U.S. patent application number 09/879025 was filed with the patent office on 2001-10-18 for optical mirror system with multi-axis rotational control.
Invention is credited to Fling, John J., Hagelin, Paul Merritt.
Application Number | 20010030817 09/879025 |
Document ID | / |
Family ID | 24194348 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030817 |
Kind Code |
A1 |
Hagelin, Paul Merritt ; et
al. |
October 18, 2001 |
Optical mirror system with multi-axis rotational control
Abstract
An optical mirror system with multi-axis rotational control is
disclosed. The mirror system includes an optical surface assembly,
and at least one leg assembly coupled to the optical surface
assembly. The at least one leg assembly supports the optical
surface above a substrate. A system and method in accordance with
the present invention can operate with many different actuator
mechanisms, including but not limited to, electrostatic, thermal,
piezoelectric, and magnetic. An optical mirror system in accordance
with the present invention accommodates large mirrors and rotation
angles. Scanning mirrors can be made with this technique using
standard surface-micromachining processes, or a deep RIE etch
process. A device in accordance with the present invention meets
the requirements for a directly scalable, high port count optical
switch, utilizing a two mirror per optical I/O port configuration.
An optical mirror in accordance with the present invention can be
utilized in, but is not limited to, the following applications:
optical add-drop multiplexers, wavelength routers, free-space
optical interconnects, chip-level optical I/O, optical scanning
displays, optical scanner (bar-codes, micro cameras), optical
storage read/write heads, laser printers, medical replacement for
glasses (incorporated with adaptive optics), medical diagnostic
equipment, optical scanning for security applications.
Inventors: |
Hagelin, Paul Merritt;
(Saratoga, CA) ; Fling, John J.; (Little River,
CA) |
Correspondence
Address: |
SAWYER LAW GROUP LLP
P.O. Box 51418
Palo Alto
CA
94303
US
|
Family ID: |
24194348 |
Appl. No.: |
09/879025 |
Filed: |
June 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09879025 |
Jun 11, 2001 |
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09549778 |
Apr 14, 2000 |
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6283601 |
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Current U.S.
Class: |
359/871 ;
359/298; 359/846; 359/872 |
Current CPC
Class: |
G02B 7/1821 20130101;
G02B 26/0833 20130101 |
Class at
Publication: |
359/871 ;
359/846; 359/298; 359/872 |
International
Class: |
G02F 001/29 |
Claims
What is claimed is:
1. An optical mirror system comprising: an optical surface
assembly; and at least one leg assembly coupled to the optical
surface assembly for supporting the optical surface above a
substrate.
2. The system of claim 1 wherein the optical surface assembly
comprises a support plate coupled to the at least one leg assembly
and an optical surface coupled to the support plate.
3. The system of claim 1 wherein the at least one leg assembly
comprises: a leg portion; a connector coupled to the leg portion
and the optical surface; and an anchor coupled to the leg portion
for coupling the leg portion to the substrate.
4. The system of claim 2 wherein the leg is coupled to the anchor
via flexible beams.
5. The system of claim 2 wherein an actuator is coupled to the leg
portion for the actuator for moving the leg portion to allow for
the rotation of the optical surface.
6. The system of claim 3 wherein the actuator comprises parallel
plate electrodes.
7. The system of claim 3 wherein the actuator comprises
electrostatic drives.
8. The system of claim 2 wherein the leg portion is flexible.
9. The system of claim 2 wherein the connector is flexible.
10. An optical mirror system comprising: an optical surface; and a
plurality of leg assemblies coupled to the optical surface for
supporting the optical surface above a substrate, wherein each of
the leg assemblies includes a leg portion, a connector coupled to
the leg portion, and the optical surface and an anchor coupled to
the leg portion for coupling the leg portion to the substrate.
11. The system of claim 10 wherein the leg portion is coupled to
the anchor via flexible beams.
12. The system of claim 10 wherein an actuator is coupled to the
leg portion for the actuator for moving the leg portion to allow
for the rotation of the optical surface.
13. The system of claim 12 wherein the actuator comprises parallel
plate electrodes.
14. The system of claim 12 wherein the actuator comprises vertical
electrostatic drives.
