(12) United States Patent
`Hoen
`
`US006253001B1
`US 6,253,001 B1
`Jun. 26, 2001
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) OPTICAL SWITCHES USING DUAL AXIS
`MICROMIRRORS
`
`(75) Inventor: Storrs T. Hoen, Brisbane, CA (US)
`
`(73) Assignee: Agilent Technologies, Inc., Palo Alto,
`CA (US)
`
`Niino, Toshiki et al., “High—PoWer and High—Ef?ciency
`Electrostatic Actuator,” IEEE, 1993, pp. 136—241.
`Trimmer, W.S.N., “Design Considerations for a Practical
`Electrostatic Micro—Motor,” Sensors and Actuators, 11,
`1987, pp. 189—206.
`
`* cited by examiner
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Primary Examiner—Phan T. H. Palmer
`
`(57)
`
`ABSTRACT
`
`(21) Appl. No.: 09/488,344
`(22) Filed:
`Jan. 20, 2000
`
`(51) Int. Cl.7 ..................................................... .. G02B 6/26
`(52) us. Cl. ............................... .. 385/17; 385/16; 385/18;
`385/ 19
`(58) Field of Search ................................ .. 385/16, 17, 18,
`385/19, 20, 25, 31; 359/291, 224, 223,
`292
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6/1988 Gabriel et al. ..................... .. 310/309
`4,754,185
`1/1995 Higuchi et al.
`310/309
`5,378,954
`7/1996 Higuchi et al.
`310/309
`5,534,740
`5,872,880 * 2/1999 Maynard ...... ..
`385/19 X
`5,960,133 * 9/1999 Tomlinson .
`.... .. 385/18
`5,986,381
`11/1999 Hoen et al. ........................ .. 310/309
`
`OTHER PUBLICATIONS
`
`Niino, Toshiki et al., “Dual Excitation Multiphase Electro
`static Drive,” IEEE, 1995, pp. 1318—1325.
`Niino, Toshiki et al., “Development of an Electrostatic
`Actuator Exceeding 1ON Propulsive Force,” IEEE, 1992,
`pp. 122—1127.
`
`In a ?rst embodiment of an optical sWitch having at least one
`dual axis micromirror, the micromirror is manipulated about
`tWo generally perpendicular axes by varying voltage pat
`terns along tWo electrostatic arrangements. The tWo elec
`trostatic arrangements may be formed to independently
`drive tWo movers, or may be formed to control a mover that
`is displaceable in tWo directions. The micromirrors and the
`movers that control the micromirrors may be integrated onto
`a single substrate. Alternatively, the micromirrors may be
`formed on a substrate that is attached to the substrate that
`includes the mover or movers. In a second embodiment of
`an optical sWitch in accordance With the invention, the
`sWitch includes tWo collimator arrays and tWo dual axis
`micromirror arrays. Each ?rst micromirror in the ?rst micro
`mirror array is dedicated to one of the collimators in the ?rst
`collimator array. Similarly, each second micromirror of the
`second micromirror array is dedicated to one of the colli
`mators of the second collimator array. By manipulating a
`?rst micromirror, an input signal from the associated ?rst
`collimator can be re?ected to any of the second micromir
`rors. By manipulating the second micromirror that receives
`the signal, the signal can be precisely positioned on the
`second collimator that is associated With the second micro
`mirror.
`
`19 Claims, 12 Drawing Sheets
`
`[10
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 1
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`

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`U.S. Patent
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`Jun. 26, 2001
`
`Sheet 1 0f 12
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`US 6,253,001 B1
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`Cisco Systems, Inc.
`Exhibit 1009, Page 2
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`

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`U.S. Patent
`
`Jun. 26, 2001
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`Sheet 2 0f 12
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`US 6,253,001 B1
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`FIG. 3
`
`FIG. 2
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`Cisco Systems, Inc.
`Exhibit 1009, Page 3
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 3 0f 12
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`US 6,253,001 B1
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`FIG. 5
`
`FIG. 4
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`Cisco Systems, Inc.
`Exhibit 1009, Page 4
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 4 0f 12
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`US 6,253,001 B1
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`8\
`
`)0
`
`FIG. 6
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`Cisco Systems, Inc.
