(12) United States Patent
`Hoen
`
`US006253001B1
`
`(10) Patent No.: US 6,253,001 B1
`(45) Date of Patent: Jun. 26, 2001
`
`(54) OPTICAl, SWITCHES USING DUAl, AXIS
`MICROMIRRORS
`
`(75)
`
`Inventor: Storrs T. Hoen, Brisbane, CA(US)
`
`(73) Assignee: Agilent Technologies, Inc., Polo Alto,
`CA (US)
`
`Niino, Toshild et al., "High@ower and High Efficiency
`Electrostatic Actuator," IEEE, 1993, pp. ] 36 241.
`Trimmer, W.S.N., "Design Considerations for a Practical
`Electrostatic Micro-Motor," Sensors and Actuators, 11,
`] 987, pp. 189~06.
`
`* cited by examiner
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted undcr 35
`U.S.C. 154(b) by 0 days.
`
`Primary Examiner~han T. H. Palmer
`
`(57)
`
`ABSTRACT
`
`(21) Appl. No.: 09/488,344
`
`(22) Filed:
`
`Jan. 20, 2000
`
`Int. CI.7 ....................................................... G02B 6/26
`(51)
`(52) U.S. 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
`
`4,754,185
`5,378,954
`5,534,740
`5,872,880 *
`5,960,133 *
`5,986,381
`
`6/1988 Gabriel ct al ........................ 310/’309
`1/1995 Higuchi et al ....................... 310/309
`7/1996 Higuehi et al ....................... 310/’309
`2/1999 Maynard ............................ 385/19 X
`9/1999 Tomlinson ............................. 385/18
`11/1999 Hoen et al ........................... 310/’309
`
`OTHER PUBLICATIONS
`
`Niino, Toshiki et al., "Dual Excitation Multiphasc 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 first embodiment of an optical switch having at least one
`dual axis micromirror, the micromirror is manipulated about
`two generally peq~endicular 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 displaccable in two dircctions. 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 first micromirror in the first micro-
`mirror array is dedicated to one of the collimators in the first
`collimator array. Similarly, each second micromirror of the
`second micromirror array is dedicated to one of the colE-
`mators of the second collimator array. By manipulating a
`first micromirror, an input signal from the associated first
`collimator can be reflected 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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-1
`
`

`

`U.S. Patent
`US. Patent
`
`Sheet 1 of 12
`Jun. 26, 2001 Sheet 1 of 12
`Jun. 26, 2001
`
`US 6,253,001 B1
`US 6,253,001 B1
`
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—2
`Exhibit 1009-2
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 2 0f 12
`jun. 26, 2001 Sheet 2 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
`
`FIG.3
`
`42
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`
`38\
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—3
`Exhibit 1009-3
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 3 0f 12
`Jun. 26, 2001 Sheet 3 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—4
`Exhibit 1009-4
`
`

`

`U.S. Patent
`
`f04teehS
`1002672
`Jun. 26, 2001 Sheet 4 of 12
`
`US 6,253,001 B1
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`Exhibit 1009-5
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`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 5 0f 12
`Jun. 26, 2001 Sheet 5 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
`
`FIG.7
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`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009-6
`Exhibit 1009-6
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 6 0f 12
`Jun. 26, 2001 Sheet 6 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
`
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—7
`Exhibit 1009-7
`
`

`

`U.S. Patent
`
`Jun. 26, 2001 Sheet 7 of 12
`
`US 6,253,001 B1
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`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-8
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 8 0f 12
`Jun. 26, 2001 Sheet 8 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—9
`Exhibit 1009-9
`
`

`

`U.S. Patent
`
`Jun. 26, 2001 Sheet 9 of 12
`
`US 6,253,001 B1
`
`~,~ L FORCE
`~ ~’~ ~-F’~~- - - - - -~-~
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`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-10
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 10 0f 12
`Jun. 26, 2001 Sheet 10 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
`
`100
`
`102
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`FIG. 13
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—11
`Exhibit 1009-11
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 26, 2001
`Sheet 11 0f 12
`Jun. 26, 2001 Sheet 11 of 12
`
`US 6,253,001 B1
`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1009—12
`Exhibit 1009-12
`
`

