111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006984917B2
`
`(12) United States Patent
`Greywall et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,984,917 B2
`Jan.10,2006
`
`(54) OlYJ.'ICAL ELEMENT HAVING TWO AXES
`OF ROTATION FOR USE IN TIGHTLY
`SPACED MIRROR ARRAYS
`
`(75)
`
`Inventors: Dennis S. Greywall, Whitehouse
`Station, NJ (US); Dan M. Marom,
`Howell, NJ (US)
`
`(73)
`
`Assignee: Lucent Technologies Inc., Murray Hill,
`NJ (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 169 days.
`
`(21) Appl. No.: 10/164,537
`
`(22) Filed:
`
`Jun. 6, 2002
`
`(65)
`
`(51)
`
`Prior Publication Data
`us 2004/0212864 A1
`
`Oct. 28, 2004
`
`Int. Cl.
`H02N 1!00
`G02B 26/08
`G028 26/10
`
`(2006.01)
`(2006.01)
`(2006.01)
`
`(52) U.S. C l. .... .................. 310/310; 359/198; 359/224;
`359/226; 359/385
`
`(58) Field of C lassification Search ................ 310/309;
`359/223-224, 872, 198, 225; 385/18
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,223,969 A *
`5,867,297 A •
`5,912,608 A
`5.920,417 A
`6,201,631 Bl
`6,389,190 B2 •
`6,690,850 Bl *
`6,819,822 B2 •
`* cited by examiner
`
`6/1993 Jeandeau .................... 359/196
`2/1999 Kiang et al. ................ 359/198
`6/1999 Asada ........................ 335/222
`7/1999 Jonoson ...................... 359/223
`3/2001 Greywall .................... 359/245
`5/2002 Solgaard et al. .............. 385/18
`2/2004 Greywall ..................... 385/18
`tl/2004 Behin et al. .................. 385/18
`
`Primary Examiner-Karl Tarnai
`
`(57)
`
`ABSTRACT
`A rotatable element includes a plate, a plate support, a cradle
`and a c radle support. The plate is coupled to the cradle via
`the plate support. The cradle is coupled to a surrounding
`frame by the cradle support. The plate and cradle are
`suspended over a cavity so that, in conjunction with the plate
`support and the cradle support, both the plate and cradle are
`capable of freely rotating about different axes of rotation
`when suitably actuated. Since the plate is capable o( rotating
`independently of the cradle, yet also rotates when tbe cradle
`is rotated, the plate is rotatable about two axes of rotation.
`In some cases, the axis of rotation of the plate is perpen(cid:173)
`dicular to the axis of rotation of the cradle. Since tbe cradle
`doe;:s not surround tbe plate, tbe plates of adjacent rotatable;:
`elements can be placed very close to one another (i.e., as
`close as about 1 micron) to provide, for example, an array of
`very-closely-spaced mirrors.
`
`22 Claims, 6 Drawing Sbects
`
`0001
`
`Capella 2013
`Ciena/Coriant/Fujitsu v. Capella
`IPR2015-00816
`
`
`
`
`
`

`

`U.S. Patent
`
`Jan.10, 2006
`
`Sheet 1 of 6
`
`US 6,984,917 B2
`
`FIG. 1
`
`1
`
`534
`
`r------ ...,
`I
`I
`
`302
`
`)300
`
`s
`
`3
`
`304
`
`3080
`
`T
`
`lr
`c
`
`_jA
`
`312
`
`T
`
`314
`lp~
`3
`
`9pc
`
`9ct
`
`534
`
`304
`
`AL
`
`~
`\l '
`''
`
`I
`
`I
`
`r--------,
`L---------.J
`--I
`
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`wm c
`
`r-, ~ r-,
`I }
`
`I
`I
`I
`
`I
`I
`I
`
`I
`I
`I
`L_
`
`310
`
`0002
`
`

`

`U.S. Patent
`
`Jan. tO, 2006
`
`Sheet 2 of 6
`
`US 6,984,917 B2
`
`FIG. 2
`
`w
`
`~r-
`
`308
`
`"
`
`PORTION OF
`ROTATABLE
`ELEMENT
`
`T
`L
`.__'-4-22__. _l
`
`430
`
`0003
`
`PORTION OF
`SUPPORT
`
`