`Exhibit 1009, Page 5
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`

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`U.S. Patent
`
`Jun. 26, 2001
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`Sheet 5 of 12
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`US 6,253,001 B1
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`Cisco Systems, Inc.
`Exhibit 1009, Page 6
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 6 0f 12
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`US 6,253,001 B1
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`FIG. 7A
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`Cisco Systems, Inc.
`Exhibit 1009, Page 7
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 7 0f 12
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`US 6,253,001 B1
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`}
`
`:
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`III]
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`88
`
`FIG. 8
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`FIG. 10
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`Cisco Systems, Inc.
`Exhibit 1009, Page 8
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 8 0f 12
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`US 6,253,001 B1
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`1 2V
`
`0V
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`0V 1 2V
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`0V 1 2V 1 2V
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`0V 1 2V
`
`FIG. 9
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`64/
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 9
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 9 0f 12
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`US 6,253,001 B1
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`5o
`
`25 -
`
`FORCE, #N
`0
`
`-25 _
`
`-50
`
`LATERAL FORCE
`
`OUT-OF-PLANE FORC
`
`MOTOR GAP, #m
`
`FIG. 11
`
`OUT-OF-PLANE FORCE
`
`MOTOR GAP, Mm
`
`FIG. 12
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 10
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`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 10 0f 12
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`US 6,253,001 B1
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`FIG. 13
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 11
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`

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`U.S. Patent
`
`Jun. 26, 2001
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`21f011LI.66_.nS
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`US 6,253,001 B1
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`Cisco Systems, Inc.
`Exhibit 1009, Page 12
`
`

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`U.S. Patent
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`Jun. 26, 2001
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`Sheet 12 0f 12
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`US 6,253,001 B1
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`FORM AN ARRAY OF SURFACE ELECTROSTATIC MOVERS _j_ 134
`AND SURFACE ELECTROSTATIC ARRANGEMENTS
`
`I
`
`1
`FORM AN ARRAY OF DUAL Ax|S MICROMIRRORS f 36
`
`I
`
`SUPPORT THE MICROMIRRORS
`FOR MANIPULATION BY THE MOVERS
`
`f 138
`
`I
`
`TILE MICROMIRROR ARRAYS
`
`I
`
`142
`POSITION MICROMIRROR AND COLLIMATOR ARRAYS f
`
`FIG. 17
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 13
`
`

`

`US 6,253,001 B1
`
`1
`OPTICAL SWITCHES USING DUAL AXIS
`MICROMIRRORS
`
`TECHNICAL FIELD
`
`The invention relates generally to optical switches and
`more particularly to optical cross-connected sWitches having
`micromirrors that are individually manipulated.
`
`BACKGROUND ART
`Continuing innovations in the ?eld of ?beroptic technol
`ogy have contributed to the increasing number of applica
`tions of optical ?bers in various technologies. With the
`increased utiliZation of optical ?bers, there is a need for
`ef?cient optical devices that assist in the transmission and
`the sWitching of optical signals. At present, there is a need
`for optical sWitches that direct light signals from an input
`optical ?ber to any one of several output optical ?bers,
`Without converting the optical signal to an electrical signal.
`The coupling of optical ?bers by a sWitch may be
`executed using various methods. One method of interest
`involves employing a micromirror that is placed in the
`optical path of an input ?ber to re?ect optical signals from
`the input ?ber to one of alternative output ?bers. The input
`and output ?bers can be either uni-directional or bidirec
`tional ?bers. In the simplest implementation of the mirror
`method, the input ?ber is aligned With one of tWo output
`optical ?bers, such that When the mirror is not placed in the
`optical path betWeen the tWo ?bers, the aligned ?bers are in
`a communicating state. HoWever, When the mirror is placed
`betWeen the tWo aligned ?bers, the mirror steers (i.e.,
`re?ects) optical signals from the input ?ber to a second
`output ?ber. The positioning of the mirror relative to the path
`of the input ?ber can be accomplished by using an apparatus
`that mechanically moves the mirror. There are number of
`proposals to using micromachining technology to make
`optical signals. In general, the proposals fall into tWo
`categories: in-plane free-space sWitches and in-plane guided
`Wave sWitches. Free-space optical sWitches are limited by
`the eXpansion of optical beams as they propagate through
`free space. For planar approaches, the optical path length
`scales linearly With the number of input ?bers. SWitches
`larger than 30x30 require large mirrors and beam diameters
`on the order of 1 millimeter
`For these planar
`approaches, the number (N) of input ?bers scales linearly
`With the beam Waist and the siZe of the optical components.
