0001
`
`Capella 2013
`Cisco v. Capella
`IPR2014-00894
`
`

`
`U.S. Patent
`
`Jan. 10,2006
`
`Sheet 1 of6
`
`US 6,984,917 B2
`
`FIG.
`
`1
`
`_.________.
`J__J
`|——.——a-4-.—
`
`0002
`0002
`
`

`
`U.S. Patent
`
`Jan. 10,2006
`
`Sl1cct20f6
`
`US 6,984,917 B2
`
`FIG. 2
`
`PORTION or
`
`W \
`
`—’||‘—
`
`303 ('3 ROTATABLE
`
`SUPPORT
`
`0003
`0003
`
`

`
`U.S. Patent
`
`Jan. 10,2006
`
`Sl1cct3 0f6
`
`US 6,984,917 B2
`
`..........4§ $3anE.3...3am
`
`8....
`
`anan
`
`m.Q.E~
`
`an65%
`
`0004
`0004
`
`
`

`
`U.S. Patent
`
`Jan. 10,2006
`
`Sheet 4 of6
`
`US 6,984,917 B2
`
`FIG. 5
`
`0005
`0005
`
`

`
`U.S. Patent
`
`Jan. 10,2006
`
`Sheet 5 of6
`
`US 6,984,917 B2
`
`FIG.6
`
`0006
`0006
`
`

`
`U.S. Patent
`
`Jan
`
`. 10, 2006
`
`Sheet 6 of 6
`
`US 6,984,917 B2
`
`FIG. 7
`
`950
`
`3
`
`OO-i
`
`1 OOO
`‘T
`
`FIG. 8
`
`ROTATABLY COUPLING A PLATE TO A
`CRADLE IN A FIRST SUBSTRATE
`
`ROTATABLY COUPLING THE CRADLE
`
`TO THE FIRST SUBSTRATE
`
`1002
`
`1004
`
`FORMING AT LEAST TWO ELECTRODES
`
`AT A FIRST REGION IN A SECOND
`
`IOOB
`
`SUBSTRATE
`
`FORMING AT LEAST TWO ELECTRODES
`
`AT A SECOND REGION IN THE
`
`1008
`
`SECOND SUBSTRATE
`
`ALIGNING THE FIRST SUBSTRATE
`
`WITH THE SECOND SUBSTRATE
`
`ATTACHING THE FIRST SUBSTRATE TO
`
`THE SECOND SUBSTRATE
`
`10lO
`
`1OI2
`
`0007
`0007
`
`

`
`US 6,984,917 B2
`
`1
`()P'I‘ICAL IELEMENT HAVING TWO AXES
`OF ROTATION FOR USE IN TIGHTLY
`SPACED MIRROR ARRAYS
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to micro—electro—
`mechanical systems. More particularly, the present inven-
`tion relates to an optical element that is movable about two
`perpendicular axes.
`
`BACKGROUND OF THE INVENTION
`
`‘Jl
`
`IU
`
`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 of the cradle.
`
`Electrodes are disposed in the cavity beneath each rotat-
`able element. In one embodiment, two electrodes are dis-
`posed in the cavity under the rotatably-coupled portion of
`the cradle, on opposite sides of its axis of rotation. Similarly,
`two electrodes are disposed in the cavity beneath the plate,
`on opposite sides of its axis of rotation.
`When an electrical potential is applied across the plate
`and one of its underlying electrodes, the plate rotates out-
`of-plane, i.e., out of the plane defined by the cradle, which
`is the plate in which the plate lies when it is in its quiescent
`or unactu ated position, about its axis of rotation toward the
`electrified electrode. This provides one axis of rotation for
`the plate. When an electrical potential is applied across the
`cradle and one of its underlying electrodes, the cradle rotates
`out-of-plane, i.e., of the substrate or frame, about its axis 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 an
`optical function. For cxatnple, in some embodiments, the
`plate functions as a mirror. Unlike prior-art gimbaled mir-
`rors, in which the gimbal completely surrounds the mirror,
`in a rotatable element in accordance with the principles of
`the invention, the cradle does not completely surround or
`encircle the plate, e.g., mirror. Consequently, adjacent mir-
`rors in an may of rotatable elements can, advantageously, be
`very closely spaced. This makes them suitable for use in
`some optical applications in which the prior-art gimbaled
`mirrors cannot be used.
