Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02468132 2012-12-14
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Doc. No.: 10-568 CA CIP2
Patent
ELECTRODE CONFIGURATION FOR PIANO MEMS MICRO1VIIRROR
CROSS-REFERENCE TO RELATED APPLICATIONS
[01] The present application claim priority from United States Patent
Application No.
10/445,360, which claims priority from United States Patent Application No.
60/383,106 filed
May 28, 2002. The present application also claims priority from United States
Patent
Applications Nos. 60/504,210 filed September 22, 2003; 60/537,012 filed
January 20, 2004;
and 60/558,563 filed April 2, 2004.
TECHNICAL FIELD
[02] The present invention relates to a micro-electro-mechanical (MEMs)
mirror device
for use in an optical switch, and in particular to an electrode arrangement
for a 2d gimbal ring
MEMs mirror device.
BACKGROUND OF THE INVENTION
[03] Conventional MEMs mirrors for use in optical switches, such as the one
disclosed
in United States Patent No. 6,535,319 issued March 18, 2003 to Buzzetta et al,
to redirect
beams of light to one of a plurality of output ports include an electro-
statically controlled
mirror pivotable about a single axis. Tilting MEMs mirrors, such as the ones
disclosed in
United States Patent No 6,491,404 issued December 10, 2002 in the name of
Edward Hill, and
United States Patent Publication No. 2003/0052569, published March 20, 2003 in
the name of
Dhuler et al, comprise a mirror pivotable about a central longitudinal axis,
and a pair of
electrodes, one on each side of the central longitudinal axis for actuating
the mirror. The
Dhuler et al reference discloses the positioning of electrodes at an angle to
the mirrored
platform to improve the relationship between the force applied to the mirror
and the gap
between the mirror and the electrodes. The MEMs mirror device, disclosed in
the
aforementioned Hill patent, is illustrated in Figure 1, and includes a
rectangular planar surface
2 pivotally mounted by torsional hinges 4 and 5 to anchor posts 7 and 8,
respectively, above a
substrate 9. The torsional hinges may take the form of serpentine hinges,
which are disclosed
in United States Patent No 6,327,855 issued December 11, 2001 in the name of
Hill et al, and
in United States Patent Publication No. 2002/0126455 published September 12,
2002 in the
name of Robert Wood. In order to position conventional MEMs mirror devices in
close
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proximity, i.e. with a high fill factor, fill factor=width/pitch, they must be
positioned with their
axes of rotation parallel to each other. Unfortunately, this minor
construction restraint greatly
restricts other design choices that have to be made in building the overall
switch.
[04] When using a conventional MEMs arrangement, the minor 1 positioned on
the
planar surface 2 can be rotated through positive and negative angles, e.g. 2
, by attracting one
side 10a or the other side 10b of the planar surface 2 to the substrate 6.
Unfortunately, when
the device is switched between ports at the extremes of the devices rotational
path, the
intermediate ports receive light for fractions of a millisecond as the minor 1
sweeps the optical
beam past these ports, thereby causing undesirable optical transient or
dynamic cross-talk.
[05] One solution to the problem of dynamic cross-talk is to initially or
simultaneously
rotate the mirror about a second axis, thereby avoiding the intermediate
ports. An example of a
MEMs mirror device pivotable about two axes is illustrated in Figure 2, and
includes a minor
platform 11 pivotally mounted by a first pair of torsion springs 12 and 13 to
an external gimbal
ring 14, which is in turn pivotally mounted to a substrate 16 by a second pair
of torsion springs
17 and 18. Examples of external gimbal devices are disclosed in United States
Patents Nos.
6,529,652 issued March 4, 2003 to Brenner, and 6,454,421 issued September 24,
2002 to Yu et
al. Unfortunately, an external gimbal ring greatly limits the number of minors
that can be
arranged in a given area and the relative proximity thereof, i.e. the fill
factor. Moreover, the
external gimbal ring may cause unwanted reflections from light reflecting off
the support
frame. These references also require at least four electrodes to actuate each
mirror.
[06] Another proposed solution to the problem uses high fill factor
mirrors, such as the
ones disclosed in United States Patent No. 6,533,947 issued March 18, 2003 to
Nasiri et al,
which include hinges hidden beneath the mirror platform. Unfortunately, these
types of minor
devices require costly multi-step fabrication processes, which increase costs
and result in low
yields, and rely on four different pairs of electrodes for actuation.
