(12) United States Patent
`Wagener et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,631,222 B1
`Oct. 7, 2003
`
`US006631222B1
`
`RECONFIGURABLE OPTICAL SWITCH
`
`OTHER PUBLICATIONS
`
`E. Murphy, Opticall’iber 7~lecommunicationslllB, Chapter
`10, edited by T. Koch and I. Kamino~v, Academic Press.
`
`C.R. Doerr, Proposed WDM Cross Connect Using A Planar
`Arrangement of Waveguide Grating Routers and Phase
`Shifters, Photonics Technology Letters; vol. 10, No. 4, Apr.
`1998.
`C.R. Giles, et al., "Low-Loss ADD/DROP Multiplexers for
`WDM Lightwavc Networks," Tenth International Confer-
`ence on Integrated Optics and Optical Fibre Communica-
`tion, IOOC, vol. 3, Jun. 29, 1995.
`
`JDS Uniphase Corporation, Add-Drop Modules, Product
`Bulletin 2000, Ontario, Canada.
`
`D.O.Culverhouse et al., Low-loss all-fiber acousto-optic
`tunable filter, OpticalSociet.v ofAmerica, vol. 22, No. 2, Jan.
`15, 1997, pp. 96-98.
`
`Roberto Sabella et al., "Impact of Transmission Performance
`on Path Routing in All-Optical Transport Networks,", Jour-
`nal ofLightware l~chnolog~; vol. 16, No. 11 (Nov. 1998),pp.
`1965-1971.
`
`(54)
`
`(75)
`
`(73)
`
`(*)
`
`Inventors: Jefferson L. Wagener, Aberdeen, WA
`(US); Tliolrras Andrew Strasser,
`Warren, NJ (US)
`
`Assignee: Photuris, Inc., Piscataway, NJ (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.: 09/571,833
`
`(22) Filed:
`
`May 16, 2000
`
`Int. Cl.7 .................................................. G02B 6/35
`(51)
`(52) U.S. Cl .............................. 385/16; 385/17; 385/18;
`385/31
`(58) Field of Search .............................. 385/16, 17, 18,
`385/’24, 31, 33, 47; 359/131, 196, 212,
`127, 124
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`* cited by examiner
`
`Nosu et al ..................... 370/3
`1/1981
`4,244,045 A
`Levinson ................. 350/96.18
`12/1986
`4,626,066 A
`Calvani ct al .............. 359/127
`12/1995
`5,479,082 A
`Schimpe ...................... 385/24
`4/1996
`5,504,827 A
`Scobey ....................... 359/127
`12/1996
`5,583,683 A
`Fevrier et al ............... 359/124
`3/1997
`5,612,805 A
`Ford
`........................... 385,/22
`4/1997
`5,621,829 A
`Duck et al .................. 357/127
`* 9/1998
`5,808,763 A
`Jayaraman et al ............ 372/50
`11/1998
`5,835,517 A
`Jungerman et al ............ 385/17
`11/1998
`5,841,917 A
`Russell et al .................. 385/7
`6/1999
`5,915,050 A
`Duck ct al .................. 359/127
`* 7/1999
`5,920,411 A
`Danagher et al ............ 359/124
`9/1999
`5,959,749 A
`Tomlinson ................... 385/18
`9/1999
`5,960,133 A
`10/1999
`5,974,207 A
`Aksyuk et al ................ 385,/24
`MacDonald ................. 385/16
`* 12/1999
`6,005,993 A
`Hendrix ...................... 359/127
`* 12/1999
`6,008,920 A
`Michalicek et al ......... 359/224
`2/2000
`6,028,689 A
`Braun
`........................ 359/124
`* 6/2000
`6,075,632 A
`Lin et al ....................... 385/24
`6,289,148 BI * 9/2001
`6,327,398 B1 12/2001 Solgaard ct al ............... 385/18
`
`FOREIGN PATENT DOCUMENTS
`
`Primm:v Examiner--John D. Lee
`Assistant Examiner--Juliana K. Kang
`(74) Attorney, Agent, or Firm~ayer Fortkort & Williams,
`PC; Stuart H. Mayer, Esq.