`
`BRIEF DL-L-3CRIl’I'I()N 017 THE DRAWINGS
`
`FIG. 1 depicts a rotatable element having a cradle and a
`plate, in accordance with the principles of invention.
`FIG. 2 depicts a torsional support that rotatably couples
`rotatable elements to other rotatable or non-rotatable ele-
`merits.
`
`An array of individually—addressable, movable, micro-
`machined mirrors can be used in optical communications
`networks to route or switch optical signals, e.g., optical cross
`connect, etc. Each mirror in the array is supported over a
`group of electrodes in such a way that the mirrors are free
`to move, e.g., rotate about an axis, etc., when actuated, such
`as by applying a voltage 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
`described in U.S. Pat. No. 6,?.[ll,63l, which is incorporated
`by reference herein.
`It is desirable to provide a high density of optical transfer
`for communications applications.
`In particular,
`in some
`applications, e.g., de-multiplexing, etc., the mirrors must be
`very tightly spaced {about 1 to 2 microns) to enable flat pass
`bands with high spectral eiiiciency. Gimbaled mirrors, as
`exemplified by those described in US. Pat. No. 6,201,631,
`are not suitable for such applications because the gimbals _
`present a limitation as to how 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.
`In fact, the minimum gap is somewhat larger than this, since
`the minimum gap must also take into account
`the gap
`between the mirror and the gimbal and the gap between the
`gimbal and the support. Furthermore, some minimum sepa-
`ration distance must be provided between adjacent gimbals
`to maintain the integrity of the substrate layer to which the
`gimbals are attached.
`It
`is possible to fabricate gimbaled mirrors that are
`somewhat smaller than the exemplary structure disclosed in
`the ’63l patent. Nevertheless, with the structure of prior-art
`gimbalcd mirrors, it is not currently possible to achieve a
`mirror spacing of less than about 15 to 20 microns between
`prior-art girnhaled mirrors. Consequently, prior-art gim-
`baled-mirror arrays are not suitable for use in applications
`that require very close perimeter-to-perimeter spacing, e.g.,
`about 15 microns or less between adjacent mirrors in a
`mirror array.
`
`20
`
`3U
`
`40
`
`45
`
`50
`
`55
`
`SUMMARY OF THE INVENTION
`
`that
`An array of rotatable elements, e.g., mirrors, etc.,
`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
`one another.
`
`This is achieved, in accordance with the principles of the
`invention, by a rotatable element that includes a plate, a plate
`
`(10
`
`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. 1 along the line B—B and in the direction
`indicated, but with the plate partially rotated.
`FIG. 5 depicts an array of rotatable elements in accor-
`dance with the principles of the invention.
`l'iI(i. 6 depicts a de-multiplexer in accordance with the
`principles of the invention.
`FIG. '7 depicts an illustrative optical energy distribution of
`a spatially resolved WDM signal as a function of position at
`the front focal plane of a collimatingffocusing lens where an
`array of rotatable mirrors is positioned.
`FIG. 8 depicts a method for making a rotatable element or
`an array of rotatable elements in accordance with the prin-
`ciples of the invention.
`0008
`0008
`
`

`
`3
`DETAILED DESCRIPTION
`
`US 6,984,917 B2
`
`4
`
`The terms listed below are given the following definitions
`for the purposes of this specification.
`“(?oupled" means that (coupled) elements interact with
`one another, e.g., by a direct physical connection, by an
`indirect mechanical linkage, 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
`indirectly linked, such as through a third element, etc. When
`two elements that are indirectly linked are referred to as
`“coupled," it means that movement of one of the coupled
`elements influences, e.g., imparts motion to, etc., the other
`coupled element. This ability to influence is not necessarily
`reciprocal as between the two coupled elements.