`Thus, the overall sWitch siZe groWs as N2. It is estimated that
`a 100x100 sWitch Would require an area of 1 m2, Which
`Would be a very large sWitch. Moreover, constraints such as
`optical alignment, mirror siZe, and actuator cost are likely to
`limit the sWitch to much smaller siZes. One planar approach
`claims that the optical sWitch can be designed so that it
`scales With the optical path difference, rather than the overall
`optical path. If this is possible, it Would certainly alloW
`larger sWitches. HoWever, the optical path difference also
`scales linearly With the number of input ?bers for a planar
`approach, so the sWitch groWs very large as it is scaled to
`large ?ber counts.
`For guided Wave approaches, beam expansion is not a
`problem. HoWever, loss at each cross point and the dif?culty
`of fabricating large guided Wave devices are likely to limit
`the number of input ?bers in such sWitches.
`For both approaches, constraints such as loss, optical
`component siZe, and cost tend to increase With the number
`of ?bers. There is a need for an optical cross connect sWitch
`Which scales better With the number of input and output
`?bers. Some free-space optical systems can achieve better
`
`10
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`15
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`25
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`35
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`45
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`55
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`65
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`2
`scaling. These systems make use of the fact that it is possible
`to use optical steering around in tWo directions to increase
`the optical ?ber count. Recently, optical sWitches that use
`such mirrors have been announced. The systems use pieZo
`electric elements or magnetically or electrostatically actu
`ated micromirrors. The actuation method for these
`approaches is often imprecise. To achieve a variable sWitch,
`it is typically necessary to use a very high level of optical
`feedback.
`What is needed is a micromachine that enables steering of
`optical signals from at least one input to a number of
`alternative outputs, Where the arrangement of the outputs is
`not limited to a linear con?guration. What is further needed
`is a method of fabricating and arranging arrays of the
`micromachines such that the sWitching is accurate and
`repeatable.
`
`SUMMARY OF THE INVENTION
`
`In one embodiment of an optical sWitch, a micromachine
`for steering optical signals includes utiliZing electrostatic
`forces to manipulate a dual-aXis micromirror. The micro
`mirror is supported adjacent to a substrate to enable move
`ment of the micromirror relative to the substrate. A ?rst
`surface electrostatic arrangement is con?gured to generate
`electrostatic forces for rotating the micromirror about a ?rst
`aXis. Similarly, a second surface electrostatic arrangement is
`con?gured to generate electrostatic forces for rotating the
`micromirror about a second aXis. The tWo electrostatic
`arrangements may be used to drive a single mover that
`controls the positioning of the micromirror, or may be used
`to drive separate movers.
`Preferably, an array of micromirrors is formed on a
`substrate. In one application, the micromirrors are formed
`separately from the electrostatically driven movers. For
`eXample, a micromirror substrate may be formed to include
`an array of micromirrors in a side-by-side relationship, With
`the micromirrors being supported to alloW rotation about
`perpendicular ?rst and second aXes. The micromirror sub
`strate may then be attached to a mover substrate on Which
`the movers are incorporated, such that the micromirrors are
`generally parallel to the paths of the movers. Each micro
`mirror may be connected to a projection that eXtends toWard
`the mover substrate and that is controlled by at least one of
`the movers. In this embodiment, the movers manipulate the
`projections in a manner similar to manipulation of joysticks.
`In another embodiment, the micromirrors and movers are
`integrated onto a single substrate. Each micromirror may be
`supported on the substrate by means of a frame. A ?rst
`mover is driven by electrostatic forces to manipulate the
`position of the frame, thereby rotating the micromirror about
`one aXis. A second electrostatically driven mover may be
`connected to the micromirror to rotate the micromirror about
`the second aXis. HoWever, there may be embodiments in
`Which a single mover is used to control rotations about both
`aXes. For eXample, the mover may be electrostatically driven
`in tWo perpendicular directions.