15. The system of claim 11 wherein the leg portion is flexible.
16. The system of claim 10 wherein the connector is flexible.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a
Microelectromechanical System (MEMS) fabricated optical mirror
system that is capable of being tilted on two orthogonal axes, by
means of electrostatically driven comb drives. Particular
application to the use of these mirrors in the deflection of
optical space beams is emphasized.
BACKGROUND OF THE INVENTION
[0002] Fiber optic communication systems currently employ
electro-optic switching systems to route signals at central office
switching centers. These electro-optic systems rely on converting
the light output from each "incoming" fiber into electrical form,
extracting the data content in the resultant electrical signal,
then utilizing conventional electrical switches to route the data
content to a modulatable optical source that is coupled to a
"destination" optical fiber. This detection switching remodulation
process is expensive, complex, power consuming, and subject to
component failure.
[0003] Alternate "All Optical" switching systems, employing
mechanically actuated bulk optic and MEMS fabricated devices
currently exist. These devices utilize electromagnetic,
piezoelectric and electrostatic actuators to physically move
prisms, mirrors and portions of optical fibers to affect switching
of signals between optical fibers.
[0004] In addition fiber-to-fiber switches employing Grating
Waveguides, Rowland Circle Gratings, and planar gratings, permit
dedicated switching based on optical wavelength.
[0005] Cascaded binary tree configurations, employing switchable
optical couplers using electrostatically variable index material,
(Lithium Niobate and polymers), as well as Mach Zender
interferometers utilizing thermoelectric heaters to affect
unbalance, are also currently state of the art.
[0006] Many of the MEMS switches employ a space-beam deflection
system similar to the electrical "Cross Bar" switch common in
telephone system. This approach requires that the number of mirrors
for a given input/output port count be determined by the square of
the port count figure. The overwhelming number of mirrors dictated
by this approach exceeds that which can be produced with any
realistic process yield, and survive any reasonable operating
period.
[0007] Except for some of the MEMS electrostatically actuated
devices, none of the above methods of optical switching meets the
requirements currently being specified for high fiber port count,
(up two 1024 by 1024) Optical Cross Connect switches. Problems of
cost, reliability, insertion loss, polarization sensitivity,
isolation, wavelength dependence, power consumption, and in some
instances, switching speed, either individually or collectively
mitigate against their use. Accordingly, what is needed is a system
and method for overcoming the above-identified issues under the
constraint of a simple CMOS-compatible fabrication process.
[0008] An optical mirror system design is desired that has
high-resolution 2-D scanning capability and deflection capability,
made with a surface-micromachining process. In order to achieve
high-resolution, large mirror size and rotation angles are
necessary.
[0009] The present invention addresses such a need.
SUMMARY OF THE INVENTION
[0010] An optical mirror system with multi-axis rotational control
is disclosed. The mirror system includes an optical surface
assembly, and at least one leg assembly coupled to the optical
surface assembly. The at least one leg assembly supports the
optical surface above a substrate. A system and method in
accordance with the present invention can operate with many
different actuator mechanisms, including but not limited to,
electrostatic, thermal, piezoelectric, and magnetic. An optical
mirror system in accordance with the present invention accommodates
large mirrors and rotation angles. Scanning mirrors can be made
with this technique using standard surface-micromachining
processes, or a deep RIE etch process.
[0011] A device in accordance with the present invention meets the
requirements for a directly scalable, high port count optical
switch, utilizing a two mirror per optical I/O port configuration.
An optical mirror in accordance with the present invention can be
utilized in, but is not limited to, the following applications:
optical add-drop multiplexers, wavelength routers, free-space
optical interconnects, chip-level optical I/O, optical scanning
displays, optical scanner (bar-codes, micro cameras), optical
storage read/write heads, laser printers, medical replacement for
glasses (incorporated with adaptive optics), medical diagnostic
equipment, optical scanning for security applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an optical mirror system in accordance
with the present invention.
[0013] FIG. 2 illustrates a side view of a preferred embodiment of
the optical surface and support plate in accordance with the
present invention.
[0014] FIG. 3 illustrates a top view of a vertical comb drive
actuator in accordance with the present invention.
[0015] FIG. 4 illustrates a side view of the vertical comb drive
actuator of FIG. 3.
