Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
1998-12-18
2002-01-01
Chang, Audrey (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S224200, C359S291000
Reexamination Certificate
active
06335831
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of modulation of an incident light beam by the use of a mechanical grating device. More particularly, this invention discloses a multilevel mechanical grating device which has a significant improvement in the output of the diffracted light beam by approximating a continuous blaze grating with m discrete levels.
BACKGROUND OF THE INVENTION
Electro-mechanical spatial light modulators have been designed for a variety of applications, including image processing, display, optical computing and printing, Optical beam processing for printing with deformable mirrors has been described by L. J. Hornbeck; see U.S. Pat. No. 4,596,992, issued Jun. 24, 1986, entitled “Linear Spatial Light Modulator and Printer”. A device for optical beam modulation using cantilever mechanical beams has also been disclosed; see U.S. Pat. No. 4,492,435, issued Jan. 8, 1995 to Banton et al., entitled “Multiple Array Full Width Electromechanical Modulator,” and U.S. Pat. No. 5,661,593, issued Aug. 26, 1997, to C. D. Engle entitled “Linear Electrostatic Modulator”. Other applications of electromechanical gratings include wavelength division multiplexing and spectrometers; see U.S. Pat. No. 5,757,536, issued May 26, 1998, to Ricco et al., entitled “Electrically-Programmable Diffraction Grating”.
Electro-mechanical gratings are well known in the patent literature; see U.S. Pat. No. 4,011,009, issued Mar. 8, 1977 to Lama et al., entitled “Reflection Diffraction Grating Having a Controllable Blaze Angle”, and U.S. Pat. No. 5,115,344, issued May 19, 1992 to J. E. Jaskie, entitled “Tunable Diffraction Grating”. More recently, Bloom et al. described an apparatus and method of fabrication for a device for optical beam modulation, known to one skilled in the art as a grating-light valve (GLV): see U.S. Pat. No. 5,311,360, issued May 10, 1994, entitled “Method and Apparatus for Modulating a Light Beam”. This device was later described by Bloom et al. with changes in the structure that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbon and substrate; 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast; 3) solid supports to fix alternate ribbons and 4) an alternative device design that produced a blazed grating by rotation of suspended surfaces; see U.S. Pat. No. 5,459,610, iggued Oct. 17, 1995, to Bloom et al., entitled “Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate,” and U.S. Pat. No. 5,808,797, issued Sep. 15, 1998 to Bloom et al., entitled “Method and Apparatus for Modulating a Light Beam.” Bloom et al. also proented a method for fabricating the device; see U.S. Pat. No. 5,677,783, issued Oct. 14, 1997, entitled “Method of Making a Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate”.
The GLV device can have reflective coatings added to the top surface of the ribbons to improve the diffraction efficiency and lifetime of the GLV device. Preferred methods of fabrication use silicon wafers as the substrate materials requiring the device to operate in reflection for the wavelengths of interest. An increase in reflectivity ig important to reduce damage of the top surface of the ribbons and avoid mechanical effects that might be attributed to a significant increase in the temperature of the device due to light absorption.
For GLV devices, the positions and heights of the ribbons have been symmetric in design. One drawback to this design is an inability to isolate the optical intensity into a single optical beam. This relatively poor optical efficiency is primarily due to the symmetry of the actuated device, which produces pairs of equal intensity optical beams. Each period of the improved grating must include more than two ribbons and create an asymmetric pattern of the ribbon heights. By creating an asymmetric pattern for the heights of the ribbons, the intensity distribution of the diffracted optical beams is asymmetric and can produce a primary beam with a higher optical intensity. Furthermore, by adjusting the asymmetry of the pattern of ribbon positions and heights, the intensity distribution of the diffracted optical beams can be altered. In this way, the device can be used to switch between various diffracted optical beams.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mechanical grating device wherein the diffraction efficiency of a blazed grating is accomplished.
The object is achieved by a mechanical grating device comprising:
a base having a surface;
a spacer layer having an upper surface, is provided above the base, and a longitudinal channel is formed in said spacer layer, said channel having a first and second opposing guide wall and a bottom;
a plurality of spaced apart deformable ribbon elements disposed parallel to each other and spanning the channel, said deformable ribbon elements defining a top and a bottom surface and are filed to the upper surface of the spacer layer on each side of the channel, said deformable elements are organized in groups of N elements wherein N is greater than 2; and
each of said groups forms a pattern of discrete levels in an actuated state wherein the pattern has n levels wherein n is greater than 2.
It is a further object of the present invention to provide an electro-mechanical grating device wherein the diffraction efficiency of a blazed grating is accomplished.
The object is achieved by an electro-mechanical grating device comprising:
a base having a surface;
a spacer layer, having an upper surface, is provided above the base, and a longitudinal channel is formed in said spacer layer, said channel having a first and second opposing side wall and a bottoms
a first conductive layer being provided below the bottom of the channel;
a plurality of spaced apart deformable ribbon elements disposed parallel to each other and spanning the channel, said deformable ribbon elements defining a top and a bottom surface and are fixed to the upper surface of the spacer layer on each side of the channel, said deformable elements are organized in groups of N elements wherein N is greater than 2;
each of said groups forms a pattern of discrete levels in an actuated state wherein the pattern has n levels wherein n is greater than 2; and
a second conductive layer being part of each actuable ribbon element.
An advantage of the mechanical grating device of the invention is that the position of the ribbons across the area of the substrate and the periodic sequence of the ribbon heights can be used to improve the diffraction efficiency of the optical beam. This invention presents a periodic sequence of ribbon heights that resembles a blazed grating with discrete levels and is predicted to significantly increase the optical diffraction efficiency. The multi-level mechanical grating device can be fabricated using methods that are compatible with the microelectronics industry. The device is more reliable and more appropriate for printing applications than other blazed mechanical and/or electro-mechanical gratings in the patent literature. Further advantageous effects of the present invention are disclosed in the dependent claims.
REFERENCES:
patent: 4011009 (1977-03-01), Lama et al.
patent: 4492435 (1985-01-01), Banton et al.
patent: 4596992 (1986-06-01), Hornbeck
patent: 4936665 (1990-06-01), Whitney
patent: 5115344 (1992-05-01), Jaskie
patent: 5311360 (1994-05-01), Bloom et al.
patent: 5459610 (1995-10-01), Bloom et al.
patent: 5661593 (1997-08-01), Engle
patent: 5677783 (1997-10-01), Bloom et al.
patent: 5757536 (1998-05-01), Ricco et al.
patent: 5808797 (1998-09-01), Bloom et al.
patent: 5949570 (1999-07-01), Shiono et al.
patent: 6172796 (2001-01-01), Kowarz et al.
Kowarz Marek W.
Kruschwitz Brian E.
Chang Audrey
Close Thomas H.
Eastman Kodak Company
Shaw Stephen H.
Winstedt Jennifer
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