`

`e •
`00 .
`~
`~ ...,.
`(D = ...,.
`-= =
`
`"""' 9
`N g
`e-.
`
`~
`
`00 =(cid:173)~
`~ ...
`
`~ -~
`
`FIG. 3
`
`304
`
`1/3 T0-
`
`_i __ j __
`T~-
`- I -
`1 --t
`
`534C
`
`5340
`
`302
`
`FIG. 4
`
`0004
`
`304
`312
`304
`312
`~ ezzzzzzz?)/????77777777?1~ ~
`532
`,J
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`7
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`>
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`I
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`7
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`------
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`7
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`
`\c
`,.....
`co
`N
`
`534C
`
`534A
`
`5348
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 10, 2006
`Jan. 10, 2006
`
`Sheet 4 of 6
`Sheet 4 of 6
`
`US 6,984,917 B2
`US 6,984,917 B2
`
`FIG. 5
`FIG. 5
`
`/700
`
`312
`
`r==uF
`
`304
`
`n~
`
`uu
`
`304
`
`nn
`
`300
`~
`
`312
`
`uu
`
`304
`
`nn
`
`
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`/.~:
`',%/
`
`uu
`
`nn
`
`
`
`uu
`
`nn
`
`312
`
`uu
`
`nn
`
`0005
`0005
`
`

`

`U.S. Patent
`
`Jan.10, 2006
`
`Sheet 5 of 6
`
`US 6,984,917 B2
`
`c
`I
`,..,..,
`00
`00
`
`g)
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`
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`
`(""-.j
`I
`,..,..,
`00
`00
`
`0006
`
`

`

`U.S. Patent
`
`Jan.10, 2006
`
`Sheet 6 of 6
`
`US 6,984,917 B2
`
`FIG. 7
`
`FIG. 8
`
`1000
`~
`
`ROTATABLY COUPUNG A PLATE TO A
`CRADLE IN A FIRST SUBSTRATE
`t
`ROTATABLY COUPUNG THE CRADLE
`TO THE FIRST SUBSTRATE
`t
`FORMING AT LEAST TWO ELECTRODES
`AT A FIRST REGION IN A SECOND
`
`SUBSTRATE '
`
`FORMING AT LEAST TWO ELECTRODES
`AT A SECOND REGION IN THE
`SECOND SUBSTRATE
`t
`AUGNING THE FIRST SUBSTRATE
`WITH THE SECOND SUBSTRATE
`t
`ATTACHING THE FIRST SUBSTRATE TO
`THE SECOND SUBSTRATE
`
`-- 1002
`-- 1004
`-- 1006
`-- 1008
`-- 1010
`-- 1012
`
`0007
`
`

