`(HI) Patent No.:
`US 6,798,992 Bl
`(45} Date of Patent:
`Bishop et a1.
`*Sep. 28, 2004
`
`US()[16?98992BI
`
`(54) METHOD AND DEVICE FOR OPTICALLY
`CROSSCONNI‘ZCTING ()l’l‘lCAL SIGNALS
`USING TILTING MIRROR MEMS WITH
`[)RII'T MONITORING FEA’I‘URE
`
`(T5)
`
`inventors: David John Bishop, Summit. NJ (US);
`Randy Clinton Giles, Whippany, NJ
`(US)
`
`(T3) Assignees: Agere Systems Inc, Allentown, PA
`(US); Ltloent 'l'eclrnologies lnc.,
`Murray Hill. NJ {US}
`
`(*i Notice:
`
`Subject to any disclaimer, the term oftlris
`patent is extended or adjusted under 3:3
`USE.
`|54[h) by [I days.
`
`(58)
`
`(56)
`
`398315, 46, 49,
`Field of Search
`398.48. 50, 52, 55, 56, 12. 19; 356F311;
`385.41%, 17, 18, 1‘), Ell—24, 33, 119
`
`References Cited
`US. PATENT DOCUMENTS
`
`3,9001 Schroeder el al.
`0,198,856 B1 "
`lfii2flit1 Hhalla elal.
`.
`(1.3013102 I‘ll
`‘
`
`0,2002 Giles et al.
`6.411.?51 Bl
`‘
`
`132002 Sparks et al.
`(1.42435? BI
`‘
`OTHER PUBLICATIONS
`
`..
`
`385,-”?
`33.5fm
`385,316
`385m“)
`
`U.S. application No. 09.r'5121?4 (Aksyuk et a1)li1ed on Feb.
`24, 2000."
`
`This patent is subject to a terminal dis-
`claimcr.
`
`(21) Appl. Nu: 09,518,070
`
`(23)
`
`Filed:
`
`Mar. 2, 2009
`
`60
`
`Related US. Application Data
`Provisional a \Iieation No. infirm-1,450. filed on Nov. 101
`1901:
`H
`Int. CL?
`(51)
`(52) U.S. CI.
`
`HIM] 14300
`398,515; 39850; 39852;
`
`39855: 398,56: 393ml: 398,49; 398E47;
`398.-"48; 398I46; 385.316; 385.47“; 385.518;
`385.319; 385t'20; 385.21; 385.22; 385.03;
`385.24; 385133; 385.-’Il‘); 356t'i'3.1
`
`* cited by examiner
`
`Primary Exaritiner—i lanh Ph an
`(5 'r')
`ABSTRACT
`
`A device and method for detecting rotational drift of mirror
`elements in a MEMS tilt mirror array used in an optical
`crossconnecl. The optical crossconnect directs optical sig-
`nals from an input lilaer to an output fiber along an optical
`path by rotatabl],r positioning mirror elements in desired
`positions. A monitoring device disposed outside of the
`optical path is used to obtain images of the MEMS array or
`to transmit and receive a test signal through the erossmnneet
`for detecting the presence of mirror element drift.
`
`16 Claims, 2 Drawing Sheets
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`
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 1
`Exhibit 1006, Page 1
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`U.S. Patent
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`Sep. 28, 2004
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`Sheet 1 on
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`Us 6,798,992 Bl
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 2
`Exhibit 1006, Page 2
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`
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`U.S. Patent
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`Sep. 28,2004
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`Sheet 2 on
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`Us 6,798,992 Bl
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`FIG. 3
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 3
`Exhibit 1006, Page 3
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`US 6,798,992 Bl
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`1
`METHOD AND IIEVICE FOR OI’TICALLY
`CROSSCONNECTING OPTICAL SIGNALS
`USING TILTING MIRROR MEMS WITH
`DRIFT MONITORING FEA'I‘URE
`
`This application is based on US. Provisional Application
`Ser. No. 603164.459 tiled on Nov. 10, 1999.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention pertains to liber optic communica—
`tions systems and. more particularly, to monitoring devices
`and methods for monitoring shifts in optical crossconnect
`configurations utilizing micro electromechanical systems
`(MEMS) tilting mirror arrays.
