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`U5006631222l31
`
`(I2) United States Patent
`([0] Patent No.:
`US 6,631,222 Bl
`
`Wagoner et al.
`(45) Date of Patent:
`Oct. 7, 2003
`
`(54) RECONFICURARLE OPTICAL SWITCH
`
`O'I'IIER PUlil..l(.'t'\'I'lONS
`
`(75)
`
`ltWeIltflrS: Jefl‘emm 1.. Wagener. Aberdeen, WA
`(US); Tlmmas Andrew Sim-SSH,
`Warren, NJ (US)
`.
`.
`)
`l heturls, Inc" Plsealaway, NJ (US)
`Subjccl lo anyI disclaimer, the lerm of this
`patent Lg extended or adjusted under 35
`U,S_(f_ 154"” by [] days,
`
`(73) Axslgnel...
`(‘) Notice:
`
`(:1) App]. No.1 09571333
`,
`M33" 16’ 200"
`Fllcd:
`(22)
`
`........................... 0028 $35
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`38534, 3] , 33, 47; 359tl31, 196, 212,
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`(56)
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`References Cited
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`_
`FOREIGN PA'l'ENT DOCUMENTS
`
`|.-'. Murphy. Optical Fiber iii?icCOmttthtfcaft'OflS MB. Chapter
`III, edited by 'l'. Kneh and I. Kaminttw, Academic Press.
`(LR. Doerr. Proposed WDM (Truss Connecl Using, A Planar
`Arrangement of Waveguide Grating Rnulcrs and Phase
`Shii‘lem, Pirates-tics Tecttrtatom' Letters, vol. 10, N0. 4. Apr.
`1998‘
`CR. Giles,et £11.. "Low—Loss Ami-"DROP Multiplexers for
`WDM Lightwave Nelwurks," Tenlh International Confer-
`ence on Integrated Oplicts and Optical Fibre Communica-
`tion. IDOL“, v01. 3. Jun. 29. 1995.
`JDS Uniphase Corporation. Add—Drop Modules. Pmducl
`Bullelitt 2000, Ontario, Canada.
`[).0.Cu1verhou3e el al.. Low—10m all—filter acousto—optic
`tunahle filler. ()ptrc'aISOCI'ety ofAttterica, vol. 22. No. 2,.lan.
`15. 199?. pp. 96—98.
`Roberto Sabella et a|_."Impactnl"l‘ransmis€inn Performance
`on Path Routing in All—Oplicul Transport Networksffllmtr-
`rmi Uffjghtlmre Twittering}; vol. 16, No. II (Nov. 1998).pp.
`1965—1971.
`
`*
`
`'
`‘t-lb .
`Cl“ ”mm"
`
`Primary EA'atttr'rrer—Iohn D. Lee
`Axsistrtttt Exrrrrtiner—Juliana K. Kang
`('34) Attorney. Agent, or Firm—Mayer Fnrlkorl & Williams,
`PC; 51'1"“ H- Mayer. Esq-
`.
`.
`1
`All“ RM'T
`(57)
`[or
`An optical switch includes all
`Ieasl one inpul purl
`reeelvtng a WDM Uptlcal signal havtng a plltralll)f of wave—
`length components, at least three oulpul ports, and a plural-
`ily of wavelenglh seleclive elemenls each seleeling one of
`the wavelength components from among the plurality of
`wavelength components. A plurality of optical chlTlan‘i are
`also provided. each of which are associaled with one of [he
`wavelength selective elements. Each cf the Uplical elements
`direct the seleeled wavelength eernpuncnl [hat is Iseleeled by
`JES asaocrated selecled element In a given one 01 [he outpul
`ports independently of every other wavelength eomponertl.
`The given output port is variably selectable from among all
`the output ports.
`
`JP
`
`bit-880m
`
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`
`Stl‘JSS
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`88 Claims. 3 Drawing Sheets
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`auto,
`343
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`314
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`313
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`K TI.T mm:
`=2 EULKLENS
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 1
`Exhibit 1025, Page 1
`
`

`

`US. Patent
`
`()ct. 7,2003
`
`Sheet 1 01's
`
`US 6,631,222 B1
`
`‘INPUT
`
`14fl
`
`NWAVELENGTHS
`
`
`
`1.1.7L2---1N
`
`12
`
`FIG.1
`
`FIG.3 FUNCTIONALITY
`DIAGRAM
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 2
`Exhibit 1025, Page 2
`
`

