(12) United States Patent
`Ma et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,567,574 B1
`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); Ste?'en Gloeckner,
`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
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/680,648
`(22) Filed:
`Oct. 6, 2000
`
`(51) Int. Cl.7 ................................................ .. G02B 6/26
`
`(52) US. Cl. ............................ .. 385/16; 385/18; 385/19
`
`(58) Field of Search .................................... .. 385/16—20
`
`(56)
`
`References Cited
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`(List continued on neXt page.)
`
`Primary Examiner—Ellen E. Kim
`(74) Attorney, Agent, or Firm—Arien Ferrell; Fitch, Even,
`Tabin & Flannery
`(57)
`
`ABSTRACT
`
`A modular three-dimensional (3D) optical sWitch that is
`scalable and that provides monitor and control of MEMS
`mirror arrays. A ?rst sWitch module includes an array of
`input channels. Light beams received from the input chan
`nels are directed toWard a ?rst Wavelength selective mirror.
`The light beams are re?ected off of the ?rst Wavelength
`selective mirror and onto a ?rst array of moveable micro
`mirrors. The moveable micromirrors are adjusted so that the
`light beams re?ect therefrom and enter a second sWitch
`module Where they impinge upon a second array of move
`able micromirrors. The light beams re?ect off of the second
`array of moveable micromirrors and impinge upon a second
`Wavelength selective mirror. The light beams re?ect off of
`the second Wavelength selective mirror and into an array of
`output 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 re?ection from the
`second moveable micromirror that it hits. The position data
`is used to determine the angles of the moveable micromir
`rors in the data path.
`
`(List continued on neXt page.)
`
`71 Claims, 14 Drawing Sheets
`
`E
`
`Module- 1
`Detector Array-1
`
`118
`
`Module-2
`Detector Array-2
`
`19A
`
`128
`
`100
`/
`
`122
`
`120
`
`182
`
`l ‘36 (9x; \ 9 7%
`
`Cisco Systems, Inc.
`Exhibit 1023, Page 1
`
`

`

`US 6,567,574 B1
`Page 2
`
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`3/1992 Hornbeck
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`9/1993 Lin
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`2/1994 Rice et a1. .................. .. 385/17
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`6/1996 Dorsey, n1 ............... .. 604/118
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`5,627,669 A
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`5,646,928 A
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`8/1997 Lin
`5,748,812 A * 5/1998 Buchin ...................... .. 385/18
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`7/1998 Goossen et al. .......... .. 359/245
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`9/1998 McDonald ..... ..
`
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`5,923,798 A
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`31333 iii’?sri’it'a'r'. ...........
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`4/2000 Neukermans
`6,087,747 A
`7/2000 Dhuler et a1. ............... .. 310/90
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`8/2000 Laor
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`8/2000 Laor
`6,101,299 A * 8/2000 Laor ......................... .. 385/16
`2
`1151;311:150“
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`
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`
`FOREIGN PATENT DOCUMENTS
`
`.......... .. G02B/6/26
`.......... .. G02B/6/26
`
`.......... .. G02B/6/26
`
`EP
`EP
`EP
`EP
`EP
`W0
`W0
`WO
`WO
`W0
`W0
`W0
`W0
`W0
`WO
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`W0
`
`0962796
`1033601
`1039325
`1061389
`1067421
`W0 9304388
`WO 96/24870
`9624870
`0880040
`WO 99/63374
`WO 99/63531
`WO 99/66354
`9966354
`WO 99/67666
`9967666
`W0 (lo/05832
`W0 (lo/20899
`0020899
`W0 00/25161
`W0 00/68719
`WO 00/73839
`WO 00/75711
`WO 00/77556
`W0 01/06543
`WO 01/07945
`W0 01/13151
`WO 01/24384
`WO 01/25848
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`
`12/1999
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`5/2000
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`12/2000
`12/2000
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`2/2001
`2/2001
`4/2001
`4/2001
`4/2001
`
`OTHER PUBLICATIONS
`
`Fujita’ Hirqyuki’ “Application of micromachining technol'
`ogy to optical devices and systems,” SPIE/vol. 2879, p.
`2—11~
`DeWa, Andrew S., “Development of a Silicon TWo—Axis
`Micromirror for an Optical Cross—Connect,” Solid—State
`Sense-r and Amalgam Workshop’ p‘ 93796‘ -
`Vdovm, Gleb, Micromachmed adaptive mirrors,” Labora
`tory of Electronic Instrumentation, Delft University of Tech
`nology
`Hornbeck, Larry J., “Deformable—Mirror Spatial Light
`Modulators,” SPIE Critical Reviews Series/vol. 1150, p.
`86_102~
`1 134
`Fan Li “,,Thesis
`>
`_
`>
`>
`’P~ _
`-
`W- Plyawa?anametha, “MEMS Technology for Optical
`Crosslinks for Micro/Nano Satellites,” International Con
`ference on Integrated Nano/Microtechnology for Space
`Applications, Houston, TX, NOV_ 1_6, 1998, pp 1_2_
`L. Fan, “TWo—Dimensional Optical Scanner With Large
`Angular Rotation Realized by Self—Assembled Micro—El
`evator,” Proc. IEEE LEOS Summer Topical Meeting on
`Optical MEMS, paper WB4, Monterey, CA, Aug. 20—22,
`1998, pp. 1—8.
`
`* cited by CXarniner
`
`Cisco Systems, Inc.
`Exhibit 1023, Page 2
`
`

