United States Patent
`Ma et al.
`
`(10) Patent No.: US 6,567,574 B1
`(45) Date of Patent: May 20, 2003
`
`US006567574B1
`
`(54) MODULAR THREE-DIMENSIONAl,
`OPTICAl, SWITCH
`
`(75)
`
`Inventors: Jian Ma, San Diego, CA (US); Ezekiel
`John Joseph Kruglick, San Diego, CA
`(US); Daniel J. Reiley, San Diego, CA
`(US); Philippe Jean Marchand,
`Poway, CA (US); Steffen Gloeckner,
`San Diego, CA (US)
`
`(73) Assignee:
`
`Omm, Inc., San Diego, CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patcnt is cxtcndcd or adjusted undcr 35
`U.S.C. 154(b) by 0 days.
`
`(21)
`
`Appl. No.: 09/680,648
`
`(22)
`
`Filed:
`
`Oct. 6, 2000
`
`(51)
`
`Int. CI.7 .................................................. G02B 6/26
`
`(52)
`
`U.S. Cl ............................... 385/16; 385/18; 385/19
`
`(58)
`
`Field of Search ...................................... 385/16-20
`
`(56)
`
`References Cited
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`
`(l,ist continued on next page.)
`
`Primary Examiner~flen E. Kim
`(74) Attorrze); Agent, or Finn~Arien Ferrell; Fitch, Even,
`Tabin & Flannery
`
`(57)
`
`ABSTRACT
`
`A modular three-dimensional (3D) optical s~vitch that is
`scalable and that providcs monitor and control of MEMS
`mirror arrays. A first switch module includes an array of
`input channels, l,ight beams received from the input chan-
`nels are directed toward a first wavelength selective mirror.
`The light beams are reflected off of the first wavelength
`selective mirror and onto a first array of moveable micro-
`mirrors. The moveable micromirrors are adjusted so that the
`light beams reflect therefrom and cntcr a second switch
`module where they impinge upon a second array of move-
`able micromirrors. The light beams reflect off of the second
`array of moveable micromirrors and impinge upon a second
`wavelength selective mirror. The light beams reflect off of
`the second wavelength selective mirror and into an array of
`output channels. The alignment or misalignment of a data
`path through thc switch is detected by directing two monitor
`beams throngh 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 refiection from the
`second moveable micromirror that it hits. The position data
`is used to determine the angles of the moveable micromir-
`rots in thc data path.
`
`(List continued on next page.)
`
`71 Claims, 14 Drawing Sheets
`
`Module.1
`
`Modele-2
`
`102
`
`Oetector Array-1
`
`Detector Array-2
`
`Petitioner Ciena Corp. et al.
`Exhibit 1023-1
`
`

`

`US 6,567,574 B1
`Page 2
`
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`
`3/1982 Pcterson
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`9/1984 Mumzhiu ................ 350/96.15
`8,/1985 Iwasaki ...................... 350/6.1
`1/1986 Hornbeck
`6/1986 Hornbeck
`12,/1986 Levinson
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`5/1987 Hornbeck
`12/1987 Hornbeck
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`3/1992 Hornbeck
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`’Esai
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`’Esai
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`7/1999 Aksyuk et al ................ 385/19
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`FOREIGN PATENT DOCUMENTS
`
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`
`12/1999
`9/’2000
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`12/’2000
`1/2001
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`12/1999
`12/1999
`12/1999
`12/1999
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`2/2000
`4/’2000
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`5/’2000
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`12/’2000
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`
`OTHER PUBLICAI’IONS
`
`Fujita, Hiroyuki, "Application of micromachining technol-
`ogy to optical devices and systems," SPlE/vol. 2879, p.
`2-11.
`Dewa, Andrew S., "Development of a Silicon Two Axis
`Micromirror for an Optical Cross Connect," Solid~qtale
`Sensor and Actuator Workshop, p. 93-96.
`Vdovin, Gleb, "Micromachined adaptive mirrors," Labora-
`tory of Electronic Instrumentation, Delft University of Tech-
`nology.
`Hornbeek, Larry J., "Deformable-Mirror Spatial Light
`Modnlators," SPIE Critical Reviews Series/vol. 1150, p.
`86 102.
`Fan, Li, "," Thesis, p. 1-134.
`W. Piyawattanametha, "MEMS Technology for Optical
`Crosslinks for Micro/Nano Satellites," InternationaI Con-
`ference on Integrated Nano/Microtechnology for Space
`Applications, Houston, TX, Nov. 1-6, 1998, pp. 1-2.
`1,. Fan, "Two Dimensional Optical Scanner with Large
`Angular Rotation Realized by Self’Assembled Micro~l-
`evator," Proc. IEEE LEOS Summer Topica! Meeting ~n
`Optical MEMS, paper WB4, Monterey, CA, Aug. 20-22,
`1998, pp. 1~8.
`
`* cited by examiner
`
`Petitioner Ciena Corp. et al.
`Exhibit 1023-2
`
`

