||||||||||l|I|l||I|I|||||||||||||||||||||||||lllll||||||||||||I|||||||||
`USOU656'.-"5't'4B1
`
`(12) United States Patent
`Ma et al.
`
`(in) Patent N0.:
`(45) Date of Patent:
`
`US 6,567,574 B1
`May 20, 2003
`
`(54) MODULAR THREE-DIMENSIONAL
`0l’I'lCAL SWITCH
`
`(75)
`
`Inventors: Jinn Mn, San Diego, CA (US); Ezekiel
`Jnhn Joseph Kruglick, San Dicgo, CA
`(US); Danie! J. Reilcy, San Diego. (TA
`(US); Philippe Jean Marchand,
`Poway, (IA (US); Steffen (llocckncr.
`San Diego, CA (US)
`
`(73) Assignee: Omm, Inc.. San Diego, CA (US)
`
`{ * } Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`t.=’.S.C. 154{b) by 0 days.
`
`(21) Appl. ..\ru.: o9;6sn,54s
`
`(22)
`
`Filed:
`
`Oct. 6, 2000
`
`(51)
`
`Int. Cl.7
`
`()'l'l-l ER PL‘ I-3l.I(fPt'l”l UNS
`
`lluja, Marlin, "MEMS Struclure—MicromirrorArray,“ Pro-
`ceedings of SI’lE.’vol. 4019. 1). 556-566.
`Hoissicr, Alain, "Space division optical switching system of
`medium capacities," l’rococdings: Fiber Optic Broadband
`Networks, p. 55-70.
`Laor,
`llerzei, "New Optical Switch Development,“ 7th
`European Conference on Optical Communication. Sep.
`8-11, 1981 Bclla Ccntcr.
`Bright. Victor M.. "Selected Papers on Optical ME.MS."
`SPIE Milestone Scrics, vol. MS 153.
`
`(List continued on next page.)
`
`Prr'mnr_v Exarrriner—Ellcr1 E. Kim
`(74) /li'n't')?'.NE}§ Agent, or Fir-m—A.rien Ferrell; Fitch, Even.
`Tztbin tit Flanrtcry
`
`G023 626
`
`(57)
`
`ABSTRACT
`
`(52) US. Cl.
`
`............................ .. 385!l6; 385ll.8; 385;’l‘)
`
`(58)
`
`Field nfSearI.:l1 .................................... .. 3SS.»’l|5—2{J
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3_.43tJ.(J57 A
`3,89t'i__3h'2 A
`-1_.D03__ti55 A
`4_.2i)8,(i94 A
`4_.234,l45 A
`4,256,921 A
`4,303,303 A
`
`21969 Genaltr
`'r'rl9'r'5 Street
`_______________________ __ _'1'l8.I'6-’t-1']
`1.11977 Wasilko
`356.t'4
`t);’l98fl Tomlinson
`llr'l.‘J8fl Leiboff
`M1981 Trehcux at al.
`t2rt981 Aoyarna
`
`244.-LL16
`l‘.’9,rl8
`
`35[h'96.2
`
`(List continued on next page.)
`l-‘(JREIGN 1’/\'l'l;'.N’l‘ D(J(IUMl3N'l'S
`
`EP
`EP
`[-'.P
`EP
`EP
`El’
`
`0510629
`0880040
`0002 533
`0903607
`0921702
`oritizsss
`
`ID)’I 992
`lUl998
`32' I 090
`M999
`M999
`12rt999
`
`.......... .. GU2B.t'6r26
`
`ooztsrzem
`
`....... ..
`
`I~1o3t§;tt”r;"‘1o'3
`
`is
`A modular thrce-dimensional (SD) optical switch that
`scalable and that provides monitor and control of MEMS
`mirror arrays. A first switch module includes an array of
`input channels. Light bcarns rcccivcd from the input chan-
`nels are directed toward a first wavelength selective mirror.
`The light beams are rcllcctcd oil" of the first wavelength
`selective mirror and onto a first array of moveable micro-
`mirrors. The rnoveahle micrornitrors are adjusted so that the
`light beams reflect
`therefrom and enter it second switch
`module where they impinge upon at second array of move-
`ahle micromirrors The light beams rctlect off of the second
`array of moveable micromirrors and impinge upon a second
`wavelength sclective mirror. The light beams reflccl oil? of
`the S-‘.cC()t'I{l wavelength selective mirror and into an array of
`outpttt channels. The alignment or misalignment of a data
`path through the switch is detected by directing two monitor
`beams through the data path. one in the forward direction
`and one in the reverse direction. The position of each of the
`monitor beams is detected after its reflection from the
`second movcahic nticromirror that it hits. The position data
`is used to determine the angles of the moveable rnicromir—
`tors in thc tlata path.