`

`US 6,984,917 B2
`
`1
`OPI'ICAL ELEMENT HAVLNG TWO AXES
`OF ROTATION FOR USE IN TIGHTLY
`SPACED MIRROR ARRAYS
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to micro-electro(cid:173)
`mechanical systems. More particularly, the present inven(cid:173)
`tion relates to an optical e lement that is movable about two
`perpendicular axes.
`
`BACKGROUND OF THE INVENTION
`
`5
`
`10
`
`2
`support, a cradle and a cradle support. The plate is rotatably
`coupled to the cradle via the plate support. Likewise, the
`cradle is rotatably coupled to a surrounding frame, e.g.,
`substrate, etc., by the cradle support. The rotatable element
`is suspended over a cavity so that, in conjunction with the
`plate support and the cradle support, both the plate and
`cradle are capable of freely rotating. In some embodiments,
`the axis of rotation of the plate is perpendicular to the axis
`of rotation o( the cradle.
`Electrodes are disposed in the cavity beneath each rotat(cid:173)
`able element. In one embodiment, two electrodes are dis(cid:173)
`posed in the cavity under the rotatably-coupled portion of
`the cradle, oo opposite sides of its axis of rotation. Similarly,
`JS two electrodes arc disposed io the cavity beneath the plate,
`on opposite sides of its axis of rotation.
`When an electrical potential is applied across the plate
`aocl one of its underlying electrodes, the plate rotates out(cid:173)
`of-plane, i.e., out of the plane defined by the cradle, which
`20 is the plate in which the plate Lies when it is in its quiescent
`or uoactualed position, about its axis of rotation toward the
`electrified electrode. Tbis provides one axis of rotation for
`the plate. When ao electrical potential is applied across the
`cradle and one of its underlying electrodes, the cradle rotates
`25 out-of-plane, i.e., of the substrate or frame, about its a.xis of
`rotation toward the electrified electrode. As the cradle
`rotates, the plate rotates with it. Furthermore, the plate can
`be rotated independently of the cradle, providing it with a
`second axis of rotation.
`The plate is advantageously capable of providing ao
`optical f11oction. For example, in some embodiments, the
`plate functions as a mirror. Unlike prior-art gimbaled mir(cid:173)
`rors, in which the gimbal completely surrounds tbe mirror,
`in a rotatable element in accordance with the principles of
`35 the i nvention, the cradle does not completely surround or
`encircle the plate, e.g., mirror. Consequently, adjacent mir(cid:173)
`rors io ao may of rotatable elements cao, advantageously, be
`very closely spaced. Tbis makes them suitable for usc in
`some optical applications in which the prior-an gimbaled
`40 mirrors cannot be used.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`An array of individually-addressable, movable, micro(cid:173)
`machined mirrors cao be used in optical communications
`networks to route or switch optical signals, e.g., optical cross
`connect, e tc. Each mirror in the array is supported over a
`group of e lectrodes in such a way tbat the mirrors are free
`to move, e.g., rotate about ao axis, etc., when actuated, such
`as by applying a vollage across a mirror and one or more of
`the underlying electrodes. By varying the amount that a
`mirror tilts, or the direction in which it tilts, or both, an
`optical signal that is incident on the mirror can be directed
`to a desired location, such as a particular optical fiber.
`Some newer mirror arrays have mirrors that are rotatable
`about two perpendicular axes of rotation, e.g., as is
`descnbed in U.S. Pat. No. 6,201,631, which is incorporated
`by reference herein.
`It is desirable to provide a bigh density of optical transfer
`for communications applications. In particular, in some 30
`applications, e.g., de-muJtiplexing, etc., the mirrors must be
`very tigbtly spaced (about 1 to 2 microns) to enable fla t pass
`bands with high spectral efficiency. Gimbaled mirrors, as
`exemplified by those described in U.S. Pat. No. 6,201,631,
`are not suitable for such applications because the gimbals
`present a limitation as to bow close adjacent mirrors can be
`to one another. In particular, there must be a gap between
`adjacent mirrors that is at least twice the width of a gimbal.
`ln fact, the minimum gap is somewhat larger than this, since
`the minimum gap must also lake into account the gap
`between the mirror and the gimbal and the gap between the
`gimbal and the support. Furthermore, some minimum sepa(cid:173)
`ration distance must be provided between adjacent gimbals
`to maintain the integrity of the substrate layer to which the
`gimbals are auached.
`It is possible to fabricate gimbaled mirro rs that are
`somewhat smaller than the exemplary structure disclosed io
`the '631 patent. Nevertheless, with the structure of prior-art
`gimbaled mirrors, it is not currently possible to achieve a
`mirror spacing of less than about 15 to 20 microns between so
`prior-art gim baled mirrors. Consequently, prior-art giro(cid:173)
`baled-mirror arrays are not suitable for use in applications
`that require very close perimeter-to-perimeter spacing, e.g.,
`about 15 microns or les.s between adjacent mirrors in a
`mirror array.
`
`45
`
`FIG. 1 depicts a rotatable clement having a cradle aod a
`plate, io accordance with tbc principles of invention.
`FIG. 2 depicts a torsional support that rotatably couples
`rotatable elements to other rotatable or non-rotatable ele(cid:173)
`ments.
`FIG. 3 depicts a cross-sectional view of the rotatable
`element of FIG. 1 along the line A- A and in the direction
`indicated, but with the cradle partially rotated.
`FIG. 4 depicts a cross sectional view of the rotatable
`element of FIG. l along the line B-B and in the direction
`55 indicated, but with the plate partially rotated.
`FIG . 5 depicts an array of rotatable elements in accor(cid:173)
`dance with the principles of the invention.
`FIG. 6 depicts a de-multiplexer in accordance with the
`60 principles of the iovcotioo.
`FIG. 7 depicLS ao illustrative optical energy distribution of
`a spatially resolved WDM signal as a f11nction of position at
`the front focal plane of a collimating/focusing lens where ao
`array of rotatable mirrors is positioned.
`FIG. 8 depicts a method for making a rotatable element or
`an array of rotatable e lements in accordance with the prin(cid:173)
`ciples of the invention.
`0008
`
`SUMMARY OF Tiffi INVENTION
`
`An array of rotatable elements, e.g., mirrors, etc., that
`avoids some of drawbacks of the prior art is disclosed. In
`particular, although the rotatable elements in the array are
`movable about two axes of rotation that have different
`orientations, e.g., are perpendicular to one another, etc., they
`are nevertheless capable of being positioned very closely to
`ooe another.
`'This is achieved, in accordance with the princ iples of the
`invention, by a rotatable element that includes a plate, a plate
`
`65
`
`

