides accurate control of the reflective surfaces' planarity and positional relationships, thereby minimizing phase errors in the reflected radiation.
REFERENCES:
patent: 4751509 (1988-06-01), Kubota et al.
patent: 5661592 (1997-08-01), Bornstein et al.
patent: 5841579 (1998-11-01), Bloom et al.
Choksi et al., “Maskless extreme ultraviolet lithography,”J. Vac. Sci. Technol.B 17(6), Nov./Dec. 1999, pp. 3047-3051.
Folta, J.A. et al., “High density arrays of micromirrors,” Feb. 1999, pp. 1-9 (UCRL-ID-133164/National Technical Information Service, US Dept. of Commerce, Springfield, VA 22161).
Dang Hung Xuan
Townsend and Townsend / and Crew LLP
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