`

`US. Patent
`
`Oct. 7, 2003
`
`Sheet 2 01'3
`
`US 6,631,222 B1
`
`
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 3
`Exhibit 1025, Page 3
`
`
`

`

`US. Patent
`
`Oct. 7, 2003
`
`Sheet 3 01'3
`
`US 6,631,222 B1
`
`
`
`m_._oz_m
`
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`III
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 4
`Exhibit 1025, Page 4
`
`

`

`US 6,631,222 Bl
`
`1
`RECONFIGURABLE OPTICAL SWITCH
`
`S‘I'A'l'L‘M L‘N'l‘ 0F RELATED APPLICATIONS
`
`'lltis application claims the benefit of priority to US.
`Provisional Patent Application Ser. No. fittilSEBtt‘J, filed
`l-‘eb. I4, 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
`llexibly routing light in a wavelength-selective manner.
`BACKGROUNI) 01" T] [E [NVEN'l‘lUN
`
`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 eifectiveiy
`reconstruct
`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 AddeIop Multiplexers (DADM) and Optical Cross—
`Conneets (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 Iiber path
`and in other cases each dropped wavelength is directed onto
`its own fiber path. OXCs are more flexible devices than
`(JAIJMs, which can redistribute in virtually any arrange-
`ment the components of multiple WUM input signals onto
`any number of output paths.
`The functionality of the previously mentioned reconfig-
`urable optical elements can he achieved with a variety of
`different devices. For example, a common approach
`employs any of a number of different broadband switching
`fabrics inserted between a pair of demultiplexerst'
`multiplexers. Examples of OADM elements are disclosed in
`US. Pat. Nos. 5,504,827. 5,612,805. and 5.959349. and
`general OXC‘ switching architecture is reviewed by E.
`Murphy in chapter ll] of Optical Fiber 1'i:lecwmriimientions
`”[8. 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 UXC can direct a given wavelength
`onto any output because a conventional OXC uses a rela—
`tively complex MxM device for the switching fabric. while
`()ADMs are less flexible due to their use of an array of 2x2
`optical switches that can only direct between one of two
`outputs. 'l‘wo alternate approaches to tmDMs employ swit-
`chable mirrors effectively inserted between a device that
`simultaneously performs wavelength demultiplexing and
`
`10
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`40
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`45
`
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`55
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`bf]
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`65
`
`2
`multiplexing. The first of these approaches uses a thin film
`dielectric demultiplexerlmultiplexer that is traversed twice
`by the wavelengths {e.g., US. Pat. No. 5,974,207), while the
`second approach uses dispersion from a bulk difl‘raction
`grating to demultiplex (separate) the wavelength channels
`before they reflect elf an array of tiltable mirrors (US. Pat.
`No. 5,960,133). Another set of OADM technologies employ
`4-port devices that drop multiple wavelengths onto a single
`fiber output in a reconfigurable manner, and thus require an
`additional demultiplexer if the channels need to undergo
`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 minor array (Ford
`et al., Postdeadline papers LEOS ‘9'},
`lEEE lasers and
`Electro-Optics Society). Asccond realization uses integrated
`silica waveguide technology (e.g., [)oerr, llilLL‘ Fhot. Tech.
`fell ’98) with thermo—optic phase shifters to switch between
`the add and drop states for each wavelength. Another
`four-port UADM employs a fiber optic circulator and an
`optional tunable fiber grating reflector to route the dropped
`channels (e.g., C. R. Giles, [00C ’95, J DS 3000 catalog)
`All of the aforementioned conventional optical switching
`technologies have shortcomings. These devices generally
`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
`wavelengths, each onto its own fiber (e.g. demuxt'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
`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 lose (2-5 dBinode),
`they are typically less flexible because they are implemented
`as fixed wavelength (JAIJMs that cannot be reconfigured.
`These devices are also inflexible because as you scale them
`so that
`they drop more wavelengths their loss, cost. size
`andtor complexity increase to the point that the more flexible
`OXC alternatives become more attractive. Recently, as
`shown in US. Pat. No. 5,479,082, some flexibility has been
`added to these lowest cost ()ADM 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
`expense of higher insertion loss {for Demuxiswitchos). lim—
`ited wavelength resolution (for bulk grating approaches),
`andt'or higher cost
`for additional Muxt'Demux equipment
`used in connection with four-port devices.
`One particular limitation of the conventional OXC and
`OADM approaches, which demultiplex the incoming signal
`before optical switching is performed.
`is that each 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 preselected wavelength component
`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-
`lengths lo a given output pon, should that become necessary.
`This functionality is desirable when a unique element within
`the network is accessible through a particular port. and it is
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 5
`Exhibit 1025, Page 5
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`US 6,631,222 Bl
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`3
`desirable to (a) change the wavelength channel directed to
`that port, or (b) direct additional wavelengths over tltat
`particular fiber accessed via tltat port. ‘l‘wo situations wltere
`this functionality proves useful is when a link needs to be
`restored using an alternate wavelength. or when the infor-
`mation capacity directed to a specific port needs to be
