Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
1999-09-21
2001-08-14
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S291000, C359S214100, C359S221200, C359S224200, C359S295000
Reexamination Certificate
active
06275326
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the field of microelectromechanical devices and systems and in particular to communication, telemetry, and information processing using microelectromechanical devices and systems.
BACKGROUND OF THE INVENTION
Microelectromechanical devices have become increasingly used for applications for which no comparable non-mechanical electronic device is available. Even for switching applications for optical communication, telemetry, and information processing systems, for which non-mechanical electronic devices do exist, a need for augmented capabilities is frequently met by microelectromechanical devices.
Nevertheless, as increasing numbers of devices are fit into ever-smaller spaces, optical microelectromechanical devices (hereinafter, “MEMS”) and particularly their constituent actuatable MEMS elements present an increasing problem of sensing their respective actuated positions. One frequently used technique for handling this problem involves illuminating the constituent elements with infrared radiation, typically coherent radiation, detecting the pattern of reflected radiation with a high-resolution infrared video camera, and employing a computer to calculate the respective positions from the detected pattern. Unfortunately, as the number of MEMS elements in a given area increases, and as their speed of actuation increases, the computer software required for timely, accurate calculations becomes ever more complex and less reliable.
Such position detection techniques may be termed indirect techniques. It has become desirable to have reliable direct detection techniques.
While some MEMS sensors for directly detecting the position of a actuated element have been developed for some applications, their feasibility is not readily apparent for dense arrays of MEMS elements requiring a correspondingly dense array of electronic actuation circuits. Position sensing must not interfere with element actuation.
SUMMARY OF THE INVENTION
According to the invention, direct position detection of MEMS elements is achieved without interference with their electronic actuation. It has been recognized, according to the invention, that position detection circuitry can have elements in common with MEMS element actuation circuitry, so long as the detection circuitry and actuation circuitry are operationally independent of each other.
Thus, in a microelectromechanical device having a microelectromechanical movable element, a base with respect to which the element is movable, and means for moving the movable element with respect to the base, there is provided means independent of the moving means, but in proximity thereto, for sensing the actual position of the movable element with respect to the base.
Advantageously, according to one feature of the invention, this sensing arrangement is densely integratable with large numbers of MEMS elements and their actuation circuits. Preferably, each movable MEMS element is associated with at least one sensor specifically arranged for that movable MEMS element. Optical cross-connect switching circuits provide an exemplary application of this type.
According to a further feature of the invention, the sensing means can employ any of a plurality of sensing gages, for example, strain gages, capacitive gages, piezoelectric gages, and piezoresistive gages, among others. Advantageously, such gages can be employed whether the actuation movement is linear, rotary, or a combination of linear and rotary.
In a first specific embodiment of the invention, MEMS strain gages are mounted under the MEMS element. The amount of strain is directly proportion to the movement of the MEMS element. Without increasing the amount of area occupied by the MEMS element, a plurality of strain gages per MEMS element may be used.
In a second specific embodiment of the invention, MEMS capacitance gages are integrated with the MEMS element. Movement of the MEMS element changes the capacitance between a plate on the back of the MEMS element and a plate on the mounting base of the MEMS element. Advantageously, the two plates can be the same as those used for actuating the MEMS element. Independence of actuation and sensing resides in actuating movement by essentially DC or low frequency voltage, while the capacitance measurement is made at a higher frequency not affecting actuation.
It is a further advantage of the present invention that sensing arrangements for arrays of MEMS elements are relatively easy to design and have a shorter response time and greater reliability than the prior art reflected light arrangements.
Further features and advantages of the invention will become apparent from the following description.
REFERENCES:
patent: 4560925 (1985-12-01), Niven et al.
patent: 4738500 (1988-04-01), Grupp et al.
patent: 5283682 (1994-02-01), Ostaszewski
patent: 5392151 (1995-02-01), Nelson
patent: 5408253 (1995-04-01), Iddan
patent: 6108118 (2000-08-01), Minamoto
Bhalla Kulbir Singh
Gottlieb Albert Maxwell
Ben Loha
Lucent Technologies - Inc.
Wisner Wilford L.
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