`

`U.S. Patent
`
`May 20, 2003
`
`Sheet 1 0f 14
`
`US 6,567,574 B1
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`Exhibit 1023, Page 3
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`U.S. Patent
`
`May 20, 2003
`
`Sheet 2 0f 14
`
`US 6,567,574 B1
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`Cisco Systems, Inc.
`Exhibit 1023, Page 4
`
`

`

`US. Patent
`
`May 20, 2003
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`Sheet 3 0f 14
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`US 6,567,574 B1
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`Cisco Systems, Inc.
`Exhibit 1023, Page 5
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`Exhibit 1023, Page 5
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`

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`U.S. Patent
`
`May 20, 2003
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`Cisco Systems, Inc.
`Exhibit 1023, Page 6
`
`

`

`U.S. Patent
`
`May 20, 2003
`
`Sheet 5 0f 14
`
`US 6,567,574 B1
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`Cisco Systems, Inc.
`Exhibit 1023, Page 7
`
`

`

`U.S. Patent
`
`May 20, 2003
`
`Sheet 6 6f 14
`
`US 6,567,574 B1
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`Cisco Systems, Inc.
`Exhibit 1023, Page 8
`
`

`

`U.S. Patent
`
`May 20, 2003
`
`Sheet 7 0f 14
`
`US 6,567,574 B1
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`
`Cisco Systems, Inc.
`Exhibit 1023, Page 9
`
`

`

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`
`May 20, 2003
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`Exhibit 1023, Page 10
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`Exhibit 1023, Page 12
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`Exhibit 1023, Page 12
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`Exhibit 1023, Page 14
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`Clsco Systems, Inc
`Exhibit 1023, Page 15
`
`Cisco Systems, Inc.
`Exhibit 1023, Page 15
`
`