`Each surface electrostatic arrangement includes at least
`tWo sets of electrodes. For a particular surface electrostatic
`arrangement, a ?rst set of drive electrodes may be formed
`along a surface of a mover, While a second set of drive
`electrodes is formed along a surface of the substrate. The
`lengths of the electrodes are perpendicular to the direction of
`travel by the mover. The drive electrodes are electrically
`coupled to one or more voltage sources that are used to
`provide an adjustable pattern of voltages to at least one of
`the sets of drive electrodes. The change in the electrostatic
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 14
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`

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`US 6,253,001 B1
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`15
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`3
`force that results from variations in the voltage patterns
`causes movement of the mover. As an example, the ?rst set
`of drive electrodes may be electrically connected to a
`voltage source that provides a ?xed pattern of voltages,
`While the second set is electrically connected to a micro
`controller that is con?gured to selectively apply different
`voltages to the individual drive electrodes. The recon?gu
`ration of the applied voltage pattern modi?es the electro
`static forces betWeen the substrate and the mover, thereby
`laterally displacing the mover.
`Each surface electrostatic arrangement preferably
`includes levitator electrodes on the same surfaces as the
`drive electrodes. Unlike the drive electrodes, the levitator
`electrodes are positioned With the length of the electrodes
`parallel to the direction of travel by the mover. An accept
`able ?xed voltage pattern along the levitator electrodes is
`one that alternates betWeen high and loW voltages. Repul
`sive electrostatic forces betWeen the levitator electrodes
`cause the mover to be spaced apart from the substrate. Since
`the levitator electrodes are parallel to the travel direction of
`the mover, the levitator electrodes are not misaligned When
`the mover is displaced laterally. Moreover, the repulsive
`electrostatic forces generated betWeen the tWo sets of levi
`tator electrodes operate to negate any attractive forces
`generated by the drive electrodes.
`In a separate embodiment of the invention, an optical
`sWitch is con?gured to include tWo separate arrays of dual
`axis micromirrors and tWo separate arrays of optical signal
`conductors, such as collimators. One of the arrays of micro
`mirrors is positioned relative to a ?rst collimator array such
`that each dual axis micromirror is dedicated to one of the
`collimators to receive incident optical signals. The second
`array of micromirrors is positioned relative to the ?rst
`micromirror array to alloW an optical signal re?ected at the
`?rst array to be directed to any one of the micromirrors of
`the second array. That is, by manipulating a particular dual
`axis micromirror in the ?rst array, an optical signal incident
`to the particular micromirror can be re?ected to any one of
`the micromirrors of the second array. The second collimator
`array is positioned relative to the second array of micromir
`rors such that the optical signal re?ected by a micromirror of
`the second array is directed to an associated one of the
`collimators in the second collimator array. That is, the
`micromirrors of the second array are uniquely associated
`With the collimators of the second array, but can be manipu
`lated to provide compensation for the angle of the beam
`from the ?rst array. In this embodiment of the optical sWitch,
`the manipulation of micromirrors may be accomplished by
`means other than electrostatic forces, Without diverging
`from the invention.
`Returning to the embodiment in Which the manipulation
`of the micromirrors is implemented by varying generated
`electrostatic forces, a method of fabricating optical micro
`machines includes forming surface electrostatic movers on a
`surface of a substrate and includes supporting micromirrors
`relative to the substrate such that each micromirror is
`rotatable about substantially perpendicular ?rst and second
`axes and is manipulable by movement of at least one of the
`movers. As previously noted, the movers and the micromir
`rors may be formed on separate substrates or may be
`integrally fabricated on a single substrate. The movers and
`the mover substrate include the arrays of drive electrodes
`and levitator electrodes. The electrostatic surface actuation
`method is Well suited for the positioning of micromirrors
`Within the described optical sWitch, since each micromirror
`may be tilted to approximately 10° on each of the tWo axes
`and is relatively large from a micromachine perspective. A
`
`45
`
`55
`
`65
`
`4
`micromirror may be on the order of approximately 1 mm
`Wide. The mover that drives a micromirror can be displaced
`along actuation distances of approximately 100 pm, With
`very precise and repeatable positioning. Adequate electro
`static forces may be generated using voltages of 12 volts or
`loWer. The loW voltage operation alloWs the optical sWitch
`to be coupled With complementary metal-oxide semicon
`ductor (CMOS) circuitry.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of a 16x16 optical sWitch
`using dual axis micromirror arrays in accordance With the
`invention.