`“Stress" means tensile stress or compressive stress.
`“Torsional" refers to a twisting motion {of a connector,
`etc.) such as results from two opposing turning forces acting
`at right angles to the rotational axis (of the connector, etc.).
`“(Tradle," which is used as H. 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.,
`a substrate, etc. Movement of the cradle causes the cradled
`element to move. That is, the orientation 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” or “Optical Function" means an *
`ability of alfecting an optical signal in some predictable way.
`Example of optical functionalities include, without limita-
`tion. the ability to reflect. diflract, filter, modulate, polarize,
`focus, or collimate an optical signal.
`In other words, an
`element that is characterized by such functionality is capable
`of functioning as a lixed-rellectivity mirror. a diffraction
`grating, an optical filter, an optical modulator, a polariner or
`a lens, respectively. An additional optical functionality is the
`ability to function as a wavelength-selective switch. In some
`variations, an element will intrinsically possess an optical
`functionality, e.g., due to its composition, etc. In some other
`variations, an element can be modified or processed in some
`way, such as by depositing a rellective material, or by
`depositing layers of material have particular refractive indi-
`ces, or by depositing and patterning layers to create an
`optical device (a modulator), etc., so that
`it
`is capable of
`performing an optical function.
`I.A. Structure of a Rotatable Element in Accordance with the
`
`Principles of the Invention
`FIG. 1 depicts rotatable element 300. Rotatablc element
`300 includes plate 302, cradle 304, plate support 306 and
`cradle support 310, inter-related as shown. Rotatable ele-
`ment 300 is coupled to stationary frame 312. More particu-
`larly, cradle support 310 couples cradle 304 to frame 312.
`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 that is "above” axis 3—3 in FIG.
`1, has a reflective surface such that
`it
`functions as a
`fixed-refiectivity mirror. It is will be understood, however,
`that in some variations of the illustrative embodiment, plate
`
`particular, cross—piece 428 is capable of flexing, as neces-
`sary, to absorb any stresses on connector 422, as commonly
`arise during fabrication procedures. Connector 422 and
`0009
`0009
`
`‘Jl
`
`IU
`
`1U
`
`3U
`
`40
`
`4-5
`
`50
`
`55
`
`(10
`
`302 has a different optical functionality, such as one or more
`of the other functionalities listed above. Those skilled in the
`
`art will know how 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
`support 306. That is, plate support 306 enables plate 302 to
`rotate about rotational axis 3-3 when the plate is suitably
`actuated. In similar fashion, cradle 304 is rotatably coupled
`to frame 312 via cradle support 310. The cradle support
`enables cradle 304 to rotate about rotational axis 4—4 when
`
`I.
`the cradle is suitably actuated. As depicted in FIG.
`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-
`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
`308/\ and 3080 {for plate support 306) and torsional mem-
`bers 308C and 308D (for cradle support 310). Members 308
`are referred to as “torsional" members because they twist to
`enable an attached 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-
`tions, etc., of an element that moves, e.g., plate 302, etc. The
`other end of each of the paired torsional members depends
`from opposed regions of an element
`that functions as a
`support for the movable element.
`Thus, in the illustrative embodiment, one end of each of
`torsional members 308/-\ and 308]} depend from respective
`opposed sides 314 and 316 of plate 302. i.e., the element that
`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 end of each of
`torsional members 308(.‘ and 308D depends from opposed
`portions 318 and 320 of cradle 304-, i.e., an element that
`moves, while the other end 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 308D 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 in a
`“T” configuration. Connector 422 couples two elements: (1)
`an element that moves and (2) its support structure. For
`example, with regard to torsional members 308A and 308B,
`connector 422 couples plate 302 to cradle 304. As to
`torsional members 308C and 308D, connector 422 couples
`cradle 304 to frame 312. The axis of rotation (ofthe element
`that moves) is aligned with the paired torsional members
`308 that couple the element to its support structure.
`In the illustrative embodiment depicted in FIG. 2, end 424
`of connector 422 is attached to the support structure. eg.