DETAILED DESCRIPTION
[0016] The present invention relates to an optical mirror and more
particularly to an optical mirror system with a multi-axis
rotational control. The following description is presented to
enable one of ordinary skill in the art to make and use the
invention and is provided in the context of a patent application
and its requirements. Various modifications to the preferred
embodiment and the generic principles and features described herein
will be readily apparent to those skilled in the art. Thus, the
present invention is not intended to be limited to the embodiment
shown but is to be accorded the widest scope consistent with the
principles and features described herein.
[0017] FIG. 1 illustrates an optical mirror system in accordance
with the present invention. In a preferred embodiment, the optical
mirror system 100 in accordance with the present invention includes
a plurality of support legs 102a-102c coupled to a support plate
101, via a plurality of connectors 108. The support plate 101 is
coupled to an optical surface 103 through a via 109.
[0018] FIG. 2 illustrates a side view of a preferred embodiment of
the optical surface 103 and support plate 101 in accordance with
the present invention. The optical surface 103 is comprised of
three laminated layers 103a-103c. Layer 103a is the support layer
which can be made of polysilicon. The reflective layer 103b
(typically a thin metal) has thermal coefficient (TCE) much greater
than the layer 103a, causing unwanted curvature of the optical
surface in response to temperature variation. A third layer 103c
can be added "on top" or "beneath" the reflective layer 103b having
TCE lower than both the other layers. The TCE/thickness of this
third layer 103c is selected to control the temperature-induced
curvature.
[0019] Preferably oxide is utilized for the third layer 103c.
However, materials other than "oxide" could be used for the third
layer 103, provided their TCEs match the needed parameters.
[0020] The mirror substrate is connected to the support plate 101
through a via 109. The support plate 101 provides a mechanical
attachment point for the actuators, isolating the optical surface
103 from the distorting micromechanical forces of the actuators.
Supporting the optical surface 103 with a single, central
connection results in symmetric mechanical boundary conditions. Any
shallow curvature induced in the optical surface 103 by thermal or
intrinsic stresses will result in a parabolic deformation of the
optical surface 103, which can be corrected with spherical optics.
In addition, the support plate 101 provides extra surface area for
increased heat dissipation from the optical surface 103, resulting
in greater optical power handling capability.
[0021] Each of the connectors 108a-108c (FIG. 1) are coupled to an
actuator 105. FIG. 3 illustrates a top view of a vertical comb
drive actuator in accordance with the present invention. FIG. 4
illustrates a side view of the vertical comb drive actuator of FIG.
3. In this embodiment, there are three portions to the actuator
system 105, first end portion 302, second end portion 304 and a
middle portion 306. The end portions 302 and 304 engage the middle
portion 306 through interdigitated teeth 308 and 310. In this
embodiment, each of the end portions 302 and 304 comprise three
electrically isolated actuators 302a-302c and 304a-304c,
respectively.
[0022] Accordingly, if actuators 302a and 304a are activated, the
system 105 pulls "up". If actuators 302b and 304b are activated the
system 105 holds the current position and if actuators 302c and
304c are activated the system 105 pulls down. Accordingly, the
actuator system 105 can move the mirror in various ways dependent
upon the voltages applied to the motors 302a-302c and 304a-304c.
Although this actuator system 105 has been described in the context
of a three position (up, down and hold position) system, one of
ordinary skill in the art readily recognizes that a two position
(up or down), (hold position or down), (hold position or up) could
be provided by using two actuators rather than the three actuators
in the system disclosed herein.
[0023] Referring back to FIG. 1, each of the legs 108 is coupled to
a substrate by an anchor 107. Although a plurality of legs are
shown, one of ordinary skill in the act recognizes there may be as
few as one leg and that use would be within the spirit and scope of
the present invention.
[0024] The optical surface 103 is suspended on a plurality of
support legs 102 that lift it above the surface of a chip. The
support legs 102 cause the mirror to tilt through a large angle.
The tilt-angle is greater than the angle that could be obtained
using a standard sacrificial layer (typically 1-3 microns) as
separation between the mirror and a substrate.