`
`(List conlin ued on next page.)
`
`71 Claims, 14 Drawing Sheets
`
`
`
`FNC 1019
`
`

`
`US 6,567,574 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`12.72000 Redmer
`6,157,026 A
`12/2000 Ferguson
`6,160,930 A
`272001 Bhalla
`5,183,814 31
`212001 Tachibe
`5,195,190 B1
`312001 Garcia
`6,198,130 B1
`3.720111
`Isekj
`5,193,555 B1
`3192001 McCIelland
`E),2D1,629 B1
`372001 Aksyuk
`5,204,946 131
`472001 Kawase
`6,219,133 131
`472001 Wang
`6,219,168 B1
`4/2001 H6666
`6,219,472 B1
`472001 Riza
`6,222,954 131
`385/16
`............. ..
`6,320,993 B1 ‘ 113001 Laor
`6,327,398 B1 ‘ 120001 Soigaard el. al.
`............ .. 335117
`
`FOREIGN P1‘-YTENT DOCUMENTS
`0962796
`1271999
`1933991
`979999
`1039325
`9.32111]
`1951339
`1379999
`1957431
`“Z991
`WO 93434383
`311993
`167096724870
`871996
`9624870
`871996
`0830010
`231999
`W0 99.153374
`1211999
`W0 99.163501
`12/1999
`WO 99165324
`1211999
`9966334
`12.31999
`WO 99157666
`1211999
`9967666
`1271999
`“'0 9'9*'99333
`379999
`“'°99’9999°
`‘"2999
`0020399
`412000
`W0 999519‘
`59999
`W0 113163719
`11.721130
`W0 99373339
`1379999
`wo 00775711
`1272000
`11170 00777556
`1272000
`W0 0.1115543
`172001
`11170017079-15
`272001
`W0 01f131.'J1
`ZKZCDI
`W0 D1/24384
`-1-{Z001
`“'0 91135343
`‘W991
`‘K100112753?
`4792331
`
`13?
`51’
`E1’
`51’
`F-P
`W0
`1170
`we
`W0
`W0
`we
`W0
`W0
`W0
`1170
`‘V0
`“'0
`W0
`“'0
`W0
`W0
`wo
`wo
`W0
`W0
`WC
`W0
`W0
`W0
`
`002376726
`GDZBIEQ5
`
`'
`G02B76.‘26
`
`OTHER PUBLICMONS
`Fujita, Hiroyuki, “Application of micromachjning technol-
`ogy to optical devices and systems,” SPIE7'voI. 2879, p.
`2-11.
`Dewa, Andrew 3., “Development of a Silicon 'l'wo—Axis
`Micromirror for an Optical Cros6—Con1:1ect," SolidnState
`Sensor and Actuator Workshop, 13. 93—96.
`Vdovin, Glob. “Mic1'omach1'.ned adaptive mirrors,” Labora-
`tory of Electronic Instrtlmentation, Delft University of Tech-
`nology.
`Hornbock. Larry 1., “Defor1nablo—Mirror Spatial Light
`Modulators," SPIE Critical Reviews Seriesfvol. 1150, p.
`80-102.
`l-‘an, Li, “,"'l'!1esis, p. 1-134.
`W. Piyawattanametha, “MEMS Technology for Optical
`Crosslirtks for Micro7Nano Satellites,” International!‘ C017-
`ference on Integrated Nor1o.’Mic7-orecimology for Space
`Appficarions, Houston, TX, Nov. 1-6, 1998, pp. 1-2
`L. Fan, “'I\1vo—Din:1cnsional Optical Scanner with Large
`Angular Rotation Realized by Self—Assembled Micro—El-
`evator," Proc. IEEE LEGS Summer Topics! Meeting on
`Optical MEMS, paper WB4, Monterey, CA, Aug. $22,
`1998, pp. 145.
