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`
`
`USOORE42368E
`
`(19) United States
`(12) Reissued Patent
`Chen et al.
`
`(10) Patent Number:
`
`(45) Date of Reissued Patent:
`
`US RE42,368 E
`May 17, 2011
`
`[54) RECONFIGURABLE OPTICAL ADD—DROP
`MULTIPLEXERS W'ITH SERVO CONTROL
`AND DYNAMIC SPECTRAL POWER
`MANAGEMENT CAPABILITIES
`
`(75)
`
`inventors: Tail (5 hen. San Jose. CA (US); Jeffrey P.
`Wilde. Morgan Hill. CA {US}: Joseph
`E. Davis. Morgan Ilill. CA (US)
`
`(73) Assignee: Capella Photonics. Inc., San Jose. CA
`(US)
`
`(21) Appl.No.; 121816.084
`
`[22)
`
`l’iled:
`
`Jun. 15, 2010
`Related U.S. Patent Documents
`
`Reissue of:
`
`[64)
`
`Patent No.1
`Issued:
`Appl. No.:
`Filed:
`
`6,879,750
`Apr. 12. 2005
`101745.364
`Dec. 22, 2003
`
`U.S. Applications:
`[63) Confirmation of application No. 101005.714, filed on
`Nov. 7. 2001. now Pat. No. 6,687.43]. which is a
`continuation oi'application No. 091938.426. filed on
`Aug. 23. 200]. now Pat. No. 6.625346.
`
`(60) Provisional application No. 601277.217. filed on Mar.
`l9. 2001.
`
`(51}
`
`Int. Cl.
`(2006.01)
`G02B 6/28
`(2006.01)
`1104.! 14/02
`(52) U.S. (11.
`................ 385124: 385110: 385133; 38587:
`398183
`
`385124.
`(58) Field ofClassificatian Search
`385111, 10. 37. 34. 33: 398179. 82. 83. 84.
`398188. 87
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U .S. PA’l‘liN’l‘ DOCUMENTS
`5.414.540 A
`$1995 Patel et al.
`5.629.790 A
`5:199? Neukenmms elal.
`5.145.271 A
`4-1998 Ford eta].
`5.835.458 A
`11-1998 Bischeletal.
`5.960.133 A
`0.51999 Tomlinson
`5.9 74.2 0? A
`[0.“ I999 Aksyuk el al.
`252000
`.VIiclIAIicek El al.
`6.0 28,6 89 a
`6.204.946 Bl
`3.52001 Aksyuk elal.
`6.205.269 Bl
`3-“2001 Morton
`6.222.954 Bl
`432001 Riza
`6.256.430 Bl
`7.’2UU|
`Jin ctal.
`6.263.135 Bl
`152001 Wade
`6.289.155 Bl
`952001 Wade
`10-2001 Ford
`6,307.65? 131
`6.418.250 Bl
`732002 Corhosicro et al.
`1232002 Bouevilch el al.
`6.408.822 32
`
`(Continued)
`
`Brian M llealy
`Primmji' Evaminer
`(74) Altar-net: Agent. or I‘imi — Barry N. Young
`
`[57)
`
`ABSTRACT
`
`This invention provides a novel wavelength-septarating-rout-
`ing {WSR} apparatus that uses a difli'action grating to sepa—
`rate a ntulti—wavelength optical signal by wavelength into
`multiple spectral channels. which are then focused onto an
`array of correSponding channel niicromimirs. The channel
`microntirrors are individually controllable and continuously
`pivotable to reflect the spectral channels into selected output
`ports. As such. the inventive WSR apparatus is capable of
`routing the spectra] Channels on a channel-by-channci basis
`and coupling any spectral channel into any one ofthe output
`ports. The WSR apparatus of the present invention may be
`further equipped with servo-control and spectral powernntan-
`agentent capabilities. thereby maintaining the coupling efli-
`ciencies of the spectral channels into the output ports at
`desired values. The WSR apparatus of the present invention
`can be used to construct a novel class ofdynamically recon-
`figurable optical add—drop multiplexers (OADMs) for WDM
`optical networking applications.
`
`22 Claims. 12 Drawing Sheets
`
`
`
`103
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 1
`Exhibit 1001, Page 1
`
`

