(12) United States Patent
`Goldstein et al.
`
`(10) Patent No.: US 6,243,507 B1
`(45) Date of Patent: Jun. 5, 2001
`
`US006243507B1
`
`(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) Apph No.: 09/472,682
`
`(22) Filed:
`
`Dec. 27, 1999
`
`Related U.S. Application Data
`(60) Provisional application No. 60/137,840, filed on Jun. 7,
`1999.
`
`Int. CI.7 ....................................................... G02B 6/12
`(51)
`(52) U.S. CI .................................. 385/13; 385/17; 385/’18;
`385/19
`Iqeld of Search ............................ 385/16 19, 12 14;
`359/212, 223, 225; 250/’216, 234
`
`(58)
`
`(56)
`
`Reli~rences Cited
`
`U.S. PAI’ENT DOCUMENTS
`
`5,136,671
`8/1992 Dragone ................................. 385/’46
`5,155,623
`10/1992 Miller et al .......................... 359/’495
`5,206,497
`4/1993 Lee .................................... 250/’201.1
`5,960,132
`9/1999 Lin ......................................... 385/18
`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, voh 5, No. 4, Dcc. 1996, pp. 231-237.
`
`B. Behin et al., "Magnetically Actuated Micromirrors for
`Fibe~Optic Switching," Soli~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
`Actuator& vol. A, No. 33 (1992), pp. 249-256.
`T. Akiyama et al., "A Quantitative Analysis of Scratch Drive
`Actuator Using Buckling Motion," IEEE VVbrkshop 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," 1Uh 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 Micrmnachine 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 QuanmmElectronics, voh 5, No. 1, Jan./Fcb. 1999,
`pp. 4-9.
`
`(List continued on next page.)
`
`Primary Examiner~arren Schuberg
`Assistant Exammer~ayez Assai
`
`(57)
`
`ABSTRACT
`
`Integrated connection-verification system for use in a micro-
`electro-mechanical system (MEMS) crossconnect device.
`Fhe system uses application ol a dithering signal such as a
`sinusoidal bias to an electrode plate associated with a
`micro-mirror switching element to dither the nricro-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 tnicro-mirror, the connection path between the
`desired input and output ports is verified.
`
`11 Claims, 9 Drawing Sheets
`
`5O
`
`20
`
`10
`
`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 Crossconnccts Exploiting Nctwork Connection-
`Symmetry," IEEE Photonics TechnoloKy Letters; vol. 10,
`No. 10, Oct. 1998, pp. 1425 1427.
`E. L. Goldstein et al., "National~Scale Networks Likely to
`Be Opaque," Lighm’ave, Feb. 1998, pp. 91-95.
`C-K. Chan et al., "A Novel Optical-Path Supervisory
`Scheme for Optical Cross Connects in All0Optical 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 Configuration Monitoring," IEEE LECS
`Summer Topical Meeting: Optical MEMS, Monterey, Cali-
`fornia, Juh 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 of 9
`Sheet 1 0f 9
`
`US 6,243,507 B1
`US 6,243,507 B1
`
`FIG. i
`
`5O
`
`2O
`
`
`
`I\
`_ I I
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1022-3
`Exhibit 1022-3
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 2 0f 9
`Sheet 2 of 9
`
`US 6,243,507 B1
`US 6,243,507 B1
`
`
`
`
`
`FIG.2
`
`MICRO-HINGES
`
`v,e-’;';'l
`
`ZOOMm5.00W3.0120x22.1
`Acc.VSpotMagnw0l————{
`
`I"’
`
`
`
`
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-4
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 3 0f 9
`Sheet 3 of 9
`
`Us 6,243,507 B1
`US 6,243,507 B1
`
`PLATE
`
` ELECTRODE
`
` SPRING-LATCH
`
`
`
`
`MICRO-MIRROR
`SpotMagn120x
`
` 500W3.0 Acc.V
`
`
`SIDE-LATCH
`
`3 F
`
`IG.
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1022-5
`Exhibit 1022-5
`
`