`
`“ cited by examiner
`
`4,317,611
`4,322,126
`4,365,863
`4,431,258
`4,470,662
`4,534,615
`4,566,935
`4,596,992
`4,626,066
`4,630,883
`4,662,746
`4,710,732
`4,796,263
`4,932,745
`4,956,619
`4,989,941
`5,028,939
`5,037,173
`5,096,279
`5,168,535
`5,172,262
`5,177,348
`5,199,088
`5,247,593
`5,256,869
`5,283,844
`5,291,324
`5,311,410
`5,317,659
`5,410,371
`5,412,506
`5,420,946
`5,436,986
`5,440,654
`5,444,801
`5,522,796
`5,524,153
`5,621,829
`5,627,669
`5,646,928
`5,647,033
`5,661 ,591
`5,748,812
`5,774,604
`5,786,925
`5,808,780
`5,841,917
`5,867,297
`5,878,177
`5,903,687
`5,914,801
`533,798
`5,933,269
`5,943,454
`5,963,367
`5,969,465
`5,994,159
`5,995,688
`6,002,818
`6,031,946
`6,031,947
`6,044,706
`6,087,747
`6,097,858
`6,097,860
`6,101,299
`6,1 23,996
`6,134,031
`6,134,042
`6,137,106
`6,137,105
`6,137,926
`
`A
`A
`A
`A
`A
`A
`A
`A
`A
`A
`A
`A
`A
`A
`R
`.4
`A
`.4
`A
`A
`A
`A
`A
`A
`
`SP>->3-3‘-P3'ID>39->>3’?>P>>>13'P3?’?>I>>>>>l>3bZ>>ib?>>>>>3-'>>>)>
`
`A
`A
`
`-
`
`"
`
`35036.2
`
`311982 Peterson
`3/1982 Minowa et al.
`123982 Brotlssaud
`231984 Fye ..... ..
`35071.6
`
`911984 Mumzhiu
`. 350195.15
`871985 Iwasalri
`35076.1
`171986 1166111661:
`671986 Hornbeck
`1271986 Levinson
`1271986 Taylor
`5/1987 Hombeclr
`1211937 Ilorrlbeck
`1711989 Rampolla .................... 372510
`6/1990 Blonder
`9
`21%? wk
`771991 Hornbeclr
`8,119.91 Sampsen
`371992 Homheck
`1271992 1Jl.0l'
`........................... 385716
`124992 Hombeck
`1,1993 L30,
`3,1993 May,
`971993 Lin
`10,1993 Lin
`.. 385117
`.
`'2/I994 Rice et al.
`3171994 Hinteflong ________________ __ 3597135
`5,1994 HS“
`5,1994 Lac
`4,1995 bmbm
`571995 Feldblum
`571995 Tsai
`7,719.95 Tsai
`871995 l.an1he1't,.Ir.
`871995 Laughriu
`671996 Dorsey. 111
`6,1995 [30,
`'
`4,1997 Fm,
`5_{E99';r Orino
`—,.,199-,. W"
`7,1199‘? Laughfin
`8,1997 Lin
`571998 B1.1cl11'.1:1
`571998 McDonald
`‘H1998 Gooascn ct 81
`359K245
`9.11998 McDonald .......
`. 35919290
`
`11/1998 Jungeman °‘ "1’
`' 3851”
`271999
`
` King et 8]. . .
`. ‘3597'I98
`Karasan
`311999
`511999
`YotmgDhuler
`671999
`..... .. 385719
`771999
`...... ..
`Aksyuk et al.
`Robinson
`371999
`. 359/280
`
`..... .. 335/22
`8/I999
`...... ..
`Aksyuk 61 81.
`10.11999
`Aksyuk
`
`Neukermans et a].
`10.11999
`1171999
`Aksyuk et al.
`1111999
`Faleln
`1210.999
`272000
`272000
`412000
`772000
`872000
`8/2000
`872000
`972000
`1072000
`109000
`1072000
`1072000
`JUIZOOD Maynard
`l17‘2UUU Kuroyanagi
`1172000 Copner
`
`............... .. 6047118
`
`. 385718
`
`3101333
`.. 438.152
`385.114
`
`

`
`U.S. Patent
`
`May 20, 2003
`
`Sheet 1 of 14
`
`US 6,567,574 B1
`
`§\\
`
`
`
`||lA'||“.l..\1|“«hr/....|I/.z...|..W«.»I
`
`
`
`ILIl....
`
`N.m=EaE
`
`»..£=taE
`
`L______________________________
`
`3
`
`o:
`
`
`
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 2 of 14
`
`US 6,567,574 Bl
`
`2%HE
`
`ll’0;‘millIflu?A_.mom._d::E‘
`
` /I__qm__IH_mqom._.._0,04...._duh_D_Kt____,__HLHTeaam.I§\DH_HD”_W:$.19.:_LE;
`
`
`/d___Wm;92RodH_God/.¢®/fhmcpkug.2__
`..II..
`J_.I.:a=an1IJ._1IIIIIuIIJ.