`cradle 304, etc., while the other end. end 426, couples to the
`element that moves via crossvpiece 428. Cross—piece 428
`functions as a “shock absorber" for connector 422.
`In
`
`

`
`US 6,984,917 B2
`
`5
`
`cross—piece 428 each include widened region 430 near points
`of attachment. This widened region decreases stress con-
`centration at the points of attachment.
`It will he understood that other types, e.g., configurations,
`of torsional members, as are known in the art, can be used.
`l?‘urthem1ore, other types of members,
`i.e., non-torsional
`members, that are suitable for rotatably coupling two ele-
`ments can suitably be used as well.
`FIGS. 3 and 4 depict cross—sectional views of rotatable
`element 300 depicted in FIG. 1. 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-3, viewed in the direction
`shown. As depicted in those Figures, plate 302 and cradle
`304 are suspended over cavity 532 so that they are free to
`rotate. Electrodes 534A, 534B, 534C‘, and 534D are dis-
`posed in cavity 532. More particuiarly, electrodes 534A and
`53413 underlie plate 302. with 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.
`When 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 534D. As a conse-
`quence, cradle 304 rotates outcf-plane of frame 312 about
`axis 4—4 such that the portion of cradle 304 that overlies
`electrode 534-I) 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. although, 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 534-B is drawn toward that
`electrode, rotating out-of-plane of cradle 304 about axis
`3—3. Since plate 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 element 300 to move as
`has been described, electrodes 534, plate 302, and cradle 304
`must be electrically coupled to a controlled voltage source.
`The controlled voltage source and the various electrical
`connections are not depicted in the Figures For the sake of
`clarity and to aid in focusing the reader on elements that are
`germane to an understanding of the principles of the inven-
`tion.
`It is notable that in prior-art gimbaled mirrors, the gimbal
`completely surrounds the mirror. In contrast,
`in rotatable
`element 300, cradle 304 does not completely surround plate
`302.
`In fact,
`if region 303 (see FIG. 1) of plate 302 is
`considered to be the “mirror," then cradle 304 does not
`surround any part of the "mirror.” Stated dilferently,
`in
`rotatable element 300, the segment of rotational axis 3-3
`that is delined by the location of torsional members 308A
`and 308B does not overlap or intersect
`the segment of
`rotational axis 4—4 that
`is defined by the location of
`torsional members 308C and 3081). This is in contrast to the
`corresponding “segments” of the two rotational axes of the
`prior~art gimhaled mirrors, wherein the segments do over-
`lap, ie, in the center of the mirror.
`'I'he difference in structure between prior-art gimbaled
`mirrors and rotatable element 300 can be described in yet
`
`6
`another way. In particular, in prior-art gimbaled mirrors, the
`center of mass of all the electrodes for a given gimbaled
`mirror aligns with the 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 center of mass ol’ plate 302.
`As described later in this specification, these difierences
`in structure enable rotatable element 300 to be used in a
`variety of applications, notably optical communications, [or
`which the prior-art gimbaled mirrors are unsuitable.
`
`EXAMPLE
`
`An illustrative design for rotatable element 300 in accor-
`dance with the principles of the invention is presented in this
`Example.
`Tables 1 and II, below, provide performance parameters
`for rotatable element 300. The parameters are given as a
`function of:
`
`(1) Length, l.. of connector 422 of torsional members 308
`(see, FIG. 2).
`(2) Width, W, of connector 422 of torsional members 308
`(see, FIG. 2).
