Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1998-12-18
2001-01-09
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S291000, C359S295000, C359S572000, C359S224200
Reexamination Certificate
active
06172796
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 electro-mechanical grating device which has a significant improvement in the output of the diffracted light beam by approximating a continuous blaze grating with n discrete levels. Furthermore, the invention relates to a method for operating a multilevel mechanical and electro-mechanical grating device.
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 Electro-mechanical Modulator,” and U.S. Pat. No. 5,661,593, issued Aug. 26, 1997, to C. D. Engle entitled “Linear Electrostatic Modulator”. Other applications of electro-mechanical 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, issued 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 presented 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 is 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 position and height of the ribbons has 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 actuated ribbons, the intensity distribution of the diffracted optical beams is asymmetric and can produce a primary beam with a higher optical intensity. The direction of this primary diffracted beam can be switched by creating a different second actuated state for the ribbon heights. Unique to this work is the use of multiple heights in a GLV to create an asymmetric grating profile for improved optical diffraction efficiency that can be switched between two actuated states.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for operating a mechanical grating device so that an improved optical diffraction efficiency can be achieved. Furthermore, with the inventive method light can be efficiently and independently coupled into three different angles.
The object is achieved by a method for operating a mechanical grating device having a plurality of spaced apart deformable ribbon elements disposed parallel to each other in the unactuated state and spanning a channel, wherein the ribbon elements define a top surface and each ribbon element defines a discrete level, said deformable ribbon elements are organized in groups of N elements wherein N is greater than 2, the method comprising the steps of:
providing a beam of light;
applying a first actuation force pattern to the ribbon elements of each group for a certain amount of time thereby generating a first pattern in each group wherein the pattern comprises N different levels thereby diffracting the incident light beam into a first direction; and
applying a second actuation force pattern to the ribbon elements of each group for a certain amount of time thereby generating a second pattern in each group wherein the second pattern comprises N different levels thereby diffracting the incident light beam into a second direction different from the first direction.
Another object of the present invention is to provide a method for operating an electro-mechanical grating device so that an improved optical diffraction efficiency can be achieved. Furthermore, with the inventive method light can be efficiently and independently coupled into three different angles.
The above object is achieved by a method for operating an electro-mechanical grating device having a plurality of spaced apart deformable ribbon elements disposed parallel to each other in the unactuated state and spanning a channel, wherein the ribbon elements define a top surface and each ribbon element defines a discrete level, said deformable ribbon elements are organized in groups of N elements wherein N is greater than 2 and a plurality of standoffs are provided, wherein according to the longitudinal direction of the device at least N-2 standoffs are associated with each group, the method comprising the steps of:
providing a beam of light;
applying a first electrostatic actuation force pattern to the ribbon elements of each group for a certain amount of time thereby generating a first pattern in each group wherein the pattern comprises N different levels thereby diffracting the incident light beam into a first direction; and
applying a second electrostatic actuation force pattern to the ribbon elements of each group for a certain amount of time thereby generating a second pattern in each group wherein the second pattern comprises N different levels thereby diffracting the incident light beam into a second direction different from the first direction.
A further object of the invention is to provide a electro-mechanical grating device which has improved optical diffraction efficiency and improves the contrast of an electro-mechanical multilevel grating device. Furthermore the electro-mechanical grating device should operate as a three-way light valve.
This object is achieved by an electro-mechanical grating d
Kowarz Marek W.
Kruschwitz Brian E.
Eastman Kodak Company
Epps Georgia
Noval William F.
Shaw Stephen H.
Thompson Timothy
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