`

`us RE42,368 E
`Page 2
`
`U .S. PATENT DOCUMENTS
`532003
`Ma et a].
`6.567.574 Bl
`6.600.851 132
`7-2003
`Aksyuk 01 al.
`933003
`Wilde el al.
`6.625.346 B2
`6.631.222 Bl
`[052003
`W'agener el 31.
`Ford et 2:].
`[032003
`6.634.810 Bl
`232004
`Chen el al.
`6.687.431 B2 ’3
`1072004
`Bouevilch el al.
`6.810.169 B2
`
`6.879.750 132*
`6.898.348 B2
`6.989.921 132
`7.183.633 B2
`200150131691 Al
`200330043471 Al
`
`4:"! 005
`5!}? 005
`132006
`2-‘2007
`9.52 003
`3:"2 003
`
`Chen el :11.
`Mommv et :11.
`Bernstein cl al.
`Daneman ct al.
`Garretl el al.
`Beiser et a].
`
`385-"24
`
`385.524
`
`‘5‘ cited by examiner
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 2
`Exhibit 1001, Page 2
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 1 of 12
`
`US RE42,368 E
`
`new
`
`a;.9”.
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 3
`Exhibit 1001, Page 3
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 2 of 12
`
`US RE42,368 E
`
`103
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 4
`Exhibit 1001, Page 4
`
`

`

`US. Patent
`
`May 17, 2011
`
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`May 17, 2011
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 7
`Exhibit 1001, Page 7
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 6 of 12
`
`US RE42,368 E
`
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`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 8
`Exhibit 1001, Page 8
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 7 of 12
`
`US RE42,368 E
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 9
`Exhibit 1001, Page 9
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`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 8 of 12
`
`US RE42,368 E
`
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 10
`Exhibit 1001, Page 10
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 9 of 12
`
`US RE42,368 E
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 11
`Exhibit 1001, Page 11
`
`

`

`US. Patent
`
`May 17, 2011
`
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`
`US RE42,368 E
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 12
`Exhibit 1001, Page 12
`
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`May 17, 2011
`
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`US RE42,368 E
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 13
`Exhibit 1001, Page 13
`
`

`

`US. Patent
`
`May 17, 2011
`
`Sheet 12 0112
`
`US RE42,368 E
`
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`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 14
`Exhibit 1001, Page 14
`
`