`(3) Gap, Ta, 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:
`
`‘Jr
`
`I0
`
`20
`
`30
`
`length, II, of plate 303:
`width, w . of plate 302:
`width, w£’_.. of cradle 304:
`width, 1.\‘,_. of cradle 304:
`
`length, t‘,., of cradle 304:
`
`length. l_._. of cradle 304:
`gap, gm:
`
`gap. gd:
`
`40
`
`150 microns
`'.-'9 microns
`Jet-0 microns (at widest point)
`‘I9 microns (rectangular portion above
`electrodes)
`150 microns (rectangular portion above
`electrodes)
`331 microns (length of frrll cradle .304)
`3 microns (gap between plate 302
`and cradle 304)
`3- microns (gap between cradle 304
`and Erame 3-12,1
`
`thickness of plate 302:
`thickness of cradle 304:
`length of cross piece 428:
`length of widened region
`430:
`width of widened region
`430:
`
`1 micron
`1 micron
`6 microns
`1
`rttlcrurl
`
`1 micron
`
`The angle of rotation, :12, 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
`constraint on rotation is that continued rotation ofcradle 304
`
`will result in the cradle making contact with underlying
`electrode 534. The angle of rotation at contact, :1:,,,,,__.,,, is
`dependent upon the width, w’r, of cradle 304 (ie, the width
`of the portion oi‘ the cradle that is above the electrodes) and
`the gap, T0, between the cradle and an underlying electrode.
`With a width, w '6, of 79;’2=39.5 microns, and a gap, T0, of
`10 microns. q1,am_,,=8.2 degrees. This is one limitation on
`angle of rotation, 41, of cradte 304.
`The second constraint on rotation arises due to the use of
`
`45
`
`50
`
`55
`
`(10
`
`an electrostatic force (in the illustrative embodiment) as the
`actuating force. In particular, due to the nature of electro-
`statics, an instability occurs when the displacement of an
`element equals or exceeds 1/3 of the gap between the
`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
`0010
`
`

`
`US 6,984,917 B2
`
`7
`is
`rotates)
`in a “vcrtical" direction (as it
`for example,
`restricted to a distance that is less than 1.6 of the distance
`
`between cradle 304 and underlying electrode 534 (see, FIG.
`3). In other words:
`Displacc rm: nt.-el/.1 T_,
`
`[4]
`
`This distance defines critical angle of rotation, $6, of
`cradle 304-. The cradle cannot be rotated beyond this point.
`This behavior is well known to those skilled in the art. For
`the configuration and dimensions provided above, the criti-
`cal angle of rotation for cradle 304, dip, is 12.6 degrees.
`For the Example,
`the critical angle of rotation, q:,., is
`greater than the angle of rotation at contact, t1>,,,,,c,_: 12.6:-8.2.
`Consequently, rotation of cradle 304 is limited by contact
`(not instability) to 8.2 degrees.
`The same considerations apply to plate 302. For plate 302,
`the angle of rotation at contact, 0,,,m,,, is 7.7 degrees. The
`critical angle of rotation, 0,._, is 9.2 degrees. Like cradle 304,
`the rotation ofplate 302 is limited by contact, which, for this
`example, is 7.? degrees.
`
`T/\I3I..l_-I I
`Performance of Rotatable Element for 'l' = It) microns
`
`To
`-c,rm1>
`10
`10
`10
`10
`
`Connector
`Width 4,.-rm>
`0.30
`0.35
`0.35
`0.40
`
`Connector
`Length -earn:
`8
`10
`13
`12
`
`\-’‘’,.,,-,i“,
`<vo|ts>
`I12
`I35
`114
`135
`
`V“__,“1-G,
`<volts>
`134
`138
`126
`.149
`
`Table I shows the voltage requirement at the critical angle
`of rotation for both cradle 304, which is \/“",_,,.,,.,._,,,,,., and for
`plate 302, which is V“m.”.m,. 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-
`mum angle of rotation for both plate 302 and cradle 304 is
`less than the critical angle of rotation.)
`Table II, below, provides the same type of information as
`Table l, but for a configuration wherein the gap, To, between
`plate 302 or cradle 304 and electrodes 534 is increased to 12
`microns. For this illustration, ¢,,m,,, =9.9 degrees, tPC=15.2
`degrees and 0 ,,,,,c_,,, is 9.2 degrees and 0:: 11.1 degrees. As
`before, the voltage that is required to obtain the maximum
`(for this illustration) cradle rotation of 9.9 degrees and the
`maximum (for this illustration) plate rotation ot'9.2 degrees
`will be less than the critical voltages shown.