`FIG. 2 is a top vieW of a schematic representation of a ?rst
`embodiment for positioning tWo arrays of dual axis micro
`mirrors in accordance With the invention.
`FIG. 3 is a side vieW of the representation of FIG. 2.
`FIG. 4 is a top vieW of a second embodiment for posi
`tioning dual axis arrays of mirrors in accordance With the
`invention.
`FIG. 5 is a side vieW of the representation of FIG. 4.
`FIG. 6 is a top vieW of a micromirror array in accordance
`With one embodiment of the invention.
`FIG. 7 is a side vieW of one of the micromirrors of FIG.
`6 connected to a mover substrate having actuators for
`manipulating the micromirror about tWo axes.
`FIG. 7A is a top vieW that isolates the pair of actuators for
`manipulating the micromirror of FIG. 7.
`FIG. 8 is a bottom vieW of a mover of FIG. 7, shoWing
`vertically oriented driver electrodes and horiZontally ori
`ented levitator electrodes.
`FIG. 9 is a side vieW of the mover and mover substrate of
`FIG. 7, shoWing voltage patterns along the drive electrodes
`at one particular time.
`FIG. 10 is an end vieW of one arrangement of levitator
`electrodes on the mover and mover substrate of FIG. 7,
`shoWing possible voltage patterns along the levitator elec
`trodes.
`FIG. 11 shoWs graphs of lateral forces (i.e., in-plane
`forces) and out-of-plane forces for surface electrostatic
`drives having a surface area of 1 mm2 and having both drive
`electrodes and levitator electrodes.
`FIG. 12 shoWs graphs of lateral forces (i.e., in-plane
`forces) and out-of-plane forces When the 1 mm2 drive
`includes only drive electrodes.
`FIG. 13 is a top vieW of another embodiment of a
`micromachine having electrostatically driven movers Which
`manipulate a micromirror about tWo axes.
`FIG. 14 is a top vieW of one of the movers and a frame
`of the micromachine of FIG. 13.
`FIG. 15 is a side vieW of the mover and frame of FIG. 14,
`shoWn in a rest position.
`FIG. 16 is a side vieW of the mover and frame of FIG. 15,
`but shoWn in an operational state.
`FIG. 17 is a process ?oW of steps for fabricating an optical
`sWitch in accordance With the invention.
`
`DETAILED DESCRIPTION
`
`With reference to FIG. 1, an optical sWitch 10 is shoWn as
`including a ?rst collimator array 12, a second collimator
`array 14, a ?rst micromirror array 16, and a second micro
`mirror array 18. The optical cross-connect sWitch utiliZes
`dual axis micromirrors to de?ect input optical beams to any
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 15
`
`

`

`US 6,253,001 B1
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`6
`42. Also shoWn in the ?gure is the longest optical path 44
`that can occur When sWitching any one of the input colli
`mators to any one of the output collimators. In this design,
`the longest optical path is 7.3 W. The relationship betWeen
`the longest optical path and the siZe of the collimator arrays
`places a limit on the number of optical ?bers that can be
`coupled With a particular beam Width. Table 1 summariZes
`the constraints placed on the optical sWitch by the angular
`divergence of a Gaussian beam traveling in free space. The
`parameter \/A characteriZes the radial index pro?le in the
`graded index (GRIN) lens (i.e., n(r)=n0><(1—Ar2/2)). A suit
`able manufacturer of graded index lenses is NSG America,
`Inc. in Somerset, N.J.
`
`5
`one of the output optical elements. In the description of FIG.
`1, the ?rst collimator array 12 Will be described as com
`prising the input elements and the second collimator array
`14 Will be described as comprising the output elements.
`HoWever, this is not critical. The individual conductors may
`be bi-directional elements, so that optical signals propagate
`in both directions. Moreover, the use of collimators is not
`critical if other means of controlling beam expansion can be
`substituted.