`

`US RE42,368 E
`
`1
`RECONFIGU RABLE OPTICAL ADD-DROP
`MULTIPLEXERS WI'I'II SERVO CONTROL
`AND DYNAMIC SPECTRAL POWER
`MANAGEMENT CAPABILITIES
`
`Matter enclosed in heavy brackets [ ] appears in the
`original patent but forms no part of this reissue specifica-
`tion; matter printed in italics indicates the additions
`made by reissue.
`
`1U
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of US. application Ser.
`No. l0f005.714. filed Nov. 7. 200] now U.S. Pat. No. 6.687".
`43]. which is a continttation of U.S. application Ser. No.
`091938.426. filedAug. 23. 2001. now US. Pat No. 6.625.346
`which claims the benefit of U .5. application Ser. No. 6049.77,
`217. filed Mar. 19. 2001.
`
`FIELD OF THE INVENTION
`
`This invention relates generally to optical communication
`systems. More specifically.
`it relates to a novel class of
`dynamically reconfigurable optical add-drop multiplexers
`(GADMS) for wavelength division multiplexed optical net-
`working applications.
`
`BAC KGROUN D
`
`As fiber-optic conununication networks rapidly spread
`into every walk 0 t‘modern life. there is a growing demand for
`optical components and subsystems that enable the Iibe -
`optic conunuuications networks to be increasingly scalable.
`versatile. robust. and cost—effective.
`Contemporary fiber—optic conununications networks com-
`monly employ wavelength division multiplexing (WDM). for
`it allows multiple int'on'nation (or data) channels to be simul-
`taneously transmitted on a single optical fiber by using dif-
`ferent wavelengths and thereby significantly enhances the
`information bandwidth ofthe fiber. The prevalence of WDM
`technology has made optical add—drop multiplexers indis—
`pensable building blocks oi'modern fiber»optic cottununica-
`tion networks. An optical add-drop multiplexer (0ADM)
`serves to selectively remove (or drop) one or more wave-
`lengths from a multiplicity o [wavelengths on an optical fiber,
`hence taking away one or more data channels from the lrallic
`stream on the fiber. It further adds one or more wavelengths
`back onto the fiber. thereby inserting new data channels in the
`same stream of traffic. As such. an OADM makes it possible
`to launch and retrieve multiple data channels (each charac-
`terized by a distinct wavelength) onto and from an optical
`fiber respectively. without disrupting the overall traffic flow
`along the fiber. Indeed. careful placetnent of the 0.’\I)Ms can
`dramatically improve an optical coimnunication network‘s
`flexibility and robustness. while providing significant cost
`advantages.
`Conventional OADMs in the art typically employ militi-
`plexersfdemultiplexers (e.g._ waveguide grating routers or
`arrayed-waveguide
`gratings).
`tunable
`filters.
`optical
`switches. and optical circulators in a parallel or serial archi-
`tecture to accomplish the add and drop functions. In the
`parallel architecture. as exemplified in U.S. Pat. No. 5.974.
`207. a demultiplexer (e.g.. a waveguide grating router) first
`separates a multi-wavelength signal into its constituent spec-
`tra] components. A wavelength switchinglrouting means
`
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`(e.g.. a combination of optical switches and optical circula—
`tors) then serves to drop selective wavelengths and add others.
`Finally. a multiplexer combines the remaining (i.e. . the pass-
`through) wavelengths into an output mold-wavelength opti-
`cal signal. in the serial architecture. as exemplified in U .3.
`Pat. No. 6.205.269. tunable filters (cg, Bragg fiber gratings)
`in combination with optical circulators are used to separate
`the drop wavelengths from the pasSAthrough wavelengths and
`subsequently launch the add channels into the pass-through
`path. And if multiple wavelengths are to be added and
`dropped. additional multiplexers and demultiplexers are
`required to demultiplex the drop wavelengths and multiplex
`the add wavelengths, respectively. irrespective of the under-
`lying architecture. the OADMs currently in the art are char—
`acteristically high in cost. and prone to significant optical loss
`accumulation. Moreover. the designs of these ()ADMs are
`such that it is inherently difficult to reconfigure them in a
`dynamic fashion.
`U.S. Pat. No. 6.204.946 lo Askyuk et a1. discloses an
`()ADM that makes use of free-space optics in a para] 1e] con-
`struction. In this case. a tnulti—wavelength optical signal
`emerging from an input port is incident onto a ruled diffrac-
`tion grating. The constituent spectral channels thus separated
`are then focused by a focusing lens onto a linear array of
`binary micromachincd mirrors. Each micromirror is config-
`ured to operate between two discrete states. such that it either
`retroretleets its corresponding spectral channel back into the
`input port as a pass—through channel. or directs its spectral
`channel to an output port as a drop channel. As such. the
`pass-through signal (i.e._. the combined pass-through chan-
`nels) shares the some input port as the input signal. An optical
`circulator is therefore coupled to the input port. to provide
`necessary routing of these two signals. Likewise, the drop
`channels share the output port with the add channels. An
`additional optical circttlator is thereby coupled to the output
`port, from which the drop channels exit and the add channels
`are introduced into the output port. The add channels are
`subsequently combined with the pass-timough signal by way
`of the diffraction grating and the binary micromirrors.
`Although the aforementioned CADM disclosed by Askyuk
`et a]. has the advantage ol‘perlbrming wavelength separating
`and routing in free space and thereby incurring less optical
`loss. it suffers a number of limitations. First. it requires that
`the pass-through signal share the same portt'fiber as the input
`signal. An optical circttlator therefore has to be implemented,
`to provide necessary routing ofthese two signals. Likewise.
`all the add and drop channels enter and leave the OADM
`through the same output port. hence the need for another
`optical circulator. Moreover. additional means must be pro
`vided to multiplex the add channels before entering the sys—
`tem and to deinttltiplex the drop channels alter exiting the
`system. This additional multiplexing/demultiplexing require-
`ment adds more c0st and complexity that can restrict the
`versatility of the OADM thus-constructed. Second. the opti-
`cal circulators implemented in this OADM for various rout-
`ing purposes introduce additional optical losses. which can
`accumulate to a substantial amount. Third. the constituent
`optical components must be in a precise alignment. in order
`for the system to achieve its intended purpose. 'Ihere are.
`however. no provisions provided for maintaining the requisite
`alignment: and no mechani sins implemented for overcoming
`degradation in the alignment owing to environmental effects
`such as thermal and mechanical disturbances over the course
`
`of operation.
`US. Pat. No. 5.906.133 to Tomlinson discloses an OADM
`that makes ttse of a design similar to that of Aksyttlt et al.
`There are input. output, drop and add ports implemented in
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 15
`Exhibit 1001, Page 15
`
`

