(12) United States Patent
`Goldstein et al.
`
`US006243507B1
`US 6,243,507 B1
`Jun. 5, 2001
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) CONNECTION-VERIFICATION IN OPTICAL
`MEMS CROSSCONNECTS VIA MIRROR
`DITHER
`
`(75) Inventors: Evan Lee Goldstein, Princeton;
`Lih-Yuan Lin, Middletown; Leda
`Maria Lunardi, Marlboro, all of NJ
`(Us)
`(73) Assignee: AT&T Corp., New York, NY (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/472,682
`(22) Filed:
`Dec. 27, 1999
`
`Related US. Application Data
`(60) Provisional application No. 60/137,840, ?led on Jun. 7,
`1999.
`
`(51) Int. Cl.7 ..................................................... .. G02B 6/12
`(52) US. Cl. ............................... .. 385/13; 385/17; 385/18;
`385/ 19
`(58) Field of Search .......................... .. 385/16—19, 12—14;
`359/212, 223, 225, 250/216, 234
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`8/1992 Dragone ............................... .. 385/46
`5,136,671
`10/1992 Miller et al. ....................... .. 359/495
`5,155,623
`4/1993 Lee .............. ..
`. 250/2011
`5,206,497
`9/1999 Lin ........................ .. 385/18
`5,960,132
`6,144,781 * 11/2000 Goldstein et al. ................... .. 385/18
`
`OTHER PUBLICATIONS
`
`H. Toshiyoshi et al., “Electrostatic Micro Torsion Mirrors for
`an Optical Switch Matrix,” Journal of Microelectrome
`chanical Systems, vol. 5, No. 4, Dec. 1996, pp. 231—237.
`
`B. Behin et al., “Magnetically Actuated Micromirrors for
`Fiber—Optic Switching,” Solid—State Sensor and Actuator
`Workshop, Hilton Head, South Carolina, Jun. 8—11, 1998,
`pp. 273—276.
`K. S. J. Pister et al., “Microfabricated Hinges,” Sensors and
`Actuators, vol. A, No. 33 (1992), pp. 249—256.
`T. Akiyama et al., “A Quantitative Analysis of Scratch Drive
`Actuator Using Buckling Motion,” IEEE Workshop on
`Micro Electro Mechanical Systems, Amsterdam, The Neth
`erlands, Jan. 29—Feb. 2, 1995, pp. 310—315.
`R. T. Chen et al., “A Low Voltage Micromachined Optical
`Switch By Stress—Induced Bending,” 12th IEEE Interna
`tional Conference On Micro Electro Mechanical Systems,
`Orlando, Florida, Jan. 17—21, 1999, 5 pages.
`Cronos Integrated Microsystems, Inc., “Three—Layer Poly
`silicon Surface Micromachine Process,” Aug. 24, 1999, pp.
`1—8 (http://mems.mcnc.org).
`L. Y. Lin et al., “Free—Space Micromachined Optical
`Switches for Optical Networking,” IEEE Journal of Selected
`Topics in Quantum Electronics, vol. 5, No. 1, J an./Feb. 1999,
`pp. 4—9.
`
`(List continued on neXt page.)
`Primary Examiner—Darren Schuberg
`Assistant Examiner—FayeZ Assai
`(57)
`ABSTRACT
`
`Integrated connection-veri?cation system for use in a micro
`electro-mechanical system (MEMS) crossconnect device.
`The system uses application of a dithering signal such as a
`sinusoidal bias to an electrode plate associated with a
`micro-mirror switching element to dither the micro-mirror.
`The optical signal from the dithering micro-mirror is fed
`through a beam splitter, a portion of the optical signal thus
`being directed to a photodetector. If intensity modulation in
`the optical signal corresponding to the frequency of the
`dithering signal is detected by the photodetector associated
`with the micro-mirror, the connection path between the
`desired input and output ports is veri?ed.