`
`
`Tmfl15%..L.rkfim--..mu
`@m,,_.éwe__w:_fimzmz\\_//TmzmzI___HH
`Illl
`
`I I_
`
`8_\&.mLE2:M3%.:
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sl1ect3 0f14
`
`US 6,567,574 B1
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 4 of 14
`
`US 6,567,574 B1
`
`FIG.3B
`
`'
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 5 of 14
`
`US 6,567,574 Bl
`
`.
`
`‘ ‘
`
`‘as:-5.93::
`‘
`.\
`
`us.\n'o-.-a...a.-Mu-....-vruv-:mo..I;>5:I-r.-.-1III=u-u-ulninunp:1" L,‘..
`--4
`
`
`
`
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 6 of 14
`
`US 6,567,574 B1
`
`

`
`U.S. Patent
`
`May 20, 2003
`
`Sheet 7 of 14
`
`US 6,567,574 B1
`
`

`
`U.S. Patent
`
`May 20, 2003
`
`Sheet 8 of 14
`
`US 6,567,574 B1
`
`
`
`W3(“Amay
`
`FIG.7
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sl1cct90f14
`
`US 6,567,574 B1
`
`
`
`;m\w5u£>\wl.m_..;%Z
`
`
`f\/\_AWE__mg.T.m_m.CmM___@fl(t5fi_\_HUUH_HHmmmfi/2_we
`.H.3'1!!!Nil4I._O
`Ill__Ila’ia__,“IV!
`
` _W_9:__9.gdmzmr\\_fl//Tmzmz#1._7/_3....nm_0,2\\Q__cH_0.8/«Q_:_
`_EafifiL.Tu|1ma1..
`
`
`
`11111111911---;
`
`m.GHQ
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 10 of 14
`
`US 6,567,574 B1
`
`_._
`
`O.m__
`
`0....
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 11 of 14
`
`US 6,567,574 B1
`
`0....
`
`

`
`U.S. Patent
`
`May 20, 2003
`
`Sheet 12 of 14
`
`US 6,567,574 B1
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sl1ect13 of 14
`
`US 6,567,574 B1
`
`

`
`US. Patent
`
`May 20, 2003
`
`Sheet 14 of 14
`
`US 6,567,574 B1
`
`mum
`
`

`
`US 6,567,574 B1
`
`1
`MODULAR THREE-DIMENSIONAL
`OPTICAL SWITCH
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates generally to the field of
`optical switching. More specifically, the present invention
`relates to micro electro mechanical systems (MEMS) tech-
`nology scanning mirrors for optical cross-connects and
`switches.
`2. Discussion of the Related Art
`
`Optical switching plays an important role in telecommu-
`nication networks, optical instntmentation, and optical sig-
`nal processing systems. Optical switches can be used to turn
`the light output of an optical fiber on or ofi, or, alternatively,
`to redirect
`the light
`to various different fibers, all under
`electronic control.
`
`Optical switches that provide switchable cross connects
`between an array of input fibers and an array of output fibers
`are often referred to as “optical cross-connects". Optical
`cross-connects are a fundamental building block in the
`development of an all-optical communications network.
`Specifically, in a fiber-optic communications network that
`uses electronic cross-connects, data travels through many
`fiber-optic segments which are linked together using the
`electronic cross-connects. Information is convened from
`light into an electronic signal, routed to the next circuit
`pathway, then converted back into light as it travels to the
`next network destination. In an all-optical communications
`network, on the other hand, the electronic cross-connects are
`replaced with optical cross-connects, which eliminates the
`need to convert the signals between light and electronic
`form. Instead. inforrnation travels: through the entire network
`in the form of light, which significantly increases the net-
`\vcrk’s ability to handle higher transmission speeds, reduces
`power dissipation,
`increases reliability, and reduces cost
`because the cost of the electrical devices are eliminated.
`
`There are many different types of optical switches. In
`terms of the switching mechanism, optical switches have
`been previously categorized as belonging to one of two
`general classes. The first general class of optical switches
`employs a change of refractive index to perform optical
`switching and can be referred to as “integrated optical
`switches” or “electro-optic switches.” The refractive index
`change can be induced by electro-optic,
`thermal-optic,
`aceusto-optic, or free-carrier elfects. The second general
`class of optical switches may be referred to as “bulk opto-
`mechanical switches" or simply “optomechanical switches."
`Such switches employ physical motion of one, or more,
`optical elements to perform optical switching. Specifically,
`an input fiber, typically engaged to a lens,
`is physically
`translatable from a first position to at least a second position.
