U.S. patent application number 10/122320 was filed with the patent office on 2002-08-15 for vertical comb drive actuated deformable mirror device and method.
This patent application is currently assigned to MEMS OPTICAL, INC.. Invention is credited to Clark, Rodney L., Hammer, Jay A., Karpinsky, John R..
Application Number | 20020109894 10/122320 |
Document ID | / |
Family ID | 26718458 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020109894 |
Kind Code |
A1 |
Clark, Rodney L. ; et
al. |
August 15, 2002 |
Vertical comb drive actuated deformable mirror device and
method
Abstract
A deformable mirror includes a vertical comb actuator having a
reflective surface attached thereto. The vertical comb drive
includes stationary elements interspersed with moving elements.
When a potential difference is provided between these elements, the
moving elements are pulled downward, thereby deforming the
reflective surface. The vertical comb drive typically includes a
plurality of actuators, which are individually electrically
addressed. Each actuator may be an array of interspersed elements
or a cavity and corresponding tooth. Springs support the moving
elements and bias the reflective surface in an original position.
The vertical comb drive provides a large stroke and substantially
linear voltage-versus-displacement curve throughout the stroke.
Inventors: |
Clark, Rodney L.; (Gurley,
AL) ; Hammer, Jay A.; (Huntsville, AL) ;
Karpinsky, John R.; (Huntsville, AL) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
MEMS OPTICAL, INC.
|
Family ID: |
26718458 |
Appl. No.: |
10/122320 |
Filed: |
April 16, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10122320 |
Apr 16, 2002 |
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09049121 |
Mar 27, 1998 |
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6384952 |
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60041725 |
Mar 27, 1997 |
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Current U.S.
Class: |
359/224.1 |
Current CPC
Class: |
B81B 2203/053 20130101;
G02B 26/06 20130101; B81B 2201/042 20130101; G02B 26/0841 20130101;
B81B 2203/0136 20130101; G02B 2006/12104 20130101; B81B 3/0062
20130101; B81B 3/0086 20130101 |
Class at
Publication: |
359/224 ;
359/223; 359/198 |
International
Class: |
G02B 026/08 |
Goverment Interests
[0003] The U.S. Government has rights in the present application
under Contract BMDO 96-002,003.
Claims
What is claimed is:
1. A deformable mirror comprising: a vertical comb drive; and a
reflective surface attached to said vertical comb drive.
2. The deformable mirror according to claim 1, further comprising a
spring for biasing said vertical comb drive to maintain said
reflective surface in an original position absent application of a
voltage to said vertical comb drive.
3. The deformable mirror according to claim 1, wherein said
vertical comb drive comprises a first array of stationary elements
and a second array of moving elements correspondingly interspersed
with said first array, said reflective surface being attached to
said second array.
4. The deformable mirror according to claim 3, further comprising a
layer covering tops of elements of said second array.
5. The deformable mirror according to claim 4, a spring for
suspending said first array relative to said second array, said
spring being attached to said layer.
6. The deformable mirror according to claim 3, wherein said
stationary elements and said movable elements are circular.
7. The deformable mirror according to claim 3, wherein said
stationary elements and said movable elements are planar.
8. The deformable mirror according to claim 4, wherein said layer
is attached directly to said reflective surface.
9. The deformable mirror according to claim 4, further comprising a
post attaching said layer to said reflective surface.
10. The deformable mirror according to claim 9, wherein said post
is in a center of said reflective surface.
11. The deformable mirror according to claim 3, wherein voltage is
applied to each stationary element of said first array individually
or each moving element of said second array individually.
12. The deformable mirror according to claim 3, wherein said
vertical comb drive comprises an array of vertical comb
actuators.
13. The deformable mirror according to claim 12, means for
individually providing voltage to each actuator of said array.
14. The deformable mirror according to claim 12, further comprising
springs for individually suspending each of said second array of
each actuator in said array.