[07] An object of the present invention is to overcome the shortcomings of
the prior art
by providing a MEMs minor device that can pivot about perpendicular axes using
a limited
number of electrodes.
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SUMMARY OF THE INVENTION
[08] Accordingly, the present invention relates to a micro-electro-mechanical
device
mounted on a substrate comprising:
[09] a pivoting member pivotally mounted on said substrate about first and
second axes,
said pivoting member including a first and a second supporting region on
opposite sides of
said first axis;
[10] a first hinge extending from said substrate rotatable about the first
axis;
[11] a gimbal ring surrounding said first hinge;
[12] a second hinge extending from said gimbal ring to said pivoting member
rotatable
about the second axis;
[13] a first electrode beneath the first supporting region for pivoting the
pivoting
member about the first axis;
[14] a second electrode beneath the second supporting region for pivoting the
pivoting
member about the first axis; and
[15] a third electrode beneath a portion o f said pivoting member a long the
first axis,
adjacent said second hinge.
BRIEF DESCRIPTION OF THE DRAWINGS
[16] The invention will be described in greater detail with reference to the
accompanying drawings which represent preferred embodiments thereof, wherein:
[17] Figure 1 is an isometric view of a conventional tilting MEMs mirror
device;
[18] Figure 2 is a plan view of a pair of conventional external gimbal ring
MEMs mirror
devices;
[19] Figure 3 is an isometric view of a plurality of Piano-MEMs mirror
devices;
[20] Figure 4 is an isometric view of a hinge structure of the mirror devices
of Fig. 3;
[21] Figure 5 is an isometric view of an electrode structure of the mirror
devices of Fig.
3;
[22] Figure 6 is an isometric view of a plurality of Piano-MEMs mirror devices
according to an alternative embodiment of the present invention with e
lectrode shields,
light redirecting cusps, and a raised ground plane;
[23] Figure 7 is an isometric view of a plurality of Piano-MEMs mirror devices
according to an alternative embodiment of the present invention with electrode
shields;
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[24] Figure 8 is a plan view of a pair of internal gimbal ring MEMs mirror
devices
according to the present invention;
[25] Figure 9 is an isometric view of an internal gimbal ring MEMs mirror
device
according to the present invention;
[26] Figure 10 is an isometric view of an alternative embodiment of the
internal gimbal
ring MEMs mirror devices according to the present invention;
[27] Figure 11 is an isometric view of a hinge structure of the mirror devices
of Fig. 9;
[28] Figure 12 is an isometric view of an electrode structure of the mirror
devices of
Figs. 9 and 10;
[29] Figure 13 is a graph of Voltage vs Time provided by the electrode
structure of Fig.
11;
[30] Figure 14 is an isometric view of internal gimbal ring MEMs mirror
devices
utilizing a three electrode arrangement according to the present invention;
[31] Figure 15 is an isometric view of the three electrode arrangement of
Figure 14;
[32] Figure 16 is a plan view of an ideal placement of the three electrodes of
Figures 14
and 15 relative to the pivoting platform;
[33] Figure 17 is a plan view of a possible misalignment of the three
electrodes of
Figures 14 and 15;
[34] Figure 18 is a plan view of another possible misalignment of the three
electrodes of
Figures 14 and 15;
[35] Figure 19 is a graph of Voltage vs Time for the three electrodes of
Figure 14 and
15;
[36] Figure 20 is an isometric view of another embodiment of the present
invention with
an offset section on the pivoting member;
[37] Figure 21 is a plan view of the embodiment of Figure 20;
[38] Figure 22 is an end view of the embodiment of Figures 20 and 21;
[39] Figure 23 is a schematic diagram of a wavelength switch utilizing the
mirror
devices of the present invention;
[40] Figure 24 is a schematic diagram of an input/output assembly for the
wavelength
switch of Fig 23; and
[41] Figure 25 is a schematic diagram of an alternative embodiment of an input
assembly for the wavelength switch of Fig. 23.
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DETAILED DESCRIPTION
[42] An array of "Piano" MEMs mirror devices 21, 22 and 23, which pivot about
a
single axis of rotation 93, above a substrate 25, is illustrated in Figures 3,
4 and 5. Each
mirror device 21, 22 and 23 includes a pivoting member or platform 26 defined
by first and
second substantially-rectangular planar supporting regions 27 and 28 joined by
a
relatively-thin substantially-rectangular brace 29 extending therebetween.
