(12) United States Patent
`Hoen
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,253,001 B1
`Jun. 26,2001
`
`US006253001B1
`
`OPTICAL SWITCHES USING DUAL AXIS
`MICROMIRRORS
`
`Inventor: Storrs 'l'. Hoen, Brisbane, CA (US)
`
`Assignee: Agilent Technologies, Ine., Palo Alto,
`CA (US)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C_ l54(h) by 0 days.
`
`Appl. No; 09/488,344
`Filed:
`Jan. 20, 2000
`Int. Cl.”
`U.S. Cl.
`
`Field of Search ..
`385/19, -0, -3,
`
`G02B 6/26
`385/17; 385/16; 585/18;
`385/19
`.. 385/16, 17, 18,
`1, 359/291, 224, 223,
`
`References Cited
`U.S. PAl'l:'N'l‘ D()CUMl:'N'l'S
`6/1088 Gabriel et al.
`1/1995 Higuchi et al.
`7/1996 Higuchi et al.
`2/1999 Maynard 44
`9/1999 Tornlinson
`..
`ll/1999 l-Ioen et al.
`OTI IER PUIIUCATIONS
`
`4,754,185
`5,578,934
`5,534,740
`5,872,880 *
`5,960,133 *
`5,986,381
`
`Niino, Toshiki et al., “Dual Excitation Multiphase Electro-
`static Drive," IEEE, 1995, pp. 1318-1325.
`Niirro, Toshiki et
`511., “Development of an Electrostatic
`Actuator Exceeding 1ON Propulsive Force," IE]-Jlz, 1992,
`pp. 122-1127.
`
`Niino, Toshiki et al., “l-ligh—Powe1 and High—l:lllicieney
`Electrostatic Actuator,” IEEE, 1993, pp. 136-541.
`Trimmer, W.S.\T., “Design Considerations for a Practical
`Electrostatic Micro—Motor," Sensors and Actuators, 11,
`1987, pp. 189-206.
`
`* cited by examiner
`
`Primary F.mntiI1er—Plian T. H. Palmer
`
`ABSTRACT
`(57)
`In a first 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 arrangenients. The two elec-
`trostatic arrangements may be formed to independently
`drive two movers, or may be formed to control a mover that
`is displaeeable in two directions, The micromirrors and the
`movers that control the micromirrors may be integrated onto
`a single substrate, Alternatively, the micromirrors may be
`[otnred 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 ml‘ the
`second micromirror array is dedicated to one of the colli-
`mators of the second collimator array. By manipulating a
`first micromirror. an input signal from the associated first
`collimator can be reflectcd to any of the second micromir-
`tors. Ry manipulating the second mieromirror 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 1018-1
`
`

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`U.S. Patent
`
`Jun. 26,2001
`
`4|.0ChS
`
`pl0.1
`
`2.1
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`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-2
`
`

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`U.S. Patent
`
`Jun. 26,2001
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`Sheet 2 of 12
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`US 6,253,001 B1
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`E
`
`E
`
`N.®_n_
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`_.\E/._
`
`2.
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-3
`
`

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`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 3 of 12
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`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-4
`
`

`
`%@©O
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`mm8
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`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-5
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 5 of 12
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`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-6
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 6 of 12
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`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-7
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 7 of 12
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`US 6,253,001 B1
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`76\
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-8
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 8 of 12
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`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-9
`
`

`
`U.S. Patent
`
`Jun. 26, 2001
`
`Sheet 9 Of 12
`
`US 6,253,001 B1
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`FORCE, ‘MN
`
`LATERAL FORCE
`
`OUT-OF-PLANE FORC
`
`MOTOR GAP, /2m
`
`FIG. 11
`
`LATERAL FORCE
`
`OUT-OF-PLANE FORCE
`
`MOTOR GAP, ,um
`
`FIG. 12
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-10
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 10 of 12
`
`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-11
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`cl01.14|.0ChS
`
`2.1
`
`US 6,253,001 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1018-12
`
`