`
`(57)
`
`ABSTRACT
`
`An optical switch includes at least one input port for
`receiving a WDM optical signal having a plurality of wave-
`lcngth components, at lcast thmc output ports, and a plural-
`ity of wavelength selective elements each selecting one of
`the wavclcngth components from among thc plurality of
`wavelength components. A plurality of optical elements are
`also provided, each of which are associated with one of the
`~vavelength selective elements. Each of the optical elements
`direct the selected wavelength component that is selected by
`its associated selected element to a given one of the output
`ports independently of every other wavelength component.
`The given output port is variably selectable frona among all
`the output ports.
`
`JP
`
`60-88907
`
`* 5/1985
`
`88 Claims, 3 Drawing Sheets
`
`30_~0
`
`DIELECTRIC 3,01
`
`315
`
`A3,~’° 302
`
`Petitioner Ciena Corp. et al.
`Exhibit 1025-1
`
`

`

`U.S. Patent
`
`Oct. 7, 2003
`
`Sheet 1 of 3
`
`US 6,631,222 B1
`
`~d I111 /
`
`Petitioner Ciena Corp. et al.
`F__xhi~t 1025-2
`
`

`

`U.S. Patent
`US. Patent
`
`Oct. 7, 2003
`Oct. 7, 2003
`
`Sheet 2 0f 3
`Sheet 2 of 3
`
`US 6,631,222 B1
`US 6,631,222 B1
`
`x004m<0_.=w
`
`waxy—.25:.K
`
`
`
`mzm;x430D
`
`Z
`
`dolm
`
`Petitioner Ciena Corp. et al.
`Petitioner Ciena Corp. et al.
`Exhibit 1025-3
`Exhibit 1025-3
`
`
`

`

`U.S. Patent
`US. Patent
`
`Oct. 7, 2003
`Oct. 7, 2003
`
`Sheet 3 0f 3
`Sheet 3 of 3
`
`US 6,631,222 B1
`US 6,631,222 B1
`
`
`
`X
`
`m._02_w
`
`.552.
`
`Alllllllul
`
`aa.mmoamw
`Petitioner Ciena Corp. et al.
`Mmm
`Exhibit 1025-4
`
`
`

`

`US 6,631,222 B1
`
`1
`RECONFIGURABLE OPTICAL SWITCH
`
`SI’ATEMENT OF RELA3’ED APPLICAI’IONS
`
`This application claims the benefit of priority to U.S.
`Provisional Patent Application Ser. No. 60,/182,289, filed
`Feb. 14, 2000, entitled "An all Optical Router With Petabyte
`Per Second Switching Capability. "
`
`FIELD OF THE INVENTION
`
`The invention relates generally to an optical communica-
`tions system and more particularly to an optical switch for
`flexibly routing light in a wavelength-selective manner.
`
`BACKGROUND OF THE INVENTION
`
`Significant interest exists in multi-wavelength communi-
`cation systems, which are typically referred to as Wave-
`length Division Multiplexed (WDM) systems. These sys-
`tems use a WDM optical signal having different wavelength
`components that support different streams of information.
`While WDM systems were initially investigated to increase
`the information capacity that a fiber could transmit between
`two points, recent improvements in optical filtering
`technology, among other things, has led to the development
`of switching elements which allow a complex network of
`paths to be constructed that differ from wavelength to
`wavelength. Furthermore, in addition to the availability of
`wavelength dependent switching elements in which a given
`wavelength is routed along a given path, reconfigurable
`optical elements have become available. Such reconfig-
`urable optical elements can dynamically change the path
`along which a given wavelength is routed to effectively
`reconstn~ct the topology of the network as necessary to
`accommodate a change in demand or to restore services
`around a network failure.
