Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Reexamination Certificate
2000-06-05
2004-04-27
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
C385S016000, C385S018000, C359S900000
Reexamination Certificate
active
06728016
ABSTRACT:
The present invention relates to the field of optical switching. More particularly, the present invention relates to techniques for positioning optical reflectors in optimal positions.
BACKGROUND OF THE INVENTION
A micro-electro-mechanical-system (“MEMS”) device is a micro-sized mechanical structure having electrical circuitry fabricated using conventional integrated circuit (“IC”) fabrication methods. One type of MEMS device is a microscopic gimbaled mirror device. A gimbaled mirror device includes a mirror component, which is suspended off a substrate, and is able to pivot about an axis caused by, for example, electrostatic actuation. Electrostatic actuation creates an electric field that causes the mirror component to pivot. The electrostatic actuation is typically induced by pairs of parallel plate electrodes residing beneath the movable members of the gimbaled mirror device.
By allowing the mirror component to pivot, the mirror component is capable of having an angular range of motion. The gimbaled mirror may be used to reflect light in X and Y axes.
MEMS mirrors typically resonate at a relatively low resonant frequency. When moving the mirrors to create new paths, MEMS mirrors typically show a strong tendency to resonate. Significant oscillations in the order of 30 follow an abrupt move, while overshoots approach 75%.
A 3D mirror has two axes, and therefore two significant resonances. There will be others that will be excited during normal activity. For example vertical vibrations of various parts of the assembly, and the flexing of the frame. Additionally, there can be a great deal of cross coupling between the driving forces on the two axes. A change in voltages to rotate one axis can also modify the torque on the other axis. Similarly, a change in the angular position of one axis can modify the torque exerted on the other axis.
One approach to solving these problems is to use position sensors and active feedback loops. However, addition of sensors, feedback loops and control processing adds complexity to the device. Further, component drift may give rise to instabilities, and the creation of resonances and overshoot.
Overshoot can be a problem, putting a mirror into an unstable region, or causing excessive movement beyond the working range of a mirror. Overshoot may lead to mirror lockup or breakage.
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 of moving reflectors in an optical cross-connect switch is described. In one embodiment, the optical cross-connect switch identifies a reflector path avoiding possible interference with other reflectors, predicts the reflector path from pre-computed tables, and moves the reflector in a straight line in target reflector plane coordinates from initial position to target 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
Keating Adrian
White Kevin
Blakely , Sokoloff, Taylor & Zafman LLP
Calient Networks, Inc.
Phan James
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