`

`U.S. Patent
`
`Jun. 26, 2001 Sheet 12 of 12
`
`US 6,253,001 B1
`
`FORM AN ARRAY OF SURFACE ELECTROSTATIC MOVERS
`AND SURFACE ELECTROSTATIC ARRANGEMENTS
`
`FORM AN ARRAY OF DUAL AXIS MICROMIRRORS
`
`SUPPORT THE MICROMIRRORS
`FOR MANIPULATION BY THE MOVERS
`
`TILE MICROMIRROR ARRAYS
`
`POSITION MICROMIRROR AND COLLIMATOR ARRAYS
`
`FIG. 17
`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-13
`
`

`

`US 6,253,001 B1
`
`1
`OPTICAL SWITCHES USING DUAL AXIS
`MICROMIRRORS
`
`TECIINICAL FIELD
`
`’lhe 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 field of fiberoptic technol-
`ogy have contributed to the increasing number of applica-
`tions of optical fibers in various technologies. With the
`increased utilization of optical fibers, there is a need for
`efficient optical devices that assist in the transmission and
`the switching of optical signals. At prcsent, thcrc is a nccd
`for optical switches that direct light signals from an input
`optical fiber to any one of ~veral output optical fibers,
`without converting the optical signal to an electrical signal.
`The coupling of optical fibers by a switch may be
`executed using various methods. One mcthod of interest
`involves employing a micromirror that is placed in the
`optical path of an input fiber to reflect optical signals from
`the input fiber to one of alternative output libers. The input
`and output fibers can be either uni-directinnal or bidirec-
`tional fibers. In the simplest implementation of the mirror
`method, the input fiber is aligned with one of two output
`optical fibcrs, such that when the mirror is not placed in the
`optical path between the two fibers, the aligned fibers are in
`a communicating state. However, when the mirror is placed
`between the two aligned Iibers, the mirror steers (i.e.,
`reflects) optical signals from the input fiber to a second
`output fiber. The positioning of the mirror relative to the path
`of the input fiber can be accomplished by using an apparatus
`that mcchanically moves the mirror. Thcrc arc 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
`frcc space. For planar approachcs, thc optical path length
`scalcs linearly with the numbcr of input fibers. Sxvitchcs
`larger than 30x30 require large mirrors and beam diameters
`on the order of 1 millimeter (mm). For these planar
`approaches, the number (N) of input fibers scales linearly
`with the beam waist and the size of the optical components.
`Thus, the overall switch size grows as N"~. It is estimated that
`a 100xl00 switch would rcquirc an area of 1 mz, which
`would be a vcry large switch. Morcovcr, constraints snch 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
`largcr switches. Howcvcr, the optical path difference also
`scales linearly with the number of input fibers for a planar
`approach, so the switch grows very large as it is scaled to
`large fiber counts.
`For guided wave approaches, beam expansion is not a
`problem. However, loss at cach cross point and thc difficulty
`of fabrieafing large guided wave devices are likely to limit
`the number of input fibers in such switches.
`For both approaches, constraints such as loss, optical
`component size, and cost tend to increase with the number
`of fibers. There is a need for an optical cross connect switch
`which scales better xvith the number of input and output
`fibers. Some free-space optical systems can achieve better
`
`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 fiber count. Rcccntly, optical switches that use
`such mirrors have been announced. Thc systems use piczo-
`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 nccdcd is a micromachinc that cnablcs stccring 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 configuration. 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
`~0 for steering optical signals includes utilizing electrostatic
`
`forces to manipulate a dual-axis micromirror. The micro-
`mirror is supported ac~iacent to a substrate to enable move-
`ment of the micromirror relative to the substrate. A first
`surface electrostatic arrangement is configured to generate
`:s electrostatic forces for rotating the micromirror about a first
`
`axis. Similarly, a second surface electrostatic arrangement is
`configurcd to gcncratc electrostatic forces for rotating the
`micromirror about a second axis. The two electrostatic
`arrangements may be used to drive a single mover that
`3o controls the positioning of the micromirror, or may be used
`
`to drNe separate movers.
`Preferably, an array of micromirrors is formed on a
`substrate. In one application, the micromirrors are formed
`35 scparately from the eleetrostatieally 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 first and second axes. The micromirror sub-
`4c~ strate may then be attached to a mover substrate on which
`the movers arc incorporated, such that the micromirrors arc
`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
`45 the movers. In this embodiment, the movers manipulate the
`projections in a manner similar to manipulation of joysticks.
`In anothcr embodiment, the micromirrors and movcrs arc
`integrated onto a single substrate. Each micromirror may be
`supported on the substrate by means of a frame. A first
`50 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
`conncctcd to the micromirror to rotate the micromirror about
`the second axis. However, there may be embodiments in
`55 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
`Vwo sets of electrodes. For a particular snrface electrostatic
`~0 arrangement, a first 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
`~5 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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-14
`
`