`Examples of reconfigurable optical elements include opti-
`cal Add[Drop Multiplexers (OADM) and Optical Cross-
`Connects (OXC). OADMs are used to separate or drop one
`or more wavelength components from a WDM signal, which
`is then directed onto a different path. In some cases the
`dropped wavelengths are directed onto a common fiber path
`and in other cases each dropped wavelength is directed onto
`its own fiber path. OXCs are more flexible devices than
`OADMs, which can redistribute in virtually any arrange-
`ment the components of multiple WDM input signals onto
`any number of output paths.
`The functionality of the previously mentioned reconfig-
`urable optical elements can be achieved with a variety of
`different devices. For example, a common approach
`employs any of a number of different broadband s~vitching
`fabrics inserted between a pair of demultiplexers/
`muhiplexers. Examples of OADM elements are disclo~d in
`U.S. Pat. Nos. 5,504,827, 5,612,805, and 5,959,749, and
`general OXC switching architecture is reviewed by E.
`Murphy in chaptcr 10 of Optical Fiber Telecommunications
`IIIB, edited by T. Koch and I. Kaminow. As shown in these
`references, these approaches sequentially demultiplex the
`wavelengths, perform the necessary switching and then
`remultiplex, where the OXC can direct a given wavelength
`onto any output because a conventional OXC uses a rela-
`tively comtflex MxM device for the switching fabric, while
`OADMs are less flexible due to their use of an array of 2x2
`optical switches that can only direct between one of two
`outputs. Two alternate approaches to OADMs employ swit-
`chable mirrors effectively inserted between a device that
`simultaneously performs ~vavelength demultiplexing and
`
`2
`multiplexing. The first of these approaches uses a thin film
`dielectric demultiplexer!multiplexer that is traversed twice
`by the wavelengths (e.g., U.S. Pat. No. 5,974,207), while the
`second approach uses dispersion from a bulk diffraction
`5 grating to demultiplex (separate) the wavelength channels
`before they reflect off an array of tiltable mirrors (U.S. Pat.
`No. 5,960,133). Another sct of OADM technologies cmploy
`4-port devices that drop multiple wavelengths onto a single
`fiber output in a reconfigurable manner, and thus require an
`10 additional dcmultiplcxcr if the channcls nccd to undcrgo
`broadband optoelectronic conversion at the receiver. One
`realization of such functionality uses fiber optic circulators
`added to a two-port version of the previously-described
`diffraction grating demultiplexer and tilt mirror array (Ford
`~s et ah, Postdeadline papers LEOS ’97, IEEE Lasers and
`Electro-Optics Society). A second realization uses integrated
`silica waveguide technology (e.g., Doerr, IEEE Phot. Tech.
`Lett ’98) with thermo-optic phase shifters to switch between
`the add and drop states for each wavelength. Another
`2o four-port OADM employs a fiber optic circulator and an
`optional tunable fiber grating reflector to route the dropped
`channels (e.g., C. R. Giles, IOOC ’95, JDS 2000 catalog)
`All of the aforementioned conventional optical switching
`technologies have shortcomings. These devices generally
`25 fall into two classes with respect to their shortcomings: very
`flexible devices with high cost and high optical loss, and
`lower flexibility devices, which are less expensive and have
`lower optical loss. The most flexible OXCs can be pro-
`grammed to switch the path of any of a large number of
`3o wavelengths, each onto its own fiber (e.g. demux/mux with
`switches), however these devices may have up to 20 dB of
`insertion loss and therefore require an optical amplifier to
`compensate for the loss. This substantially adds to the cost
`of an already expensive device. Because these devices are so
`35 costly, less flexible alternatives such as fiber gratings and
`thin film filters are often used. While these devices have a
`significantly lower cost and insertion loss (2-5 dB!node),
`they are typically less flexible because they are implemented
`as fixed wavelength OADMs that cannot be reconfigured.