15. The deformable mirror according to claim 14, further comprising
an anchor for supporting said springs.
16. The deformable mirror according to claim 1, wherein said
vertical comb drive comprises plurality of cavities and teeth
interdigitally mounted with said cavities, said reflective surface
being attached to said teeth.
17. The deformable mirror according to claim 16, further comprising
a top layer between the teeth and the reflective surface.
18. The deformable mirror according to claim 16, further comprising
a conductor for individually connecting each tooth of said teeth to
a voltage source.
19. A method of deforming a mirror comprising: attaching the mirror
to a vertical comb actuator; and applying a voltage to the vertical
comb actuator.
20. The method according to claim 19, wherein said vertical comb
drive comprises an array of vertical comb actuators and said
applying individually applies voltage to said vertical comb
actuators.
21. A deformable mirror comprising: a vertical electrostatic comb
drive including a first array of stationary elements and a second
array of moving elements correspondingly interspersed with said
first array; a reflective surface attached to said second array; a
layer covering tops of elements of said second array; and a
resilient member for suspending said first array relative to said
second array, said resilient member being attached to said
layer.
22. The deformable mirror according to claim 21, wherein said
stationary elements and said movable elements are circular.
23. The deformable mirror according to claim 21, wherein said
stationary elements and said movable elements are planar.
24. The deformable mirror according to claim 21, wherein said layer
is attached directly to said reflective surface.
25. The deformable mirror according to claim 21, wherein voltage is
applied to each stationary element of said first array individually
or each moving element of said second array individually.
26. The deformable mirror according to claim 21, wherein said
vertical comb drive comprises an array of vertical comb
actuators.
27. The deformable mirror according to claim 21, wherein said
vertical comb drive comprises plurality of cavities and teeth
interdigitally mounted with said cavities, said reflective surface
being attached to said teeth.
28. The deformable mirror according to claim 21, wherein said
resilient member is a torsionsal spring.
29. A displaceable surface comprising: a vertical electrostatic
comb drive; a surface attached to said vertical comb drive, wherein
said vertical comb drive comprises a first array of stationary
elements and a second array of moving elements correspondingly
interspersed with said first array, said surface defining a plane
and being attached to said second array, said surface being
displaced in a direction orthogonal to the plane thereof when said
vertical electrostatic comb drive is actuated; a layer covering
tops of elements of said second array; and a bar for suspending
said second array relative to said first array.
30. The displaceable surface of claim 29, wherein a mirror is
provided in said surface.
31. The displaceable surface of claim 29, wherein said bar produces
a torsional force to return the deformable surface to a position
corresponding to the position before the surface is displaced.
32. The displaceable surface of claim 29, wherein said bar is
attached between said surface and a wall.
33. The displaceable surface of claim 29, wherein the vertical
electrostatic comb drive is provided on a substrate and said
surface is generally parallel to said substrate.
34. The displaceable surface of claim 29, wherein said surface is
reflective.
Description
[0001] CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] This application claims priority under 35 U.S.C.
.sctn.119(e) of provisional application U.S. Ser. No. 60/041,725
filed on Mar. 27, 1997 which is hereby incorporated by reference in
its entirety.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The present invention relates to adaptive optics. More
particularly, it relates to the use of a vertical comb drive to
actuate the deformable mirror in an adaptive optical system.
[0006] 2. Description of Related Art
[0007] Atmospheric turbulence has frustrated astronomers ever since
telescopes were invented. Atmospheric turbulence introduces
aberrations on the wavefront of visible light, causing stars to
twinkle and distant objects to shimmer. Atmospheric turbulence also
limits the resolution of microscopes, endoscopes, and other optical
imaging systems.
[0008] Adaptive optics systems can be used to measure and
compensate for rapidly fluctuating wavefront complex, expensive,
unreliable and difficult to maintain, thus putting them out of
reach of amateur astronomers or commercial users. Current adaptive
Optics systems are also very heavy and operate at relatively slow
speed making them unsuitable for airborne applications where the
fluctuating wavefront distortions move past the aperture at a much
faster rate than stationary systems.