`2. Description of the Related Art
`In fiber optic communication systems, signal routing is
`essential for directing an optical signal carrying data to an
`intended location. Existing routing techniques typically
`experience optical power loss due to ineflicient coupling of
`optic signals between input and output fibers. This increases
`the dependence on optical power sources (e.g.. pump lasers)
`which are used to compensate for power losses by injecting
`optical power back into the optical system. The need for
`optical power sources increases the overall cost of the
`optical system.
`Another criteria for signal routing is the ability to direct
`a signal received from one of a plurality of input libers or
`ports to any of a plurality of output fibers or porLs without
`regard to the frequency of the optical signal.
`Free-space optical cmssconnecLs allow interconnecting
`among input and output ports in a reconfigurable switch
`fabric. An example oisueh an optical crossconnect utilizing
`mirco—clectrornechanical systems (MEMS) tilting mirror
`devices is disclosed in commonly owned and copending
`US. patent application Ser. No. tt9t41058o, filed Oct. 1,
`1999. By adjusting the tilt angles of the MEMS mirror
`devices, optical signals can be directed to various
`destinations, i.e. to numerous output fibers.
`MEMS devices and,
`in particular, tilting mirror devices
`are susceptible to unwanted movement or drill due to
`external factors such as temperature changes and mechanical
`fatigue experienced by actuator elements used to deploy and
`control the individual mirror elements. As a result, optical
`signal power may be lost due to misalignment of thc
`retlected optical signal with its intended target (e.g. an
`output fiber]. Accordingly, a system is desired to monitor
`MEMS optical crossconnect configuration to provide for
`displacement adjustment.
`SUMMARY OF THE INVENTION
`
`An optical erossconnect device having a monitoring fea-
`ture for detecting optical signal drift is provided. The device
`provides optical connection of optic signals between input
`fibers and output fibers by using a MEMS tilt minor array.
`The MEMS array includes a plurality of tiltable mirror
`elements which are positionable in an intended orientation
`for directing optical signals, but which are susceptible to
`drift that causes degradation in the optical coupling oi" the
`signals to the output libers. A monitoring device positioned
`outside of the optical path dynamically monitors the position
`of one or more of the mirror elements to detect drift.
`
`In a preferred embodiment, the monitoring device is a
`camera for obtaining an image of one or more mirror
`clemcnts.
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`In another embodiment, the monitoring device comprises
`an optical transmitter and an optical receiver for transmitting
`a test signal
`through the optical crossconnect to monitor
`mirror position dril‘t.
`In yet another embodiment, a pattern is formed on one or
`more ot‘ the mirror eteme ms and an image or reflection of the
`pattern is obtained for determining the presence of mirror
`drift.
`
`A method is also described for monitoring mirror clement
`positions of mirror elements in a MEMS Iill mirror array
`used in an optical crossconnect. The method is used with a
`MEMS mirror array having mirror ctemean disposed at
`desired tilt positions for crossconnecting an optic signal
`between an input Iiber and an output liber along an optical
`path. A monitoring device disposed ouLside of the optical
`path monitors the positions of the mirror elements to detect
`when position drift occurs. The mirror positions are then
`adjusted by forming control signals based on the detected
`drift and applying the control signals to the drifted mirror
`elements.
`
`Other objects and features of the present invention will
`become apparent from the following detailed description
`considered in conjunction with the accompanying drawings.
`It
`is to be understood, however,
`that
`the drawings are
`designed solely for purposes of illustration and not as a
`definition of the limits of the invention, for which reference
`should be made to the appended claims. It should be further
`understood that the drawings are not necessarily drawn to
`scale and that, unless otherwise indicated, they are merely
`intended to conceptually illustrate and explain the structures
`and procedures described herein.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings, wherein like reference numerals denote
`similar elements throughout the several views.