`

`3
`DETAlLEO DESCRIPTION
`
`US 6,984,917 B2
`
`'The terms listed below are given the following definitions
`for the purposes of this specification.
`"Coupled" means that (coupled) elements interact with 5
`one another, e.g., by a direct physical connection, by an
`indirect mecbanicalliokage, through electrostatic, magnetic
`or optical interaction, etc. The coupled elements can, but do
`not have to be, physically attached to one another. For
`example, in some instances, two coupled elements will be 10
`indirectly linked, such as through a third element, e tc. When
`two elements that are indirectly linked are referred to as
`'·coupled," it means that movement of one of the coupled
`elements in1lucnces, e.g., imparts motion to, etc., the other
`coupled clement. This ability to io1lucncc is not necessarily JS
`reciprocal as between the two coupled clements.
`·'S tress" means tensile stress or compressive stress.
`"Torsional" refers to a twisting motion (of a connector,
`etc.) such as results [rom two opposing turning forces acting
`at right angles to the rotational axis (of the connector, etc.). 20
`"Cradle," which is used as a noun, refers to a movable
`support element that supports (cradles) an element, e.g., a
`plate, etc., that is free to move. Furthermore, the cradled
`element is free to move independently of the cradle. The
`cradle itself is movably supported by another element, e.g., 25
`a substrate, etc. Movement of the cradle causes the cradled
`element to move. That is, the orie ntation in space of the
`cradled element changes as the cradle moves. The term
`·'cradle," as used herein, is not intended to imply any
`particular structure and none is to be inferred.
`''Frame," which is used as a noun, refers to a stationary
`support element that supports an element that is free to
`move. The frame can be, for example, a substrate layer that
`surrounds the mechanical (movable) elements.
`"Optical Functionality" o r "Optical Function" means an 35
`ability of affecting ao optical signal in some predictable way.
`Example of optical fuoctiooali ties include, without limita(cid:173)
`tion, the ability to reflect, diffract, filter, modulate, polarize,
`focus, or collimate an optical signal. In other words, an
`element that is characterized by such functionality is capable 40
`of functioning as a (ixed-rel~ectivity mjrror, a diffraction
`g rating, an optical fi ller, an optical modulator, a polarizer or
`a lens, respectively. An additional optical functionality is the
`ability to function as a wavcleogth-selectivc switch. In some
`variations, an element will intrinsically possess an optical 45
`functionality, e.g., due to its composition, etc. In some other
`variations, an element can be modified or proces.<;ed in some
`way, such as by depositing a rellective material, or by
`depositing layers of material have particular refractive indi(cid:173)
`ces, or by depositing and palleming layers to create an 50
`optical device (a modulator), etc., so thai it is capable of
`performing an optical function.
`
`LA. S tructure of a Rotatable Element in Accordance with the
`Principles of the Invention
`FIG. 1 depicts rotatable element 300. Rotatable element
`300 includes plate 302, cradle 304, plate support 306 and
`cradle support 310, inter-related as shown. Rotatable ele(cid:173)
`ment 300 is coupled to stationary frame 312. More particu(cid:173)
`larly, cradle support 310 couples cradle 304 to frame 312. 60
`Plate 302 is advantageously, but not necessarily, capable of
`performing an optical function.
`For the illustrative embodiment, portion 303 of plate 302,
`i.e., the portion of the plate thai is ·'above" axis 3-3 in FIG.
`1, bas a reflective surface such that it functions as a
`fixed-reflectivity mirror. It is will be understood, however,
`that in some variations of the illustrative embodiment, plate
`
`4