`In each position, the input fiber optically connects with a
`dilferent output fiber. In this way, a spatial displacement of
`a rcfiectcd beam is afifected
`
`Optomechanical switches olfer many advantages over
`electro-optic switches. Optomechanical switches have both
`lower insertion loss and lower crosstalk compared to electro~
`optic switches. Further, optomechanical switches have a
`high isolation between their ON and OFF states.
`Furthermore, optomechanical switches are bidirectional, and
`are independent of optical wavelength, polarization, and
`data modulation formal. An optornechanical switch can be
`implemented either in a free-space approach or
`in a
`waveguide (e.g., optical fiber) approach. The free-space
`
`20
`
`25
`
`30
`
`3-5
`
`45
`
`Si]
`
`60
`
`65
`
`2
`approach is more scalable, and offers lower coupling loss
`compared to the waveguide approach.
`A number of different nzticromacbining technologies have
`been developing. Recently, a micrcmachining technology
`known has micro electro mechanical systems (MEMS)
`technology has been shown to olfer many advantages for
`building optomechanical switches. MEMS technology is
`technology characteristic of sizes from a few millimeters to
`hundreds of micrometers. MEMS technology is similar to
`semiconductor electronics fabrication except that the result-
`ing devices possess mechanical functionality, as well as
`electronic andlor optical functionality. MEMS technology is
`currently used to fabricate movable microstntctures and
`nticroactuatcrs. MEMS can significantly reduce the size,
`weight and cost of optomechanical switches. The switching
`time can also he reduced because of the lower mass of the
`smaller optomechanical switches.
`Many MEMS optomecbanical switches and cross-
`connects employ movable micromirrors. MEMS movable
`rnicromirror assemblies may be used for optical scanning.
`That is, MEMS mirror assemblies may be used to rapidly
`traverse a range of positions in a coordinate axis. Thus,
`MEMS mirror assemblies may be used as a basic building
`block for optical scanners. Optical scanners are ideal for use
`in optical cross-connects. Optical scanners function by
`changing the angle of the optical beam with respect to the
`information medium. Various diiferent types of scanners are
`capable of operating in one dimension (l_D), two dintensions
`(21)). or even three dimensions (3D).
`A 2D optical cross~connect (or switch) can be constructed
`by using MEMS micromirrors that move in only ll). For
`example, by using vertical micromirrors, where the mirror
`surface is perpendicular to the substrate, a simple cross-
`connect (or matrix switch) with a regular planar array of
`switching cells can be realized. The input and output fibers
`are arranged in the same plane as the matrix substrate. When
`a switching or cross-connect operation is performed, the
`optical beam is redirected by one or more of the vertical
`micromirrcrs, but
`the optical beam does not
`leave the
`common plane of the input and output fibers. Thus, the
`vertical micrcmirrors move in 1D and are used to perform
`optical cross-connections in 2D.
`A disadvantage of 2!) optical cross-connects (or switches)
`is that they are limited in the number of input and output
`fibers that they can support since those fibers are arranged in
`the same plane as the matrix substrate. In today's rapidly
`expanding communications systems there is a strong
`demand for higher capacity optical switches. Thus, there is
`a need for optical cross-connects and switches that can
`support a greater number of input and output fibers and that
`have the ability to cross-connect any of the input fibers with
`any of the output fibers
`SUMMARY OF‘ THE INVENTION
`
`The present invention advantageously addresses the needs
`above as well as other needs by providing a method of
`detecting alignment of an optical path through an optical
`switch. The method includes the steps of: directing a first
`monitor beam in a forward direction along at least a portion
`of the optimal path, the at least a portion of the optical path
`including reflection ofi of a first moveable optical redirect-
`ing device and a second moveable optical redirecting device;
`detecting a position of the first monitor beam that is reflected
`otfof the second moveable optical redirecting device; direct-
`ing a second monitor beam in a reverse direction along the
`at least a portion of the optical path; and detecting a position
`
`

`
`US 6,567,574 B1
`
`3
`of the second monitor beam that is reflected olf of the first
`moveable optical redirecting device.
`The present invention also provides a method of switch-
`ing an optical input channel to an optical output channel. The
`method includes the steps of: directing a light beam that
`originates from the optical
`input channel
`toward a first
`moveable optical redirecting device; reflecting the light
`beam (ill of the first tnoveable optical redirecting device and
`onto a second rnoveable optical redirecting device; reflecting
`the light beam offof the second moveable optical redirecting
`device; directing the light beam reflected oil of the second
`moveablc optical redirecting device into the optical output
`channel; and directing a tirst monitor beam along at least a
`portion of a same path traveled by the Light beam.