`
`11 Claims, 9 Drawing Sheets
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-1
`
`

`

`US 6,243,507 B1
`Page 2
`
`OTHER PUBLICATIONS
`
`L. Y. Lin et al., “High—Density Micromachined Polygon
`Optical Crossconnects Exploiting Network Connection—
`Symmetry,” IEEE Photonics Technology Letters, vol. 10,
`No. 10, Oct. 1998, pp. 1425—1427.
`E. L. Goldstein et al., “National—Scale Networks Likely to
`Be Opaque,” Lightwave, Feb. 1998, pp. 91—95.
`C—K. Chan et al., “A Novel Optical—Path Supervisory
`Scheme for Optical Cross Connects in A1100ptical Transport
`
`NetWorks,” IEEE Photonics Technology Letters, vol. 10, No.
`6, Jun. 1998, pp. 899—901.
`L. Y. Lin et al., “Optical Cross—connect Integrated Systesm
`(OCCIS): A Free—Space Micromachined Module for Signal
`and SWitching Con?guration Monitoring,” IEEE LECS
`Summer Topical Meeting: Optical MEMS, Monterey, Cali
`fornia, Jul. 20—22, 1998, 3 pages.
`
`* cited by examiner
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-2
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 1 0f 9
`Sheet 1 0f 9
`
`US 6,243,507 B1
`US 6,243,507 B1
`
`
`
`Petitioner Ciena Corp. et 21].
`Exhibit 1022-3
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-3
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 2 0f 9
`
`US 6,243,507 B1
`
`
`
`‘ MICRO-HINGES
`
`FIG. 2
`
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`
`
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`
`
`
`
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`
`
`
`
`5.00 W 5.0 120x 22.1
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-4
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 3 0f 9
`
`US 6,243,507 B1
`
`5
`r—
`1,5
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`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-5
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 4 0f 9
`Sheet 4 0f 9
`
`US 6,243,507 B1
`US 6,243,507 B1
`
`FIG. 4
`
`
`
`Petitioner Ciena Corp. et 21].
`Exhibit 1022-6
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-6
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 5 0f 9
`
`US 6,243,507 B1
`
`305065
`
`E933 mew °
`
`0
`
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`
`m 65%
`
`ozazomlmmi
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-7
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 6 0f 9
`
`US 6,243,507 B1
`
`FIG. 6
`
`
`
`RESPONSE (4H2, ZOmV/div)
`
`-~~
`
`-
`
`1-’
`
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`l.
`
`BIAS
`VOLTAGE
`(2H2, 30v)
`
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`
`.2
`
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`
`—25.000 ms
`
`0.000 s
`
`25.000 ms
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-8
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 7 0f 9
`
`US 6,243,507 B1
`
`RESPONSE
`
`—25.000 ms
`
`0.000 s
`
`25.000 ms
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-9
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 8 0f 9
`
`US 6,243,507 B1
`
`FIG. 10
`
`—500.00 ms
`
`0.000 s
`
`500.00 rns
`
`(4H2,
`
`'
`
`i.
`
`BIAS
`VOLTAGE
`(2H2, 30v)
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`
`0.000 s
`
`500.00 ms
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-10
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 9 0f 9
`Sheet 9 0f 9
`
`US 6,243,507 B1
`US 6,243,507 B1
`
`FIG. 12
`FIG. 12
`
`RESPONSE
`(4H2.
`20mV/d'w)
`
`BIAS
`VOLTAGE
`(20:, 40v)
`
`4
`
`
`
`
`-500.00 ms
`-500.00 ms
`
`0.000 s
`0.000 s
`
`500.00 ms
`500.00 ms
`
`Petitioner Ciena Corp. et 21].
`Exhibit 1022-11
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-11
`
`

`

`US 6,243,507 B1
`
`1
`CONNECTION-VERIFICATION IN OPTICAL
`MEMS CROSSCONNECTS VIA MIRROR
`DITHER
`
`This nonprovisional application claims the bene?t of
`US. Provisional Application No. 60/137,840, ?led Jun. 7,
`1999.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`This invention relates to a connection veri?cation system
`in an optical rnicro-electro-rnechanical systern (MEMS)
`crossconnect device.