`302 bas a different optical functionality, such as one or more
`of the other functionalities listed above. Those skilled in the
`art will know bow to use standard techniques to modify plate
`302, e.g., via metallization, via thin-film optics techniques,
`via lithography, etc., so it provides an optical function.
`Plate 302 is rotatably coupled to cradle 304 via plate
`support306. That is, plate support 306 enables plate 302 to
`rotate about rotational axis 3- 3 when the plate i'i sujtably
`actuated. In similar fashion, cradle 304 is rolatably coupled
`to frame 312 via cradle support 310. The cradle support
`enables cradle 304 to rotate about rotational axis 4-4 when
`the cradle is suitably actuated. As depicted io FIG. 1 ,
`rotational axis 3-3 is aligned with plate support 306 and
`rotational axis 4-4 is aligned with cradle support 310.
`Furthermore, rotational axis 3-3 is perpendicular to rota(cid:173)
`tional axis 4-4.
`In the illustrative embodiment, plate support 306 and
`cradle support 310 are each implemented as paired torsional
`members 308, individually identified as torsional members
`308A aod 308B (for plate support 306) aod torsional mem(cid:173)
`bers 308C and 308D (for cradle support310). Members 308
`arc referred to as "torsional" members because they twist to
`enable an auached element, e.g., plate 302, cradle 304, etc.,
`to rotate (see, Definitions, above).
`With continuing reference to the illustrative embodiment
`depicted in FIG. 1, one end of each of the paired torsional
`members depends from opposed regions, e.g., sides, por(cid:173)
`tions, etc., of an element that moves, e.g., plate 302, etc. The
`other end of each of the paired torsional members depends
`30 from opposed regions of ao element that functio ns as a
`support for the movable element.
`Thus, io the illustrative embodiment, one cod of each of
`torsional members 308A and 308B depend from respective
`opposed sides 314 and 316 of plate 302, i.e., the elemeotthat
`moves. The other end of torsional members 308A and 308B
`depend from opposed portions of cradle 304, i.e., the ele-
`ment that supports plate 302. Likewise, one cod of each of
`torsional members 308C and 3080 depends from opposed
`portions 318 and 320 of crad le 304, i.e., an element that
`moves, while the other eod depends from opposed portions
`of frame 312, i.e., the element that supports cradle 304.
`As depicted in FIG. 1, torsional members 308A and 308B
`are substantially recessed within plate 302 and torsional
`members 308C and 3080 are substantially recessed within
`cradle 304. Recessing torsional members 308 in this fashion
`decreases what would otherwise be a larger gap between the
`rotatable element, e.g., plate 302, etc., and the structure to
`which it's coupled, e.g., cradle 304, etc.
`FIG. 2 provides further detail of torsional members 308.
`As depicted in FIG. 2, torsional member 308 includes
`connector 422 and cross-piece 428, which are joined io a
`"T ' configuration. Connector 422 couples two elements: (1)
`an elemem that moves and (2) its support structure. For
`example, with regard to torsional members 308A and 308B,
`ss connector 422 couples plate 302 to cradle 304. As to
`torsional members 308C and 3080, connector 422 couples
`cradle 304 to frame 312. The axis of rotation (of the clement
`that moves) is aligned with the paired torsional members
`308 that couple the element to its support structure.
`In tbciUustrative embodiment depicted in FIG. 2, e nd 424
`of connector 422 is allacbed to the support structure, e.g.,
`cradle 304, etc., while the other end, cod 426, couples to the
`element that moves via cross-piece 428. Cross-piece 428
`functions as a "shock absorber" for connector 422. In
`65 particular, cross-piece 428 is capable of lle>..'ing, as neces(cid:173)
`sary, to absorb any stresses on connector 422, as commonly
`arise during fabrication procedures. Connector 422 and
`0009
`
`