`increased by adding additional WDM wavelengths down the
`same liber.
`In view of the important role of optical switching to the
`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 switching
`element that is inexpensive. imparts relatively low loss to
`optical signals and which is sufficiently llcxihle to direct
`each and every wavelength component front any input port
`to any output port independently of one another.
`SUMMARY 017 T] [E INVENTION
`
`invention provides an optical switch that
`'llte present
`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 componean. A
`plurality of optical elemean 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—
`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
`switch includes a free space region disposed between the
`input port and the wavelength selective elements.
`In accordance with another embodiment of the invention.
`the wavelength selective elements are thin lilrn tillers each
`transmitting thercthrough a dilferent one of the wavelength
`componean 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
`the positions the mirrors reflect the wavelength component
`incident thereon to a dilferent one of the output ports. The
`tiltable mirrors may be actuated by a micro-
`electromechanical system or a piezoelectric system, for
`example.
`The present invention also provides a method for direct-
`ing at least first and second wavelength components of a
`WIJM signal. which includes a plurality of wavelength
`componean,
`from an input port
`to selected ones of a
`plurality of output porLs. The method begins by demulti—
`plexing the first wavelength component from the WDM
`signal. The first wavelength component is then directed to a
`given output port. The second wavelength component is also
`demultiplexed from the WUM signal and directed to one of
`the output ports selected independently from the given
`output port.
`In accordance with one aspect of the invention. the step of
`rte-multiplexing and directing the second wavelength com-
`ponent is performed after the step of demultiplexing and
`directing the lirst wavelength component.
`In accordance with another aspect of the invention, the
`steps of directing the first and second wavelength compo-
`
`10
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`[5
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`3t]
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`nents includes the steps of directing the first and second
`wavelength components through a free space region.
`In accordance with yet another aspect ol‘the invention, the
`first wavelength is demultiplexed by a thin film tiller having
`a passhand corresponding to the lirsl wavelength.
`In accordance with another aspect of the invention. the
`first wavelength component
`is directed through the free
`space region by a liltable 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 dernultiplexing and directing steps are performed by a
`plurality of tunable, wavelength selective cottplers.
`BRIEF DESCRIPTION OF Tllli DRAWINGS
`
`1 shows the functionality to he achieved by an
`1“] G.
`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.
`1710.3 shows an alternative embodiment of the invention
`that employs wavelength dependent acoustic null couplers.
`HG. 4 shows another alternative embodiment of the
`invention that employs multiplexersldemultiplcxcrs.
`BETA] LED D flit .‘Rll’l’lUN
`
`1 shows the functionality to be achieved by an
`FIG.
`optical switching fabric constructed in accordance with the
`present
`invention. A wavelength division multiplexed
`(WDND signal is received on input port ll]. Additional input
`ports may also he 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, 14:,
`.
`.
`. 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 porLs. 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 HS.
`1
`in a variety of ditferent
`ways. The different arrangements can be broadly divided
`into two categories. in the lirsl category, tillers having lixed
`transmission and reflection bands may be employed which
`enable independent direction of the wavelength components
`onto different optical paths. Alternatively,
`in the second
`category, tunable fillers may be employed which direct the
`wavelength components along fixed paths.
`FIG. 2 illustrates a first embodiment of the optical switch—
`ing clement constructed in accordance with the present
`invention.
`In [’16. 2.
`the optical switching element 300
`comprises an optically transparent substrate 303. a plurality
`of dielectric thin film filters 301, 302, 303, and 304, a
`plurality of collimating lens pairs 3211 and 321:, 3221 and
`322:, 152.7131 and 323:, 324] and 324:, a plurality of tiltablc
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 6
`Exhibit 1025, Page 6
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`US 6,631,222 Bl
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`5
`mirrors 315, 316,317, and 318 and a plurality of output ports
`340,, 3403,
`.
`.
`. 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
`ol'thin filn1 filters 301 and 303 and the second filter array is
`composed of thin film filters 302 and 304. Individual ones of
`the collimating lens pairs 321—324 and tiltablc mirrors
`315—318 are associated with each of the thin film filters. As
`described below, each thin film litter, along with its associ-
`ated collimating lens pair and tiltable mirror efi‘ectively
`forms a narrow band, free space switch, it}. a switch that
`routes individual wavelength components along different
`paths. The overall pltysicat dimensions of switching element
`300 will be determiner] 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 lilters 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
`WIJM optical signal received by thin film filter 301, only the