`4o These devices are also inflexible because as you scale lhem
`so that they drop more wavelengths their loss, cost, size
`and!or complexity increase to the point thai the more flexible
`OXC alternatives become more allractive. Recently, as
`shown in U.S. Pat. No. 5,479,082, some flexibility has been
`45 added to these lowest cost OADM devices so that they can
`selectively drop or pass a predetermined subset of wave-
`lengths that was previously designated as fixed. In addition,
`the previously described reconfigurable OADM devices
`offer somewhat enhanced flexibility, but typically at the
`5o expense of higher insertion loss (for Demuxiswitches), lim-
`ited wavelength resolution (for bulk grating approaches),
`and!or higher cost for additional Mux/Demux equipment
`used in connection with four-port devices.
`One particular limitation of the conventional OXC and
`s50ADM approaches, which demultiplex the incoming signal
`bcforc optical switching is pcrformcd, is that cach output
`port can only drop a particular fixed wavelength that cannot
`be altered. In this configuration each switch is arranged so
`that it only receives a prcsclcctcd wavclcngth componcnt
`6o from the demultiplexer, and therefore can only output that
`particular wavelength. Unless subsequent optical switching
`is used, the flexibility of these devices is limited since it is
`not possible to redirect a given wavelength from one output
`port to another output port or to redirect multiple wave-
`(,5 lengths to a given output port, should that become necessary.
`This functionality is desirable when a unique element within
`the network is accessible through a particular port, and it is
`
`Petitioner Ciena Corp. et al.
`Exhibit 1025-5
`
`

`

`US 6,631,222 B1
`
`3
`desirable to (a) change the wavelength channel directed to
`that port, or (b) direct additional wavelengths over that
`particular fiber accessed via that port. Two situations where
`this fnnctionality proves useful is when a link needs to be
`restored using an alternate wavelength, or when the infor- 5
`marion capacity directed to a specific port needs to be
`increased by adding additional WDM wavelengths down the
`same fiber.
`In vicw of thc important rolc of optical switching to thc
`flexibility and thus the value of an optical communications
`network, it would be advantageous to provide a switching
`element that does not have the shortcomings of the previ-
`ously mentioned devices.
`Accordingly, there is a need for an optical s~vitching
`element that is inexpensive, imparts relatively low loss to
`optical signals and which is sufficiently flexible to direct
`cach and cvcry wavclcngth componcnt from any input port
`to any output port independently of one another.
`
`10
`
`15
`
`4
`nents includes the steps of directing the first and second
`wavelength componeuts through a free space region.
`In accordance with yet another aspect of the invention, the
`first wavelength is demultiplexed by a thin film filter having
`a passband corresponding to the first wavelength.
`In accordance with another aspect of the invention, the
`first wavelength component is directed through the ~ee
`space region by a tiltable mirror.
`In accordance with another aspect of the invention, the
`demultiplexing and directing steps are performed by a
`plurality of narrow band free space switches. Alternatively,
`the demultiplexing and directing steps are performed by a
`plurality of tunable, wavelength selective couplers.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`DETAILED DESCRIPTION
`
`FIG. 1 shows the functionality to be achieved by an
`optical switching fabric constructed in accordance with the
`present invention. A wavelength division multiplexed
`(WDM) signal is received on input port 1~. Additional input
`ports may also be provided to accept additional WDM
`signals. Optical switching fabric 12 is designed to direct the
`individual wavelength components of the WDM signal to
`select ones of the output ports 141, 14z, . . . 14,,. That is,
`switching fabric 12 can selectively direct any wavelength
`component from any input port to any output port, indepen-
`dent of the routing of the other wavelengths.
`It should be noted that switching fabric 12 operates in a
`symmetric manner so that any wavelength components
`directed to any of the output ports can be alternatively
`directed to any of the input ports. Accordingly, one of
`ordinary skill in the art will recognize that the switching
`paths are reciprocal, and thus the terms input and output as
`used herein are not limited to elements that transmit a WDM
`signal or wavelength component in a single direction rela-
`tive to the switching fabric. In other words, when light enters
`the device from any so-called output port, this output port
`serves as an input port, and similarly, any so-called input
`port can equally serve as an output port.