`FIG. 1 is a planar view of an example of a MEMS mirror
`array used in connection with the present invention;
`FIG. 2 is a schematic representation of an optical cross-
`oonncct monitoring device in accordance with one embodi—
`ment of the present invention; and
`FIG. 3 is a schematic representation of a monitoring
`device for a "folded“ optical crossconnect in accordance
`with another embodiment of the present invention.
`DETAILED DESCRIPTION OF THE.
`PREFERRED EMBODIMENTS
`
`Arrays of two-axis tilt mirrors implemented using micro-
`electromechanieal systems (MEMS) technology in accor-
`dance with the invention allow for the construction of large
`scale optical crossconnects for use in optical systems. Opti—
`cal crossconnects are commonly employed to connect a
`number of input optical paths to a number of output optical
`paths. Atypical requirements of optical crossconnects is that
`any input be capable of being connected to any output. One
`example of a MEMS mirror array It] is depicted in FIG. I.
`The mirror array 10 includes a plurality of tilt mirrors 12
`formed on a substrate 11, mounted to actuation members or
`springs 14 and controlled by electrodes (not shown). Each
`mirror 12 is approximately 100—500 Microns across. may be
`shaped as square, circular or elliptical, and is capable of
`operativety rotating or tilting about orthogonal X-Y axes,
`with the tilt angle being selectively determined by the
`amount of voltage applied to the control electrodes. Further
`details of the operation of the MEMS mirror array 10 are
`found in copending U.S. patent application Ser. No. toms,
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 4
`Exhibit 1006, Page 4
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`US 6,798,992 B]
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`178, filed Oct. 8, 1999, the entire contents of which are
`incorporated herein by reference. The general concept of
`utilizing two or more such tilt mirror arrays 1|} to form an
`optical crossconnecl is disclosed in copending US. patent
`application Ser. No. 091410.586, filed Oct. 1, 1999, the entire
`contents of which are also incorporated herein by reference.
`'Ihe use of one or more MEMS tilt mirror arrays in
`conjunction with a lens array is disclosed in co-pending US.
`patent application Ser. No. (191512.174, filed Feb. 24, 21100.
`the entire content of which is also incorporated herein by
`reference. As disclosed in that application, various optical
`erossconnccl configurations of compact size [i.e. minimal
`spacing between crossconnect components) and exhibiting
`minimal optical power loss can be realized. One such optical
`erossconnecl 1111] diwussed in the aforementioned applica—
`tion is depicted in FIG. 2. Crosseonnect 101} receives input
`optic signals 108 through a plurality of optic fibers 1.12,
`preferably formed in an array as is well known in the art. For
`ease of illustration fiber array 110 is shown as a one—
`dimensional array having four fibers 112a. 1121). 112c, 112d.
`11 is in any event to be understood that fiber array 112 as well
`as other fiber arrays discussed herein are preferably two-
`dimensional arrays such as, for example. NxN arrays.
`Fiber array 112 transmits the optical signals 108 to an
`array of lenses 114 that function as collimating lenses. The
`lens mm)! 114 is positioned relative to liber array 112 so that
`each lens communicates with a corresponding fiber for
`producing pencil beams 116 from the optic signals 1.18.
`Thus, beam 116a is produced from a signal carried by fiber
`112a, beam 116d is produced from a signal carried by fiber
`112d, etc.
`A first MEMS Iilt mirror array 118, also referred to as the
`input array, is positioned in alignment with lens array 114 so
`that each mirror element 12 will receive a corresponding
`beam 11 IS. The mirror elements are operatively tilted, in a
`manner discussed in application Ser. No. 091415.178,
`to
`reflect
`the respective beams 116 to a second or output
`MEMS mirror array 122 positioned in optical communica-
`tion with MEMS array 11.8. Depending on the tilt angle of
`each mirror element in input MEMS array 118, the reflected
`signals can be selectively directed to specific mirror ele-
`ments in output MEMS array 122. To illustrate this
`principle, beam 116:: is shown in FIG. 2 generating reflec-
`tion beams 120.0 and 1209‘ and beam 116dI is shown in the
`figure generating reflection beams 120d and 12M. These
`beams are received by mirror elements in the output MEMS
`array 122 and are directed as beams 124 to an output lens
`array 126. An output fiber array 128 is aligned with lens
`array 126 to receive and output optical signals 129. Thus,
`lens array 126 couples beams 124 into the output fiber array
`128.