Typically, each
planar surface is coated with a reflective coating, e.g. gold, for
simultaneously reflecting a
pair of sub-beams of light traveling along parallel paths, as will be
hereinafter discussed.
Each brace 29 acts like a lever and is pivotally mounted to anchor posts 30
and 31 via first
and second torsional hinges 32 and 33, respectively. The anchor posts 30 and
31 extend
upwardly from the substrate 25. The ends of the first torsional hinge 32 are
connected to
the anchor post 30 and the brace 29 along the axis 193,, Similarly, the ends
of the second
torsional hinge 32 are connected to the anchor post 31 and the brace 29 along
the axis 0y.
Preferably, each of the first and second torsional hinges 32 and 33 comprises
a serpentine
hinge, which are considerably more robust than conventional torsional beam
hinges. The
serpentine hinge is effectively longer than a normal torsional hinge, which
spans the same
distance, thereby providing greater deflection and strength, without requiring
the space that
would be needed to extend a normal full-length torsional hinge.
[43] With particular reference to Figure 5, each platform 26 is rotated by the
selective
activation of a first electrode 36, which electro-statically attracts the
first planar section 27
theretowards or by the selective activation of a second electrode 37, which
electro-
statically attracts the second planar section 28 theretowards. A gap 38 is
provided between
the first and second electrodes 36 and 37 for receiving the anchor posts 31,
which extend
from the substrate 25 to adjacent the platforms 26.
[44] In the disclosed open loop configuration, the angular position of the
platforms 26
depend non-linearly on the voltage applied by the electrodes 36 (or 37), i.e.
as the applied
voltage is increased linearly, the incremental change in angular platform
position is greater
as the voltage increases. Accordingly, there is a maximum voltage, i.e. an
angular
platform position, at which the platform angular position becomes unstable and
will
uncontrollably tilt until hitting part of the lower structure, e.g. the
electrode 36. This
maximum voltage sets the range of angular motion that the platform 26 can
travel. The
instability in the platform's angular position is a result of the distance
between the platform
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26 and the electrode 36 (the hot electrode) decreasing more rapidly at the
outer free ends of
the platform 26 than at the inner sections, nearer the pivot axis 0y. As a
result, the force
per unit length along the platform 26 increases more rapidly at the outer free
ends of the
platform 26 than the inner sections. To increase the platform's range of
angular motion,
the field strength, i.e. the force per unit area, that is sensed at the outer
free ends of the
platform 26 must be reduced. With reference to Figures 5, this is accomplished
by
providing the electrodes 36 and 37 with a two-step configuration. Upper steps
36a and 37a
are positioned proximate the inner end of the platform 26, i.e. the Y axis,
while lower steps
36b and 37b are positioned under the outer free ends of the platform 26,
thereby making
the gap between the platforms 26 and the electrodes 36 and 37 greater at the
outer free end
than the inner end. The area of the lower steps 36b and 37b can also be made
smaller,
thereby reducing the force per unit area sensed by the outer free end of the
platform 26.
Multi-step electrodes, e.g. three or more can also provide a more even
distribution of force.
[45] A consequence o f closely packed micro-mirrors i s that the a ctuation of
as ingle
mirror will impart a torque, i.e. an angular rotation, onto adjacent mirrors
as a result of
fringing electric fields. In an effort to minimize this cross-talk, electrode
grounding shields
41 are positioned on the substrate 25 around or on either side of the first
and second
electrodes 36 and 37 forming electrode cavities, which are electrically
isolated from each
other. Figure 5 illustrates C-shaped grounding shields 41, which include
lateral portions
41a for partially surrounding the first and second electrodes 36 and 37. The
grounding
shields 41 are kept at ground potential, i.e. the same as the mirrored
platforms 26, while
one of the first and second electrodes is held at an activation voltage, e.g.
100 Volts.
[46] Trace lines 36c and 37c electrically connect the electrodes 36 and 37,
respectively,
to a voltage supply (not shown). Since the trace lines 36c and 37c also act as
a hot
electrode, i.e. contributing to the total torque applied to the platform 26,
covering the traces
36c and 37c with a ground plane 43 (Figure 6) also reduces the force applied
to the outer
free end of the platform 26.
