Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-12-13
2002-11-26
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S295000, C359S290000, C359S223100, C359S230000, C359S245000
Reexamination Certificate
active
06487001
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to micro-electromechanical systems (MEMS) devices. More particularly, the present invention relates to improvements in electrodes for use in MEMS devices.
BACKGROUND OF THE INVENTION
MEMS devices have been used in a variety of optical applications. The prior art is replete with examples of MEMS-based optical modulators, add-drop filters, attenuators and routers.
Each optical MEMS device typically incorporates a “mirror” that is capable of altering the path of a received optical signal or simply attenuating the signal's intensity. The mirror, which is usually realized as a movable beam or plate, is configured to use either optical interference principles or simple reflection to provide the above-stated capabilities. In optical MEMS devices that rely on simple reflection, the movable beam typically comprises polysilicon or silicon that is coated with metal to provide a reflective surface. The movable beam is usually configured for movement via one of the two arrangements that are described below.
In a first arrangement
100
depicted in
FIG. 1A
(top view) and
FIG. 1B
(side view), movable, electrically conductive beam
102
is cantilevered over a cavity
104
. Flat planar electrode
106
is disposed within cavity
104
beneath movable beam
102
. In a second arrangement
200
depicted in
FIG. 2A
(top view) and
FIG. 2B
(side view), movable, electrically conductive beam
202
is suspended by supports
208
A and
208
B over cavity
204
. Flat planar electrodes
206
A and
206
B are disposed in cavity
204
beneath movable beam
202
.
As a potential difference is developed across movable beam
102
and electrode
106
of first arrangement
100
, an electrostatic force is generated. The force bends movable beam
102
toward electrode
106
. Similarly, as a potential difference is developed across movable beam
202
and either one of electrodes
206
A or
206
B, an electrostatic force is generated that draws the movable beam towards the actuated electrode. Supports
208
A and
208
B twist to allow movable beam
202
to move in such fashion. As beam
102
and beam
202
move, the path followed by an optical signal that is reflected therefrom is altered.
Both arrangement
100
and arrangement
200
suffer from a significant shortcoming. In particular, the actuation voltage necessary to achieve the required amount of mirror rotation (for sufficiently altering the path of an optical signal) is large (i.e., about 150 volts for a typical design). There is a need, therefore, to reduce the actuation voltage requirements of electrostatically-driven, MEMS-based, movable mirrors.
SUMMARY OF THE INVENTION
Some embodiments of the present invention provide an electrode that is capable of reducing the actuation voltage of MEMS-based mirrors.
An electrode in accordance with the present teachings declines in height along its length from a first end thereof to second end thereof. In one embodiment, the decline in height of the electrode along its length is regular or linear such that the electrode has a wedge-shaped profile. In another embodiment, the height of the electrode declines in discrete steps such that the electrode has a stepped profile.
In use, the electrode is disposed beneath a MEMS mirror (e.g., a beam, etc.). The first end of the electrode is disposed proximal to an axis of rotation or axis of bending of the mirror. Due to the geometry of the present electrode, the gap between the MEMS mirror and the surface of the electrode can be smaller than the gap between a MEMS mirror and the flat-planar electrodes in the prior art. Consequently, in such embodiments, the voltage requirement for a MEMS mirror that is actuated by the present electrode is reduced relative to voltage requirement for a MEMS mirror that is actuated by electrodes of the prior art.
REFERENCES:
patent: 6201631 (2001-03-01), Greywall
Agere Systems Inc.
Dang Hung Xuan
Tra Tuyen
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