[0009] FIG. 1 illustrates a simple adaptive optics application. A
micromachine deformable mirror 100, fabricated as an integrated
circuit, is mounted onto a printed circuit board substrate 110. A
wavefront sensing and correction microchip 120 is mounted on the
substrate 110 next to the deformable mirror 100. The printed
circuit board contains drive electronics 115 that connect the
wavefront sensor chip 120 to the deformable mirror 100 chip.
Incident light 130 is reflected off the micromachine deformable
mirror 100. The reflected light 140 then passes through a beam
splitter 150. A portion of the reflected light 140 is redirected
onto the wavefront sensor 120 by the beam splitter 150.
[0010] The wavefront sensor 120 detects any aberration in the
wavefront of the reflected light 140. Once it aberration is
subtracted from the wavefront, and a corrected wave of light is
reflected from the deformable mirror 100. The wavefront sensor 120
drives the deformable mirror 100 via the drive electronics 115 to
correct for the detected aberration.
[0011] The primary obstacles to wider use of adaptive optics
systems are cost, complexity, and reliability. Should reliable, low
cost solid state adaptive optic systems become commercially
available, many new applications can be envisioned. Laser
communications is an example of such a market. Laser communication
systems can support the signal bandwidth needed for High Definition
Television without the need to run fiber optic cables between a
remote mobile unit and a roving camera crew. Current laser
communications have limited range due to atmospheric distortions
that cause beam bending and scatter energy from the beam. An
adaptive optic system capable of correcting for these effects can
greatly extend range and improve performance.
[0012] A low cost adaptive optics system would find immediate
applications in optical microscopes. Such a system could produce
significantly improved imaging in difficult medical environments,
improving the performance of conventional and confocal microscopes.
A low cost adaptive optics system has potential to enhance the
operational performance of all clinical microscopes in use
today.
[0013] A low cost adaptive optics system would also find
applications in endoscopy. Here the adaptive optics system can be
used for both imaging and transmitting the laser energy for
endoscopic surgical procedures. There is considerable medical
instrumentation and diagnostic equipment in the market place today.
However, higher resolution imaging and more accurate placement of
laser energy is needed to improve these instruments.
[0014] A low cost adaptive optic system could also find application
in ophthalmology and optometry. In this application a small low
power laser device is used to create an artificial guide star on
the retina of the eye. The spot of light reflected off the retina
forms a source to drive a wavefront sensor of an adaptive optic
system. The kind of retinal camera that stands to benefit even more
from adaptive optics is the confocal scanning laser ophthalmoscope
(CSLO). Many clinical applications require the ability to optically
section the retina in depth. Such sectioning can be achieved with
confocal imaging in principle but current CSLOs do not tap the
potential of confocal imaging because the retinal image quality is
too poor. A CSLO equipped with adaptive optics could reap the full
benefit of confocal imaging, improving the transverse resolution of
current instruments by a factor of three and the axial resolution
by a factor of ten.
[0015] Typical adaptive optics systems are composed of at least
three core elements: (1) a wavefront sensor to detect optical
aberrations, (2) electronic circuitry to compute a correction, and
(3) a deformable mirror to apply the correction. The deformable
mirror is a critical component of an adaptive optics system. It is
used to apply the correction to the distorted wavefront. In current
technology, the deformable mirror is also the most expensive
component of the adaptive optical system. In order to realize a low
cost adaptive optical system, a low cost deformable mirror must be
developed. The current art presents three alternative technologies
for deformable mirrors: liquid crystals, stacked piezoelectrics,
and Micro-Electro-Mechanical Systems ("MEMS").