`2. Description of Related Art
`Optical crossconnects (OXCs) have emerged as a prom
`ising means of carrying out optical-layer provisioning and
`restoration in future, high-capacity WDM (Wavelength
`division multiplexing) netWorks.
`As technologies for optical sWitching advance, enhancing
`the netWorking functionality of OXCs has become increas
`ingly important, and doing so via integrated and loW-cost
`approaches becomes particularly desirable. One important
`requirement for the OXC is connection-veri?cation for
`netWork surveillance. That is, it is desired to verify that an
`optical signal is being properly sWitched and carried Within
`the system to the desired output port or ?ber.
`What is still desired is a simple, cost-effective connection
`veri?cation system for use in a MEMS optical crossconnect
`netWork.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`2
`optical signal from an input port to a desired output port,
`cornprising sWitching an optical signal from the input port to
`the desired output port With a rnicro-rnirror having an optical
`signal input side and an optical signal output side, the
`rnicro-rnirror connected to a substrate, applying a dithering
`signal to an electrode plate in association With the rnicro
`rnirror to dither the rnicro-rnirror, and splitting the optical
`signal on the optical signal output side of the rnicro-rnirror
`into a detection portion and an output portion With a beam
`splitter located on the substrate at the optical signal output
`side of the rnicro-rnirror, the beam splitter directing the
`detection portion of the optical signal to a photodetector
`located beneath the beam splitter. The connection path is
`veri?ed When the photodetector detects alterations in inten
`sity of the detection portion of the optical signal correspond
`ing to the dithering signal applied to the electrode plate.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an illustration of the rnirror-dither scheme for
`pilot-tone coding and on-chip signal monitoring in the
`free-space MEMS OXC of the invention.
`FIG. 2 is a SEM (scanning electron microscope) photo
`graph of a free-rotating hinged rnicro-rnirror in a free-space
`MEMS OXC of the invention.
`FIG. 3 is a SEM photograph of the rnicro-sWitch mirror
`with an integrated electrode.
`FIG. 4 is a schematic diagram of a rnicroactuated free
`rotating sWitch rnirror.
`FIG. 5 is a SEM photograph of the bearn-splitter/
`photodetector rnonitor module of the invention.
`FIGS. 6—9 are frequency responses of the rnicro-rnirror at
`various frequencies and biases, While FIGS. 10—12 are
`frequency responses of the rnicro-rnirror at various biases,
`the upper traces representing signals from the photodetector,
`the loWer traces representing biases on the electrode.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`In a conventional netWork, there is access to the bit
`strearns traveling Within the system. This enables easy
`manipulation of a bit stream, for example by turning signals
`on and off to represent bits, in order to verify that the bit
`stream is being sWitched to the proper output port. The
`methodology was simple and straightforWard.
`HoWever, this conventional technology cannot be utiliZed
`in optical crossconnect systems because access to the system
`as in the conventional technology is not available. That is, in
`conventional electronic systems, information can be
`manipulated at the bit level because of the devices used in
`such a system. HoWever, in optical crossconnect systems,
`the equipment includes lenses, etc., that do not afford
`manipulation of bits. As a result, it is not possible in optical
`crossconnect systems to look at information bits and deter
`mine therefrorn What they are connected to. Thus, neW
`connection veri?cation technology must be developed in
`order to con?rrn that the sWitches Within the optical cross
`connect are properly connecting an input optical signal to
`the desired output port.