[47] Figure 6 also illustrates an alternative configuration for the electrode
36, in which
the two step hot electrode 36 is sunken slightly below a surrounding grounded
metallic
surface, which is a continuation of the ground plane 43. A small vertical step
44 between
the hot electrode 36 and the surrounding ground plane 43 is a dielectric
surface that
isolates the hot electrode 36 from the surrounding ground plane 43. This
arrangement
reduces the angular drift of the platform 26, which is caused by a build up of
electrostatic
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charges on exposed dielectric or insulating surfaces. The electric field
generated by these
electrostatic charges perturbs the electric field generated by the applied
voltage from the
electrodes 36 and 37, thereby causing the angular position of the platform 26
to drift over
time. The present arrangement limits the exposed dielectric to the small
vertical surface
44, which generates electrostatic field lines that do not significantly affect
the field lines
between the hot electrodes 36 and 37 and the ground plane 43. To further
reduce the
angular drift of the platform 26, the vertical surface 44 can be under cut
beneath the ground
plane 43 at a slight negative angle ensuring that the gap between the hot
electrode 36 and
the ground plane 43 is substantially zero. The ground plane 43 could also be
positioned
slightly below the hot electrodes 36 and 37 to create the vertical step.
[48] Since the MEMs mirror devices 21, 22 and 23 are for use in optical
devices, i.e.
wavelength blockers and multiple wavelength switches (see Figure 23), which
include a
grating for dispersing the light into spectral wavelength component channels,
it is an
important performance requirement that the spectral response has a high
rejection of light
between the selected wavelength channels. Unfortunately, in conventional MEMs
devices,
light passes b etween the mirrors and is reflected off the substrate back into
the optical
device, thereby leading to a deterioration in the isolation between the
wavelength channels.
Accordingly, the present invention provides back reflection cusps 50, defined
by angled,
curved or concave reflecting surfaces intersecting along a ridge, extending
longitudinally
below the gap between the platforms 26, for scattering any light passing
between the
mirrored platforms 26 in a direction substantially parallel to the surface of
the platforms
26.
[49] To further eliminate cross-talk between adjacent electrodes, additional
platform
shields 42 (Figure 7) can be added to the underside of the planar supporting
regions 27 and
28, outside or inside of the electrode shields 41. Typically, in the rest
position, the two
different sets of shields 41 and 42 do not overlap; however, as the platform
26 tilts the
platform shields 42 begin to overlap the grounding shielding 41. The added
protection
provided by overlapping shielding is particularly advantageous, when the tilt
angle of the
platform 26 is proportional to the voltage applied to the electrode 36 (or
37), such as in
open loop configurations. Accordingly, the greater the tilt angle, the greater
the required
voltage, and the greater the amount of potential cross-talk, but consequently
the greater the
amount of shielding provided by the overlapping ground and platform shields 41
and 42,
respectively. Back reflection cusps 50 are also provided for reasons
hereinbefore
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discussed. A single structure 50 between adjacent electrodes can replace the
pair of
adjacent shields 41.
[50] With reference to Figures 8, a pair of internal gimbal ring MEMs mirror
devices
131 and 132 are illustrated mounted adjacent each other on a substrate 133.
The present
invention enables mirrors 134 and 135 to be positioned relatively close
together, i.e. with a
high fill factor, while still providing the two degrees of motion provided by
the more
complicated prior art.
[51] With further reference to Figure 9, a first torsion hinge 137, preferably
in the form
of a rectangular beam, is fixed, proximate the middle thereof, to the
substrate 133 via a
central anchor post 138. The supporting structure for the mirror device of the
present
invention is based on a single anchor post 138, rather than the dual anchor
points required
in the aforementioned external gimbal ring devices. The first torsion hinge
137 provides
for rotation Oy about a first axis Y, and may also include a serpentine hinge
140, as
illustrated in mirror device 131, or any other torsional hinge known in the
art. Opposite
sides of a n internal gimbal ring 139 are connected to opposite ends of the
first torsion
hinge 137, whereby the first torsion hinge 137 bisects the internal gimbal
ring 139. The
internal gimbal ring 139 is preferably not flexible, but can take various
geometric forms,
although rectangular or circular frames would be the most convenient to
fabricate and use.