[0016] Phase Modulating Liquid Crystal Display (LCD), devices offer
low weight, low cost, and low power alternatives to large
opto-mechanical devices. Also, cost effective bulk manufacturing
methods currently exist for these devices. However, current LCD
devices suffer from limited fill factor, limited bandwidth, and
inadequate dynamic range. Bandwidth limitations will preclude the
use of LCD's for airborne or missile applications.
[0017] Stacked piezoelectrics ("SPZT") utilize a new generation of
piezoelectric technology that costs less and features the best
advantages of actuators made from piezoelectric ("PZT") or lead
manganese niobate ("PM") technologies. However, current SPZT
devices suffer from high current operation, significant actuator
nonuniformity, relatively high power dissipation, and moderate
hysteresis effect. Moreover, these devices are relatively expensive
when compared to liquid crystals or MEMS devices.
[0018] The recent advent of MEMS technology offers an alternative
for the construction of cost effective mechanical mirror actuators.
The technology is based upon the well established fabrication
methods used to manufacture integrated circuits. Micromachining
promises major improvements in overall performance and reduction of
cost. The MEMS deformable mirrors have shown the lowest fabrication
cost, lowest power consumption, lowest mass, lowest volume,
elimination of hysteresis, elimination of polarization effects.
best power on, and lowest non-uniformity of any current deformable
mirror technology. An additional advantage of this technology is
that integrated electronic circuits can be fabricated directly on
the same substrate as the micromirror. This allows for significant
system simplification in that mirror drive electronics can be
fabricated directly on the mirror substrate. MEMS technology offers
light weight components, thus making it entirely suitable for
ground based, airborne, and even hand held wavefront correction
applications.
[0019] However, prior MEMS deformable mirror designs have been
based on the electrostatic parallel plate capacitor actuators. This
method of actuation has been successful but produces actuators with
limited stroke, e.g., less than one micron, and a nonlinear
voltage-versus- displacement curve. The nonlinear curve results
from the 1/r dependence of the attractive force on gap distance.
Recently, new MEMS actuator concepts have been demonstrated which
use electrostatic comb drives to produce large stroke and linear
voltage verses displacement curves. Unfortunately the current
designs do not produce the vertical displacements necessary for use
in an optical system.
SUMMARY OF THE INVENTION
[0020] It is therefore an object of the present invention to
provide a low cost deformable mirror for use in an adaptive optics
system which overcomes the problems noted above. It is further an
object of the present invention to provide a deformable mirror with
a high stroke and substantially linear voltage-versus-displacement
curve.
[0021] These and other objects of the present invention may be
realized by providing a deformable mirror by combining a vertical
comb drive with a reflective surface. The deformable mirror may
also include a spring for biasing the vertical comb drive to
maintain the reflective surface in an original position absent
application of a voltage to the vertical comb drive.
[0022] The vertical comb drive may include a first array of
stationary elements and a second array of moving elements
correspondingly interspersed with the first array. The reflective
surface would be attached to the second array. A layer covering
tops of elements of the second array may be provided. A spring may
be used to suspend the first array relative to the second array,
preferably via the layer. The stationary elements and the movable
elements may be circular or planar. The layer may be attached
directly to the reflective surface or with a post which is
preferably in a center of the layer. Voltage may be applied to each
stationary element of the first array individually or each moving
element of the second array individually.
[0023] The vertical comb drive may include an array of vertical
comb actuators. Each actuator of the array may be individually
addressed to provide a voltage thereto. Springs for individually
suspending each of the second arrays of each actuator in the array
may be provided. Preferably, an anchor for supporting the springs
is also provided.
[0024] The vertical comb drive may include a plurality of cavities
and teeth interdigitally mounted with said cavities, the reflective
surface being attached to the teeth. A top layer may be provided
between the teeth and the reflective surface. A conductor for
individually connecting each tooth of the teeth to a voltage source
may also be provided.
