Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-06-05
2003-08-26
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C385S018000, C250S227140
Reexamination Certificate
active
06610974
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to the field of optical switching. More particularly, the present invention relates to techniques for positioning optical reflectors into optimal positions.
BACKGROUND OF THE INVENTION
One type of prior art microelectromechanicalsystem (“MEMS”) device is a gimbaled reflector or mirror, which is fabricated using integrated circuit (“IC”) techniques. The gimbaled mirror is used to reflect light in X and Y axes. Gimbaled mirrors typically use electrostatic actuation to move the mirror. The electrostatic actuation is typically induced by pairs of parallel plate electrodes residing beneath the movable members of the gimbaled mirror device.
One problem with a typical prior art gimbaled MEMS mirror is determining the actual position of the mirror. One prior technique uses strain gauges on the gimbals to monitor the physical position of the mirror. One disadvantage of that technique is the need for extra wiring for the strain gauges. The strain gauges and concomitant wiring add complexity and expense and take up valuable space.
Another problem with a typical prior art gimbaled MEMS mirror device is the difficulty of accurately maintaining a particular mirror position or a particular path of reflected light over time. Different temperatures may cause different expansions and contractions of the materials making up the gimbaled mirror device. Gimbals may weaken over time and through use. Electronics, including amplifiers and strain gauges, may drift over time and also may be affected by temperature. The forces needed to maintain a position of the mirror of the gimbaled mirror device may thus change with temperature and time. The geometry of an assembly holding multiple gimbaled mirror devices may also change with temperature and time. A resulting problem from a drifting mirror position is that the path of light reflected by the gimbaled mirror will change. A small change in mirror position could lead to a large change in the position of an end of a beam of light.
SUMMARY OF THE INVENTION
A method for positioning a movable reflector in an optical switch is described. A set of optical power values are generated by measuring optical power related to optical reflections from the movable reflector for a plurality of positions of the movable reflector. A processor is used to generate a mathematical approximation of a relationship of optical power versus reflector position based on the set of optical power values. A position of the movable reflector is chosen based on a point in the mathematical approximation of the relationship of optical power versus reflector position.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.
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Hunt Peter
White Kevin
Blakely , Sokoloff, Taylor & Zafman LLP
Calient Networks, Inc.
Kao Chih-Cheng Glen
Kim Robert H.
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