Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-02-22
2003-04-22
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227140
Reexamination Certificate
active
06552328
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of sensors for detecting mechanical motion, and more particularly to an opto-electro-mechanical coupling technique for MicroElectroMechanical systems (MEMS).
BACKGROUND OF THE INVENTION
Micro-Electro-Mechanical Systems (MEMS) integrate mechanical elements, such as microsensors and microactuators, and electronics on a common substrate through the utilization of microfabrication technology. MEMS are typically micromachined using integrated circuit (IC) compatible batch-processing techniques that selectively etch away parts of a silicon wafer or add new structural layers. They range in size from several micrometers to many millimeters. These systems sense, control, and actuate on a micro scale and function individually or in arrays to generate effects on a macro scale. The mechanical motion of the microsensors can be induced or altered by, for example, electric fields, chemical reactions, external motion, thermal changes, mechanical state elements, and growth of bio-agents that alter the mass of the mechanical structure.
One of the key challenges in MEMS design is finding a way to reliably detect and transmit information regarding the position and velocity of on-chip mechanical elements. A variety of electro-mechanical coupling techniques are currently employed in the MEMS field, each of which is best suited to specific applications. Some of the existing coupling techniques include, for example, capacitive measurement of the gap between two materials, spatial modulation of optical beams via rotating mirrors, optical corner cube reflectors, gratings, piezoresistive measurement of deflection, exploitation of piezoelectric effects, magnetic coupling, electro-static gratings, and sensing of fields emitted from atomic force microscopy tips to characterize the distance to the surface of an object. Virtually all of these coupling techniques produce an electrical signal or an optical signal. Conventional coupling techniques that produce an optical signal, however, require precision alignment to read out the optical signal.
“Transmission of information using wavelength tunable Vertical-Cavity Surface-Emitting Lasers (VCSEL) is known in the prior art. VCSELs are usually grown by Molecular Beam Epitaxy (MBE) or Metal-Organic Vapor Deposition (MOCVD). They typically comprise a quantum well gain region embedded inside a one optical wavelength (&lgr;) thick cavity between two end mirrors. The mirrors are doped n and p type to form a p-i-n diode around the active layer. The mirrors are typically made of alternating high and low refractive index materials such as gallium arsenide and aluminum arsenide, each ¼&lgr; thick.”
The ability to modulate the wavelength of light emitted by a VCSEL is also known in the prior art. The cavity resonance of a laser can be written as nL=m(&lgr;/2) where n is the refractive index of the cavity, L is the length of the cavity, m is an integer, and &lgr; is the wavelength. By combining a vertical cavity laser structure with a monolithically micromachined deformable membrane, wavelength tuning can be accomplished by changing the cavity length.
As MEMS moves into high temperature and high radiation environments, it becomes increasingly important to perform as many information processing functions as possible in the mechanical domain. The mechanical properties of materials are far more robust than the electrical properties in some harsh environments, such as aerospace, in that they are inherently immune to radiation effects.
In light of the foregoing, there is a need for a system and a method that directly couples mechanical motion of on-chip microsensors and microactuators to the optical domain for transmission without requiring precision alignment of an optical path.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a system and method that directly couples mechanical motion of on-chip microsensors and microactuators to the optical domain for transmission that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
“In accordance with the purposes of the present invention, as embodied and broadly described, the invention provides a method for coupling mechanical motion of a microsensor to an optical domain including providing a microsensor comprising a mechanical structure that is responsive to a physical phenomenon of measurement interest and providing at least one VCSEL having an output wavelength comprising an optical cavity with two ends and a reflector at each end. One of the reflectors of the VCSEL is then coupled to the mechanical structure and the change in the output wavelength of the VCSEL due to the change in optical cavity length resulting from the mechanical structure's response to the physical phenomenon is measured.”
In another embodiment, the invention provides a micromechanical sensor including a micromechanical member that is responsive to a physical phenomenon of measurement interest. The sensor further includes a VCSEL including an optical cavity with two ends and a reflector at each end, wherein one of the reflectors is coupled to the mechanical structure and wherein the VCSEL outputs a signal having a wavelength corresponding to the physical phenomenon of interest.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention.
REFERENCES:
patent: 5331658 (1994-07-01), Shieh et al.
patent: 5771253 (1998-06-01), Chang-Hasnain et al.
patent: 6127765 (2000-10-01), Fushinobu
patent: 6263002 (2001-07-01), Hsu et al.
patent: 6301274 (2001-10-01), Tayebati et al.
Berlin Andrew A.
Hung Elmer S.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kim Robert H.
Thomas Courtney
Xerox Corporation
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