`

`U.S. Patent
`US. Patent
`
`Sheet 1 of 14
`May 20, 2003 Sheet 1 of 14
`May 20, 2003
`
`US 6,567,574 B1
`US 6,567,574 B1
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`flyflu’fl.vll./lflt/
`
`72%.:
`
`a:
`
`atepr0Can.mCren.mt.ueP
`Petitioner Ciena Corp. et al.
`ow3201HumInXE
`Exhibit 1023-3
`
`
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`May 20, 2003
`
`Sheet 2 of 14
`Sheet 2 of 14
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`US 6,567,574 B1
`US 6,567,574 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1023-4
`Exhibit 1023-4
`
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`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 3 of 14
`May 20, 2003 Sheet 3 of 14
`
`US 6,567,574 B1
`US 6,567,574 B1
`
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1023-5
`Exhibit 1023-5
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 4 of 14
`May 20, 2003 Sheet 4 of 14
`
`US 6,567,574 B1
`US 6,567,574 B1
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`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1023-6
`Exhibit 1023-6
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 5 of 14
`May 20, 2003 Sheet 5 of 14
`
`US 6,567,574 B1
`US 6,567,574 B1
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1023-7
`Exhibit 1023-7
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 6 of 14
`May 20, 2003 Sheet 6 of 14
`
`US 6,567,574 B1
`US 6,567,574 B1
`
`
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1023-8
`Exhibit 1023-8
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 7 of 14
`May 20, 2003 Sheet 7 of 14
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`US 6,567,574 B1
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`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1023-9
`Exhibit 1023-9
`
`

`

`U.S. Patent
`US. Patent
`
`May 20, 2003
`Sheet 8 of 14
`May 20, 2003 Sheet 8 of 14
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`US 6,567,574 B1
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`Petitioner Ciena Corp. et al.
`Exhibit 1023-10
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`U.S. Patent
`US. Patent
`
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`May 20, 2003
`May 20, 2003 Sheet 9 of 14
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`US 6,567,574 B1
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`Petitioner Ciena Corp. et al. I
`Petitioner Ciena Corp. et al.
`Exhibit 1023-11
`Exhibit 1023-11
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`U.S. Patent
`US. Patent
`
`May 20, 2003
`May 20, 2003
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`Sheet 10 0f 14
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`US 6,567,574 B1
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`Exhibit 1023-12
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`U.S. Patent M.y 20, 2003
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`Exhibit 1023-14
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`U.S. Patent
`US. Patent
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`Sheet 13 0f 14
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`May 20, 2003
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`Exhibit 1023-15
`Exhibit 1023-15
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`

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`U.S. Patent
`US. Patent
`
`May 20, 2003
`May 20, 2003
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`Sheet 14 of 14
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`Petitioner Ciena Corp. et al.
`Exhibit 1023-16
`Exhibit 1023-16
`
`