`component with wavelength 3.1 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 1.: and reflects all other
`wavelengths. in the same manner, the thin film filters 303
`and 304 transmit componean with wavelengths l3, and 1.4,
`respectively, and reflect all other wavelengths.
`'lhus,
`the
`present invention demultiplexes wavelengths through a plu-
`rality of thin film filters with dilierent pass bands.
`The tiltable mirrors 315-318 are any mirrors that can be
`precisely titled on 2 axes and are preferably small and very
`reliable. The exemplary mirrors discussed here are sup—
`ported by one or more tlexure arms that employ a micro-
`electromcchanical system (MEMS). Actuation of the fiexure
`arms tilLs 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 actuators,
`for example.
`In operation, a WDM optical signal composed of different
`wavelengths 11, 1:, L3 and IL. is directed from the optical
`input port 312 to a collimator lens 314. The WUM 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 3.,
`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. ‘llte wavelength component 1,, which is
`transmitted through the thin film filter 301, is converged by
`the collimating lens 321I onto the tiltablc mirror 315.
`Tiltable mirror 315 is positioned so that wavelength com‘
`ponent l. is reflected from the mirror to a selected one of the
`output ports 340,340,, via thin film filters 302—304, wltich
`all reflect wavelength component 1.1. The 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 3.2,
`13.3, and L, are reflected by thin film filter 301 back into
`substrate 308 and directed to thin film 302. Wavelength
`component 1: is transmitted through thin film filter302 and
`lens 3221 and directed to a selected output port by Iiltable
`mirror 316 via thin film filters 303-304, which all reflect
`wavelength component i-:- Similarly, all other wavelength
`
`Ill
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`
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`
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`45
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`65
`
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`componean are separated in sequence by the thin film filters
`303—304 and subsequently directed by tiltable mirrors
`3l7—318 to selected output porLs. By appropriate actuation
`of the tiltable mirrors. each wavelength component can he
`directed to an output port that is selected independently of all
`other wavelength components. Any wavelengths that have
`not been redirected by any ol‘ the tiltable mirrors may be
`received by an optional bypass port or fiber 343. Although
`the enthodiment of HG. 2 is configured to selectively switch
`four wavelengths,
`it will be recognized that the invention
`more generally may selectively switch any number of wave-
`lengths by employing a corresponding number of narrow
`band. free space switches.
`A number or important advantages are achieved by the
`embodiment ol'thc invention shown in FIG. 2. For example,
`because tree space switching is employer], 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
`the number of connections required in FIG. 2 is compared to
`the number of connect ions required by the embodiment of
`the invention shown in l-‘lG. 4.
`The following description sets forth for illustrative pur-
`poses only one particular example of the embodiment ol‘the
`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 5t| mm and a length of 90 mm. Asinglc 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
`block. The focal length of the lens is chosen such that light
`exitng a Corning SMF-ZST” fiber and passing thru a lens
`results in a collimated optical beam with a width oft mm.
`Al
`the output. an array of collimating lenses is provided.
`each of which couples light to one fiber in the output array.
`The fiber ends are polished fiat and have an anti-reflective
`coating. An optional bypass port or
`fiber may also be
`provided, which collects any wavelengths received at
`the
`input fiber that has not been transmitted through any of the
`thin film filters. The bypass fiber provides an output for
`future upgrades that use additional wavelengths not resonant
`in the original device. Alternately, this port might also be
`used if cost or loss restrictions make it preferable to switch
`a subset oithe total incident wavelengths, where the remain-
`ing (unswitched) wavelengths bypass the switching fabric.
`The first and second array of narrow band free—space
`switches each include eight thin film filters. The thin film
`filters are each a three-cavity resonant thin fittn filter with a
`surface dimension of 10 mm by 10 mtn. tn the first array, the
`first thin Iilm Iiller, which is located it] mm from the edge
`ol'the substrate, is bonded with optical-quality, index match—
`ing epoxy to the substrate and has a passband centered at
`194.0 1'] [2 (1545.32 rim). The optical pass band is nominally
`0.4 nm wide at
`-U.5 dB down from the peak, with an
`isolation of better than ‘22 dB starting 1w GHZ from thc
`center wavelength. A 5 mm focal length collimating lens is
`bonded to the thin film filter. A commercially available,
`micro-electromechanical (MEMS) tiltable mirror is then
`positioned at
`the focal point of the lens. Voltages can be
`applied to the tiltable mirror to vary its angular orientation
`along two axes. Typical angles over which the mirror is
`adjusted do not exceed 30".
`The first array also includes a second narrow band l'rcc—
`space switch located 10 mm from the first free-space switch.
`The thin film filter employed in this switch has a center
`optical wavelength of 193.8 'l'llz (1546.92 nm). Six addi-
`tional narrow band frce~space switches are located along the
`substrate having center wavelengths of 1543.52 nn1, 1550.12
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1025, Page 7
`Exhibit 1025, Page 7
`
`