`A single optical ?ber 20 is shoWn as being connected to
`the ?rst collimator array 12. In practice, there is likely to be
`sixteen optical ?bers connected to the 4x4 array. The num
`ber of elements in the array is not critical to the invention.
`The essential aspect of the optical sWitch is that each
`micromirror is individually manipulable along tWo physical
`axes. In FIG. 1, only one micromirror 22 is shoWn in the ?rst
`array 16 and only the tWo micromirrors 26 and 28 are shoWn
`in the second array 18. HoWever, there is a separately
`manipulable dual axis micromirror for each of the sixteen
`segments of the ?rst array and each of the sixteen segments
`of the second array.
`Each input ?ber, such as the ?ber 20, is coupled to its oWn
`collimator in the ?rst collimator array 12. An input optical
`signal 30 from the ?ber 20 exits from the collimator array 12
`as a slightly converging beam. The converging beam is
`directed to be incident to a particular micromirror 22 in the
`?rst micromirror array 16. Thus, each micromirror in the
`?rst array is dedicated to one of the collimators. HoWever,
`each micromirror is manipulated to redirect an incident
`beam to any one of the micromirrors in the second array 18.
`For example, the dashed lines from the micromirror 22 of
`the ?rst array 16 to the micromirror 28 of the second array
`18 represents a redirection of the input beam 30 as a result
`of manipulation of the micromirror 22. In the preferred
`embodiment, the manipulation of a micromirror, such as
`micromirror 22, is achieved using electrostatic forces.
`Nevertheless, other approaches may be employed.
`When the micromirror 22 is pivoted along one of its axes,
`the re?ected beam 32 Will sWeep horiZontally across the
`second micromirror array 18. On the other hand, When the
`micromirror 22 is pivoted about its second axis, the re?ected
`beam 32 Will sWeep vertically across the second array 18.
`Each of the micromirrors, such as micromirror 26, in the
`second array is dedicated to one of the collimators of the
`second collimator array 14. The dual axis capability of the
`second micromirrors alloWs each micromirror to be pre
`cisely positioned, so as to compensate for the angle at Which
`the beam arrives from a particular micromirror of the ?rst
`micromirror array 16. Thus, the micromirror 26 is precisely
`positioned about each of its tWo axes of rotation and
`redirects the optical beam 36 to the corresponding collimator
`34 in the array 14. The rotation of micromirror 26 depends
`upon Which micromirror of the ?rst array 16 is directing an
`optical beam to micromirror 26. The optical sWitch 10 of
`FIG. 1 is symmetrical, so that light beams can pass equally
`ef?ciently in either direction.
`As Will be explained more fully beloW, one feature of the
`three-dimensional nature of the design of FIG. 1 is that it is
`possible to easily vary the scale of the optical sWitch 10 to
`accommodate very large ?ber counts. FIG. 2 illustrates a top
`vieW of an optical sWitch 38. No particular number of input
`and output ports is intended to be shoWn in the draWing.
`Rather, FIG. 2 shoWs the locations of various optical ele
`ments in order to determine the relationship betWeen the
`Width of the collimator array and the maximum optical path
`length. All of the indicated dimensions of the sWitch are
`referenced to the Width
`of the collimator arrays 40 and
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`TABLE 1
`
`Commercial GRIN Lens Collimators
`
`1.0 mm
`diameter
`IA =
`0.481/mm
`
`2.0 mm
`diameter
`IA =
`0.237/mm
`
`4.0 mm
`diameter
`IA =
`0.148/mm
`
`99
`
`156
`
`407
`
`317
`
`1041
`
`507
`
`121 x 121
`
`625 x 625
`
`1156 x 1156
`
`13.2
`
`56
`
`143
`
`6 x 3 x 1.5
`
`25 x 13 x 6
`
`62 x 34 x 15
`
`20
`
`Parameter
`
`Maximum
`symmetrical
`beam length (mm)
`Associated Waist
`om)
`Crossconnect
`size
`Collimator array
`Width
`(mm)
`System size
`(l x W x h, cm3)
`
`For a given collimator, there is a maximum length that an
`optical beam can travel and have the same Waist at both ends
`of the beam. This length is called the maximum symmetrical
`beam length in Table 1, and it groWs approximately as the
`square of the collimator diameter. Since the optical path in
`the system 38 groWs linearly With the collimator diameter, it
`is alWays possible to achieve larger ?ber counts by using
`larger collimators. This fact is borne out in Table 1, Where
`1.0 mm diameter collimators can be used to achieve a
`121x121 sWitch, While 4.0 mm collimators can be used to
`achieve a 1000x1000 sWitch at the expense of increased
`optical system siZe. The number of ?ber inputs should
`increase approximately as the square of the collimator
`diameter, assuming that the Waist of the beam leaving the
`collimator scales as the diameter of the collimator. This is
`not indicated by the three collimators analyZed for Table 1,
`presumably because of the difficulties in doping the GRIN
`lenses.