Spring arms 141 and 142, which define a second torsion hinge, extend outwardly
from
opposite sides of the internal gimbal ring 139 perpendicular to the first
torsion hinge 137.
Each of the spring arms may also include a serpentine hinge as hereinbefore
described.
The second torsion hinge provides for rotation 0õ about a second axis X, which
is
perpendicular to the first axis Y, but still substantially in the same plane
as the mirrors 134
and 135. A generally rectangular platform 143, for supporting one of the
mirrors 134 or
135, is mounted on the ends of the spring arms 141 and 142. Preferably, the
platform 143
is comprised of a pair of rectangular planar surfaces 144 and 145 joined
together by a pair
of elongated braces 147 and 148, which extend on either side of the internal
gimbal ring
139 parallel with the spring arms 141 and 142.
[52] Fabrication of the preferred embodiment illustrated in Figures 8 and 9,
is simplified
by having all of the structural elements, i.e. the first torsional hinge 137,
the gimbal ring
139, the spring arms 141 and 142, and the first and second planar surfaces 144
and 145, in
the same upper substrate layer and having coplanar upper surfaces, whereby the
same basic
process steps are used as are used to fabricate the MEMs device illustrated in
Figure 1. In
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particular, a single photolithographic step is used to identify the structural
elements,
followed by a deep reactive ion etching (DRIE) step used to remove the
unwanted portions
of the upper substrate. Finally the moveable elements in the upper substrate
are released
from the lower substrate by removal of a sacrificial layer therebetween.
[53] Figures 10 and 11 illustrate an array of internal gimbal ring MEMs mirror
devices
201 utilizing a first pair of serpentine torsional hinges 202 for pivoting a
rectangular
platform 203, including first and second planar supporting regions 203a and
203b, about a
first axis of rotation 0x, and a second pair of serpentine torsional hinges
204 for rotating the
platform 203 about a second axis of rotation Oy above a base substrate 205.
The first pair
of serpentine torsional hinges 202 extend from a single anchor post 206, which
extends
upwardly from the base substrate 205 through the center of the platform 203,
i.e. at the
intersection of the minor and major axes thereof. Outer ends of the first pair
of torsional
serpentine torsional hinges 202 are connected to a rectangular gimbal ring
208, which
surrounds the first pair of serpentine hinges 202, at points along the minor
axes (Or) of the
platform 203. The second pair of serpentine torsional hinges 204 extend from
opposite
sides of the gimbal ring 208 into contact with the platform 203, at points
along the major
axis (0õ) of the platform 203.
[54] To provide a full range of motion for the platform 143 or 203, a set of
four two-step
electrodes 211, 212, 213 and 214 are provided (See Fig. 12); however, for the
present
invention only the first, second and third electrodes 211, 212 and 213 are
required to roll
the mirrors out of alignment with any intermediate output ports and then back
into
alignment with a designated output port. As in Figure 5, each of the
electrodes 211, 212,
213 and 214 include an upper step 211a, 212a, 213a, and 214a, and a lower step
211b,
212b, 213b, 2 14b, respectively, for reasons discussed hereinbefore.
Accordingly, first,
second and third voltages can be established between the platform 143 or 203
and the first
electrode 211, the second electrode 212 and the third electrode 213,
respectively. Initially,
the first and second electrodes 211 and 212 are activated to rotate the
platform 143 or 203
about Ox. Subsequently, the first voltage is gradually lowered to zero, while
the third
voltage is gradually increased until it is equivalent to the second voltage
(See Fig 13). To
minimize unwanted effected caused by ringing, i.e. vibration of the mirrors
caused by an
abrupt start or stop, the first, second and third voltages are increased and
decreased
gradually, e.g. exponentially, as evidenced in Figure 13, which illustrates
the voltages
curves for the various electrodes (first, second and third) over the actuation
time of the
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mirror device. Various mirror tilting patterns can be designed based on the
desired
characteristics, e.g. attenuation, of the light.