[0025] These and other objects of the present invention may also be
realized in accordance with a method of deforming a mirror
including attaching the mirror to a vertical comb actuator and
applying a voltage to the vertical comb actuator. The vertical comb
drive may include an array of vertical comb actuators and the
applying individually applies voltage to the vertical comb
actuators.
[0026] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0028] FIG. 1 is a schematic of a simple adaptive optics
system;
[0029] FIG. 2 is a perspective cross-sectional view of a single
deformable mirror element having a vertical comb drive of the
present invention;
[0030] FIG. 3 is a perspective cross-sectional view of an
alternative embodiment of the present invention;
[0031] FIG. 4A is a side cross-sectional view of another
alternative embodiment of the present invention;
[0032] FIG. 4B is a bottom view of the configuration shown in FIG.
4A; and
[0033] FIG. 5 is a cross section of two adjacent actuators in
accordance with the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0034] As noted above, typical MEMS have been based on
electrostatic parallel plate capacitor actuators. The separation
between the plate determines the amount of stroke available, but an
increase in the separation increase the voltage required to deform
the mirror. Thus, an increase in the stroke invariably increases
the voltage. Further, since this separation between the plates is
changing throughout the stroke, the response of the deformable
mirror to the applied voltage is nonlinear. Electrostatic comb
drives have been demonstrated to produce a large stroke and linear
operation, but do not produce the vertical displacement required
for use in deformable mirror applications.
[0035] Therefore, in accordance with the present invention, a
vertical comb mirror actuator (VCAM) having a set of interdigitized
shells for actuating a deformable mirror is provided. The VCAM
includes a set or array of stator shells and a corresponding set or
array of movable slider shells. The mirror membrane is attached to
the slider shells. Introducing a voltage potential between the
stator shells and the slider shells pulls the slider shells down,
deforming the thin membrane mirror. The vertical displacement is
the result of a force created by the edge capacitance between the
slider shells and the stator shells. The force generated by the
comb drives is independent of the relative position of the two
electrode plates and is linear while the plates overlap. This
essentially eliminates the non-linear voltage-verses-displacement
curve so problematic in the prior art. Unlike the parallel plate
design, the gap between these elements remains constant throughout
the stroke. In addition to the substantially linear operation of
the VCAM, the VCAM can also provide a high stroke, e.g., 20 .mu.m,
with relatively low voltages, e.g., 35-100 volts.
[0036] The actual design of the shells may vary in accordance with
a desired application. The shape of the shells is typically
designed to maximize surface area between the shells. The other
design parameters of the shells include the width of the shells,
the width of the gap between the shells, and the number of shells.
The length of the shells is determined by the required stroke. For
example, when the actuator is to have a stroke of greater than six
microns, the typical requirement to correct for atmospheric
distortions, applying a maximum of two hundred volts, and a
frequency response of 10 kHz, a working design has a shell width of
ten microns, an inter-shell gap of five microns and seven slider
shells.
[0037] The actuator also preferably includes a spring for mounting
or suspending the slider shells, biasing the slider shells in a
neutral position when no voltage is applied to the stator shells,
and preventing horizontal, i.e., side-to-side movement, of the
slider shells. Preferably, a spring is positioned at each of the
four corners of the actuator element and is attached at one end to
a wall provided next to the actuator and at the other end either to
the mirror itself or to the slider shells. Thus, the dimensions of
the spring also affect the actuator design. A working spring design
for the design parameters noted above is a folded spring having two
legs, each leg having a length of one hundred twenty-five microns,
a width of twenty microns, a spacing between the legs being ten
microns and the space between the last leg and the mirror or
surface adjoining the slider shells being five microns, and the
spring having a spring constant of 12.4 .mu.N/.mu.m.
[0038] When providing an array of multi-element actuators, the
larger the spacing between the actuators, the less force is needed
to move one actuator with respect to adjacent actuators. For the
above stroke or throw of six microns, and delta motion between
adjacent actuators of one micron, the actuators should be spaced by
approximately five hundred microns. The number of actuators in the
array is application dependent, and is a design criteria to be
considered by those skilled in the art.
