Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-12-10
2001-08-28
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S572000, C359S573000, C359S231000
Reexamination Certificate
active
06282012
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to modulating an incident light beam with a mechanical grating device and more particularly to a method for actuating a mechanical grating device that functions to diffract a light beam.
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. Electro-mechanical gratings for spatial light modulation are well known in the patent literature; see U.S. Pat. No. 5,311,360, issued May 10, 1994, to Bloom et al., entitled “Method and Apparatus for Modulating a Light Beam”. This device, which is also known as a grating light valve (GLV), 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”.
According to the prior art, for operation of the GLV device, an attractive electrostatic force is produced by a single polarity voltage difference between the ground plane and the conducting layer atop the ribbon layer. This attractive force changes the heights of the ribbons relative to the substrate. Modulation of the diffracted optical beam is obtained by appropriate choice of the voltage waveform. The voltage needed to actuate a ribbon a certain distance depends on several factors including the stress in the ribbon material, the distance between the ribbons and substrate, and the ribbon length.
It is well known that the ribbon elements of the GLV device possess a resonant frequency which depends primarily on the length of the ribbons and the density and tension of the ribbon material; see for example “Silicon Microfabrication of Grating Light Valves,” Ph.D. Thesis, Stanford University 1995, Chapter 3, by F. S. A. Sandejas. When a ribbon is actuated or released, it rings at its resonant frequency, which is typically between 1 and 15 MHz. The mechanical response of the ribbon elements is damped by the surrounding gas as described in “Squeeze Film Damping of Double Supported Ribbons in Noble Gas Atmospheres,” Proc. Of Solid-State Sensor and Actuator workshop, Hilton, Head, SC, June 8-11, 198, pp. 288-291. This damping depends on the type of gas present and pressure, and determines the width of the resonant peak associated with the resonant frequency of the ribbons. As a result of this resonant ringing, the maximum frequency at which the GLV device can be operated is limited, and the diffracted light intensity contains undesirable temporal variations. There is a need therefore for a GLV device having increased operating speed and reduced temporal light intensity variations.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for actuating the ribbon elements of an electromechanical grating device so that the diffracted light intensity does not contain any undesirable temporal variations caused by the resonance of said ribbon elements, thereby producing a more ideal output that will allow higher frequency operation of the device. The above object is accomplished by a method for damping electro-mechanical ribbon elements suspended over a channel defining a bottom surface and having a bottom conductive layer formed below said bottom surface, the method comprises the steps of: providing at least one constant amplitude voltage pulse to at least one ribbon element to cause the ribbon element to contact the bottom surface of the channel; and providing at least one braking pulse to said ribbon elements wherein said braking pulse is separated by a narrow gap from said constant amplitude voltage pulse.
According to a further aspect of the invention, the above object is also accomplished by a method for damping electro-mechanical ribbon elements suspended over a channel defining a bottom surface and having a bottom conductive layer formed below said bottom surface, the method comprises the steps of: providing at least one constant amplitude voltage pulse to at least one ribbon element wherein said constant amplitude voltage pulse causes said ribbon element to be drawn into the channel wherein said ribbon element is in a suspended actuated state above the bottom of the channel; and providing at least two braking pulses to said ribbon elements wherein an initial braking pulse immediately precedes said constant amplitude voltage pulse and a final braking pulse immediately follows said constant amplitude voltage pulse.
It is an advantage of the inventive method that the light intensity diffracted by the electromechanical grating device that any undesirable temporal variations caused by the resonance of the ribbon elements are substantially reduced. The method allows high-frequency operation of the device which is especially important in applications such as displays, photofinishing printers and optical communications.
REFERENCES:
patent: 5311360 (1994-05-01), Bloom et al.
patent: 5459610 (1995-10-01), Bloom et al.
patent: 6038057 (2000-03-01), Brazas, Jr. et al.
patent: 6144481 (2000-11-01), Kowarz et al.
patent: 6172796 (2001-01-01), Kowarz et al.
patent: 6181458 (2001-01-01), Brazas, Jr. et al.
F. S. A. Sandejas, “Silicon Microfabrication of Grating Light Valves,” Jul. 1995, Ph.D. Dissertation, pp. 1-108.
Gudeman, et al., “Squeeze Film Damping of Doubly Supported Ribbons in Noble Gas Atmospheres,” Jun. 1998,Solid-State Sensor and Actuator Workshop, pp. 288-291.
Brazas, Jr. John C.
Kowarz Marek W.
Ben Loha
Close Thomas H.
Eastman Kodak Company
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