`The rotatable positions or orientations; of the individual
`minor elements 12 of arrays 118 and 122 are, however,
`alfected by environmental conditions such as temperature
`changes. As a result, once the positions of the mirror
`elements 12 are set, those intended positions may drift or
`change due (for example) to temperature variations, thereby
`adversely causing ineilicient or unintended signal routing
`and associated power losses. A similar problem may be
`caused by mechanical fatigue and stress on the actuators
`used to control mirror position, and by electric charging
`effects on the actuators. These variations can result
`in
`conditions referred to as macro~drift. wherein all of the
`minor elements in an array drill by an equal amount, and
`micro-drift,
`in which only some of the mirror element
`positions unintendedly change.
`To detect such unwanted mirror drift in optical crosscon-
`necLs in accordance with the present invention to compen-
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`sate for actual mirror positions, one or more monitoring
`devices 130, 132 are included in the crossconnect system
`100 shown in FIG. 2. The monitoring devices may be used
`to detect both macro—drift and micro—drift conditions of the
`MEMS mirror arrays 118, 122. For example, each monitor-
`ing device may be a camera or other imaging devices which
`operates independently of other cameras. Each camera is
`shown in FIG. 2. positioned outside of the optical path ofthe
`crossconneel (i.e. the path in which optical signal 116 travels
`through the crosssconnect to fiber array 128) and obtains an
`image of its respective MEMS array. Thus, camera 130 is
`focussed on MEMS array 118 and camera 132 is foeussed on
`MEMS array 122. The resulting images are then compared
`to reference images of mirror array positions stored, for
`example. in a controller block 500 containing a processor
`and a database (not shown) in a manner well-known to those
`having ordinary skill in the art. In the event that an unac—
`ceptable amount of drift
`is detected for the entire mirror
`array. feedback control signals can be generated by the
`control block 500 for adjusting the tilt angles to compensate
`for drift by applying appropriate voltages to the mirror
`actuators. [ion the other hand only certain mirror elements
`need to be adjusted, these mirrors can be identified, through
`the aforementioned image comparison with a reference
`image. and then re—positioned by applying appropriate volt-
`ages to the desired actuators.
`The monitoring system of FIG. 2 can also be employed in
`connection with a folded crossoonnect configuration, as for
`example shown in FIG. 3, wherein a single inpulioulput libcr
`array 312, single MEMS mirror array 318, and reflective
`surface element 331] comprise the folded configuration. A
`camera 340 positioned outside of the optical path 316
`obtains an image 342 of the mirror elements in the array 318
`for use in calculating and compensating for detected drift.
`As an alternative or in addition to the use of cameras,
`device 130 (FIG. 2} may comprise one or more illuminators
`(not shown) for producing, for example. one or more infra-
`red beams 131, 133 directed at mirror arrays 118, 122 and
`devices 130, 132 may comprise an infra-red detector for
`detecting the reflected infra—red beams. The illumination
`source may produce a test signal having a different wave-
`length from the signal wavelength or can be modulated to
`discriminate and distinguish it from the signal wavelength.
`The infrared beams 131, 133 may be pencil beams for
`illuminating a single mirror element which may be desig—
`nated as a reference element, such as element 16 in MG. l.
`The reflected infra-red signal will pass through the optical
`crossconneet for receipt by its respective infra-red detector.
`For example, for an infra-red test beam directed at a mirror
`element in array 118, the test beam will be reflected and
`directed to detector 131], and for an infrared beam directed
`at a mirror element
`in array 122.