`

`US 6,253,001 B1
`
`3
`force that results from variations in the voltage patterns
`causes movement of the mover. As an example, the first set
`of drive electrodes may be electrically connected to a
`voltage source that provides a fixed pattern of voltages,
`while the second set is electrically connected to a micro-
`controller that is configured to selectively apply different
`voltages to thc individual drivc electrodes. Thc rcconfigu-
`ration of the applied voltage pattern modifies the electro-
`static forces between the substrate and the mover, thereby
`laterally displacing the mover.
`Each surface electrostatic arrangement preferably
`inchldes 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 fixed 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 nmver, the levitator electrodes are not misaligued 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 configured 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 first 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 first
`micromirror array to allow an optical signal reflected at the
`first ,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 first array, an optical signal incident
`to the particular micromirror can be reflected to any one of
`the naicromirrors of the second array. The second collimator
`array is positioned relative to the second array of micromir-
`rots such that the optical signal reflected 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 first 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 thc micromirrors is implcmcnted by varying gcncratcd
`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 first 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
`
`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 ~m, with
`very precise and rcpcatablc positioning. Adcquatc 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 schcmatic diagram of a 16x16 optical switch
`using dual axis micromirror arrays in accordance with the
`invention.
`
`15
`
`FIG. 2 is a top view of a schematic representation of a first
`embodin~ent for positioning two arrays of dual axis uficro-
`mirrors in accordance with the invention.
`
`FIG. 3 is a side view" of the representation of FIG. 2.
`
`FIG. 4 is a top vicw of a second cmbodimcnt for posi-
`;0 tioning dual axis arrays of mirrors in accordance with the
`invention.
`
`FIG. 5 is a side view- of the representation of FIG. 4.
`
`25
`
`FIG. 6 is a top view of a micronrirror 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 o[ actuators for
`30 manipulating the nficronrirror 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
`35 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 possiblc voltage patterns along the lcvitator clec-
`40 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 mm"~ and having both drive
`
`45 electrodes and levitator electrodes.
`FIG. 12 shows graphs of lateral forccs (i.e., in-plane
`forces) and out-of-plane forces ~vhcn the 1 mm: drive
`inch~des only drive electrodes.
`
`FIG. 13 is a top view of another embodiment of a
`5o micromachine having electrostatically driven umvers which
`manipulate a micronrirror about two axes.
`
`FIG. 14 is a top view of one of the movers and a frame
`of thc micromachinc of FIG. 13.
`
`FIG. 15 is a side view of the mover and frame of FIG. 14,
`55 shown in a rest position.
`
`EIG. 16 is a side view of the mover and frame of EIG. 15,
`but shown in an operational state.
`
`FIG. 17 is a process flow of steps for fabricating an optical
`switch in accordancc with thc invcntion.
`
`DETAILED DESCRIPTION
`
`With reference to FIG. 1, an optical switch 10 is shown as
`including a first collimator array 12, a second collimator
`65 array 14, a first micromirror array 16, and a second micro-
`mirror array 18. The optical cross-connect switch utilizes
`dual axis micromirrors to deflect input optical beams to any
`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-15
`
`