`
`U.S. Patent
`
`Jun. 26,2001
`
`Sheet 12 of 12
`
`US 6,253,001 B1
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`FORM AN ARRAY OF SURFACE ELECTROSTAT|C MOVERS
`AND SURFACE ELECTROSTAT|C ARRANGEMENTS
`
`FORM AN ARRAY OF DUAL AXIS MICROMIRRORS
`
`SUPPORT THE MICROMIRRORS
`FOR MANIPULATION BY THE MOVERS
`
`TILE MICROMIRROR ARRAYS
`
`POSITION MICROMIRROR AND COLLIMATOR ARRAYS
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-13
`
`

`
`US 6,253,001 B1
`
`5
`
`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.
`BACKGRO UND ART
`
`Continuing innovations in the lleld of llberoptic 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
`eflicient 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 fiber to any one of several 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 method of interest
`involves employing a mieromirror that
`is placed in the
`optical path of an input fiber to rellect optical signals [rom
`the input fiber to one of alternative output fibers. The input
`and output fibers can be either uni-directional or bidirec-
`tional fibers. In the simplest implementation of the mirror
`method, the input fiber is aligned with one of two output
`optical fibers, 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 fibers,
`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 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 [ree—space switches and in—plane guided
`wave switches. Free -space optical switches are limited by
`the expansion of optical beariis as they propagate through
`free space. For planar approaches, the optical path length
`scales linearly with the number of input fibers. Switches
`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 lU0><l0O switch would require an area of I ml, which
`would he 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 line arly 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. Ilowevcr, loss at each cross point and the difliculty
`of fabricating 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 with 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. Recently, optical switches that use
`such mirrors have been announced. The systems use piezo-
`electric elements or magnetically or electrostatically actu-
`ated riiicroniirrors. 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
`feeclback.
`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 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
`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 riiicroriiirror relative to the substrate. A first
`surface electrostatic arrangement is configured to generate
`electrostatic forces for rotating the mieromirror about a first
`axis. Similarly, a second surface electrostatic arrangement is
`configured to generate electrostatic forces for rotating the
`mieromirror about a second axis.
`'|he two electrostatic
`arrangements may be used to drive a single mover that
`controls the positioning of the mieromirror, or riiay be used
`to drive separate movers.
`Preferably, an array of micromirrors is fonncd on a
`substrate. In one application, the riiicroriiirrors are formed
`separately from the electrostatically driven movers. For
`example, a mieromirror 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 mieromirror 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 ofjoystieks.
`In another embodiment, the micromirrors and movers are
`integrated onto 21 single substrate. Each mieromirror may be
`supported on the substrate by means of a frame. A first
`mover is driven by electrostatic forces to manipulate the
`position of the frame, thereby rotating the mieromirror about
`one axis. A second electrostatically driven mover may be
`connected to the mieromirror to rotate the mieromirror 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 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
`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 1018-14
`
`

`
`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 the individual drive electrodes. The reconfigu-
`ration of the applied voltage pattern modilies the electro-
`static forces between the substrate arid the rnover, 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 fixed voltage pattern along the levitator electrodes is
`one that alternates between high and low voltages Reptil-
`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 configured to include two separate arrays of dual
`axis micromirrors and two separate arrays of optical signal
`conductors, such as collim ators. 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
`collirnators 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 niicroniirror can be reflected 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 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 colliniators of the second array, but can be n1ar1ipu—
`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 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 rnicroniirror is
`rotatable about substantially perpendicular first and second
`axes and is manipulablc 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 micromaehine 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 ‘um, with
`very precise and repeatable positioning. Adequate electro-
`static forces may be generated using voltages of l2 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 16><16 optical switch
`using dual axis micromirror arrays in accordance with the
`invention.
`FIG. 2 is a top view of a schern atic representation of a first
`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 rnicromirror 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 Ievitator 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.
`in-plane
`FIG. 11 shows graphs of lateral forces (i.e.,
`forces) and out—of—pIar1e
`forces for surface electrostatic
`drives having a surface area of 1 IIIIIIZ and having both drive
`electrodes and levitator electrodes.
`in-plane
`FIG. 12 shows graphs of lateral forces (i.e.,
`forces) and out-of-plane forces when the 1 mm‘ drive
`includes only drive electrodes.
`FIG. 13 is a top view of another embodiment of ti
`rnicroniacliirie having electrostatically driven movers which
`manipulate a rriicrorriirror 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 H 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 flow 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 first collimator array 12, a second collimator
`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 1018-15
`
`

