CA2468132C - Electrode configuration for piano mems micromirror - Google Patents

Abstract

A micro-electro-mechanical (MEMs) mirror device for use in an optical switch is disclosed. A "piano"-style MEMs device includes an elongated platform pivotally mounted p roximate the middle thereof by a torsional hinge. The middle portion of the platform and the torsional hinge have a combined width less than the width of the rest of the platform, whereby several of these "piano" MEMs devices can be positioned adjacent each other pivotally mounted about the same axis with only a relatively small air gap therebetween. In a preferred embodiment of the present invention specially designed for wavelength switching applications, a greater range of arcuate motion for a mirror mounted thereon is provided by enabling the platform to rotate about two perpendicular axes. The MEMs minor device according to the preferred embodiment of the present invention enables the minor to tilt about two perpendicular axes, by the use of an "internal" gimbal ring construction, which ensures that a plurality of adjacent mirror devices have a high fill factor, without having to rely on complicated and costly manufacturing processes.

Description

A -Doc. No.: 10-568 CA CIP2 Patent 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 Doc. No.: 10-568 CA CIP2 Patent 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.

Doc. No: 10-568 CA CIP2 Patent 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;

Doc. No: 10-568 CA CIP2 Patent

[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.

Doc. No: 10-568 CA CIP2 Patent 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 Doc. No: 10-568 CA CIP2 Patent 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 Doc. No: 10-568 CA CIP2 Patent 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 Doc. No: 10-568 CA CIP2 Patent 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 Doc. No: 10-568 CA CIP2 Patent 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 Doc. No: 10-568 CA CIP2 Patent 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 _ Doc. No: 10-568 CA CIP2 Patent 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 _ Doc. No: 10-568 CA CIP2 Patent 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.

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

Claims (27)

WE CLAIM:

1. An array of micro-electro-mechanical devices mounted on a substrate, each micro-electro-mechanical device comprising:
a platform pivoting member pivotally mounted on said substrate about first and second axes, said platform pivoting member including a first and a second supporting region at opposite ends thereof and on opposite sides of said first axis;
a first torsional hinge extending from said substrate rotatable about the first axis;
a gimbal ring connected to outer ends of said first hinge;
a second torsional hinge extending from said gimbal ring to said platform pivoting member rotatable about the second axis;
a first electrode beneath the first supporting region for pivoting the platform pivoting member about the first axis;
a second electrode beneath the second supporting region for pivoting the platform pivoting member about the first axis; and a third electrode beneath a portion of said platform pivoting member along the first axis, adjacent said second hinge for pivoting the platform pivoting member about the second axis;
wherein said gimbal ring and said first and second hinges are positioned between and coplanar with said first and second supporting regions, whereby outer edges of adjacent first supporting regions are positionable in close proximity with each other with only an air gap therebetween;
wherein only a single third electrode is provided for pivoting the platform pivoting member about the second axis.

2. The device according to claim 1, further comprising electrode control means for gradually decreasing a voltage to said first electrode to a minimum, while increasing a voltage to said third electrode to a maximum, and then gradually increasing a voltage to said second electrode, while decreasing the voltage to said third electrode to a minimum, thereby indirectly rotating the platform pivoting member about the first axis.

3. The device according to claim 1 or 2, wherein a longitudinal axis of said first and second electrodes is offset from a longitudinal axis of said platform pivoting member on an opposite side of said third electrode to ensure any mask misalignment of said platform pivoting member and said first and second electrodes can be compensated by said third electrode.

4. The device according to claim 1, 2 or 3, wherein said third electrode extends from adjacent said first electrode to adjacent said second electrode passed a gap therebetween, including a U-shaped portion with arms extending beneath opposite sides of the first hinge.

5. The device according to claim 1, wherein the platform pivoting member includes an offset section extending from a side thereof, beneath which said third electrode is disposed, whereby the third electrode attracts the offset section for pivoting the platform pivoting member about the second axis.

6. The device according to claim 1, wherein the first electrode includes arms extending on either side of said second hinge; and wherein the third electrode includes arms extending on either side of said first hinge.

7. The device according to any one of claims 1 to 6, further comprising shields disposed on each side of said first electrode for limiting the amount of electrical cross-talk between adjacent first electrodes.

8. The device according to claim 7, wherein the shields extend downwardly from an undersurface of said platform pivoting member.