`

`5
`cros.s-piecc 428 each include widened region 430 ncar points
`of allachment. This widened region decreases stress con(cid:173)
`centration at the points of attachment.
`It wiU be understood that other types, e.g., configurations,
`of torsional members, as are known in the art, can be used. 5
`Furthermore, other types of members, i.e., non-torsional
`members, that arc suitable for rotatably coupling two cle(cid:173)
`ments can suitably be used as well.
`FIGS. 3 and 4 depict cross-sectional views of rotatable
`element 300 depicted in FIG. l . FIG. 3 is cross section along
`the line A-A, viewed in the direction shown, and FIG. 4 is
`a cross section along the line B-B, viewed io the direction
`shown. As depicted in those Figures, plate 302 and cradle
`304 arc suspended over cavity 532 so thai they are free to
`rotate. Electrodes 534A, 534B, 534C, and 534D are dis- JS
`posed in cavity 532. More particularly, electrodes 534A and
`534B underlie plate 302, witb one electrode on each side of
`axis-of-rotation 3-3. Electrodes 534C and 534D underlie a
`portion of cradle 304, with one electrode on each side of
`axis-of-rotation 4-4.
`Wben an electrical potential is applied across an element
`that moves, e.g., plate 302, etc., and one of the underlying
`electrodes, the element rotates out-of-plane, i.e., out of the
`plane defined by the support structure, about its axis of
`rotation toward the electrified electrode.
`For example, with reference to FIG. 3 (which shows a
`portion of cradle 304), assume that an electric potential is
`applied across cradle 304 and electrode 53 4D. As a conse(cid:173)
`quence, cradle 304 rotates out-of-plane of frame 312 about
`axis 4-4 such that the portion of cradle 304 that overlies
`electrode 534D moves downward toward that electrode (see
`FIG. 3). Since plate 302 is coupled to cradle 304, plate 302
`also rotates about axis 4-4, i.e., the cradle's axis of
`rotation, allhough, for clarity, rotation of plate 302 is not
`depicted in FIG. 3.
`Referring to FIG. 4 (which shows portions of both cradle
`304 and plate 302), assume that a potential is applied across
`plate 302 and electrode 5348. In response, the portion of
`plate 302 that overlies electrode 534B is drawn toward that
`electrode, rotating out-of-plane of cradle 304 about axis
`3- 3. Since [>late 302 rotates (about axis 4-4) when cradle
`304 rotates, plate 302 is capable of rotating about two
`perpendicular axes: axis 3-3 and axis 4-4.
`It is understood that for rotatable clement 300 to move as
`bas been described, electrodes 534, plate 302, and cradle 304
`must be electrically coupled to a controlled voltage source.
`The controlled voltage source and tbe various electrical
`connections are not depicted in the Figures for the sake of
`clarity and to aid in focusing tbe reader on elements that are
`germane to an understanding of the principles of the inven- so
`lion.
`It is notable that in prior-art gimbaled mirrors, the gimbal
`completely surrounds tbe mirror. In contrast, in rotatable
`element 300, cradle 304 does not completely surround plate
`302. To fact, if region 303 (see FIG. 1) of plate 302 is ss
`considered to be the ''mirror," then cradle 304 does not
`surround any part of the '·mirror." Stated differently, in
`rotatable element 300, tbe segment of rotational axis 3- 3
`that is defined by the location of torsional members 308A
`and 308B does not overlap o r intersect the segment of 60
`rotational axis 4-4 that is defined by the location of