`
`TABLE II
`Perforrnrtnce of Rotatable Element for T - I2 microns
`
`To
`earn:
`l 3
`12
`J 3
`12
`
`Connector
`Width <,rrn1:-
`0.30
`0.3 5
`0.35
`0.40
`
`Connector
`Length <}ll't‘t>
`3
`
`J 2
`12
`
`\«'““,.,,,;,.,,
`<\-‘oils:
`I48
`165
`"I5 1
`I 7‘)
`
`\-'9,.,;,,-M
`<volts>
`l 64
`183
`i ll?
`198
`
`As Tables I and II and the accompanying description
`indicate, for the illustrative embodiment and illustrative
`dimensions, potential differences in the range of about [00
`volts to about 200 volts will rotate plate 302 and cradle 304-
`up to about 15 degrees. Smaller voltages result
`in less
`rotation. And, generally, as the gap, To, between plate 302 or
`cradle 304- and underlying the electrodes increases,
`the
`maximum allowable rotation increases (both the angle for
`
`8
`contact and the critical angle), but so do the voltage require-
`ments. Relatively small rotations (i.c., a few degrees) are all
`that is required for many applications of rotatable element
`300.
`
`1B. Structure of an Array of Rotatable Elements In Accor-
`dance With the Principles ol‘ the Invention
`FIG. 5 depicts an array 700 of rotatable elements 300.
`Each rotatable element 300 in the array includes plate 302
`and cradle 304, as previously described, see, e.g., FIG. 1 and
`the accompanying description.
`Rotatable elements 300 are surrounded by frame 312 and
`are suspended over cavity 532, see, eg., FIGS. 3 and 4. Pairs
`olelectrodes 534- (not depicted in FIG. 5) underlie plate 302
`and a portion of cradle 304. Each rotatable element 300
`within array 700 is individually addressable. Furthermore,
`plate 302 and cradle 304 of each rotatable element 300 can
`be individually actuated. In other words, plate 302 can be
`made to rotate about either one axis, i.e., one of either the
`rotational axis of plate 302 or the rotational axis of cradle
`304, or about two axes.
`Since cradle 304 does not completely surround plate 302
`(in contrast to the manner in which the gimbal surrounds the
`mirror in prior-an gimbaled mirrors}, plates 302 of adjacent
`rotatable elements 300 in array 700 can be placed in near-
`abutting relation. More particularly, in some embodiments,
`adjacent plates 302 are placed within 15 microns of one
`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-
`cent plates 302 are advantageously placed as close as about
`1 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,
`many of which pertain to optical telecommunications. One
`sttch use is described below.
`
`I.C. Demultiplexer Incorporating an Array of Rotatable
`Mirrors
`
`The transmission capacity of optical networks is signifi-
`cantly increased using wavelength division multiplexing
`("WDM“).
`In a WDM communications network, many
`optical signals are superimposed on a single optical fiber.
`Each signal has a dilferent wavelength, which defines a
`WDM “channel."
`
`Typically, the channels in a WDM communications sys-
`tem are routed selectively along dilferent paths as a function
`of wavelength (“wavelength routing"). To accomplish this,
`optical network nodes, which provide switching and routing
`functions in an optical network, must be capable of "recog-
`nizing" each channel independent of other channels.
`One device that is capable of providing this "recognition”
`to perform wavelength routing is a de-multiplexer. The
`de-multiplexer spatially resolves the plural WDM channels
`and delivers each channel or spectral component to a desired
`output tiber.
`In accordance with the principles of the invention, an
`array of rotatable elements, as has been described herein, is
`optically coupled to lenses, a diffraction grating and an input
`and output ports to provide a dc-multiplexing capability.
`FIG. 6 depicts illustrative de-multiplexer 800, which is
`based on a de-multiplexer that is described in U.S. patent
`application Ser. No. [t9,t’9-44,800, which is incorporated by
`reference herein.
`
`‘Jl
`
`IU
`
`EU
`
`30
`
`40
`
`45
`
`50
`
`55
`
`no
`
`As depicted in FIG. 6, de—multiplexer 800 includes array
`700 of rotatable elements 300—i, i=l,m, array 836 of input?