`As explained below; the present invention can achieve the
`functionality depicted in FIG. 1 in a variety of different
`~vays. The different arrangements can be broadly divided
`into two categories. In the first category, filters having fixed
`transmission and reflection bands may be employed which
`enable independent direction of the wavelength componeuts
`onto diffcrcnt optical paths. Altcrnativcly, in the sccond
`category, tunable filters may be employed which direct the
`~vavelength components along fixed pafl~.
`FIG. 2 illustrates a first embodiment of the optical switch-
`ing element constructed in accordance with the pre~nt
`invention. In FIG. 2, the optical switching element 31111
`comprises an optically transparent substrate 3118, a plurality
`of dielectric thin film filters 3~1, 3!12, 3113, and 3114, a
`plurality of collimating lens pairs 3211 and 321z, 3221 and
`322a, 323~ and 323,~, 324~ and 324z, a plurality of tiltable
`
`Petitioner Ciena Corp. et al.
`Exhibit 1025-6
`
`FIG. 1 shows the functionality to be achieved by an
`optical switching fabric constructed in accordance with the
`present invention.
`FIG. 2 illustrates one embodiment of the optical switching
`element according to the present invention.
`FIG. 3 shows an alternative embodiment of the invention
`that employs wavelength dependent acoustic m~ll couplers.
`FIG. 4 shows another alternative embodiment of the
`25 invention that employs natfltiplexersidemultiplexers.
`
`SUMMARY OF THE INVENTION
`The present invention provides an optical switch that 2o
`includes at least one input port for receiving a WDM optical
`signal having a plurality of wavelength components, at least
`three output ports, and a plurality of wavelength selective
`elements each selecting one of the wavelength components
`from among the plurality of wavelength components. A
`plurality of optical elements are also provided, each of
`which are associated with one of the wavelength selective
`elements. Each of the optical elements direct the selected
`wavelength component that is selected by its associated
`selected element to a given one of the output ports indepen- 3,3
`dently of every other wavelength component. The given
`output port is variably selectable from among all the output
`ports.
`In accordance with one aspect of the invention, the optical 35
`switch includes a frcc space region disposed bctwccn thc
`input port and the wavelength selective elements.
`In accordance with another embodiment of the invention,
`the wavelength selective elemeuts are thin film filters each
`lransmitting lherethrough a different one of the wavelength 4o
`components and reflecting the remaining wavelength com-
`ponents.
`In accordance with yet another embodiment of the
`invention, the optical elements are mirrors that are selec-
`tively tiltable in a plurality of positions such that in each of 45
`the positions the mirrors reflect the wavelength component
`incident thereon to a different one of the output ports. The
`tiltable mirrors may be actuated by a micro-
`electromechanical system or a piezoelectric system, for
`example. 50
`Thc prcscnt invention also providcs a method for direct-
`ing at least first and second ~vavelength components of a
`WDM signal, which includes a plmality of wavelength
`componcnts, from an input port to sclcctcd ones of a
`plurality of output ports. The method begins by demulti- s5
`plexing the first wavelength componeut from the WDM
`signal. The first wavclcngth component is thcn directed to a
`given output port. The second wavelength component is also
`demultiplexed from the WDM signal and directed to one of
`the output ports selected independently from the given 6o
`output port.
`In accordance with one aspect of the invention, the step of
`demultiplexing and directing the second wavelength com-
`poncnt is pcrformcd aftcr the step of dcmultiplcxing and
`directing the first wavelength component. (~5
`In accordance with another aspect of the invention, the
`steps of directing the first and second wavelength compo-
`
`

`

`US 6,631,222 B1
`
`5
`mirrors 315,316,317, and 318 and a plurality of output ports
`3401, 340a, . . . 340,,. Substrate 308 has parallel planar
`surfaces 309 and 310 on which first and second filter arrays
`are respectively arranged. The first filter array is composed
`of thin film filters 301 and 303 and the second filter array is
`composed of thin film filters 302 and 304. lndividu a l ones of
`the collimating lens pairs 321-324 and tiltable mirrors
`315-318 are associated with each of the thin film filters. As
`described below, each thin film filter, along with its associ-
`ated collimating lens pair and tiltable mirror effectively
`forms a narrow band, free space switch, i.e. a switch that
`routes individual wavelength components along different
`paths. The overall physical dimensions of switching element
`300 will be determined by the beam diameter of the WDM
`signal.