`FIG. 3 is a side vieW of the optical sWitch 38 of FIG. 2.
`In the tWo ?gures, the ?rst and second micromirror arrays 46
`and 48 are shoWn as being planar devices and individual
`micromirrors are not shoWn. HoWever, the individually
`manipulated micromirrors are incorporated into the tWo
`arrays 46 and 48 so that any one of the input collimators in
`the collimator array 40 can be optically coupled to any one
`of the collimators in the collimator array 42.
`There are a number of available methods for increasing
`the ?ber count for a selected collimator array siZe. Firstly,
`the system may be made slightly asymmetrical by alloWing
`the optical beam to travel more than the maximum sym
`metrical beam length shoWn in Table 1. HoWever, this
`method has an associated increase in optical losses and
`crosstalk. Secondly, a different sWitch geometry can be used,
`such as that shoWn in the top vieW of FIG. 4 and the side
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 16
`
`

`

`US 6,253,001 B1
`
`7
`vieW of FIG. 5. While the geometry is different, the com
`ponents are substantially identical, so the reference numerals
`of FIGS. 2 and 3 are also used in FIGS. 4 and 5. In the
`embodiment of FIGS. 4 and 5, the maXimum beam length is
`only 4.1 W. In this case, the 4.0 mm GRIN lens could be
`used to create a 3,600><3,600 sWitch. This system design
`places more dif?cult requirements on the micromirrors of
`the arrays 46 and 48. Most notably, the micromirrors must
`be able to rotate into the plane of the substrate on Which the
`micromirrors are formed.
`
`A third method of increasing the ?ber count Would be to
`use more efficient collimators for Which the output Waist is
`a larger fraction of the collimator diameter. Afourth method
`Would be to use a close-packed ?ber array, rather than the
`square array shoWn in FIG. 1. Close packing, hoWever,
`Would only increase the number of optical ?bers by 15%,
`and it Would make the tiling to be described beloW more
`dif?cult to implement. A ?fth method is to very accurately
`control the curvature of the micromirrors, so that they can
`operate as focusing elements to compensate for the Gaussian
`beam expansion. A theoretical siXth method Would be to use
`optics in the input and output stages, so that the sWitch
`Would scale With the optical path difference, rather than With
`the total optical path length.
`
`REQUIREMENTS ON THE MICRO-OPTICAL
`COMPONENTS
`
`There are a number of constraints Which must be
`addressed in the design of an optical sWitch in accordance
`With the invention. Table 2 summariZes the optical con
`straints placed on the collimators, micromirrors, and actua
`tors. Three different siZe sWitches are identi?ed in Table 2.