`An optical path supervisory scheme has been proposed in
`C.-K. Chan, E. Kong, F. Tong and L.-K. Chen, “A Novel
`Optical-Path Supervisory Scheme For Optical Cross Con
`nects In All-Optical Transport Networks”, IEEE Photonics
`Tech. Lett., vol. 10, pages 899—901 (1998). In this scheme,
`use is made of periodic characteristics of arrayed
`Waveguide-gratings. Although adequate, this scheme is
`
`SUMMARY OF THE INVENTION
`It is therefore an object of the invention to develop a
`connection path veri?cation system for use in the MEMS
`OXC.
`This and other objects are achieved by the present inven
`tion that achieves connection path veri?cation via integrated
`pilot-tone coding schemes utiliZing rnicro-rnirror dithering
`in the MEMS crossconnect.
`In one aspect of the invention, the invention relates to a
`connection veri?cation system comprising a rnicro-rnirror
`having an optical signal input side and an optical signal
`output side, the rnicro-rnirror connected to a substrate, an
`electrode plate in association With the rnicro-rnirror and
`capable of dithering the rnicro-rnirror upon application of a
`dithering signal to the electrode plate, a beam splitter located
`on the substrate at the optical signal output side of the
`rnicro-rnirror, and a photodetector positioned beneath the
`beam splitter.
`In a further aspect of the invention, the invention relates
`to a connection veri?cation system of an optical rnicro
`electro-rnechanical crossconnect device, comprising at least
`one input port and at least one output port, a rnicro-rnirror
`having an optical signal input side and an optical signal
`output side, the rnicro-rnirror connected to a substrate, the
`rnicro-rnirror being positioned on the substrate at a 45° angle
`to an incoming optical signal from one of the at least one
`input ports and at a point of intersection of a path from the
`one input port and one of the at least one output ports, an
`electrode plate in association With the rnicro-rnirror and
`capable of dithering the rnicro-rnirror upon application of a
`dithering signal to the electrode plate, a beam splitter located
`on the substrate at the optical signal output side of the
`rnicro-rnirror, and a photodetector positioned beneath the
`beam splitter.
`In a still further aspect of the invention, the invention
`relates to a method of verifying the connection path of an
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-12
`
`

`

`US 6,243,507 B1
`
`10
`
`15
`
`20
`
`25
`
`3
`cumbersome in terms of the hardware required. The scheme
`requires a speci?c arrayed-Waveguide grating and requires
`additional ?lters to be used.
`Micro-electro-mechanical system (MEMS) technology,
`due to its unique capability of integrating optical, electrical
`and mechanical elements on a single chip, holds strong
`advantages for implementing multiple functionalities in
`integrated form.
`Free-space MEMS optical sWitches aiming at large-scale
`sWitch fabrics have been demonstrated using various
`approaches. See, for example, (1) H. Toshiyoshi and H.
`Fujita, “Electrostatic Micro Torsion Mirrors for an Optical
`SWitch Matrix”, J. Microelectromechanical Systems, vol. 5,
`no. 4, pp. 231—237, 1996, (2) L. Y. Lin, E. L. Goldstein, and
`R. W. Tkach, “Free-Space Micromachined Optical SWitches
`for Optical Networking”, IEEE J. Selected Topics in Quan
`tum Electronics: Special Issue on Microoptoelectromechani
`cal Systems (MOEMS), vol. 5, no. 1, pp. 4—9, 1999, (3) L.
`Y. Lin, E. L. Goldstein, J. M. Simmons, and R. W. Tkach,
`“High-Density Micromachined Polygon Optical Crosscon
`nects Exploiting Network Connection Symmetry”, IEEE
`Photonics Tech. Lett., vol. 10, pages 1425—1427 (1998), (4)
`R. T. Chen, H. Nguyen, and M. C. Wu, “A LoW Voltage
`Micromachined Optical SWitch by Stress-Induced
`Bending”, 12th IEEE International Conference on Micro
`Electro Mechanical Systems, Orlando, Fla., Jan. 17—21,
`1999, and (5) B. Behin, K. Y. Lau, and R. S. Muller,
`“Magnetically Actuated Micromirrors for Fiber-Optic
`SWitching”, Solid-State Sensor and Actuator Workshop,
`Hilton Head Island, SC, Jun. 8—11, 1998, each incorporated
`by reference herein in their entireties.