`Thin film filters 301-304 are well-known components (for
`example, see U.S. Pat. No. 5,583,683), which have a dielec-
`tric multilayer configuration. The thin film filters 301-304
`have a wavelength dependent characteristic, that is, their
`reflectivity and transmissivity depends on the wavelength of
`light. In particular, among the wavelength components of the
`WDM optical signal received by thin film filter 301, only the
`component with wavelength )~1 is transmitted therethrough.
`The remaining wavelength components are all reflected by
`thin film filter 301. Likewise, thin film filter 302 transmits
`only the component with wavelength Lz and reflects all other
`wavelengths. In the same manner, the thin film filters 303
`and 304 transmit components with wavelengths ?~3, and
`respectively, and reflect all other wavelengths. TN~s, the
`present invention demultiplexes wavelengths through a plu-
`rality of thin film filters with different pass bands.
`The tiltable mirrors 315-318 are any mirrors that can be
`precisely tilted on 2 axes and are preferably small and very
`reliable. The exemplary mirrors discussed here are sup-
`ported by one or more flexure arms that employ a micro-
`electromechanical system (MEMS). Actuation of the flexure
`arms tilts the mirror surface to alter the direction of propa-
`gation of an incident beam of light. Examples of such
`micro-electromechanical mirrors are disclosed in U.S. Pat.
`No. 6,028,689 and the references cited therein. Of course,
`other mechanisms may be alternatively employed to control
`the position of the mirrors, such as piezoelectric actnators,
`for example.
`In operation, a WDM optical signal composed of different
`wavelengths )~1, )~2, )k,~ and X~, is directed from the optical
`inpnt port 312 to a collimator lens 314. The WDM signal
`traverses substrate 308 and is received by thin film filter 301.
`According to the characteristics of the thin film filter 301,
`the optical component with wavelength )~ is transmitted
`through the thin film filter 301, while the other wavelength
`components are reflected and directed to thin film filter 302
`via substrate 308. The wavelength component )~1, which is
`transmitted through the thin film filter 301, is converged by
`the collimating lens 321~ onto the tiltabl¢ mirror 315.
`Tiltable mirror 315 is positioned so that wavelength com-
`ponent X1 is reflected from the mirror to a selected one of the
`output ports 340~-340~, via thin film filters 302-304, which
`all rcflcct wavclcngth componcnt ?~1- Thc particular output
`port that is selected to receive the wavelength component
`will determine the particular orientation of the mirror 315.
`As mentioned, the remaining wavelength components )~,
`L~, and ?~4 are reflected by thin film filter 301 back into
`substrate 308 and directed to thin film 302. Wavelength
`component ?~2 is transmitted through thin fihn filter 302 and
`lens 3221 and directed to a selected output port by tiltable
`mirror 316 via thin film filters 303-304, which all reflect
`wavelength component )~a. Similarly, all other wavelength
`
`components are separated in sequence by the thin film filters
`303-3~4 and subseqnently directed by tiltable mirrors
`317~18 to selected output ports. By appropriate actuation
`of the tiltable mirrors, each wavelength component can be
`5 directed to an output port that is selected independently of all
`other wavelength components. Any wavelengths that have
`not been redirected by any of the tiltable mirrors may be
`received by an optional bypass port or fiber 343. Although
`thc cmbodimcnt of FIG. 2 is configurcd to sclcctivcly switch
`~0 four wavelengths, it will be recognized that the invention
`more generally may selectively switch any number of wave-
`lcngths by cmploying a corrcsponding numbcr of narrow
`band, free space switches.