`
`US 6,253,001 B1
`
`5
`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 eler11ents.
`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 ca11 be
`substituted.
`A single optical fiber 20 is shown as being corniected to
`the first collimator array 12. In practice, there is likely to be
`sixteen optical fibers 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 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 own
`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 ir1 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 example, the dashed lines 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 micrornirror 22 is pivoted along one of its axes,
`the reflected beam 32 will sweep horizontally across the
`second micromirror array 18. On the other hand, when the
`micromirror 22 is pivoted about its seoond 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 rnicrornirrors 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 beam 36 to the corresponding collimator
`34 in the array 14. The rotation of micromirror 26 depends
`upon which micromirror of the first 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
`eflicicntly in either direction.
`As will be explained more fully below, one feature of the
`three-dimensional nature of the design of HG. 1 is that it is
`possible to easily vary the scale of the optical switch 10 to
`accommodate very large fiber counts. FIG. 2 illustrates a top
`view of an optical switch 33. 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
`
`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 colljmators. 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 lintit on the number of optical fibers that can be
`coupled with a particular beam width. Table l summarizes
`the constraints placed on the optical switch by the angular
`divergence of a Gaussian beam traveling in free space. The
`parameter v'A characterizes the radial index profile in the
`graded index (GRIN) lens (i.e., n(r)=n,,><(l—Ar2/2)). A suit-
`able rrrarrufacturer of graded index lenses is NSG Arnerica,
`Inc. in Somerset, N.J.
`
`TABLE 1
`Commercial GRIN Lens Collimators
`1.0 mm
`2.0 mm
`4.0 mm
`diameter
`diameter
`diameter
`/A =
`/A =
`/A =
`L 48]/mm
`0 ,2 37/mm
`0 :4.‘S,’n1iu
`99
`407
`‘li74l
`
`.
`
`.
`
`317
`6.7.5 x 625
`
`507
`ll55 x 1156
`
`56
`
`143
`
`25xl3xG
`
`2x34xZl5
`
`Paranieter
`lvlaximuin
`symmetrical
`beam length (iiinij
`Associated waist
`(Mm)Crosseonneet
`size
`Collirnater array
`width
`(mm)
`Sys:em size
`[I 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 l, 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 fiber counts by using
`larger collimators. This [act is borne out in Table 1, where
`1.0 mm diameter collimators can be used to achieve a
`l;Zl>-zlll switch. while 4.0 mm collimators can be used to
`achieve a l00O><l000 switch at the expense of increased
`optical system size. The number of fiber 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 l,
`presumably because of the di
`iculties 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 p anar devices and individual
`micromirrors are not shown. However,
`the individually
`manipulated rnicromirrors are incorporated into the two
`arrays 46 and 48 so that any one of the input colhmators in
`the collimator array 40 can be optically coupled to arty one
`of the collimators in the collimator array 42.
`There are a number 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 i11 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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-16
`
`