`torsional members 308C and 3080. This is in contrast to tbe
`corresponding "segments" of the two rotational axes of the
`prior-art gimbaled mirrors, wherein the segments do over(cid:173)
`lap, i.e., in the center of the mirror.
`'The difference in structure between prior-art gimbaled
`mirrors and rotatable element 300 can be described in yet
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`US 6,984,917 B2
`
`6
`another way. In particular, in prior-art gimbalcd mirrors, the
`center of mass of all the electrodes for a given gimbaled
`mirror aligns with tbe center of mass of the mirror. In
`rotatable element 300, however, the center of mass of all the
`electrodes for a given rotatable element does not align with
`the ceoter of mass of plate 302.
`As described later in this specification, these differences
`in structure enable rotatable clement 300 to be used in a
`variety of applications, notably optical communications, for
`10 which the prior-art gimbaled mirrors are unsuitable.
`
`EXAMPLE
`
`An illustrative design for rotatable element 300 in accor(cid:173)
`dance with the principles of tbe invention is presented in this
`Example.
`Tables I and II, below, provide performance parameters
`for rotatable clement 300. Tbe parameters are given as a
`function of:
`(1) Length, L, of connector 422 of torsional members 308
`(sec, FIG. 2).
`(2) Width, W, of connector 422 of torsional members 308
`(see, FIG. 2).
`(3) Gap, T 0 , between plate 302 (or cradle 304) and the
`underlying electrodes, see, e.g., FIG. 3.
`
`The dimensions of rotatable element 300 (see, FIGS. 1 and
`2) are as follows:
`
`length, I"' of plate 302:
`width, w , of plate 302:
`width, "~" of cradle 304:
`width, w' <> of cradle 304:
`
`length, 1'., of cradle 304:
`
`length. I" of cradle 304:
`gap, g,.,:
`
`gap, Scr'
`
`thickness of plate 302:
`thickness of cmdle 304:
`length of cross piece 428:
`length of widened region
`430:
`width of widened region
`430:
`
`150 microns
`19 n1ierons.
`140 microns (at widest point)
`79 microns (rectangular portion abo,•e
`electrodes)
`150 microns (rectangular portion above
`electrodes)
`331 microns (length of full cradle 304)
`3 microns (gap between plate 302
`and crad le 304)
`3 microns (gap between cradle 304
`and frame 31 2)
`
`l micron
`J micron
`6 microns
`J micron
`
`1 micron
`
`The angle of rotation, <Jl, of cradle 304 (see, FIG. 3) is
`limited by certain dimensions of rotatable mirror 300. This
`limitation results from one of two different constraints. One
`cons traint on rotation is that continued rotation of cradle 304
`will result in the cradle making contact with underlying
`electrode 534. The angle of rotation at contact, tl>rouch• is
`dependent upon tbc width, w'c• of cradle 304 (i.e., the width
`of the portion of the cradle that is above the electrodes) and
`the gap, T0
`, between the cradle and an underlying electrode.
`With a width, w 'c, of 79/2=39.5 microns, and a gap, T0 , of
`lO microns, <j>,.,,ch=8.2 degrees. This is one limitation on
`angle of rotation, <j>, of cradle 304.
`The second constraint on rotation arises due to the use of
`au electrostatic force (in tbe illustrative embodiment) as the
`actuating force. In particular, due to tbe nature of electro(cid:173)
`statics, an instability occurs when the displacement of an
`element equals or exceeds 1/3 of the gap between the
`65 attracting elements. This instability causes the movable
`element to "snap-down" and contact the fixed element.
`Consequently, the displacement of the edge of cradle 304,
`0010
`
`