`US. Pat. No. 5,960,132 describes an optical sWitch device
`that is actuated betWeen re?ective and non-re?ective states.
`US. application No. 09/472/724 entitled “Angular-Precision
`Enhancement In Free-Space Micromachined Optical
`SWitches” and based on Provisional Application No. 60/137,
`838 (?led Jun. 7, 1999), describes free-space MEMS cross
`connect optical sWitches that include mechanical angular
`alignment enhancement structures. This patent and
`co-pending application are both incorporated herein by
`reference in their entireties. The present invention may
`utiliZe the optical sWitches described in the 132 patent
`and/or the co-pending application, With or Without the
`additional mechanical angular alignment enhancement
`structures of the co-pending application. Of course, any
`other suitable sWitch mirror scheme may also be used.
`In free-space MEMS crossconnects, micromachined mir
`rors are utiliZed as the sWitching elements. These may be, for
`example, free-rotating mirrors as just discussed.
`Optical sWitches function to sWitch an optical signal from
`an input port 5, e.g., an input ?ber, to an output port 55, e.g.,
`an output ?ber When in the re?ective position. The sWitches
`are located Within an open, free space. The siZe of the matrix
`of incoming and outgoing ?bers is N><M, With N and M
`55
`being any integer greater than 1. Optical micro-mirror
`sWitching elements are typically positioned at a 45° angle to
`the direction of an incoming optical beam from an input port
`in matrix con?guration, and located at the points of inter
`section of the paths of each input port and each output port.
`Incoming optical beams may be directed to the desired
`output port through use of the micro-mirror optical sWitches.
`Other con?gurations, for example polygonal, are possible.
`When an incoming optical signal is not to be redirected by
`a particular micro-mirror, the micro-mirror remains in its
`rest position, Which is horiZontal to the substrate upon Which
`the micro-mirror is mounted, or at least out of the plane of
`
`4
`travel of the optical signal. HoWever, if an optical signal is
`to be redirected by the micro-mirror, the micro-mirror is
`moved/raised to its re?ective position, Which is a predeter
`mined position and preferably is, for example, as close to
`perpendicular, i.e., 90°, from the substrate as possible.
`The micro-mirrors of the invention may be made of any
`conventional material. For example, the micro-mirrors may
`be polysilicon, optional coated With a highly re?ective metal
`such as gold or Cr/Au, for example as in H. Toshiyoshi and
`H. Fujita, supra.
`The micro-mirror, hinge and staple may be formed by any
`conventional process. The micro-mirrors are preferably
`formed by surface-micromachining, for example as in the
`Well-knoWn MUMPsTM (the multi-user MEMS) process
`described in, for example, L. Y. Lin, E. L. Goldstein and R.
`W. Tkach, “Free-Space Micromachined Optical SWitches
`for Optical NetWorking”, IEEE Journal of Selected Topics in
`Quantum Electronics, vol. 5, no. 1, pp. 4—9, January/
`February 1999 and K. S. J. Pister, M. W. Judy, S. R. Burgett,
`and R. S. Fearing, “Microfabricated Hinges,” Sensors and
`Actuators A, vol. 33, pp. 249—256, 1992, both incorporated
`herein by reference in their entireties. In MUMPsTM, a
`polysilicon is used as the structural material, a deposited
`oxide (PSG) is used for the sacri?cial layers, and silicon
`nitride is used as an electrical isolation layer betWeen the
`silicon substrate and the polysilicon layers. The polysilicon
`layers are referred to as poly-0, poly-1 and poly-2.
`FIGS. 2, 3 and 4 shoW a preferred mirror sWitch of the
`invention. The micro-mirror 20 is mounted Within a frame,
`Which frame is connected to the substrate 15 by free-rotating
`micro-hinges 30. The hinges 30 include one or more hinge
`pins 22 and one or more hinge staples 24. Pushrods 26 are
`connected at one end to the mirror (mirror frame) and at the
`opposite end to the translation stage 18.