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`3
`
`4
`
`US RE42,368 E
`
`this case. By positioning the four ports in a specific arrange
`ment. each micro-mirror. notwithstanding switchable between
`two discrete positions. either reflects its corresponding chan-
`nel (coming from the input port) to the output port. or con-
`comitantly reflects its channel to the drop port and an incident
`add channel to the output port. As such. this (JADM is able to
`perform both the add and drop functions without involving
`additional optical components (such as optical circulators
`used in the system of Aksyuk et al.). However. because a
`single drop port is designated for all the drop charmels and a
`single add port is designated for all the add channels. the add
`channels would have to be multiplexed before entering the
`add port and the drop channels likewise need to be demoti-
`plexed upon exiting from the drop port. Moreover. as in the
`case of Askyuk et 211.. there are no provisions provided for
`maintaining requisite optical alignment in the system. and no
`mechanisms implemented for combating degradation in the
`aligmnent due to environmental effects over the course of
`operation.
`As such. the prevailing drawbacks suffered by the ()ADMs
`currently in the art are summarized as follows:
`1) The wavelength rottting is intrinsically static. rendering it
`diflicult to dynamically reconfigure these OADMs.
`2) Add andlor drop channels often need to be multiplexed
`andr‘or dentultiplexed. thereby imposing additional cont-
`plexily and cost.
`3] Stringent fabrication tolerance and painstaking optical
`alignment are required. Moreover. the optical alignment is
`not actively maintained. rendering it susceptible to envi—
`ronmental effects such as thermal and mechanical distur-
`bances over the course of operation.
`4) In an optical communication network. OADMs are typi-
`cally in a ring or cascaded configuration. In order to tuiti-
`gate the interference amongst ()ADMs. which often
`adversely affects the overall performance ofthe network. it
`is essential that the power levels of spectral channels enter-
`ing and exiting each OADM be managed in a systematic
`way. for instance. by introducing power (or gain) equaliser-
`tion at each stage. Such a power equalization capability is
`also needed for compensating for non-uni lbrm gain caused
`by optical amplifiers (cg, erbium doped fiber amplifiers)
`in the network. There lacks. however. a systematic and
`dynamic management ofthe power levels of various spec—
`tral channels in these OADMs.
`5) The inherent high cost amd heavy optical loss further
`impede the wide application of these OADMs.
`In view of the foregoing. there is an urgent need in the art
`for optical add-drop multiplexers that overcome the afore-
`mentioned shortcomings in a simple. effective, and economi-
`cal construction.
`
`SUMMARY
`
`The present invention provides a wavelength-separating-
`rouling {WSRJ apparatus and method which employ an array
`offiber collimators serving as an input port and a plurality of
`output ports; a wavelength—separator: a beani—focuser; and an
`array of channel micromirrors.
`In operation. a mold-wavelength optical signal emerges
`from the input port. The wavelength-separator separates the
`ntulti-wavelcngth optical signal into multiple spectral cilan-
`nels. each characterized by a distinct center wavelength and
`associated bandwidth. The beam-focuser focuses the spectral
`channels into corresponding spectral spots. The channel
`microniirrors are positioned such that each channel micro-
`mirror receives one of the spectral charulcls. The channel
`micromirrors are individually controllable and movable. e.g..
`
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`continuously pivotable (or rotatable), so as to reflect the spec»
`tral channels into selected ones of the output ports. As such.
`each channel micromirror is assigned to a specific spectral
`chamiel. hence the name “channel micromirror“. And each
`
`output port may receive any number ofthe reflected spectral
`channels.
`A distinct feature of the channel micromirrors in the
`present invention, in contrast to those used in the prior art. is
`that the motion. e.g.. pivoting (or rotation). of each channel
`micromirror is under analog control such that its pivoting
`angle can be continuously adjusted. This enables each chan-
`nel micromirror to scan its corresponding spectral channel
`across all possible output ports and thereby direct the spectral
`channel to any desired output port.
`In the WSR apparatus of the present invention. the wave-
`length-separator may be provided by a ruled diffraction grat-
`ing. a holographic diffraction grating. an echelle grating. a
`curved diffraction grating, a dispersing prism. or other wave-
`length-separating means known in the art. The beam-focuser
`may be a single lens. an assembly of lenses. or other beam—
`focusing means known in the art. The channel micromirrors
`may be provided by silicon micromachined mirrors. reflec-
`tive ribbons (or membranes}. or other types of beam-deflect-
`ing means known in the art. And each channel micromirnor
`may be pivotable about one or two axes. The fiber coll imators
`serving as the input and output ports may be arranged in a
`onedimensional or two—dimensional array. In the latter case,
`the channel micromirrors must be pivotable biaxially.
`The WSR apparatus of the present invention may further
`comprise an array of collimator-a] igmnent mirrors. in optical
`comnmnication with the wavelength-separator and the fiber
`collimators. for adjusting the alignment of the input multi-