`the test beam will be
`received by detector 132. Depending on the characteristics
`of the reflected and received infra-red beams—such as a
`reduction in beam power or intensity andfor a change of
`position on the detector at which the beam is received,
`etc.—macrodrift can he dynamically detected. For example,
`and as a result of a temperature change, drift may occur
`among all mirror elements in mirror arrays 118, 122. By
`measuring and detecting drift from a reference mirror ele-
`ment (e.g. mirror 16), the mirror arrays can be adjusted to
`compensate for dril't by generating appropriate feedback
`signals from control blocks 500 to be applied to mirror
`control actuators.
`
`it will be appreciated that both devices 130. 132 can
`operate as combined or dual-function sourcetreceiver
`devices wherein each device produces a signal for receipt by
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 5
`Exhibit 1006, Page 5
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`the other and receives a signal produced by the other.
`Likewise, and in connection with the folded configuration of
`FIG. 3, device 340 can be implemented by or supplemented
`with a detecton‘receivcr for receiving reflected test signals
`342, 343 generated by a source such as an infrared source
`350 for illuminating one or more mirror elements 12.
`For micro-drift compensation. the devices 130, 132 in the
`system 100 of FIG. 2 and the device 340 in the system 300
`of FIG. 3 can be connected to a scanning device which may
`be found in controller block 500 for changing the position of
`the test beam (beam 130 in FIG. 2 and beam 342 in FIG. 3)
`to illuminate multiple mirror elements. For example,
`the
`scanner can adjust the test beam position to illuminate one
`mirror element 12 at any given time for determining the tilt
`angle of each illuminated mirror.
`As another alternative, the reference mirror element 16
`may be formed with an imaging pattern 14, as for example
`by surface etching. This modification allows for the use of
`pattern recognition techniques wherein a generated pattern is
`received or monitored by a detector or camera. Detected
`movement of the pattern indicates mirror drift.
`l’attem 14
`may be specifically oriented to generate a unique pattern that
`is observable in scattered light so as to provide an enhanced
`signature when a light beam is centered on mirror 16. A
`single unique pattern may be used for all mirrors, or each '
`mirror can be coated with its own unique pattern. Entire
`pathways through the mirror array may be defined by unique
`patterning, thus helping to guide light beams through the
`array during switching.
`'lhus. while there have shown and described and pointed
`out fundamental novel features ot'the invention as applied to
`preferred embodiments thereof,
`it will be understood that
`various omissions and substitutions and changes in the form
`and details of the methods disclosed and devices illustrated,
`and in their operation, may be made by those skilled in the
`art without departing from the spirit of the invention. For
`example, it is expressly intended that all combinations ol‘
`those elements and method steps which perform substan-
`tially the same function in substantially the same way to
`achieve the same results are within the scope of the inven-
`tion. Moreover,
`it should be recognized that structures
`andi’or elements andior method steps shown ands'or
`described in connection with any disclosed form or embodi-
`ment of the invention may be incorporated in any other
`disclosed or described or suggested form or embodiment as
`a general matter of design choice.
`It
`is the intention,
`therefore, to be limited only as indicated by the scope of the
`claims appended hereto.
`What is claimed is:
`1. An optical crossconnect monitoring device for directing
`optical signals received from a plurality of input optic fibers
`along an optical path to a plurality of output optic fibers, and
`for detecting spatial shifts of the optical signals, comprising:
`a moveable mirror formed on a substrate and positioned
`within the optical path for receiving optical signals
`from one of the plurality of input optic fibers and
`directing said received signals along the optical path
`speeilie ones of the plurality of output optic fibers, said
`mirror being operativety tiltahle about a rotational axis
`to an intended angular orientation relative to said
`substrate for providing desired directional reflection of
`a one of the optical signals received by said mirror; and
`an optical monitoring device positioned outside of the
`optical path and in optical communication with said
`mirror for optically detecting rotational drift of said
`mirror relative to said intended angular orientation, said
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`detected rotational drift being indicative of optical
`signal spatial shifts.
`2. The device of claim 1, wherein said moveable mirror
`comprises a MEMS mirror array having a plurality of
`moveable mirror elements.
`3. The device of claim 2, wherein said monitoring device
`comprises a camera oriented for obtaining an image of said
`rmrror array.
`4. The device of claim 3, wherein one of said mirror
`elements is formed with a pattern for receipt of an image of
`said pattern by said camera.