[55] An improved electrode configuration is illustrated in Figures 14 and 15,
in which a
first two-step Oy electrode 236 includes an upper U-shaped step 236a, and a
lower
rectangular step 236b. The arms of the U-shaped step 236a extend from the
lower step
236b on opposite sides of the second hinge 204 beneath the first planar
supporting region
203a. Similarly, a second two-step Oy electrode 237 includes an upper U-shaped
step 237a,
and a lower rectangular step 237b. The arms of the U-shaped step 237a extend
from the
lower rectangular step 237b on opposite sides of the second hinge 204 beneath
the second
planar supporting region 203b. A single two-step Ox electrode 238 includes an
upper U-
shaped step 238a, and lower rectangular steps 238b extending from each arm of
the upper
U-shaped step. The single 0, electrode 238 extends from adjacent the first Oy
electrode 236
to adjacent the second Oy electrode 237 across the gap therebetween, and
beneath one side
of both the first and second planar supporting regions 203a and 203b. The
lower steps
238b provide a larger gap between the outer free ends of the platform 203,
when the
platform is tilted towards the first or the second 03, electrode 236 or 237.
The arms of the
upper U-shaped step 238b extend on opposite sides of the first pair of hinges
202. The
arms of the U-shaped step 238a are three to five times wider than the arms of
the U-shaped
step 236a or 237a. Multi-step electrodes are also possible to further spread
the application
of force over the length of the platform 203. Actuation of the electrodes is
controlled by an
electrode control 240, as will be discussed hereinafter with reference to
Figure 19.
[56] An unfortunate consequence of relying on only three electrodes is that a
slight
misalignment in positioning the platform 203 over the first and second Oy
electrodes 236
and 237 can result in an imbalance that can not be corrected for using the
single 0,
electrode 238. Figure 16 illustrates the ideal case, in which the longitudinal
axis of the first
electrode 236 is aligned with the longitudinal axis X of the platform 203.
However, Figure
17 illustrates the results of a mask misalignment during fabrication, in which
the
longitudinal axis X of the platform 203 has a +Ax misalignment relative to the
electrode
axis. Accordingly, actuation of the first Oy electrode 236 would introduce an
undesirable
tilt in the platform 203 towards the bottom left hand corner, which could not
be
compensated by the single 0, electrode 238. In Figure 18, the illustrated mask
misalignment, in which the longitudinal axis X of the platform 203 has a ¨Ax
misalignment relative to the electrode axis. In this case, actuation of the
first Oy electrode
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236 would introduce an undesirable tilt in the platform 203 towards the top
left hand
corner. However, this tilt can be compensated for by applying a voltage to the
single 0õ
electrode 238. Accordingly, the solution to the problem of mask misalignment
is to
introduce an intentional or predetermined ¨Ax misalignment, which would cancel
or at
least minimize any +.Ax misalignment and which could be compensated for by the
single 0õ
electrode 238.
[57] Figure 19 illustrates an electrode voltage vs time graph, detailing the
voltages of the
three electrodes 236, 237 and 238 as the platform 203 is switched from one
position to
another by an electrode control, i.e. from reflecting light from one port to
another, without
traveling directly, i.e. without reflecting light into any intermediate ports.
To prevent
undesirable "ringing" of the platform 203, the voltage VyR of the first 0),
electrode 236 is
gradually decreased as the voltage Vx of the single 0, electrode 238 is
increased. As the
voltage VyR decreases to zero, the voltage VyL of the second Oy electrode 237
gradually
increases. As the voltage VyL reaches its set amount to maintain the platform
in the
desired position, the voltage Vx is decreased to a minimum amount, assuming no
compensation voltages are required.
[58] When the size of the platform 203 is decreased, e.g. for small pitch
micro-mirrors
in the order of <100um, the electrodes 236, 237 and 238 must also be
constructed
correspondingly smaller. However, due to the fact that the electrodes
necessarily become
thinner, while sharing the same mirror section, stable tilt angles are
difficult to achieve at
high resonant frequencies. Accordingly, the size requirement of the electrode,
and the
required electrode spacing become the limiting factor in determining the
maximum fill
factor. An alternative embodiment of a three electrode configuration is
illustrated in
Figures 20 and 21, in which platform 253 are made smaller than the original
platforms 203
with first and second two-step 0), electrodes 256 and 257 positioned
therebelow. A single
Oõ electrode 258 is positioned below each offset section 259, which extends
from the side
of the platforms 253 adjacent the mid-section thereof, i.e. the area of first
and second
hinges 251 and 252. This arrangement enables the single 0õ electrode 258 to be
separated
from the other two electrodes 256 and 257, and therefore, be larger in size,
which enables
the electrostatic torque to be increased for a common voltage. The added
separation
between the electrodes 256, 257 and 258 minimizes the angular instabilities,
when the
single 0õ electrode 238 is actuated, and reduces the amount of electrical x-
talk. Preferably,
the two-step Oõ electrodes 256 and 257 include the ground plane arrangement as
disclosed
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in Figure 6 with hot electrodes sunken relative to a surrounding ground plane,
and only a
vertically extending dielectric layer, which provides a substantially zero-
width vertical gap
between the hot electrode and the ground plane.