`

`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 spccifically, thc prescnt 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-
`uication networks, optical instrumentation, and optical sig-
`nal processing systems. Optical switches can be used to turn
`the light output of an optical fiber on or off, 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 commnnications network that
`uses electronic cross-connects, data travels through many
`fiber-optic segments which are linked together using the
`electronic cross-connects. Information is converted 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, information travels through the entire network
`in the form of light, which significantly increases the net-
`work’s ability to handle higher transmission speeds, reduces
`powcr dissipation, incrcascs 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,
`acousto-optic, or free-carrier effects. The second general
`class of optical switches may be referred to as "bnlk 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
`different outpnt fiber. In this way,, a spatial displacement of
`a reflected beam is affected.
`Optomechanical switches offer 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 Olaf states.
`Furthermore, optomechanical switches are bidirectional, and
`are independent of optical wavelength, polarization, and
`data modulation format. An optomechanical switch can be
`implemented either in a free-space approach or in a
`waveguide (e.g., optical fiber) approach. The free-space
`
`2
`approach is more scalable, and offers lower coupling loss
`compared to the waveguide approach.
`A number of different micromachining technologies have
`been developing. Recently, a micromachining technology
`s known has micro electro mechanical systems (MEMS)
`technology has been shown to offer 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
`10 semiconductor electronics fabrication except that the rcsult-
`ing devices possess mechanical fiJnctionality, as well as
`electronic and/or optical ~nctionality. MEMS technology is
`currently used to fabricate movable microstructures and
`microactuators. MEMS can significantly reduce the size,
`a5 weight and cost of optomechanical switches. The switching
`time can also be reduced because of the lower mass of the
`smaller optomcchanical switches.
`Many MEMS optomechanical switches and cross-
`connects employ movable micromirrors. MEMS movable
`:0 micromirror 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 arc ideal for use
`25 in oplical cross-connects. Optical scanners fnnclion by
`
`30
`
`changing the angle of the optical beam with respect to the
`information medium. Various different types of scanners are
`capable of operating in one dimension (1D), two dimeusions
`(2D), or even three dimensions (3D).
`A 2D optical cross-conncct (or switch) can be constructed
`by using MEMS micromirrors that move in only 1D. For
`example, by using vertical micromirrors, where the mirror
`surface is perpendicular to the substrate, a sin~ple cross-
`35 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-conncct operation is pcrformcd, the
`optical beam is redirected by one or more of the vertical
`40 micromirrors, bnt the optical beam does not leave the
`common plane of the input and output fibers. Thus, the
`vertical uficromirrors move in 1D and are used to perform
`optical cross-connections in 2D.
`A disadvantage of 2D optical cross-connects (or switches)
`45 is that they arc 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
`50 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-conncct any of the input fibers with
`any of the ontput fibers.
`
`55
`
`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
`s~viteh. The method includes the steps of: directing a first
`~0 monitor beam in a forward direction along at least a portion
`of the optical path, the at least a portion of the optical path
`including reflection off 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
`~5 off of 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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1023-17
`
`