`

`US 6,984,917 B2
`
`7
`for example, in a "vertical'" direction (as it rotates) is
`res tricted to a distance that is less than ~ of the distance
`between cradle 304 and underlying electrode 534 (see, FIG.
`3). In other words:
`
`8
`contact and the critical angle), but so do the voltage require(cid:173)
`ments. Re latively small ro tations (i.e., a few degrees) are all
`that is required for many applications of rotatable clement
`300.
`
`(4) 5 LB. Structure of an Array of Rotatable Elements In Accor(cid:173)
`dance With the Principles of the Invention
`This distance defines critical angle of rotation, cpc, of
`FIG. 5 depicts an array 700 of rotatable elements 300.
`cradle 304. The cradle cannot be rotated beyond this point.
`Each rotatable clement 300 in the array includes plate 302
`This behavior is well known to those skilled in the art. For
`and cradle 304, as previously described, sec, e.g., FIG. l and
`the configuration and dimensions provided above, the criti(cid:173)
`10 the accompanying description.
`cal angle of rotation for cradle 304, cl>c• is 12.6 degrees.
`Rotatable clements 300 are surrounded by frame 312 and
`For the Example, the critical angle of rotation, cl>c• is
`arc suspended over cavity 532, sec, e.g., FIGS. 3 and 4. Pairs
`greater than the angle of rotation at contact, cp((, .. c,.: 12.6>8.2.
`of electrodes 534 (not depicted in FIG. 5) underlie plate 302
`Consequently, rotation of cradle 304 is limited by contact
`and a portion of cradle 304. Each rotatable element 300
`(not instability) to 8.2 degrees.
`IS within array 700 is individually addressable. Furthermore,
`l ne same considerations apply to plate 302. For plate 302,
`plate 302 and cradle 304 of each rotatable clement 300 can
`the angle o f rotation at contact, O,ouc~t• is 7.7 degrees. T he
`be individually actuated. In other words, plate 302 can be
`critica l angle or rotation, 0,., L<; 9.2 degrees. Like cradle 304,
`made to rotate about either one axis, i.e., ooe of either the
`the rotation of platc302 is l imited by contact, which, for this
`rotational axis or plate 302 or the rotational axis of cradle
`example, is 7.7 degrees.
`20 304, or about two axes.
`Since cradle 304 docs not completely surround plate 302
`(in contrast to the manner in which the gimbal surrounds the
`mirror in prior-art gimbalcd mirrors), plates 302 of adjacent
`rotatable clements 300 in array 700 can be placed in near(cid:173)
`abutting relation. More particularly, in some embodiments,
`adjacent plates 302 are placed within 15 microns of ooe
`another. In some other embodiments, adjacent plates 302 are
`placed within 10 microns of one another. In some additional
`embodiments, adjacent plates 302 are placed within 5
`microns of one another. In some other embodiments, adja(cid:173)
`cent plates 3 02 arc advantageously placed as close as about
`l micron from one another. The spacing between adjacent
`plates 302 will, in some instances. be dictated by application
`specifics.
`Array 700 of rotatable elements 300 has a variety of uses,
`35 many of which pertain to optical telecommunications. One
`such usc is described below.
`
`TABLE I
`
`Perfom1nnce of Rol:ltable Element for T 0 = 10 microns
`
`To
`<,ttm>
`
`Connector
`Width <,ttn1>
`
`Connector
`length <,ttm>
`
`v+a-Uical
`<VOlts>
`
`yeaili«l
`<'"OilS>
`
`25
`
`10
`10
`10
`10
`
`0.30
`0.35
`0.35
`0.40
`
`8
`10
`12
`12
`
`ll2
`125
`1H
`135
`
`124
`138
`126
`149
`
`30
`
`Table I shows the voltage requirement at the critical angle
`of rotation for both cradle 304, which is ~crir;coJ• and for
`plate 302, which is VO cnticoJ· The voltage that is required to
`obtain the maximum (for this illustration) cradle rotation of
`8.2 degrees and the maximum (for this illustration) plate
`rotation of 7.7 degrees will be less than the critical voltages
`shown. (Again, this is because, in the Example, the maxi(cid:173)
`I.C. Dcmuliiplcxcr Incorporating an Array of Rotatable
`mum angle of rotat ion for both plate 302 and cradle 304 is
`Mirrors
`less than the critical angle of rotation.)
`The transmission capacity of optical networks is signifi (cid:173)
`Table II, below, provides the same type of information as 40
`cantly increased using wavelength d ivision multiplexing
`Table I, bu t for a configuration wherein the gap, T.,, between
`('"WDM"). In a WDM communications network, many
`plate 302 or cradle 304 and e lectrodes 534 is increased to 12
`optical signals arc superimposed on a single optical fiber.
`microns. For this illustration, <l>,.,,c,, =9.9 degrees, <1> =15.2
`Each signal has a dilrcrent wavelength, which defines a
`degrees and 0 t<>ucl" is 9.2 degrees and Oc=ll.l degr;es. As
`WI)M "channel."
`before, the voltage that is required to obtain the maximum 45
`Typically, the channels in a WDM commu11ications sys(cid:173)
`(for this illustration) cradle rotation of 9.9 degrees and the
`tem arc routed selectively along different paths as a function
`maximum (for this illustration) plate rotation of 9.2 degrees
`of wavelength ("wavelength routing"). To accomplish this,
`will be less than the critical voltages shown.
`optical network nodes, which provide switching and routing
`TABLE n
`functions in an optical network, must be capable of "recog-
`50
`- - - - - - - - - - - - - - - - - - - - - nizing" each channe l independent o f other channels.
`One device that is capable of providing this .. recognition"
`Perform.1nc:e of Rotatable Eten1ent forT. • 12 microns
`to perform wavelength routing is a de-multiplexer. The
`de-mulliplcxcr spatially resolves the plural WDM channels
`and delivers each channel o r spectral component to a desired
`output fiber.
`In accordance with the principles of the invention, an
`array of rotatable e lements, as has been descnbed herein, is
`optically coupled to lenses, a diffraction grating and an input
`and output ports to provide a de-multiplexing capability.
`60 FIG. 6 depicts illustrative de-multiplexer 800, which is
`based on a de-multiplexer that is described in U.S. patent
`application Scr. No. 09/944,800, which is incorpora1ed by
`reference herein.
`As depicted in fiG. 6, de-multiplexer 800 includes array
`700 of rotatable clements 300-i, i=l,m, array 836 of input/
`outpul ports 838-j, j= I, n, array 840 of collimating/focusing
`lenses 842-k, k= I, p, diffraction grating 844, and collimat-
`0011
`
`ro
`<,ttm>
`
`12
`12
`12
`12
`
`Con