`A number of important advantages are achieved by the
`~ s embodiment of the invention shown in FIG. 2. For example,
`because free space switching is employed, the number of
`optical connections is kept to a minimum, reducing the
`insertion loss, complexity and cost of the device. This
`advantage will be more clearly demonstrated below when
`2o the number of connections required in FIG. 2 is compared to
`the number of connections required by the embodin~ent of
`the invention shown in FIG. 4.
`The following description sets forth for illustrative pur-
`poses only one particular example of the embodiment of the
`25 invention shown in FIG. 2. In this example, the substrate 308
`is a rectangular silica block having a thickness of 10 mm, a
`width of 50 mm and a length of 90 mm. A single collimating
`lens that directed light to the input fiber is fixed relative to
`the block at a 5.7° angle with respect to the normal to the
`3o block. The focal length of the lens is chosen such that light
`exiting a Coming SMF-28TM fiber and passing thru a lens
`results in a collimated optical beam with a width of 1 mm.
`At the output, an array of collimating lenses is provided,
`each of which couples light to one fiber in the output array.
`3s The fiber ends are polished flat and have an anti-reflective
`coating. An optional bypass port or fiber may also be
`provided, ~vhich collects any ~vavelengths received at the
`input fiber that has not been transmitted through any of the
`thin film filters. The bypass fiber provides an output for
`4o fi~turenpgradesthat use additionalwavelengthsnot resonant
`in the original device. Alternately, this port might also be
`used if cost or loss restrictions make it preferable to switch
`a snbset of the total incident wavelengths, where the remain-
`ing (unswitched) wavelengths bypass the switching fabric.
`45 The first and second array of narrow band free-space
`switches each include eight thin film filters. ’ltle thin film
`filters are each a three-cavity resonant thin film filter with a
`surface dimension of 10 mm by 10 mm. In the first array, the
`first thin film filter, which is located 10 mm from the edge
`so of the substrate, is bonded with optical-quality, index match-
`ing epoxy to the substrate and has a passband centered at
`194.0 Tllz (1545.32 nm). The optical pass band is nominally
`0.4 nm wide at -0.5 dB down from the peak, with an
`isolation of better than -22 dB starting 100 GHz from the
`55 center wavelength. A 5 mm focal length collimating lens is
`bonded to the thin film filter. A commercially available,
`micro-electro-mechanical (MEMS) tiltable mirror is then
`positioned at thc focal point of thc lens. Voltages can bc
`applied to the tiltable mirror to vary its angular orientation
`6o along two axes. Typical angles over which the mirror is
`adjustcd do not cxcccd 30°.
`The first array also includes a second narrow band free-
`space switch located 10 mm from the first free-space switch.
`The thin film filter employed in this switch has a center
`(~s optical wavelength of 193.8 Tllz (1546.92 nm). Six addi-
`tional narrow band free-space switches are located along the
`substrate having center wavelengths of 1548.52 nm, 1550.12
`
`Petitioner Ciena Corp. et al.
`Exhibit 1025-7
`
`

`

`US 6,631,222 B1
`
`7
`nm, 1551.72 nm, 1553.32 nm, 1554.92 nm, and 1556.52 nm,
`respectively. The center-to-center distance between each
`switch is 10 ram.
`The second array of narrow band free space switches is
`located on the substrate surface opposing the substrate
`surface on which the first array of switches is located. The
`second array of switchcs, xvhich arc also Iocatcd 10 mm
`apart from one another, are laterally oriented half way
`bctwccn thc first array of switchcs. Thc eight thin film filtcrs
`employed in the second array of switches have center pass
`band wavelengths of 1544.52 nm, 1546.12 rim, 1547.72 nm,
`1549.32 ran, 1550.92 rim, 1552.52 ran, 1554.12 ran, and
`1555.72 nm, respectively.