`

`US 6,567,574 B1
`
`3
`of the second monitor beam that is reflected off of the first
`moveable optical redirecting device.
`The prcscnt 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 off of the first moveable optical redirecting device and
`onto a second moveable optical redirecting device; reflecting
`the light beam off of the second moveable optical redirecting
`device; directing the light beam reflected off of the second
`movcablc optical redirecting dcvicc into the optical output
`channel; and directing a first 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 opfical input channel to an optical output channel that
`inclildes the steps of: direefing a light beam received from
`the optical input channel toward a first wavelength selective
`optical redirecting device; reflecting the light bean] off of the
`first wavelength selective optical redirecting device and onto
`a first moveable optical redirecting device; adjusting the first
`moveable optical redirecting device so that the light beam
`reflects therefrom and impinges upon a second moveable
`optical redirecting device; adjusting the second moveable
`optical redirecting device so that the light beam reflects
`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 sxvitch module. The first switch
`module includes an optical input channel, a first moveable
`optical redirecting device, and a first wavelength selective
`optical redirecting device positioned to reflect a light beam
`received from the optical input channel onto the first move-
`able optical redirecting device. The second s~vitch module
`includes an optical output channel, a second moveable
`optical redirecting device, and a second wavelength selec-
`tive optical redirecting device positioned to reflect the light
`beam received from the second moveable optical redirecting
`device into the optical output channel. The lirst 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
`first switch module includes an optical input channel, a first
`movcable optical redirecting device, and a first wavelength
`selective optical redirecting device positioned to reflect a
`light beam received from the optical input channel onto the
`first moveable optical redirecting device. A detector is
`configured to detect a position of a first monitor beam that
`is reflected off of the first moveable optical redirecting
`device and that at least a portion of which is transmitted
`through the first wavelength selective optical redirecting
`device.
`A better understanding of the features and advantages of
`the present invention will be obtaincd by reference to the
`following detailed description of the invention and accom-
`panying drawings which set forth an illustrative embodiment
`in which the principles of the invention are utilized.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The above and other aspects, features and advantages of
`the present invention will be more apparent from the fol-
`
`s
`
`10
`
`~s
`
`4
`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 3B are schematic, side views illustrating
`optical switches that use multiple modules of the type shown
`in FIG. 1 in accordancc with thc prescnt invention;
`FIG. 4 is a top view illustrating one of the scanner chips
`shown in FIG. 1;
`FIG. 5 is a 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 shoxvn 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 lfl are schematic, side views illustrating an
`alternative modular optical switch made in accordance with
`the present invention;
`FIG. 11 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
`30 the present invention; and
`
`20
`
`2s
`
`FIG. 13 is a schematic, side view illustrating another
`alternative modular optical switch made in accordance with
`the present invention.
`
`35
`
`DETAILED DESCRIPTION OF A PREFERRED
`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. ’lt~e scope of the invention
`should be determined with reference to the claims.
`Refcrring to FIGS. 1 and 2, therc is iflustratcd an optical
`switch lfl0 made in accordance with an embodiment of the
`present invention. The optical switch lfl0 is a three-
`45 dimensional (3D) optical switch that is capable of providing
`switchable cross connects between an array of input fibers
`and an array of output fibers. In other xvords, each of a
`plurality of singlc-xvavclcngth optical input channels from
`the input fibcrs can be dirccted to a desired optical through
`50 channel of the oulput fibers.
`Because the optical switch 100 (or optical cross-connect
`100) is a 3D switch, there are multiple rows of input and
`output fibcrs that occupy multiplc planes. In other words, the
`input and output fibers are not all arranged in the same plane
`55 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 free-space optical connec-
`tions between input and output fibers located in different
`60 planes. The use of input and output fibers in diffcrcnt plancs
`allows for a potentially greater number of input and output
`fibers than a 2D optical switch, which resufls in greater
`capacity.
`As will be discussed below, the optical switch 100 pref-
`65 erably uses 2D 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
`
`Petitioner Ciena Corp. et al.
`Exhibit 1023-18
`
`

`

`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 prelErably symmetric, which
`makes the switch 11~ 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 first module 102 and a second module
`1114. Either one of the modules 102 or 1114 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 between the first and second modules 1112, 1114 in some
`embodiments of thc invcntion.
`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
`112, a first mirror 114, a first scanner chip 116, and a first
`monitoring chip 118. Similarly, the second module 1114 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 1111 by tap couplers, and an array of moni-
`toring beams 131 (discussed below) may be tapped into
`array of output fibers 120 by tap couplers. It should be
`understood that the monitoriug beams (also referred to
`herein as the "monitoring wavelength") may either be
`tapped into the input and output fibers 110, 1211 as shown, or
`altcrnativcly, bcam splitters may bc employed in thc mod-
`ules 1112, 1114 to receive the monitoring beams indepen-
`dently of the input and output fibers II0, 120. The use of
`such beam splitters will be discussed below.
`The first mirror 114 is preferably positioned to receive
`fight beams from the array of input fibers 1111 via the inpul
`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
`II4 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 oulpul
`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 Ihe output channels and have its reflective 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 first and second mirrors 114, 124 preferably comprise
`wavelength selective mirrors or dichroic mirrors. A wave-
`length selective mirror can be used to reflect signal wave-
`lengths and transmit all or a portion of a monitoring wave-
`length. In other words, a wavelength selective mirror 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 transmissiveness
`and reflectiveness of the mirrors 114, 124 may vary greatly
`in accordance with the present invention. Preferably, the
`
`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
`5 optical beams, the wavelength selective mirrors 114, 124
`may also be referred to as wavelength selective optical
`redirecting dcviccs.
`The first scanner chip 116 provides the function of a
`director, i.e., it selects the oulput 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 116 (director) and the
`second scanner chip 126 (redirector) and the loss budget
`determine the required scan angles. The scan angles will be
`~5 discussed in more detail below.
`
`3{3
`
`35
`
`Although the illustrated optical switch 100 comprises a
`4x4 structure haviug 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
`;