[0039] The following configurations illustrate different VCAMs in
accordance with the present invention. Preferably, the deformable
mirror is a thin continuous membrane of reflective material s be
made of, for example, silicon nitride coated with metal to reflect
at a desired wavelength or electroplated metal. The more precise
the deformations need to be, the more flexible the mirror material
should be.
[0040] The combs or shells may be made by plating nickel on a
silicon substrate using a photoresist to define the combs and then
planarizing the nickel by lapping the structure, thereby forming
the combs with a multi-layer electro-forming. Alternatively, the
combs may be made in silicon with a trench refill process alone for
use with segmented mirror or using two wafers and anodic wafer
bonding for use with continuous mirrors.
[0041] FIG. 2 is a cross-section perspective view of a single
deformable mirror actuator element 200 of the present invention.
The preferred embodiment consists of two sets of interdigitized
circular shells, a set of stator shells 210 and a set of movable
slider shells 220. Preferably, a layer 230 overlies the top of the
slider shells 220 so that movement of any of the slider shells 220
affects the layer 230. The use of the layer 230 allows for a
continuous profile to be realized by the deformable mirror 250, as
opposed to the step functions which would result if the slider
shells 220 were directly attached to the deformable mirror 250.
[0042] The layer 230 is attached by a vertical post 240 to the thin
membrane mirror 250, thereby attaching the continuous membrane
deformable mirror 250 to the actuator 200. Preferably, the post is
in the center of the layer 230 and the mirror 250. The stiffness of
the post 240 will determine how much of the movement of the slider
shells 220 is translated to the mirror 250. The position and number
of posts may be varied to apply the deformation to different
regions of the mirror 250. For example, if tilt is a parameter to
be controlled, four posts, one at each corner of the actuator may
be provided. Typically for a complex shape, the single post is used
and the surface area of the mirror region effected by movement of
the actuator attached by that post smoothly abuts adjacent mirror
regions effected by adjacent actuators.
[0043] Applying an activation voltage to the actuator element 200
via the stator shells 210 pulls the slider shells 220 down, thereby
deforming the thin membrane mirror 250. The stator shells 210 may
be individually addressed. When the activation voltage is removed,
the small attached springs 260 pull the slider shells 220 back into
position, thereby reforming the thin membrane mirror 250. In
practice, an array of actuator elements 200 would be fabricated on
a single base substrate 270. The actuator elements 200 would be
individually electrically addressed to form a complete adaptive
optics deformable membrane mirror 250 by appropriately patterning
the substrate 270, or by providing individual conductors for each
shell.
[0044] FIG. 3 is a perspective cross-section of an alternative
embodiment of a single actuator 300 embodying the present
invention. The actuator element 300 of this embodiment provides
stator shells 310, slider shells 320 integral to a slider top or
layer 330, a post 340 connecting the slider shells 320 to the
deformable mirror membrane 350, springs 360 to return the
deformable mirror 350 to its initial position, and a substrate 370
upon which the actuator resides. In FIG. 3, an example of a wall
380 to which the spring 360 is attached is shown. The view in FIG.
3 is a cut away, as the wall 380 would be beneath the mirror
350.
[0045] FIG. 4A is a cross section view of yet another alternative
embodiment of an actuator embodying the present invention. Unlike
the configurations shown in FIGS. 2 and 3, in which each actuator
has multiple elements, i.e., more than two shells, and the array of
these distinct multiple element actuator, the configuration in
FIGS. 4A and 4B is a continuous array of two element actuators. In
particular, the base 470 of the actuator 400 is made of a
conductive material. In this conductive material there are holes or
cavities or trenches 410 which are either drilled, etched, or
electroformed or created by any suitable fabrication technique.