`output ports 838-j, j=1, n, array 840 of ctlllimatingffocusing
`lenses 84-2.-k, k=l, p, dilIraction grating 844, and collimat-
`0011
`0011
`
`

`
`US 6,984,917 B2
`
`9
`ingffocusing lens 846, inter-related as shown. For this appli-
`cation. rotatable elements 300-i are rotatable minors.
`Since array 700 provides rotatable mirrors that have two
`perpendicular rotation axes. inputtoutput port array 836 is
`advantageously, but not necessarily, configured as a two-
`dimensional array of ports 838—j. (If the mirrors in the array
`had only a single rotational axis, then the inputfoutput ports
`would have to be arranged linearly.) Since inputfoutput ports
`838-j are configured as a two-dimensional array, collimat-
`ingffocusing lenses 842-k should be configured as a two-
`dimensional array as well. For simplicity and clarity, input.’
`output port array 836 and array 840 of lenses are depicted in
`FIG. 6 as linear arrays.
`Array 836 has n, ports 838-j, including one input port
`838-1 and n—1 output ports 838-2, 838-3, .
`.
`.
`, 838-n. The
`assignment of port 838-]
`is arbitrary.
`Input port 838-1,
`which is typically a single-mode optical fiber. carries the
`multiple optical wavelengths (i.e., channels) K-1, l=1, q, of
`WDM signal ml.
`As WDM signal rn7& emerges from port 838-1, it diverges
`due to diffraction effects. Ports 338-j are disposed at the front
`focal plane of lens array 840. Inputfoutput port array 836 is
`aligned with lens array 840 so that each port 838—j is on the
`optical axis of its matching lens 842-k. One of lens 842-it in
`array 840 receives diverged WDM signal ml from port
`838-1 and collirnates it.
`
`Collimated WDM signal ml is received by diffraction
`grating 844. Ditlracting grating 344 causes wavelength-
`depcndent diffraction, which results in the spatial separation
`of the spectral components, i.e., constituent wavelengths, of
`a multi-wavelength signal such as WDM signal mix. Con-
`sequently, dilfraction grating 844 spatially resolves the indi-
`vidual channels ?t.-l, l=l, q, of signal ml as a function of
`wavelength.
`The diffraction of WDM signal ml. generates q signals or
`beams, one for each wavelength A.-1 through }t—q of the
`WIJM signal. Each of the diffracted signals propagates in a
`unique direction. For clarity, the optical path of only one of
`the channels or wavelengths (?.-3) is depicted in FIG. 8.
`The diffracted signals ?t.-l are received by collimatingt
`focusing lens 846 and focused at its front focal plane. Each
`of the signals A-1 through A-q focuses at a different location
`along the focal plane, as a function of its wavelength. Array
`700 of rotatable rnirrors 300-i, which is disposed at the front
`focal plane of lens 846, receives the signals K-1. Rotatable
`mirrors 3|]0—i are positioned so that each signal or channel
`1-1 is focused on a different rotatable mirror 300-i. Those
`skilled in the art will know how to design grating 844 and
`lens 846 to provide sufficient spatial separation of each
`signal at the front focal plane of lens 846.
`Each rotatable rnirror 300 can be tilted, responsive to a
`control signal, such that the rcflccted signal 7t.—l propagates
`in a new direction wherein the signal ultimately couples into
`a desired one of output ports 838-2 through 838-1; (if the
`mirror were not tilted, the reflected signal would couple back
`into input port 838-1).
`More particularly, the signals that are reflected from array
`700, which are diverging, are collimated by collimatingf
`focusing lens 846. The collirnated signals are diffracted oil‘
`of grating 844 toward array 840 of collintatingffocusing lens
`84-2—i, i=1,l<. Each signal is received by one of the lenses
`842-i, and is focused at the front focal plane of that lens.
`Each signal then couples into a desired one of output ports
`838-2. through 838-k.
`In some embodiments, the number, m, of rotatable mirrors
`300-i, equals the number, n—l, of output ports 838-j, equals
`the number, p, of collinaatinglfocusing lense