9. The device according to claim 7 or 8, wherein the shields extend upwardly from the substrate above a top surface of the first electrode.

10. The device according to any one of claims 1 to 9, wherein the first hinge comprises an anchor post extending upwardly from the substrate through a center of the platform pivoting member, and a pair of torsional hinges extending from the anchor post to the gimbal ring.

11. The device according to claim 1, wherein said first electrode includes:
a hot electrode, which generates an electric field for electro-statically attracting the first supporting region;
a trace electrode electrically connecting said hot electrode to a power source;
a ground plane covering said trace electrode, thereby reducing the amount of force applied to an outer free end of said pivoting member.

12. The device according to claim 11, wherein the ground plane extends around the hot electrode at a level different than the hot electrode defining a substantially vertical surface therebetween, wherein the substantially vertical surface comprises a dielectric surface for isolating the hot electrode from the ground plane.

13. The device according to claim 11, wherein the ground plane extends around the hot electrode at a level higher than the hot electrode defining a substantially vertical surface therebetween, wherein the substantially vertical surface comprises a dielectric surface for isolating the hot electrode from the ground plane.

14. The device according to any one of claims 1 to 13, wherein the first hinge comprises an anchor post extending upwardly from the substrate through a center of the pivoting member, and a pair of torsional hinges extending from the anchor post to the gimbal ring.

15. A method of rotating a micro electro-mechanical (MEMs) device in an optical switch about a first axis from a first position corresponding to a first output port to a second position corresponding to a second output port, while bypassing a third position therebetween corresponding to a third output port intermediate the first and second output ports, comprising the steps of:
a) providing a pivoting member pivotally mounted above a substrate about the first axis and a second axis, perpendicular to the first axis;
b) providing first and second electrodes on opposite sides of the first axis underneath the pivoting member;

c) providing a third electrode along the first axis;
d) gradually decreasing voltage to the first electrode, while gradually increasing voltage to the third electrode for rotating the pivoting member about the first axis away from the first position and for rotating the pivoting member about the second axis, respectively;
and e) gradually decreasing voltage to the third electrode, while gradually increasing voltage to the second electrode for rotating the pivoting member about the second axis and for rotating the pivoting member to the second position, respectively.

16. The method according to claim 15, further comprising offsetting a longitudinal axis of said first and second electrodes from a longitudinal axis of said pivoting member on an opposite side of said third electrode to ensure any mask misalignment of said pivoting member and said first and second electrodes can be compensated by said third electrode.

17. The method according to claim 15, further comprising providing a ground plane extending around the first electrode at a level higher than the first electrode defining substantially vertical surface therebetween, wherein the substantially vertical surface comprises a dielectric surface for isolating the first electrode from the ground plane.

18. The method according to claim 15, wherein the pivoting member includes first and second supporting regions extending from opposite sides of first and second hinges, which enable rotation about the first and second axes, respectively; and wherein said first and second hinges are positioned between said first and second supporting regions, whereby outer edges of said pivoting member are free of said hinges enabling adjacent pivoting members to be positioned in close proximity.

19. The method according to claim 18, wherein step a) includes providing an anchor post extending upwardly from the substrate between the first and second supporting regions from which the first hinge extends, and providing a gimbal ring extending from the first hinge from which the second hinge extends.

20. The method according to claim 18, wherein step a) includes providing the first and second electrodes with arms extending on either side of said second hinge.

21. The method according to any one of claims 15 to 20, wherein step c) includes extending the third electrode from adjacent the first electrode to adjacent the second electrode beneath the pivoting member.

22. The method according to any one of claims 15 to 21, wherein step c) includes providing shields between the first and third electrodes, and between the second and third electrodes for limiting the amount of electrical cross-talk therebetween.

23. The method according to claim 22, wherein step c) includes providing the shields extending upwardly from the substrate.

24. The method according to claim 22, wherein step c) further includes providing the shields extending downwardly from the pivoting member.

25. The method according to claim 22, wherein step c) includes providing the shields extending downwardly from the pivoting member and upwardly from the substrate.

26. The method according to any one of claims 15 to 25, wherein step a) includes providing the platform pivoting member with an offset section along the first axis adjacent to the first and second torsional hinges; and wherein step c) includes providing the third electrode beneath the offset section.

27. The method according to any one of claims 15 to 26, wherein step b) includes providing the first electrodes with an upper step proximate the first and second torsional hinges, and a lower step below an outer free end of the first supporting region.