`The present invention also provides a method of switch-
`ing an optical input channel to an optical output channel that
`includes the steps of: directing a light beam received front
`the optical input channel toward it first wavelength selective
`optical redirecting device; reflecting, the light beam oil of the
`first wavelength selective optical redirecting device and onto
`a tirst moveablc optical redirecting device; adjusting the tirst
`moveable optical redirecting device so that the light beam
`reflects therefrom and impinges upon a second movcablc
`optical redirecting device; adjusting the second moveable
`optical redirecting device so that
`the light beam rellects
`therefrom and impinges upon a second wavelength selective
`optical redirecting device; and reflecting the light beam off‘
`of the second wavelength selective optical redirecting device
`and into the optical output channel.
`The present invention also provides an apparatus for use
`in optical switching. The apparatus includes a first switch
`module and a second switch module. The first switch
`module includes an optical input channel, a first moveablc
`optical redirecting device. and a lirst wavelength selective
`optical redirecting device positioned to reflect a light beam .
`received from the optical input channel onto the first move-
`ablc optical redirecting device. The second switch module
`includes an optical output channel, a second movcable
`optical redirecting device, and a second wavelength selec-
`tive optical redirecting device positioned to reflect the light
`beam received from the second movcablc optical redirecting
`device into the optical output channel. The first switch
`module and the second switch module are positioned so that
`the light beam can be reflected from the first moveable
`optical redirecting device and impinge upon the second
`moveable optical redirecting device.
`The present invention also provides an apparatus for use
`in optical switching that includes a first switch module. The
`tirst switch module includes an optical input channel, a first
`moveable optical redirecting device, and a first wavelength
`selective optical redirecting device positioned to reflect ti
`light beam received from the optical input channel onto the
`first movcablc optical
`redirecting device. A detector is
`eoutigurtsd to detect a position of a first monitor beam that
`is rellected oil" of the first ntovcablc optical redirecting
`device and that at least a portion of which is transmitted
`through the first wavelength selective optical redirecting
`device.
`
`It)
`
`15
`
`4t!
`
`45
`
`Sf]
`
`55
`
`A better understanding of the features and advantages of
`the present invention will be obtained by reference to the
`following detailed description of the invention and accom-
`panying drawings which set forth an illustrative e mbodiment
`in which the principles of the invention are utilized.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`60
`
`65
`
`The above and other aspects, features and advantages of
`the present invention will be more apparent from the fol-
`
`lowing more particular description thereof presented in
`conjunction with the following drawings herein;
`FIG. 1 is a perspective view illustrating a modular optical
`switch made in accordance with the present invention;
`FIG. 2 is a schematic, side view illustrating the modular
`optical switch shown in FIG. 1;
`FIGS. 3A and 313 are schematic. side views illustrating
`optical switches that use multiple modules of the type shown
`in HO. 1 in accordance with the present invention;
`FIG. 4 is a top view illustrating one of the scanner chips
`shown in FIG. 1;
`FIG. 5 is It perspective view illustrating one of the
`micromirror assemblies shown in FIG. 4;
`FIGS. 6A and 6B are perspective views illustrating the
`operation of the micromirror assembly shown in FIG. 5;
`FIG. 7 is a top view illustrating one of the monitoring
`(detector) chips shown in FIG. 1;
`FIG. 8 is a schematic. side view further illustrating the
`operation of the modular optical switch shown in FIG. 1;
`FIGS. 9 and 10 are schematic. side views illustrating an
`alternative modular optical switch made in accordance with
`the present invention;
`FIG. II is a schematic, side view illustrating another
`alternative modular optical switch made in accordance with
`the present invention;
`FIG. 12 is a schematic. side view illustrating another
`alternative modular optical switch made in accordance with
`the present invention; and
`FIG. 13 is a schematic, side view illuslratiitg another
`alternative modular optical switch made in accordance with
`the present invention.
`Dl:"l'AlLED Dl:‘.S(.‘RlP'l‘|()N OF A PREFERl{El)
`EMBODIMENT
`
`The following description is not to be taken in a limiting
`sense, but is made for the purpose of describing one or more
`embodiments of the invention. The scope of the invention
`should be determined with reference to the claims.
`
`Referring to FIGS. 1 and 2, there is illustrated an optical
`switch 100 made in accordance with an embodiment of the
`
`three-
`invention. The optical switch I00 is a
`present
`riirncnsional (3D) optical switch that is capable ofproviding
`switchable cross connects between an array of input fibers
`and an array of output fibers.