`Scratch-drive actuators (SDAs) 45 are preferably
`employed to move the translation stage. SDAs are
`conventional, and thus an extensive discussion of the func
`tion of the SDAs is not necessary herein. For a discussion of
`the formation and function of SDAs see, for example, T.
`Akiyama and H. Fujita, “A Quantitative Analysis of Scratch
`Drive Actuator Using Buckling Motion,” in IEEE Workshop
`on Micro Electro Mechanical Systems, Amsterdam, the
`Netherlands, Jan. 29—Feb. 2, 1995, incorporated herein by
`reference in its entirety. For purposes of explaining the
`functioning of the hinged micro-mirrors of the present
`invention, it is suf?cient to note that through application of
`an appropriate voltage to the SDA, the SDA can be
`deformed or moved to a certain extent, Which deformation
`or movement is used to move the translation stage a trans
`lation distance corresponding to the extent of deformation.
`Movement of the translation stage in turn causes the push
`rods to act upon the mirror frame and rotate it up to a
`predetermined position or angle from the substrate, typically
`the 90° position discussed above.
`FIG. 1 shoWs the micro-mirror dither scheme for pilot
`tone coding and on-chip signal monitoring in the free-space
`MEMS OXC of the invention. In this scheme, an electrode
`plate 10 is associated With the micro-mirror 20.
`The electrode plate is made of any suitable material.
`Preferably, the electrode plate is also a surface
`micromachined polysilicon integrally formed during the
`MUMPs process. In this Way, the electrode plate can be
`formed With the micro-mirror. The electrode plate may be
`formed from, for example, the poly-1 layer. The electrode
`plate may be integral With the micro-mirror, or it may be
`formed to separately more, for example rotate via hinge
`joints, the same as the micro-mirror.
`
`30
`
`35
`
`45
`
`60
`
`65
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-13
`
`

`

`US 6,243,507 B1
`
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`As the electrode plate is preferably made of polysilicon,
`it is conductive. The electrode plate contacts the polysilicon
`hinge staples. A source providing the dithering signal to the
`electrode plate can be connected via conductive, e.g., poly
`silicon or gold, Wiring to either the electrode plate or the
`hinge staples. The conductive Wiring is also preferably
`formed photolithographically during the MUMPs formation
`process.
`Although the electrode plate is illustrated in FIG. 1 to
`extend around the exterior of the micro-mirror, any suitable
`con?guration of the electrode plate can be used. The only
`requirement is that the electrode plate must be capable of
`dithering the micro-mirror When a dithering signal is applied
`to the electrode plate.
`At the 90° position, i.e., the vertical, re?ective or active
`sWitch position, the micro-mirror can perform small angle
`modulation under external force. That is, the micro-mirror
`can be made to vary slightly in angle from its designed
`position to the incoming optical signal, e.g., 90° to the
`incoming optical signal. The direction of modulation is
`shoWn in FIG. 1.
`Dithering, i.e., repetitive, back-and-forth small angle
`modulation, of the micro-mirror is effected in the invention
`through application of a dithering signal to the electrode
`plate. The only requirement of the dithering signal is that it
`must be capable of inducing small angular variations in the
`micro-mirror Which can be detected by a photodetector. The
`dithering signal may be, for example, a sinusoidal bias or a
`sinusoidal pilot tone. Most preferably, the dithering signal is
`a sinusoidal bias. A sinusoidal bias causes the micro-mirror
`to dither at frequencies corresponding to the sinusoidal bias.
`On the output side of the micro-mirror optical sWitch, a
`polysilicon plate 30 is positioned at a 45° angle to both the
`substrate and the optical signal output from the micro
`mirror. This polysilicon plate also is preferably a surface
`micromachined polysilicon. The polysilicon plate may be
`?xed to the substrate in the 45° position by any suitable
`means. For example, as shoWn in FIG. 5, the polysilicon
`plate may include appropriate vertical and side supports to
`ensure the ?xing of the position of the polysilicon plate.