`

`US 6,253,001 B1
`
`one of the output optical elements. In the description of FIG.
`1, the first 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, thc use of collimators is not
`critical if other means of controlling beam expansion can be
`substituted.
`A single optical fiber 21~ is shown as being connected to
`the first cofiimator array 12. In practice, there is likely to be
`sixteen optical fibers connected to tire 4x4 array. The num-
`ber of elements in the array is not critical to the invention.
`Thc csscntial aspcct of thc optical switch is that each
`micromirror is individually manipulable along two physical
`axes. In FIG. 1, only one micromirror 22 is shown in the first
`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 first array and each of the sixteen segments
`of the second array.
`Each input fiber, such as the fiber 20, is coupled to its oxvn
`collimator in the first collimator array 12. An input optical
`signal 30 from the fiber 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
`first micromirror array 16. Thus, each micromirror in the
`first 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 cxamplc, thc dashed lincs from the micromirror 22 of
`the first 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 reflected beana 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 reflected
`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 first
`micromirror array 16. Thus, the micromirror 26 is precisely
`positioned about each of its two axes of rotation and
`redirects the optical beanr 36 to the corresponding collimator
`34 in the array 14. The rotation of micromirror 26 depends
`upon which nricromirror of the first array 16 is directing an
`optical beam to micromirror 26. The optical switch 111 of
`FIG. 1 is symmetrical, so that light beams can pass equally
`efficiently 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 111 to
`accommodate very large fiber 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 (W) of the collimator arrays 4~) and
`
`6
`42. Also shown in the figure 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 longcst optical path is 7.3 W. The relationship bctwccn
`the longest optical path and the size of the collimator arrays
`places a limit on the number of optical fibers 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 v~A charactcrizcs the radial indcx profile in the
`gradcd indcx (GRIN) lens (i.e., n(r)=nox(l-ArZ/2)). A suit-
`able manufacturer of graded index lenses is NSG America,
`Inc. in Somerset, N.J.
`
`10
`
`15
`
`TABLE
`
`Commcrclal GRIN Lens Collimators
`
`1.0 mm
`diameter
`¢’A -
`0.481/mm
`
`2.0 mm
`diameter
`¢’A -
`0.237/mm
`
`4.0 mm
`diameter
`¢’A -
`0.148imm
`
`99
`
`156
`
`407
`
`317
`
`1041
`
`5~7
`
`20
`
`Parameter
`
`symmetrical
`beam length (mm)
`Associated waist
`
`25
`
`Crossconnect
`
`121 x 121
`
`625x 625
`
`1156 x 1156
`
`Collimator array
`width
`
`30
`
`System
`(1 x w x % cm~)
`
`13.2
`
`56
`
`143
`
`6x3xl.5
`
`25x13x6
`
`62x34x 15
`
`4Q
`
`For a given collimator, there is a maximum length that an
`35 optical beam can travel and have the same waist at both ends
`of the beam. This length is called the maximum symnretrical
`beam length in Table 1, and it grows approximately as the
`square of the collimator diamcter. Since the optical path in
`the system 3g grows linearly with the collimator diameter, it
`is al~vays possible to achieve larger fiber 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
`45 optical system sizc. The number of fibcr inputs should
`increase approximately as the square of the collimator
`diameter, assuming thai the waist of the beam leaving the
`collimator scales as the diameter of the collimator. ’lhis is
`not indicated by the three collimators analyzed for Pable 1,
`50 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 figures, the first and second micromirror arrays 46
`and 48 are shown as being planar devices and individual
`55 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 41) can be optically coupled to any one
`of thc collimators in the collimator array 42.
`There are a m~mber of available methods for increasing
`the fiber 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
`~5 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
`
`~
`
`Petitioner Ciena Corp. et al.
`Exhibit 1009-16
`
`