[59] For high fill factor applications, a first planar section 253a of one
platform 253 is
positioned beside a second planar section 253b of an adjacent platform 253, as
in Figures
20 and 21, whereby adjacent mirrors have offset x axes X1 and X2, and every
other
platform pivots about the same x axis. Only the relatively closely disposed
planar sections
would require reflective material thereon, and reflective cusps 260 would only
be required
therebelow (Figure 22).
[60] Substrate-mounted, grounded cross-talk shields 261 and platform mounted
cross-
talk shields 262 are provided to further minimize the amount of electrical
cross-talk
between adjacent minors. The platform mount cross-talk shields 262 are
preferably
mounted outside of the platform mounted cross-talk shields 262 with enough
spacing to
enable rotation about both the x and the y axis; however, any combination for
offsetting the
shields 261 and 262 is possible.
[61] The "piano" MEMs mirror devices according to the present invention are
particularly u seful in a wavelength switch 301 illustrated in Figures 23, 24
and 25. I n
operation, a beam of light with a plurality of different wavelength channels
is launched via
an input/output assembly 302, which comprises a plurality of input/output
ports, e.g. first,
second, third and fourth input/output ports 303, 304, 305 and 306,
respectively. The beam
is directed to an element having optical power, such as concave minor 309,
which redirects
the beam to a dispersive element 311, e.g. a Bragg grating. The dispersive
element
separates the beam into the distinct wavelength channels (k1, 2L2, 23) , which
are again
directed to an element having optical power, e.g. the concave minor 309. The
concave
minor 309 redirects the various wavelength channels to an array of "piano"
MEMs minor
devices 312 according to the present invention, which are independently
controlled to
direct the various wavelength channels back to whichever input/output port is
desired.
Wavelength channels designated for the same port are reflected back off the
concave
minor 309 to the dispersive element 311 for recombination and redirection off
the concave
minor 309 to the desired input/output port. The concave mirror 309 can be
replaced by a
single lens with other elements of the switch on either side thereof or by a
pair of lenses
with the dispersive element 311 therebetween.
12
CA 02468132 2004-05-20
Doc. No: 10-568 CA CIP2 Patent
[62] With particular reference to Figure 24, the input/output assembly 302
includes a
plurality of input/output fibers 313a to 313d with a corresponding collimating
lens 314a to
314d. A single lens 316 is used to convert a spatial offset between the
input/output ports
into an angular offset. Figure 25 illustrates a preferred embodiment of the
input/output
assembly, in which the unwanted effects of polarization diversity are
eliminated by the use
of a birefringent crystal 317 and a waveplate 318. For incoming beams, the
lens 316
directs each beam through the birefringent crystal 317, which separates the
beam into two
orthogonally polarized sub-beams (o and e). The half waveplate 318 is
positioned in the
path of one of the sub-beams for rotating the polarization thereof by 90 , so
that both of the
sub-beams have the same polarization for transmission into the remainder of
the switch.
Alternatively, the waveplate 318 is a quarter waveplate and rotates one of the
sub-beams
by 45 in one direction, while another quarter waveplate 319 rotates the other
sub-beam by
45 in the opposite direction, whereby both sub-beams have the same
polarization. For
outgoing light, the polarization of one (or both) of the similarly polarized
sub-beams are
rotated by the waveplate(s) 318 (and 319), so that the sub-beams become
orthogonally
polarized. The orthogonally polarized sub-beams are then recombined by the
birefringent
crystal 317 and output the appropriate i nput/output p ort. The micro-electro-
mechanical
devices according to the present invention are particularly well suited for
use in switching
devices with polarization diversity front ends, since they provide a pair of
reflecting
surfaces, i.e. one for each sub-beam
13