`
`TABLE 2
`
`Commercial GRIN Lens Collimators
`
`1.0 mm
`diameter
`IA =
`0.481/mm
`
`2.0 mm
`diameter
`IA =
`0.237/mm
`
`4.0 mm
`diameter
`IA =
`0.148/mm
`
`2.08
`
`4.22
`
`6.77
`
`121 x 121
`
`625 x 625
`
`1156 x 1156
`
`13.2
`
`11.4
`
`56
`
`143
`
`10.69
`
`10.43
`
`1.0 x 0.8
`
`2.1 x 1.6
`
`3.4 x 2.5
`
`1
`
`20
`
`4
`
`20
`
`11
`
`20
`
`10.70
`
`10.34
`
`10.21
`
`11.3
`
`10.89
`
`10.55
`
`10.12
`
`10.06
`
`10.04
`
`Parameter
`
`Collimators
`
`Effective focal
`length (mm)
`Crossconnect size
`(input x output)
`Collimator array
`Width (mm)
`Angular tolerance
`on individual
`collimators (mrad)
`Micromirrors
`
`Mirror size
`(1.. X Ly. mo
`Minimum mirror
`radius of curvature
`(m)
`Dynamic angular
`range (degrees)
`Angular precision to
`direct beam to
`mirror on 2nd array
`(mrad)
`Mirror angular
`precision for
`~40 dB mode
`overlap loss (mrad)
`Mirror angular
`precision for ~0.5
`
`8
`
`TABLE 2-continued
`
`Commercial GRIN Lens Collimators
`
`1.0 mm
`diameter
`IA =
`0.481/mm
`
`2.0 mm
`diameter
`IA =
`0.237/mm
`
`4.0 mm
`diameter
`IA =
`0.148/mm
`
`150
`
`1300
`
`150
`
`1146
`
`150
`
`190
`
`152
`
`126
`
`117
`
`Parameter
`
`dB mode overlap
`loss (mrad)
`Actuators
`
`Assumed actuator
`travel (,um)
`Actuator precision
`to direct beam to
`mirror
`on 2nd array (nm)
`Actuator precision
`for ~0.5 dB mode
`overlap loss (nm)
`
`Regarding the collimators, an effective focal length equal
`to 1/\/A has been calculated for each GRIN collimator, so
`that it can be compared to standard lenses. Regarding the
`micromirrors, the micromirrors must satisfy very stringent
`requirements in order to position the optical beams precisely
`on the output collimators. The large beam Waists used in the
`sWitches mean that the mirror siZes must be large, typically
`on the order of several millimeters. Such large mirrors may
`not be possible With some of the knoWn surface microma
`chining techniques used in fabricating micromirrors. With a
`thickness of only a feW microns, these knoWn mirrors may
`not be able to maintain the desired ?atness (radius of
`curvature) to ensure that the beam propagates Without dis
`tortion. Fortunately, bonded Wafer approaches are noW
`becoming more common in the manufacture of microma
`chined components, so that it is less dif?cult to design a
`mirror having a thickness of 100 microns to several hundred
`microns. This thickness is necessary to ensure that the gold
`?lm used as a re?ective coating on the mirrors does not
`cause undue curvature.
`Each micromirror should rotate 10° around tWo perpen
`dicular aXes in order to couple any input ?ber to any output
`?ber. HoWever, the range of 10° may place difficult con
`straints on other components of the system, such as the
`actuators for manipulating the micromirrors. For the actua
`tors Which Will be described fully beloW, a 10° movement of
`a 2 mm diameter mirror requires a mover to travel approxi
`mately 50 to 100 microns. This requirement limits the types
`of micromachined drives that can be utiliZed. In the pre
`ferred embodiment, electrostatic surface actuators are uti
`liZed.
`Table 2 also includes three different angular position
`requirements for the micromirrors. An angular precision of
`~0.5 mrad is required both to position the beam on the
`second micromirror array and to achieve ~40 dB coupling
`(i.e, a maXimum overlap loss of ~40 dB) into the output
`?ber. The ~40 dB mode coupling level is selected because a
`sensor could be used to detect this signal level. At this signal
`level, the optical poWer of the output ?ber itself could be
`used to close a control loop Which positions the micromir
`rors. There is a signi?cant bene?t in performing the open
`loop control of the beam position on the second micromirror
`array. OtherWise, sensors are required along the area of the
`second micromirror array in order to steer the beam as it
`moves from one micromirror to another. Sensors may also
`be required to ensure that the beam is properly centered on
`the correct output micromirror. Similarly, if the precision for
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`Cisco Systems, Inc.
`Exhibit 1009, Page 17
`
`

`

`US 6,253,001 B1
`
`9
`the ~40 dB mode overlap loss is not met, sensors are
`required to steer the beam onto the correct output collimator.
`Brie?y, With regard to the constraints involving the
`actuators, the micromirr