`

`Sheet 4 or9
`
`\
`
`\
`
`
`
`

`

`U.S. Patent
`US. Patent
`
`n.m
`mm5:
`Jun. 5, 2001
`
`9M
`Sheet 5 of 9
`
`u,6SU
`1B705
`US 6,243,507 B1
`
`3,23%8;>33
`5_0w5285:“.\mm52%
`
`
`
`
`x<zfim8€535;
`
`
`
`m2:szmEmqu
`
`figmmnzfim93.
`
`55.:
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1022—7
`Exhibit 1022-7
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 6 of 9
`
`US 6,243,507 B1
`
`FIG. 6
`
`RESPONSE
`(4Hz, 20mV/div)
`
`BIAS
`VOLTAGE
`(2Hz, 30V)
`
`I
`
`¯
`
`\
`\
`
`(cid:128)
`
`/
`
`¯
`¯
`I
`I
`
`\
`
`\
`¯
`
`-500.00 ms
`
`0.000 s
`
`500.00 ms
`
`FIG. 7
`
`RESPONSE
`(120Hz,
`20mV/div)
`
`BIAS
`VOLTAGE
`(60Hz, 30V)
`
`-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 of 9
`
`US 6,243,507 B1
`
`FIG. 8
`
`FIG. 9
`
`RESPONSE
`(160Hz,
`20mV/div)
`
`BIAS
`VOLTAGE
`(80Hz, 3or)
`
`4
`
`RESPONSE
`(200HE,
`20mV/div)
`
`BIAS
`VOLTAGE
`(iOOHz, 3ov)
`
`I
`
`\j
`
`-25.000 ms
`
`0.00(
`
`25.000 ms
`
`Petitioner Ciena Corp. et am.
`Exhibit 1022-9
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 8 of 9
`
`US 6,243,507 B1
`
`FIG. 1 0
`
`RESPONSE
`
`20mV/div)
`
`BIAS
`VOLTAGE
`(2Hz, 20V)
`
`RESPONSE
`(4Hz,
`20mV/div)
`
`BIAS
`VOLTAGE
`(2Hz, 50V)
`
`:;~.-.~-,.,~.-~
`
`’.~.....,.~y.,.’;.._ ~,!~’~’,:?~"
`
`
`
`"..,.~.,..’~.~,.~-~.-~" ,...~-
`
`:::::::::::::::::::::::::::::::::::::::::::::::::::::::
`
`%
`
`%
`%
`
`.%
`
`-500.00 ms
`
`0.00~
`
`500.00 ms
`
`FIG.
`
`\
`\
`\
`
`\
`
`I
`I
`
`I
`
`-500.00 ms
`
`0.00~ s
`
`500.00 ms
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-10
`
`