`
`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><3,000 switch. This system design
`places more difficult 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 fiber count would be to
`use more cflicient collimators for which the output waist is
`a larger fraction of the collimator diameter. Afourth method
`would 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 fibers 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 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-OPTICAI.
`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. l'hree dillcrent size switches are identified in Table 2.
`
`TABLE 2
`Commercial GRIN Lens Collirriators
`1.0 mm
`2.0 mm
`1.0 mm
`diameter
`diameter
`diameter
`/A =
`/A =
`/A =
`0.481/niru
`0.237/rirrri
`0.148/nirri
`
`.
`
`.
`
`6.77
`H56 X1156
`
`Parameter‘
`Collirriators
`Etfcctivc focal
`lengtl: (mm)
`(frossconncct s /.e
`(input >< output)
`Collirriator array
`width (rnni)
`Angular tolerance
`on individual
`collirnators (nuad)
`Mici'oi'r1irrors
`Mirror size
`(1-x >< Ly: 111012)
`Mir.i_rnum mirror
`radius of curvature
`(In)
`Dynamic angular
`range (degrees)
`Angular precisior: to
`direct beam to
`miror on 21"“ array
`(mrad)
`Mirror angular
`precision for
`~40 dB mode
`overlap loss timrad)
`Mirror angular
`precision for -0.5
`
`8
`
`TABLE 2—continued
`Commercial GRI
`1.0 mm
`’_/‘.l”. mm
`diameter
`diamctcr
`/A :
`./A :
`0.48 l /mm
`0.23”/mm
`
`s Collimatars
`4.0 m 11
`dian-rctcr
`/A :
`0.148/mm
`
`Parameter
`
`(H5 ninrle overlap
`loss (mrad)
`Actuators
`Assumed actuatcr
`ttavel (urn)
`Actuator precision
`to direct beam to
`mirror
`en 2“ array (um)
`Actuator precision
`for ~05 dFl made
`cverlap loss (nm)
`
`Regarding the collimators, an ellective local length equal
`to l/\/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 rnicroma—
`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 flatness (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 difficult to design a
`mirror having a thickness of 100 microns to several hundred
`microns. This thickness is necessary to ensure that the gold
`film used as a refiective coating on the mirrors does not
`CflllS€ undue CllI'V€l[Ll]'€.
`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 di icult con-
`straints on other components of the system, such as the
`actuators for nianipulating the niicroniirrors. For the actua-
`tors which will be described fully below, a 10° nioveriierit of
`a 2 mm diameter mirror requires a mover to travel approxi-
`mately 50 to l00 microns. This requirement limits the types
`of micromachined drives that can be utilized. In the pre-
`ferred embodiment, electrostatic surface actuators are t1ti—
`lized.
`Table 2 also includes three different angular position
`requirements for the rnicromirrors. 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,
`21 niaxiniurii 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
`used to close a control loop which positions the micromir-
`rors. There is a significant benefit in performing the open
`loop control of the beam position on the second niicroniirror
`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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1018-17
`
`

`
`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.
`Briefly, with regard to the constraints involving the
`actuators, the micromirror properties identified above play
`an iriiportant role in determining the requirements of the
`actuators used to drive the micromirrors. For the preferred
`micromirror size and angular range, the actuators must travel
`a distance of approximately 100 microns. An actuator needs
`to be repeatedly positioned with an accuracy of ~0.1 microns
`in order to move the beam between the riiirrors on the second
`array, to position the beam in the center of a particular mirror
`in that array, and to achieve ~40 dB coupling, into the output
`fiber. This position accuracy can be provided by an electro-
`static surface actuator.
`
`PROPOSED MICROMIRROR DESIGN
`
`FIG. 6 is a top View of an array of sixteen micromirrors
`50 formed on a micromirror substrate 52. FIG. 7 is a side
`view of one of the micromirrors and the mechanism for
`manipulating the rotations of the micromirror, FIG. 7A is a
`top View of the mechanism for manipulating the micromirror
`rotations. Referring first
`to FIG. 6, each micromirror is
`coupled to a ring member 54 by first and second torsion bars
`56 and 58. The positions of the torsion bars define the first
`axis of rotation of the mirror 50. In the orientation of FIG.
`6, the first axis is a x axis. The ring member 54 is coupled
`to the substrate 52 by third and fourth torsion bars 60 and 62,
`which define the s