`

`US 6,631,222 Bi
`
`7
`nm, 1551.72 nm, 1553.32 nm, 1554.92 nm, and 1556.52 nm,
`respectively. The eenter-to-center distance between each
`switch is 10 mm.
`The wound 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 switches, which are also located 10 mm
`apart from one another, are laterally oriented half way
`between the first array of switches. The eight thitt film filters
`employed in the second array of switches have center pass
`band wavelengths of 1544.53 nm. 1546.12 nm, 1547.72 nnt.
`1549.32 nm, 1550.92 nm, 1552.52 nm, 1554.13 nm, 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 minor so that the wavelength it reflects
`is directed to a particular output fiber will ditfer from mirror
`to mirror. The operating voltages (—20 to +20 volt range) for
`steering the mirror are chosen to maximize 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 switches shown it! HG. 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 tittabte 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 axos
`its position can also undergo a spatial translation.
`[I 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
`difiicult 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 wavelength component
`is received by each of the tiltable mirrors. Accordingly,
`individual wavelength components may be monitored by
`placing a detector behind the mirror so that it receives the
`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.
`[I
`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 many other wave-
`lengths are present on the fiber,
`in which case it may be
`useful to improve the detection of eaclt wavelength compo-
`nent by encoding a small amplitude modulation with a
`unique RF frequency that is detected at the respective output
`fibers while adjusting the positions of the tiltable mirrors.
`This Rli tone can be encoded at the transmitter with a unique
`tone for every wavelength, or alternately the RF amplitude
`modulation can be temporarily encoded during mirror
`adjustment by providing a small oscillation of the mirror tilt
`that slightly changes the coupling efliciency to the fiber. The
`latter approach is beneficial itt tones that are encoded where
`they are measured, eliminating the need to track them
`throughout the network, and additionally, the tones are only
`encoded when they are needed for adjustments.
`FIG. 3 shoWs an alternative embodiment of the invention
`that employs wavelength dependent acoustic nu ll couplers to
`
`Ill
`
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`3L]
`
`4o
`
`45
`
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`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. [I the appropriate acoustic
`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 ct
`al.. Opt. Lett. 22. 96, 1997 and US. Pat. No. 5,915,050.
`As shown in FIG. 3. an input fiber 50 receiving the WUM
`signal isoonnected to art input port of a first null coupler 521.
`One output port of the first null coupler 52, is connected to
`an output tiberfid, on which one or more individual wave-
`length components are to be directed. The other output port
`is connected to an input port of a second null coupler 52:.
`Similar to the output ports of the first null coupler 521, the
`output ports of the second null coupler 52: are respectively
`connected to a second output fiber 54: 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
`additional output ports on which selected wavelength com-
`ponents may be directed.
`to operation, one or more wavelength components
`directed along the input Iiher 5|] can be directed to any
`selected output port 541, 54;,
`.
`.
`. 54,,“ by applying the
`appropriate acoustic wave for those components to the null
`couplers 521, 52:, .
`.
`. 54m preceding those connected to the
`selected output port. For example,
`it" any of the given n
`wavelength componean arc to be directed to output port 543,
`then the acoustic waves should he applied to null coupler
`523. Although this embodiment of the invention requires the
`wavelength componean to traverse the null couplers in
`serial
`[ashiom the resulting imertion loss need not be
`unacceptably large because the insertion of loss of each
`ind