`

`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 9 of 9
`
`US 6,243,507 B1
`
`FIG. 12
`
`’I
`
`.~-
`I"
`I
`I
`
`RESPONSE
`
`20mV/div)
`
`BIAS
`VOLTAGE
`(2Hz, 40V)
`
`-500,00 ms
`
`0.000 s
`
`500.00 ms
`
`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 benefit of s
`U.S. Provisional Application No. 60/’137,840, filed Jun. 7,
`1999.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`This invention relates to a connection verification system
`in an optical micro-electro-mechanical system (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 networldng functionality of OXCs has become increas-
`ingly important, and doing so via integrated and low-cost
`approaches becmnes particularly desirable. One important
`requirement for the OXC is connection-verification for
`network surveillance. That is, it is desired to verify that an
`optical signal is being properly s~vitched and carried within
`the system to the desired output port or fiber.
`What is still desired is a simple, cost-effective connection
`verification system for use in a MEMS optical crossconnect
`network.
`
`SUMMARY OF THE INVENTION
`It is therefore an object of the invention to develop a
`connection path verification system for use in the MEMS
`OXC.
`This and other objects are achieved by the present inven-
`tion that achieves connection path verification via integrated
`pilot-tone coding schemes utilizing micro-mirror dithering
`in the MEMS crossconnect.
`In one aspect of the invention, the invention relates to a
`connection verification 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
`capablc of dithcring the micro-mirror 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
`micro-mirror, and a photodetector positioned beneath the
`beam splitter.
`In a further aspect of the invention, the invention relates
`to a connection verification system of an optical micro-
`electro-mechanical crossconnect device, comprising at least
`one input port and at least one output port, a micro-mirror
`having an optical signal input side and an optical signal
`output side, the micro-mirror connected to a substrate, the
`micro-mirror 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 micro-mirror and
`capable of dithering the micro-mirror upon application of a
`dithcring signal to thc clcctrodc plate, a beam splitter located
`on the substrate at the optical signal outpnt side of the
`micro-mirror, 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
`
`2
`optical signal from an input port to a desired output port,
`comprising switching an optical signal from the input port to
`the dcsircd 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 association 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
`splittcr located on the substratc at the optical signal output
`side of the micro-mirror, the beam splittcr directing the
`detection portion of the optical signal to a photodetector
`located beneath the beam splitter. The connection path is
`verified 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.
`
`10
`
`15
`
`BRIEF DESCRIPTION OF TIlE DRAWINGS
`
`FIG. 1 is an illustration of the mirror-dither ~heme for
`:0 pilot-tone coding and on-chip signal tnonitoring in the
`
`25
`
`free-space MEMS OXC of the invention.
`FIG. 2 is a SEM (scanning electron microscope) photo-
`graph of a free-rotating hinged micro-mirror in a free-space
`MEMS OXC of the invention.
`FIG. 3 is a SEM photograph of the micro-switch mirror
`with an integrated electrode.
`FIG. 4 is a schematic diagram of a microactuated free-
`rotating switch mirror.
`FIG. 5 is a SEM photograph of the beam-splitter/
`photodetector monitor module of the invention.
`FIGS. 6 9 are frequency responses of the micro-mirror at
`various frequencies and biases, while FIGS. Ill 12 are
`frequency responses of the micro-nfirror at various biases,
`35 the upper traces representing signals from the photodetector,
`
`30
`
`the lower traces representing biases on the electrode.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`411
`
`In a conventional nctwork, thcrc is acccss to the bit
`streams travcling within the systcm. This cnablcs casy
`manipulation of a bit stream, for example by turning signals
`on and off to represent bits, in order to verify that the bit
`45 stream is being switched to the proper output port. The
`methodology was simple and straightforward.
`However, this conventional tcchnology cannot be utilized
`in optical crosseonnect systems because access to the system
`as in the conventional technology is not available. That is, in
`50 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, ctc., that do not afford
`manipulation of bits. As a result, it is not possible in optical
`55 crossconnect systems to look at information bits and deter-
`mine therefrom what they are connected to. Thus, new
`connection verification technology must be developed in
`order to confirm that the switches within the optical cross-
`connect are properly connecting an input optical signal to
`6o the desired output port.
`An optical path supervisory scheme has been proposed in
`C.-K. Chart, E. Kong, F. ’lbng and L.-K. Chert, "A Novel
`Optical-Path Supervisory Scheme For Optical Cross Con-
`nects In All-Optical Transport Networks", IEEE Photonics
`65 Tech. Lett., vol. 10, pages 899-901 (1998). In this scheme,
`use is made of periodic characteristics of arrayed-
`waveguide-gratings. Although adeqnate, this scheme is
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-12
`
`