`in other words. each of a
`plurality of single-wavelength optical input channels from
`the input fibers can be directed to a desired optical through
`channel of the output fibers.
`Because the optical switch 100 (or optical cross-connect
`100) is a 30 switch. there are multiple rows of input and
`output fibers that occupy multiple planes. In other words. the
`input and output fibers are not all arranged in the same plane
`as a common substrate. This allows an optical beam from an
`input fiber in one plane to be cross-connected or switched to
`an output fiber in a different plane. Thus, the 3D optical
`switch 100 provides an array of frcc-space optical connec-
`tions between input and output fibers located in different
`planes. The use of input and output fibers in dillerent planes
`allows for a potentially greater number of input and output
`fibers than a 2|.) optical switch, which results in greater
`capacity.
`As will he discussed below. the optical switch 100 pref-
`erably uses ED MEMS optical scanners. It has been found
`herein that 2D scanners are ideal for implementing 3D
`optical cross-connects, i.e., optical cross-connects where the
`
`

`
`US 6,567,574 B1
`
`5
`input and output fibers are not arranged in the same plane as
`a common substrate. Furthermore, the input and output of
`the optical switch 100 are preferably symmetric, which
`makes the switch 100 convenient for bidirectional operation.
`In accordance with the present invention.
`the optical
`switch 100 uses a modular scheme. Specifically, the optical
`switch 100 includes a fiist module 102 and a second module
`104. Either one of the modules 102 or 194 may be referred
`to as a 3D optical switch module that, preferably, uses
`MEMS mirror scanners. In the illustrated embodiment the
`first and second modules 102, 104 are substantially identical,
`but it should be understood that there may be minor varia-
`tions betwecn the first and second modules 102. 104 in some
`embodiments of the invention.
`
`In the illustrated embodiment, the first module 102 con-
`nects to an array of input fibers 110 and includes wavelength
`division multiplexers (WDM) 111, an input collimator array
`1.12, a first mirror 114, a first scanner chip 116, and a first
`monitoring chip 113. Similarly, the second module 104 is
`connected to an array of output fibers 120 and includes
`wavelength division multiplexers 121, an output collimator
`array 122, a second mirror 124, a second scanner chip 126,
`and a second monitoring chip 128. As an optional feature, an
`array of monitoring beams 130 may be tapped into the array
`of input fibers 110 by tap couplers, and an array of moni-
`toring beams I31 (discussed below) may be tapped into the
`array of output fibers 120 by tap couplers. It should be
`understood that
`the monitoring beams (also referred to
`herein as the “monitoring wavelength”) may either be
`tapped into the input and output fibers 110, 120 as shown, or
`alternatively, beam splitters may be employed in the mod-
`ules 1ll2, 104 to receive the monitoring beams indepen-
`dently of the input and output fibers 110, 120. The use of
`such beam splitters will be discussed below.
`The first mirror 114 is preferably positioned to receive
`light beams from the array of input fibers 110 via the input
`collimator array 112 [i.e., the input channels) and to reflect
`the light beams in a direction substantially normal to the
`array of input channels. By way of example, the first mirror
`114 may be positioned at a 45° angle with respect to the
`input channels and have its reflective surface facing the
`input channels. Similarly, the second mirror 124 is prefer-
`ably positioned to reflect light beams into the array of output
`fibers 120 via the output collimator array 122 (i.e.. the output
`channels). In the illustrated embodiment the second mirror
`124 receives the light beams from a direction substantially
`normal to the array of output channels. By way of example,
`the second mirror 124 may be positioned at a 45° angle with
`respect to the output channels and have its retlective surface
`facing the output channels. While 45° is an exemplary
`orientation for the first and second mirrors 114. 124,
`it
`should be well understood that a 45° orientation is not
`required and that the first and second mirrors 114, 124, as
`well as the first and second scanner chips 116, 126, may be
`oriented at many other angles in accordance with the present
`invention.
`
`The firs! and second mirrors 114, 124 preferably comprise
`wavelength selective minors or dichroic mirrors. A wave-
`length selective mirror can be used to reliect signal wave-
`lengths and transmit all or a portion of a monitoring wave»
`length. In other words,
`at wavelength selective minor is
`partially transmissive for all or a portion of a certain
`wavelength of light. The certain wavelength of light can
`conveniently be used as a monitoring wavelength. It should
`be well understood that the percentage of lransmissiveness
`and refiectiveness of the mirrors 114, 124 may vary greatly
`in accordance with the present invention. Preferably, the
`
`20
`
`25
`
`30
`
`3-5
`
`45
`
`Si]
`
`60
`
`65
`
`6
`wavelength selective mirrors 114, 124 comprise layered
`dielectric mirrors that are partially transparent for the moni-
`toring wavelength, but use of layered dielectric mirrors are
`not required. Because one function of a mirror is to redirect
`optical beams, the wavelength selective niinrors 114, 124
`may also be referred to as wavelength selective optical
`redirecting devices.