Inside these holes, there is another conductive material in the
form of teeth 420 which does not touch the sides of the holes, but
is electrically isolated from the base material. These teeth are
mounted on another structural base 430 that keeps the teeth 420
rigidly in place within the holes 410 in the base 400. This base
430 can be either electrically conductive or insulating, but does
need to provide a surface for the electrical conductor 440 which
connects each tooth 420 to a voltage source.
[0046] When a voltage is applied between the teeth 420 and the
actuator base 400, an electrostatic force is generated pulling the
teeth 420 into the holes 410. Note in this embodiment that the
voltage is applied to individually addressed teeth 420 which are
the moving elements of the actuator 400, rather than to the
stationary elements as in the previous embodiments. If it is
desired that this vertical motion be applied to an optical mirror
surface 450, that surface is applied to the tooth base material 430
by some suitable application method such as sputtering or vapor
deposition. As in FIGS. 2 and 3, springs attached outside of the
actuator region are provided for supporting the teeth 420 above the
cavities 410.
[0047] FIG. 4A illustrates the same embodiment as FIG. 4B, but it
is a top view instead of a cross section view. As can be seen from
the perspective shown in FIG. 4B, the teeth can be circular,
although the teeth can be any shape, e.g., rectangular, octagonal,
etc., to match the needs of any particular application or
fabrication method. Further, while the surface in FIG. 4B is
circular, it may be any desired shape, including rectangular.
[0048] The configuration of FIGS. 4A and 4B is more useful for
effecting bulk parameters, such as displacement plus tilt in two
orthogonal directions, while the configurations in FIGS. 2 and 3
are more useful for effecting complex shapes on the mirror surface,
as explained below.
[0049] FIG. 5 is a cross-section of two adjacent actuators 500
attached to the same continuous membrane mirror 560. The actuator
500 may have the configuration of actuator 200 shown in FIG. 2 or
that of the actuator 300 shown in FIG. 3. In practice, there will
be hundreds of evenly spaced actuators 500 for one continuous
membrane mirror 530.
[0050] The actuators 500 include stator 510 and sliders 520. The
sliders 520 are integrated with a slider top 530. Posts 540 attach
the slider 520 via the slider top 530 to the deformable mirror
membrane 550. The posts 540 are thus evenly spaced on the under
side of the membrane 550 and are centered on the actuator 500 and
the portion of the mirror 550 the actuator 500 is to effect. Each
actuator 500 and post 540 will pull on the mirror 550 with the
strength of the actuator force that is controlled by the amplitude
of the applied voltage.
[0051] If only one actuator 500 is actuated, it will cause a dimple
in the membrane 500 as shown in FIG. 5. The stiffness or rigidity
of the membrane 550 itself prevents the membrane from being
deflected with sharp edges at the deflection point of the posts
540. Instead, the result is the gradually curved dimple as shown in
FIG. 5, allowing the variation in the surface from one actuator to
the next to be smooth. The actuators 500 are all addressed
separately, so that when multiple actuators are actuated each with
different forces, very complex surface shapes can be produced.
[0052] In addition, springs 560 return the deformable mirror 550 to
its initial position as shown in the actuator on the left in FIG.
5. The actuator 500 resides on a substrate 570. An anchor or wall
580, for each actuator 500, serves to support the spring 560. The
actuator on the right is in the deflected position with the springs
560 bent and the membrane mirror 550 deformed. This deflection is
accomplished by applying a voltage between the stator 510 and the
slider 530, thereby resulting in an attractive force between them,
pulling the slider 530 down as shown on the right relative to the
initial position shown on the left.
[0053] Many variations in the design of the comb itself may be
realized in accordance with the present invention. The density of
the actuators is also application specific. The invention being
thus described, it will be obvious that the same may be varied in
many ways. Such variations are not to be regarded as a departure
from the spirit and scope of the invention, and all such
modifications as would be obvious to one skilled in the art are
intended to be included within the scope of the following
claims.
* * * * *