`

`US 6,243,507 B1
`
`3
`cumbersome in terms of the hardware required. The scheme
`requires a specific arrayed-waveguide grating and requires
`additional filtcrs to bc uscd.
`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 bccn 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 Elcctronics: Special Issue on Microoptoclcctromcchani-
`cal Systems (MOEMS), voh 5, no. 1, pp. 4 9, 1999, (3) L.
`¥ l.in, E. E. Goldstein, J. M. Simmons, and R. W. Tkach,
`"High-Density Micromachined Polygon Optical Crosscon-
`nects Exploiting Network Connection Symmetry", IEEE
`Photonics Tech. Lett., voh 10, pages 1425-1427 (1998), (4)
`R. T. Chen, II. Nguyen, and M. C. Wu, "A Low Voltage
`Micromachincd Optical Switch by Strcss-Induccd
`Bending", 12th IEEE International Conference on Micro
`Electro Mechanical Systems, Orlando, Fla., Jan. 1731,
`1999, and (5) B. Behin, K. Y. Lan, and R. S. Muller,
`"Magnetically Actuated Micromirrors for Fiber-Optic
`Switching", Solid-State Sensor and Actuator Workshop,
`IIilton Ilead Island, S.C., Jun. 8-11, 1998, each incorporated
`by reference hcrcin in their cntirctics.
`U.S. Pat. No. 5,960,132 describes an optical switch device
`that is actuated between reflective aa~d non-reflective states.
`U.S. application No. 09/472/724 entitled "Angular-Precision
`Enhancement In Free-Space Micromachined Optical
`Switches" and bascd on Provisional Application No. 60/’137,
`838 (filed Jun. 7, ] 999), 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 thc optical switchcs 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 crossconnccts, micromachined mir-
`rors are utilized as the switching clcments. Thesc may be, for
`example, free-rotating mirrors as just discussed.
`Optical switches function to switch an optical signal from
`an input port 8, e.g., an input fiber, to an output port 85, e.g.,
`an output fiber when in the rcflcctivc position. The sxvitchcs
`are located ~vithin an open, free space. The size of the matrix
`of incoming and outgoing fibers is NxM, with N and M
`being any integer greater than 1. Optical inicro-mirror
`switching elements are typically positioned at a 45° angle to
`the direction of an inconring optical beam from an input port
`in matrix configuration, and located at the points of inter-
`scction of thc paths of each input port and each output port.
`Incoming optical beams may be directed to the desired
`oulput port through u se of the micro-mirror optical switches.
`Other conligurations, 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
`
`20
`
`25
`
`t0
`
`15
`
`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 rellective position, which is a predeter-
`mined position and preferably is, for example, as close to
`s perpendicular, i.e., 90°, from the substrate as possible.
`The micro-mirrors of the invention may be made of any
`conventional materiah For example, the micro-mirrors may
`be polysilicon, optional coated with a highly reflective 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 MUMPs’~a (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, voh 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
`oxidc (PSG) is used for the sacrificial 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 prcferred mirror switch of the
`invention. The micro-mirror 20 is mounted within a frame,
`3o 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.
`3s 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.
`4c~ Akiyama and H. Ft~jita,"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
`45 functioning of the hingcd micro-mirrors of the present
`invention, it is sufficient to note that through application of
`an appropriate voltage to the SDA, the SDA can be
`deformed or moved to a certain extent, which defom~ation
`or movement is used to move the translation stage a trans-
`50 lation distance corresponding to the extent of deformation.
`Movement of the translation stage in turn causes the push-
`rods to act upon thc 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 1!1 is associated with the micro-mirror 211.
`The electrode plate is made of any suitable material.
`~0 Preferably, the electrode plate is also a surface-
`micromachined polysilicon integrally li0rmed during the
`MUMPs process. In this way, the electrode plate can be
`fomred with the micro-nrirror. The electrode plate may be
`formed from, for example, the poly-1 layer. The electrode
`~5 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.
`
`55
`
`Petitioner Ciena Corp. et al.
`Exhibit 1022-13
`
`