[0025] In a preferred embodiment, the support legs 102 connect
tangentially to the side of the mirror. The support legs 102 can be
rectangular or in the shape of an arc along the edge of the mirror
in the case of a round or elliptical mirror. As the support legs
tilt up, the mirror rotates slightly to relieve stress due to small
lateral movement in the support legs.
[0026] The support legs 102 can be either rigid or flexible.
Flexible legs can be used as springs, for the case in which a
parallel-plate actuator applies force to the support plate beneath
the mirror. By distributing the bending over the length of a
flexible support leg, the maximum shear and tensile stresses in the
device are reduced, compared to a rigid support leg that
concentrates the bending at flexures. Flexible actuators 105 can be
driven thermally (preferably by a resistive heater on each support
leg) to cause the mirror to tilt.
[0027] Rigid support legs can be connected to the actuators 105
near the surface of the chip. As the support leg tilts, powered by
an actuator, the attached edge of the mirror can be raised or
lowered. An actuator can be incorporated that facilitates
differential capacitance sensing.
[0028] A system and method in accordance with the present invention
can operate with many different actuator mechanisms, including
electrostatic, thermal, piezoelectric, magnetic, etc. Among
electrostatic actuators, it supports parallel-plate actuation
between the mirror or beneath the electrodes. The actuator can act
on the support plate beneath the mirror, or it can act on the
support legs. In one implementation, by adjusting the coupling of
the actuator to the support legs, the maximum rotation angle of the
mirror can be traded off against the maximum applied voltage.
[0029] An optical mirror system in accordance with the present
invention accommodates large mirrors and rotation angles. Scanning
mirrors can be made with this technique using any micromachining
processes. All-flexure designs of bi-axial scanning mirrors have
superior device density, reliability, and repeatability
characteristics. The system has the following advantages over
conventional optical mirror system architectures.
[0030] 1. Arbitrary equilibrium: The lengths of the support arms
can be changed to adjust the equilibrium position of the mirror.
The actuator does not necessarily act directly on the mirror
surface (as it would in a parallel-plate design). The equilibrium
angle can be changed without a significant change in the
performance of the device.
[0031] 2. Custom processing not necessary: This approach uses
standard micromachining processes. Since the mirror is lifted away
from the substrate by the support legs, insulation on the frame is
not necessary. The only insulator needed is at the substrate. If an
insulator in the support legs is possible, then a wider variety of
design options are also available.
[0032] 3. Nested frames and bimorphs dedicated for self-assembly
are not necessary: If bimorphs are needed, they can be incorporated
into the support legs or elsewhere. By removing nested frames and
extraneous bimorphs used in self-assembly, the size of the device
is reduced, allowing more space for actuators or a higher density
of devices.
[0033] 4. Pin-and-staple hinges not needed: The support mechanism
can be suspended on an all-flexure mounting. The tilt angle of
these supports is relatively small (within the shear and torsion
limits of a properly designed support leg or hinge), and therefore
pin-and-staple hinges are not needed.
[0034] 5. Mirror curvature symmetric and small: The mirror can be
mechanically decoupled from the undesired deformation of the
flexure hinges. By connecting the mirror to the support plate with
a single via at its center, the mirror flatness is not affected by
forces that develop in its suspension. In addition, if there is a
stress gradient in the mirror, the symmetric boundary conditions
will typically result in a parabolic shape, which can be readily
integrated into an optical system using off-the-shelf spherical
optics. Non-spherical deformations of the mirror, typically the
result of asymmetric boundary conditions, can cause deformations in
the mirror that can cause optical loss through a switch. Electrodes
directly beneath the mirror need not be used, removing creases that
can occur in the optical surface because of conformal deposition
over the electrodes.
[0035] Although the present invention has been described in
accordance with the embodiments shown, one of ordinary skill in the
art will readily recognize that there could be variations to the
embodiments and those variations would be within the spirit and
scope of the present invention. For example, although it is
disclosed in the preferred embodiment that the mirror rotates in a
first and a second direction, the mirror can rotate in a plurality
of directions (i.e. twisting motion) dependent upon the
electrostatic forces applied thereto. Accordingly, many
modifications may be made by one of ordinary skill in the art
without departing from the spirit and scope of the appended
claims.
* * * * *