`Each individual tiltable mirror has an electronics circuit to
`which a voltage is applied to steer the mirror. The voltage
`necessary to steer the mirror so that the wavelength it reflects
`is directed to a particular output fiber will differ from mirror
`to mirror. The operating voltages (-20 to +20 volt range) for
`steering the mirror are chosen to maxiurize the optical power
`coupled into the desired output fiber.
`One of ordinary skill in the art will recognize that each of
`the narrow band free space s~vitches shown in FIG. 2 do not
`necessarily require two lenses and a single mirror. Rather,
`other combinations of optical elements may be used to
`properly redirect the wavelength components. For example,
`two tiltable mirrors may be arranged to achieve the same
`result without the use of a lens. Alternatively, a single mirror
`may be used if in addition to being tiltable along two axes
`its position can also undergo a spatial translation.
`It is often important to monitor the presence and intensity
`of each individual wavelength component received by the
`switch shown in FIG. 2. This can become particularly
`dilticnlt using conventional fiber monitoring taps when the
`WDM signal includes a large number of wavelength com-
`ponents. In the present invention, this problem may be
`readily overcome since only a single ~vavelength component
`is received by each of the tiltable mirrors. Accordingly,
`individual wavelength components may be monitored by
`placing a detector behind the mirror so lhat il receives lhe
`small portion of the power of the wavelength component
`that passes through the mirror. This information combined
`with conventional tap monitoring can provide network con-
`trol and administration a more complete monitoring picture
`of light routed through the switch.
`It is also important to maintain accurate alignment
`between the tiltable mirrors in their various positions and the
`input and output fibers to optimize the power they receive
`from the mirrors. This can be accomplished by slow adjust-
`ment of the mirrors while monitoring the power coupled to
`the fiber via conventional fiber monitoring taps. However
`this approach becomes complicated if maW other wave-
`lengths are present on the fiber, in which case it may be
`useful to improve the detection of each wavelength compo-
`nent by encoding a small amplitude modulation with a
`unique RF frequency that is delecled at the respective oulput
`fibers while adjusting the positions of the tiltable mirrors.
`This RF tone can be encoded at the transmitter with a unique
`tone for cvcry wavclcngth, or altcrnatcly the RF amplitude
`modulation can be temporarily encoded during mirror
`adjustment by providing a small oscillation of the mirror tilt
`that slightly changes thc coupling cfficicncy to the fibcr. The
`latter approach is beneficial in tones that are encoded where
`they are measured, eliminating the need to track theur
`throughout thc nctwork, and additionally, the toncs arc only
`encoded when they are needed for adjustments.
`FIG. 3 shows an alternative embodiment of the invention
`that employs wavelength dependent acoustic null couplets to
`
`8
`achieve tunable wavelength filtering. Such a coupler only
`cross-couples selected wavelengths from a first to a second
`optical fiber upon application of an appropriate acoustic
`vibration to the coupling region. If the appropriate acoustic
`5 vibration is not applied, the selected wavelengths continue
`to propagate along the first optical fiber. Examples of an
`acoustic null coupler are disclosed in D. O. Culverhouse et
`al., Opt. [,ell. 22, 96, 1997 and U.S. Pat. No. 5,915,050.
`As shown in FIG. 3, an input fibcr 50 rccciving the WDM
`10 signal is connected to an input port of a first null coupler 521.
`One output port of the first null coupler 521 is connected to
`an output fibcr 541 on which onc or morc individual wavc-
`length components are to be directed. The other output port
`is contrected to an input port of a second null coupler 522.
`is Similar to the output ports of the first null coupler 521, the
`output ports of the second null coupler 522 are respectively
`connected to a second output fiber 54a and the input port of
`a third null coupler 523. As indicated in FIG. 3, additional
`null couplers may be cascaded in this manner to provide
`20 additional output ports on which selected xvavelength com-
`ponents may be directed.
`In operation, one or more wavelength components
`directed along the input fiber 50 can be directed to any
`selec