`The first scanner chip 116 provides the function of a
`director, i.e.,
`it selects the output channel. The second
`scanner chip 126 provides the function of a redirector, i.e..
`it ensures coupling into the output fibers 120. Thus, the
`director and re-director are preferably scanner based. The
`distance between the first scanner chip llfi (director) and the
`second scanner chip 126 (redirector) and the loss budget
`determine the required scan angles. The scan angles will he
`discussed in more detail below.
`
`Although the illustrated optical switch 100 comprises a
`4x4 structure having sixteen inputs and sixteen outputs, it
`should be well understood that the specific number of inputs
`and outputs can vary greatly in accordance with the present
`invention. For example, 8x8, 64x64, and larger structures
`can all be made in accordance with the teachings of the
`present invention.
`One advantage of the optical switch 100's modular
`scheme is that stand-alone optical switches can be made that
`are highly scalable. In other words, multiple modules can be
`used to accommodate large numbers of inputs and outputs.
`For example, FIGS. 3A and 3B illustrate exemplary versions
`of optical switches that are constructed using multiple
`numbers of the first and second modules 102, 104. Either
`more or fewer of the input modules 102, and either more or
`fewer of the output modules 104, may be used to accom-
`modate the desired number of inputs and outputs, respec-
`tively. It should be understood that the total number of inputs
`does not have to be equal to the total number of outputs.
`Another advantage of the modularity of the optical
`switches of the present
`invention is that
`the individual
`modules are hot swapable.
`In other words, any of the
`modules can be removed and changed while the switch is
`running. This feature makes configuring and maintaining the
`switch particularly easy.
`Referring to FIG. 4, there is illustrated the upper surface
`of an exemplary version of the first scanner chip 116. An
`identical or substantially similar chip is preferably employed
`as the second scanner chip 126. The first scanner chip 116
`includes an array 140 of moveahle mictcmirrcrs formed on
`a substrate 142. Because one function of a mirror is to
`redirect optical beams, the movable rnicromirrors may also
`be referred to as movable optical redirecting devices. Each
`of the movable micromirrors is part of an optomcchanical
`switching cell. The mirror array 140 is preferably fabricated
`in accordance with Micro Electro Mechanical Systems
`(MEMS) technology. Furthermore, the mirror array 140 is
`preferably configured to operate as a two-dimensional (ZED)
`optical scanner. 21) optical scanners with large rotation
`angles, narrow beam divergence, and high resonant fre-
`quency can be implemented with MEMS technology.
`MEMS technology is attractive for
`reducing the size,
`weight, and complexity of the optical scanners.
`The mirror array 141]
`includes several MEMS mirror
`assemblies 144. In the illustrated embodiment, the mirror
`array 140 includes a 4x4 matrix of MEMS mirror assemblies
`144. It should be well understood, however, that dilferent
`size matrices of MEMS mirror assemblies 144 may be used
`in accordance with the present invention.
`FIG. 5 illustrates an exemplary version of one of the
`MEMS mirror assemblies 144. By way of example, this
`
`

`
`US 6,567,574 B1
`
`7
`structure may he surface-microtnachined and may be fabri-
`cated by the standard surface-micromachining process
`olfered by the MEMS Technology Applications Center at
`Microelectronics Center at North Carolina (MCNC),
`Research Triangle Park, N.C., or using bulk silicon technol-
`ogy. Each of the MEMS mirror assemblies 144 includes a
`movable micronlirror 150 that is substantially parallel to the
`plane of the substrate 142 when in a neutral position. Two
`support means 152 are connected between the micromirrot
`150 and a first mirror frame support 154. 'l'wo support means
`156 are connected between the first mirror frame support
`154 and a second mirror frame support 158. By way of
`example, the suppon means 152, 156 may comprise torsion
`bars, be part of a gimbal structure, or the like. Four side
`support plates 164, 165, 166, 167 support the second mirror
`frame support 158.
`The movable micromirror 150 is preferably movable in
`two dimensions. Specifically, the position of the micromirror
`151] can be adjusted in a direction indicated by arrow 16!! by
`rotation around an axis through the support means 152. The
`position of the micrornirror 150 can also be adjusted in a
`direction indicated by arrow 16