`5. The device of claim 2, wherein said monitoring device
`comprises an illumination device for illuminating a selected
`one of said plural mirror elements with a test optical signal
`and a receiver for receiving the test signal after reflection of
`the test optical signal from said selected mirror element.
`6. The device of claim 5, wherein one of said mirror
`elements comprises a pattern for producing a reflection of
`said pattern for receipt by said receiver when said selected
`mirror element is illuminated by the test signal.
`7. The device of claim 5, wherein the plurality of input
`optic fibers and the plurality of output optic libers form an
`array of optic fibers, said device further comprising a
`reflector element disposed in optical contmunication with
`said MEMS mirror array for receiving optical signals from
`said MEMS mirror array and for reflecting the received
`optical signals back to said MEMS mirror array, said
`reflected optical signals being redirected by said MEMS
`mirror array back to said array of optic fibers for receipt by
`the output optic fibers.
`8. The device of claim 7. wherein said reflector element
`receives the test signal from said illumination device and
`reflects the test signal to said receiver.
`9. The device of claim 7, wherein said illuminating device
`and said receiver are integrally formed.
`10. The device of claim 2, wherein the plurality of input
`optic fibers and the plurality of output optic fibers form an
`array of optic fibers, said device further comprising a
`reflector element disposed in optical communication with
`said MEMS mirror array for receiving optical signals from
`said MEMS mirror array and for reflecting the received
`optical signals back to said MUMS mirror array, said
`reflected optical signals being redirected by said MEMS
`mirror array back to said array of optic fibers for receipt by
`the output optic lihers.
`11. The device of claim 2, further comprising a controller
`connected to said monitoring device anti operable for gen-
`erating a control signal in response to the detected rotational
`drift.
`12. A method of monitoring a spatial shift of optical
`signals in an optical crossconnect device which directs
`optical signals received from a plurality of input optic fibers
`along an optical path to a plurality of output optic fibers,
`comprising the steps of:
`placing a mirror formed on a substrate within the optical
`path for receiving optical signals from one of the
`plurality of input optic fibers and directing said
`received signals along the optical path to specific ones
`of the plurality ofoutput optic fibers, said mirror being
`operativety tiltabte about a
`rotational axis to an
`intended angular orientation relative to said substrate
`for providing desired directional reflection of one of the
`optical signals received by said mirror;
`positioning an Optical monitoring device outside of the
`optical path and in optical communication with said
`mirror; and
`optically detecting rotational drift of said mirror relative
`to said intended angular orientation using the optical
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 6
`Exhibit 1006, Page 6
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`monitoring device, said detected rotational drift being
`indicative of optical signal spatial shifts.
`13. The method 01‘ claim 12, wherein said moveable
`mirror comprises a MEMS mirror array having a plurality ol‘
`moveable minor elements.
`14. The method of claim 13. further comprising the steps
`of determining which of said plural mirror elements have
`experienced rotational drift, generating control signals from
`said opticall}.r detecting step, and using said control signals
`to operatively adjust rotatable positions of said rotationally
`drifted mirror elements.
`15. The method ol‘elaim 13, wherein said posilioning step
`further comprises the step of positioning an optical signal
`transmitter outside of the optical path for generating an
`optical test signal directed at said MEMS array for reflection
`by said MEMS array, and positioning an optical receiver
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`outside of said optical path for detecting said reflected lest
`signal after reflection of Ihe test signal from the MEMS
`array. and wherein said monitoring step further comprises
`monitoring a power level ol‘said lest Signal received by said
`receiver.
`16. The method of claim 13, wherein aI leasl one of said
`mirror elements is a pattern mirror element, and wherein
`said positioning step further comprises positioning an opti-
`cal signal transmitter outside of the optical path for gener-
`ating an optical test signal directed at said pattern mirror
`element for reflection by said pattern mirror element
`to
`Iherehy generate an image of the pattern, and positioning an
`optical receiver outside of said optical path for receiving and
`detecting said pattern image.
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1006, Page 7
`Exhibit 1006, Page 7
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