`The polysilicon plate functions as a beam splitter. A
`portion of the optical signal output from the micro-mirror is
`re?ected by the polysilicon plate beam splitter to a photo
`detector located under the polysilicon plate and upon the
`substrate. This is illustrated in FIG. 1. The beam splitter/
`photodetector monitor module is shoWn in FIG. 5. The beam
`splitter may be formed of any suitable material, polysilicon
`merely being an illustrative example.
`The photodetector is preferably formed by, for example,
`hybrid-integrating the photodetector into the system by Wire
`bonding as explained in L. Y. Lin, L. M. Lunardi and E. L.
`Goldstein, “Optical Cross-Connect Integrated System
`(OCCIS): A Free-Space Micromachined Module For Signal
`And SWitching Con?guration Monitoring”, IEEE LEOS
`Summer Topical Meeting: Optical MEMS, Monterey, Calif.,
`Jul. 20—22, 1998, incorporated by reference herein in its
`entirety. In particular, the photodetector may be solder
`mounted on the substrate of the free-space micro-mirror
`chip.
`Small angular variations of the micro-mirror as a result of
`the dithering signal applied to the electrode plate are trans
`formed into intensity modulation of the detected optical
`from the photodetector. Due to the high angular sensitivity
`of single-mode optics, the resulting modulation ef?ciency is
`quite high. By modulating the angle of the actuated micro
`mirror With various frequencies, a pilot-tone signal carrying
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`the connection-path information can therefore be impressed
`on the optical signal.
`In other Words, the dithering of the micro-mirror results in
`a detectable variation in the intensity of the optical beam
`arriving at the photodetector from the polysilicon plate beam
`splitter. The detection of this variation by the photodetector
`can verify that the sWitching of the optical beam Within the
`MEMS OXC occurred successfully. If an input optical signal
`is desired to be sent to a selected output port, veri?cation of
`the sWitching to that output port can be done in this scheme.
`If variation in the intensity of a pilot tone sent from the input
`port is registered at the photodetector associated With the
`optical sWitching element feeding the selected output port,
`then the necessary sWitching is properly occurring.
`To measure the bandWidth and sensitivity of the hinged
`micro-mirrors, sinusoidal signals With various frequencies
`and amplitudes are applied to the electrode. The modulated
`output electrical signal from the photodetector is then cap
`tured by an oscilloscope. FIGS. 6—9 shoW the frequency
`response of the micro-mirror at 4, 120, 160 and 200 HZ,
`respectively under 30 V bias. The upper traces represent
`signals from the photodetector; the loWer traces represent
`biases on the electrode.
`Various frequency responses betWeen 4 and 200 HZ have
`been measured. The intensity-modulation frequency of sig
`nals from the photodetector is tWice the bias frequency, as
`the mirror-angle is optimiZed When there is no bias. The
`responses remain similar betWeen 4 and 120 HZ, and start to
`decrease as the frequency rises above 120 HZ. At 200 HZ, the
`response begins to shoW signs of more complex coupling
`into the micromechanical structure, as shoWn in FIG. 9.
`Thus, the frequency applied to the electrode plate is pref
`erably kept betWeen 4 and 200 HZ, most preferably betWeen
`4 and 120 HZ for the current micro-mirror. The bandWidth
`can be increased by modifying the design of the micro
`mirror.
`The responses of the micro-mirror under various bias
`amplitudes are also measured. FIGS. 10 to 12 shoW the
`results of 20 V, 30 V and 40V biases, respectively. The
`results may suggest that the maximum angular variation of
`the micro-mirror is restricted by its mechanical structure.
`The bias amplitude is preferably maintained betWeen 10 and
`50 V, most preferably betWeen 20 and 40 V for the current
`micro-mirror.