`

`US. Patent
`
`May 20, 2003
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`Exhibit 1023, Page 16
`
`Cisco Systems, Inc.
`Exhibit 1023, Page 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 ?eld of
`optical switching. More speci?cally, 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 instrumentation, and optical sig
`nal processing systems. Optical sWitches can be used to turn
`the light output of an optical ?ber on or off, or, alternatively,
`to redirect the light to various different ?bers, all under
`electronic control.
`Optical sWitches that provide sWitchable cross connects
`betWeen an array of input ?bers and an array of output ?bers
`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.
`Speci?cally, in a ?ber-optic communications netWork that
`uses electronic cross-connects, data travels through many
`?ber-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 signi?cantly increases the net
`works 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 ?rst 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 “bulk opto
`mechanical sWitches” or simply “optomechanical sWitches.”
`Such sWitches employ physical motion of one, or more,
`optical elements to perform optical sWitching. Speci?cally,
`an input ?ber, typically engaged to a lens, is physically
`translatable from a ?rst position to at least a second position.
`In each position, the input ?ber optically connects With a
`different output ?ber. In this Way, a spatial displacement of
`a re?ected 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 OFF 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 ?ber) approach. The free-space
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`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
`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
`semiconductor electronics fabrication except that the result
`ing devices possess mechanical functionality, as Well as
`electronic and/or optical functionality. MEMS technology is
`currently used to fabricate movable microstructures and
`microactuators. MEMS can signi?cantly reduce the siZe,
`Weight and cost of optomechanical sWitches. The sWitching
`time can also be reduced because of the loWer mass of the
`smaller optomechanical sWitches.
`Many MEMS optomechanical sWitches and cross
`connects employ movable micromirrors. MEMS movable
`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 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 different types of scanners are
`capable of operating in one dimension (1D), tWo dimensions
`(2D), or even three dimensions (3D).
`A 2D optical cross-connect (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 simple cross
`connect (or matrix sWitch) With a regular planar array of
`sWitching cells can be realiZed. The input and output ?bers
`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
`micromirrors, but the optical beam does not leave the
`common plane of the input and output ?bers. Thus, the
`vertical micromirrors move in 1D and are used to perform
`optical cross-connections in 2D.
`Adisadvantage of 2D optical cross-connects (or sWitches)
`is that they are limited in the number of input and output
`?bers that they can support since those ?bers 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 ?bers and that
`have the ability to cross-connect any of the input ?bers With
`any of the output ?bers.
`
`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 ?rst
`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 re?ection off of a ?rst moveable optical redirect
`ing device and a second moveable optical redirecting device;
`detecting a position of the ?rst monitor beam that is re?ected
`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
`
`Cisco Systems, Inc.
`Exhibit 1023, Page 17
`
`

`

`US 6,567,574 B1
`
`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 accordance With the present 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 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. 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
`the present invention; and
`FIG. 13 is a schematic, side vieW illustrating another
`alternative modular optical sWitch made in accordance With
`the present invention.
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`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
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`3
`of the second monitor beam that is re?ected off of the ?rst
`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 ?rst
`moveable optical redirecting device; re?ecting the light
`beam off of the ?rst moveable optical redirecting device and
`onto a second moveable optical redirecting device; re?ecting
`the light beam off of the second moveable optical redirecting
`device; directing the light beam re?ected off of the second
`moveable optical redirecting device into the optical output
`channel; and directing a ?rst 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 from
`the optical input channel toWard a ?rst Wavelength selective
`optical redirecting device; re?ecting the light beam off of the
`?rst Wavelength selective optical redirecting device and onto
`a ?rst moveable optical redirecting device; adjusting the ?rst
`moveable optical redirecting device so that the light beam
`re?ects therefrom and impinges upon a second moveable
`optical redirecting device; adjusting the second moveable
`optical redirecting device so that the light beam re?ects
`therefrom and impinges upon a second Wavelength selective
`optical redirecting device; and re?ecting 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 ?rst sWitch
`module and a second sWitch module. The ?rst sWitch
`module includes an optical input channel, a ?rst moveable
`optical redirecting device, and a ?rst Wavelength selective
`optical redirecting device positioned to re?ect a light beam
`received from the optical input channel onto the ?rst move
`able optical redirecting device. The second sWitch module
`includes an optical output channel, a second moveable
`optical redirecting device, and a second Wavelength selec
`tive optical redirecting device positioned to re?ect the light
`beam received from the second moveable optical redirecting
`device into the optical output channel. The ?rst sWitch
`module and the second sWitch module are positioned so that
`the light beam can be re?ected from the ?rst 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 ?rst sWitch module. The
`?rst sWitch module includes an optical input channel, a ?rst
`moveable optical redirecting device, and a ?rst Wavelength
`selective optical redirecting device positioned to re?ect a
`light beam received from the optical input channel onto the
`?rst moveable optical redirecting device. A detector is
`con?gured to detect a position of a ?rst monitor beam that
`is re?ected off of the ?rst moveable optical redirecting
`device and that at least a portion of Which is transmitted
`through the ?rst Wavelength selective optical redirecting
`device.
`Abetter 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 embodiment
`in Which the principles of the invention are utiliZed.
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`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
`present invention. The optical sWitch 100 is a three
`dimensional (3D) optical sWitch that is capable of providing
`sWitchable cross connects betWeen an array of input ?bers
`and an array of output ?bers. In other Words, each of a
`plurality of single-Wavelength optical input channels from
`the input ?bers can be directed to a desired optical through
`channel of the output ?bers.
`Because the optical sWitch 100 (or optical cross-connect
`100) is a 3D sWitch, there are multiple roWs of input and
`output ?bers that occupy multiple planes. In other Words, the
`input and output ?bers are not all arranged in the same plane
`as a common substrate. This alloWs an optical beam from an
`input ?ber in one plane to be cross-connected or sWitched to
`an output ?ber in a different plane. Thus, the 3D optical
`sWitch 100 provides an array of free-space optical connec
`tions betWeen input and output ?bers located in different
`planes. The use of input and output ?bers in different planes
`alloWs for a potentially greater number of input and output
`?bers than a 2D optical sWitch, Which results in greater
`capacity.
`As Will be discussed beloW, the optical sWitch 100 pref
`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
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The above and other aspects, features and advantages of
`the present invention Will be more apparent from the fol
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`65
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`Cisco Systems, Inc.
`Exhibit 1023, Page 18
`
`