`

`US 6,253,001 B1
`
`7
`view of FIG. 5. While the gemnetry is different, the com-
`ponents are substantially identical, so the reference numerals
`of FIGS. 2 and 3 arc also used in FIGS. 4 and 5. In the
`embodiment of FIGS. 4 and 5, thc maximum bcam length is
`only 4.1 W. In this case, the 4.0 mm GRIN lens could be
`used to create a 3,600x3,600 switch. This system design
`places inore difficult requirements on the tnicromirrors of
`the arrays 46 and 48. Most notably, the nricronrirrors must
`be able to rotate into the plane of the substrate on which the
`micromirrors arc formed.
`
`A third method of increasing the fiber count would be to
`use more efficient collimators for which the output waist is
`a largcr fraction of the collimator diameter. A fourth method
`wonld be to use a close-packed fiber array, rather than the
`square array shown in FIG. 1. Close packing, however,
`would only increase the number of optical libers by 15%,
`and it would make the tiling to be described below- more
`difficult to implement. A fifth 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 nse
`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 TIIE MICRO-OPTICAL
`COMPONENTS
`
`There are a number of constraints which must be 30
`addrcssed in the design of an optical switch in accordance
`with the invention. Table 2 summarizes the optical con-
`straints placed on the collimators, mieromirrors, and actua-
`tors. Three different size switches are identilied in Table 2.
`
`TABI,E 2-continued
`
`Commercial GRIN Lens Collimators
`
`t.0 mm
`diameter
`,/A =
`0.4817mm
`
`2.0 mm
`diameter
`~A =
`0.237/mm
`
`4.0 mm
`diameter
`CA =
`0.148jmm
`
`150
`
`-+300
`
`150
`
`-+146
`
`150
`
`-+90
`
`*52
`
`*26
`
`-17
`
`Parameter
`
`dB mode overlap
`loss (mrad)
`Acalators
`
`Assumed actuator
`~ravel @m)
`Actuator precision
`~o direct beam to
`mirror
`on 2’’a anay (rim)
`Actuator precision
`for ~’2.5 dB mode
`overlap loss (nm)
`
`t0
`
`15
`
`2o
`
`Regarding the collimators, an effective focal length equal
`to 1i~!A has been calculated for each GRIN collimator, so
`that it can be compared to standard lenses. Regarding the
`micromirrors, the tnicromirrors must satisfy very stringent
`2s requirements in order to position the optical beams precisely
`on the output collimators. The large beam waists used in the
`s~vitches nrean 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 fcw microns, thcsc known mirrors may
`not be able to maintain the desired flatness (radins of
`curvature) to ensure that the beam propagates without dis-
`tortion. Fortunately, bonded wafer approaches are now
`35 becoming more common in the manufacture of microma-
`chined components, so that it is less difficult to design a
`mirror having a thic ~kness of 100 microns to several hundred
`microns. This thic "kncss is necessary to cnsurc that the gold
`film used as a reflective 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 fiber to any output
`fiber. However, the range of 10° may place difficult con-
`straints on other components of the system, such as the
`45 actuators for tnanipulating 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-
`50 ferred embodiment, electrostatic surface actuators are nfi-
`lized.
`Table 2 also includes three different anNtlar position
`requirements for the micromirrors. An angular precision of
`-0.5 mrad is required both to position the beam on the
`55 second micromirror array and to achieve -40 dB coupling
`(i.e, a maximum overlap loss of ~40 dB) into the output
`fiber. 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 fiber itself could be
`~0 used to close a contr