`In all cases, the intensity variation of the optical signal at
`the output of the sWitch fabric is expected to permit accept
`able monitoring performance Without imposing bit errors in
`transponder-based WDM netWorks.
`A pilot-tone-based encoding scheme in free-space
`MEMS-based optical crossconnects is thus achieved. The
`scheme utiliZes free-rotating sWitch mirrors With dither
`electrode plates and integrated micro-optics. Through this
`scheme, connection veri?cation Within the MEMS OXC can
`be readily and cost-effectively achieved.
`What is claimed is:
`1. A connection veri?cation system comprising
`a micro-mirror having an optical signal input side and an
`optical signal output side, the micro-mirror connected
`to a substrate,
`an electrode plate in association With the micro-mirror
`and capable of dithering the micro-mirror upon appli
`cation of a dithering signal to the electrode plate,
`a beam splitter located on the substrate at the optical
`signal output side of the micro-mirror, and
`a photodetector positioned beneath the beam splitter.
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-14
`
`

`

`US 6,243,507 B1
`
`7
`2. The connection veri?cation system according to claim
`1, Wherein the system is Within an optical micro-electro
`mechanical crossconnect device.
`3. The connection veri?cation system according to claim
`2, Wherein the optical micro-electro-mechanical crosscon
`nect device includes at least one input port and at least one
`output port, the micro-mirror being located on the substrate
`in a line of travel of an incoming optical signal from one of
`the at least one input ports and at a point of intersection of
`a path from the one input port and one of the at least one
`output ports When in a re?ective position.
`4. The connection veri?cation system according to claim
`1, Wherein the electrode plate is connected to a source of the
`dithering signal via conductive Wiring.
`5. The connection veri?cation system according to claim
`1, Wherein the micro-mirror is connected to the substrate via
`hinge joints permitting free rotation of the micro-mirror.
`6. The connection veri?cation system according to claim
`1, Wherein one or more of the micro-mirror, the electrode
`plate and the beam splitter are comprised of a surface
`micromachined polysilicon.
`7. A connection veri?cation system of an optical micro
`electro-mechanical crossconnect device, comprising
`at least one input port and at least one output port,
`a micro-mirror for one of the at least one input ports and
`having an optical signal input side and an optical signal
`output side, the micro-mirror connected to a substrate,
`and capable of being moved to a re?ective position so
`as to sWitch an incoming optical signal from the one
`input port to a predetermined output port When the
`micro-mirror is in a re?ective position,
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`an electrode plate in association With the micro-mirror
`and capable of dithering the micro-mirror upon appli
`cation of a dithering signal to the electrode plate,
`a beam splitter located on the substrate at the optical
`signal output side of the micro-mirror, and
`a photodetector positioned beneath the beam splitter.
`8. A method of verifying the connection path of an optical
`signal from an input port to a desired output port, comprising
`sWitching an optical signal from the input port to the
`desired output port With a micro-mirror having an
`optical signal input side and an optical signal output
`side, the micro-mirror connected to a substrate,
`applying a dithering signal to an electrode plate in asso
`ciation With the micro-mirror to dither the micro
`mirror, and
`splitting the optical signal on the optical signal output side
`of the micro-mirror into a detection portion and an
`output portion With a beam splitter located on the
`substrate at the optical signal output side of the micro
`mirror, the beam splitter directing the detection portion
`to a photodetector located beneath the beam splitter.
`9. The method according to claim 8, Wherein the dithering
`signal is a sinusoidal bias.
`10. The method according to claim 8, Wherein the con
`nection path is veri?ed When the photodetector detects
`alterations in intensity of the detection portion of the optical
`beam corresponding to the dithering signal applied to the
`electrode plate.
`11. The method according to claim 8, Wherein the optical
`signal from the input port includes a pilot tone.
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`Petitioner Ciena Corp. et al.
`Exhibit 1022-15
`
`