`

`US 6,243,507 B1
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`5
`As the electrode plate is preferably made of polysilicon,
`it is conductive. The electrode plate contacts the polysilicon
`hingc staples. A source providing the dithering signal to the
`electrode platc can bc connected via condnctive, 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
`configuration 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, reflective 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. Thc 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. Thc only rcquircmcnt of thc dithcring 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
`fixcd to the substratc in the 45° position by any suitable
`means. For example, as shown in FIG. $, the polysilicon
`plate may include appropriate vertical and side supports to
`ensure the lixing 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
`reflected 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. Phe 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 Confignration Monitoring", IEEE LEOS
`Summer Topical Meeting: Optical MEMS, Monterey, Calif.,
`Jut. 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 modulafion of the detected optical
`from the photodetector. Due to the high angular sensitivity
`of single-mode optics, the resulting modulation efficiency is
`quite high. By modulating the angle of the actuated micro-
`mirror with various frequencies, a pilot-tone signal carrying
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`35
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`15
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`the connection-path information can therefore be impressed
`on the optical signal.
`In othcr xvords, the dithcring of the micro-mirror results in
`a detectable variation in the intensity of the optical beam
`s 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, verification of
`10 the switching to that output port can be done in this schcme.
`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 xvith various frequencies
`and amplitudes arc 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
`20 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 li-equency, as
`the mirror-angle is optimized when there is no bias. The
`responses remain similar between 4 and 120 Hz, and start to
`30 decrease as the frequency rises above 120 Hz. At 200 Hz, the
`response begins to show" signs of more complex coupling
`into the micromeehanical 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. ’ltm bandwidth
`can be increased by modifying the design of the micro-
`mirror.
`The rcsponscs of thc micro-mirror undcr various bias
`amplitudes are also measured. FIGS. 1~) to 12 show the
`4c~ 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
`4s micro-mirror.
`In all cases, lhe 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.
`50 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 verification within the MEMS OXC can
`55 be readily and cost-effectively achieved.
`What is claimed is:
`1. A connection verification 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
`
`s
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`8
`an electrode plate in association with the micro-mirror
`2. The connection verification system according to clainr
`and capable of dithering the micro-mirror upon appli-
`I, wherein the system is within an optical micro-electro-
`cation of a dithering signal to the electrode plate,
`mechanical crossconncct dcvicc.
`a beam splitter located on the substrate at the optical
`3. Thc connection vcrification systcm according to claim
`signal output side of the micro-mirror, and
`2, wherein the optical micro-electro-mechanical crosscon-
`a photodetector positioned beneath the beam splitter.
`nect device includes at least one input port and at least one
`8. A mcthod of verifying thc connection path of an optical
`output port, the micro-mirror being located on the substrate
`signal from an input port to a desired output port, comprising
`in a line of travel of an incoming optical signal frmn one of
`switching an optical signal from the input port to the
`the at least one input ports and at a point of intersection of
`desired output port with a micro-mirror having an
`a path from the one input port and one of the at lcast one
`optical signal input side and an optical signal output
`output ports when in a rcflcctivc position.
`side, the micro-mirror connected to a substrate,
`4. The connection verification system according to claim
`applying a dithering signal to an electrode plate in asso-
`1, wherein the electrode plate is connected to a source of the
`ciation with the micro-mirror to dither the micro-
`dithering signal via conductive wiring.
`mirror, and
`5. The connection verification system according to claim
`splitting the optical signal on the optical signal output side
`I, wherein the micro-mirror is connected to the substrate via
`of the micro-mirror into a detection portion and an
`hingc joints pcrmitting frcc rotation of the micro-mirror.
`output portion with a beam splitter located on the
`6. The connection verification system according to claim
`s~lbstrate at the optical signal outpnt side of the micro-
`1, wherein one or more of the micro-mirror, the electrode
`mirror, the beam splitter directing the detection portion
`plate and the beam splitter are comprised of a surface-
`to a photodetector located beneath the beam splitter.
`micromachined polysilicon.
`9. The method according to claim 8, wherein the dithering
`7. A connection verification system of an optical micro-
`signal is a sinusoidal bias.
`electro-mechanical crossconnect device, comprising
`10. The method according to claim 8, wherein the con-
`at least one input port and at least one output port,
`nection path is verified when the photodctcctor detects
`a micro-mirror for one of the at least one inpnt ports and 25 alterations in intensity of the detection portion of the optical
`having an optical signal input side and an optical signal
`beam corresponding to the dithering signal applied to the
`output side, the micro-mirror connected to a substrate,
`electrode plate.
`and capable of being moved to a reflective position so
`11. The method according to claim 8, wherein the optical
`as to switch an incoming optical signal from the one
`signal from the input port includes a pilot tone.
`input port to a predetermined output port when the 30
`micro-mirror is in a rcflcctivc position,
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`Petitioner Ciena Corp. et al.
`Exhibit 1022-15
`
`