`

`US 6,567,574 B1
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`5
`input and output ?bers 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. Speci?cally, the optical
`sWitch 100 includes a ?rst module 102 and a second module
`104. Either one of the modules 102 or 104 may be referred
`to as a 3D optical sWitch module that, preferably, uses
`MEMS mirror scanners. In the illustrated embodiment the
`?rst and second modules 102, 104 are substantially identical,
`but it should be understood that there may be minor varia
`tions betWeen the ?rst and second modules 102, 104 in some
`embodiments of the invention.
`In the illustrated embodiment, the ?rst module 102 con
`nects to an array of input ?bers 110 and includes Wavelength
`division multiplexers (WDM) 111, an input collimator array
`112, a ?rst mirror 114, a ?rst scanner chip 116, and a ?rst
`monitoring chip 118. Similarly, the second module 104 is
`connected to an array of output ?bers 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 ?bers 110 by tap couplers, and an array of moni
`toring beams 131 (discussed beloW) may be tapped into the
`array of output ?bers 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 ?bers 110, 120 as shoWn, or
`alternatively, beam splitters may be employed in the mod
`ules 102, 104 to receive the monitoring beams indepen
`dently of the input and output ?bers 110, 120. The use of
`such beam splitters Will be discussed beloW.
`The ?rst mirror 114 is preferably positioned to receive
`light beams from the array of input ?bers 110 via the input
`collimator array 112 (i.e., the input channels) and to re?ect
`the light beams in a direction substantially normal to the
`array of input channels. By Way of example, the ?rst mirror
`114 may be positioned at a 45° angle With respect to the
`input channels and have its re?ective surface facing the
`input channels. Similarly, the second mirror 124 is prefer
`ably positioned to re?ect light beams into the array of output
`?bers 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 re?ective surface
`facing the output channels. While 45° is an exemplary
`orientation for the ?rst and second mirrors 114, 124, it
`should be Well understood that a 45° orientation is not
`required and that the ?rst and second mirrors 114, 124, as
`Well as the ?rst and second scanner chips 116, 126, may be
`oriented at many other angles in accordance With the present
`invention.
`The ?rst and second mirrors 114, 124 preferably comprise
`Wavelength selective mirrors or dichroic mirrors. A Wave
`length selective mirror can be used to re?ect 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 re?ectiveness of the mirrors 114, 124 may vary greatly
`in accordance With the present invention. Preferably, the
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`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 mirrors 114, 124
`may also be referred to as Wavelength selective optical
`redirecting devices.
`The ?rst 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 ?bers 120. Thus, the
`director and re-director are preferably scanner based. The
`distance betWeen the ?rst 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
`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 speci?c 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 ?rst 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 con?guring and maintaining the
`sWitch particularly easy.
`Referring to FIG. 4, there is illustrated the upper surface
`of an exemplary version of the ?rst scanner chip 116. An
`identical or substantially similar chip is preferably employed
`as the second scanner chip 126. The ?rst scanner chip 116
`includes an array 140 of moveable micromirrors formed on
`a substrate 142. Because one function of a mirror is to
`redirect optical beams, the movable micromirrors may also
`be referred to as movable optical redirecting devices. Each
`of the movable micromirrors is part of an optomechanical
`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 con?gured to operate as a tWo-dimensional (2D)
`optical scanner. 2D 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 comp