`wavclength signal and directing the spectral channels into the
`selected output ports by way of angular control of the colli—
`mated beams. Each collimator—aligmnent mirror may be
`rotatable about one or two axes. The collimator—alignment
`mirrors may be arranged in a one-dimensional or two-dimen-
`sional array. First and second arrays of imaging lenses may
`additionally be optically interposed between the collimator-
`alignment mirrors and the fiber collimators in a telecentric
`arrangement. thereby “imaging" the collimator—alignment
`mirrors onto the corresponding fiber collimators to ensure an
`optimal alignment.
`The WSR apparatus of the present invention may further
`include a servo-control assembly. in commtmication with the
`channel micromirrors and the output ports. The servo-control
`assembly serves to monitor the power levels of the spectral
`channels coupled into the output ports and further provide
`control of the chamiel micromjrrors on an individual basis. so
`as to maintain a predetenm'ned coupling efiiciency of each
`spectral channel in one of the output ports. As such. the
`servo-control assembly provides dynamic control of the cott-
`pling ofthe spectral channels into the respective output ports
`and actively manages the power levels of the spectral chan-
`nels coupled into the output ports. (If the WSR apparatus
`includes
`an array of collimator—alignment mirrors as
`described above. the servo—control assembly may addition—
`ally provide dynamic eontroi of the collimator-alignment
`mirrors.) Moreover. the utilimtion of such a servo-control
`assembly effectively relaxes the requisite fabrication toler-
`ances and the precision of optical alignment during assembly
`of a WSR apparatus of the present invention, and funher
`enables the system to correct for shill in optical alignment
`over the course of operation. A WSR apparatus incorporating
`a servo-control assembly tints described is termed a WSR-S
`apparatus. tlrereinafter in the present invention.
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 16
`Exhibit 1001, Page 16
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`the WSR-S (or WSR) apparatus of the
`Accordingly.
`present invention may be used to construct a variety of optical
`devices. including a novel class of dynamically reconfig-
`urable optical add—drop multiplexers (OADMs). as exempli-
`lied in the following embodiments.
`One embodiment of an ()AI'JM of the present invention
`comprises an aforementioned WSR—S (or WSR) apparatus
`and an optical combiner. The output ports of the WSRAS
`apparatus include a pass-through port and one or more drop
`ports. each carrying any number of the spectral channels. The
`optical combiner is coupled to the pass-through port. serving
`to combine the pass-through channels with one or more add
`spectral channels. The combined optical signal constitutes an
`output signal ofthe system. The optical combiner may be an
`le (N22) broadband fiber-optic coupler.
`for instance.
`which also serves the purpose of multiplexing a multiplicity
`of add spectral channels to be coupled into the system.
`In another embodiment ofan OADM of the present inven-
`tion. a first WSR-S (or WSR) apparatus is cascaded with a
`second WSR-S (or WSR) apparatus. The output ports of the
`first WSR—S (or WSR) apparatus include a passthrough port
`and one or more drop ports. The second WSR-S (or WSR)
`apparatus includes a plurality of input ports and an exiting
`port. The configuration is such that the pass-through channels
`from the first WSR-S apparatus and one or more add channels
`are directed into the input ports of the second WSR-S appa-
`ratus. and consequently multiplexed into an output multi-
`wavelength optical signal directed into the exiting port of the
`second WSR-S apparatus. That is to say that in this embodi—
`ment. one WSR-S apparatus (cg. the first one) effectively
`performs a dynamic drop function. whereas the other WSR-S
`apparatus (cg. the second one) carries out a dynamic add
`function. And there are essentially no ['iJndamental restric-
`tions on the wavelengths that can be added or dropped. other
`than those imposed by the overall communication system.
`Moreover. the underlying OADM architecture thus presented
`is intrinsically scalable and can be readily extended to any
`number of the WSR-S (or WSR) systems. if so desired for
`performing intricate add and drop functions in a network
`environment.
`
`Those skilled in the art will recognize that the aforemen-
`tioned embodiments provide only two of many embodiments
`of a dynamically reconfigurable OADM according to the
`present invention. Various changes. substitutions. and alter-
`nations can be made herein. without departing from the prin-
`ciples and the scope of the invention. Accordingly. a skilled
`artisan can design an OADM in accordance with the present
`invention. to best suit a given application.
`All in all. the OADMs of the present invention provide
`many advantages over the prior art devices. notably:
`1) By advantageously employing an array of channel micro-
`mirrors that are individually and continuously control-
`lable. an OADM of the present invention is capable of
`routing the spectral channels on a chaimel-by-channel
`basis and directing any spectral channel into any one o f the
`output ports. As such. its underlying operation is dynami—
`cally reconfigurable. and its underlying architecture is
`intrinsically scalable to a large number of channel counts.
`2) The add and drop spectral channels need not be multi-
`plexed and demultiplexed before entering and after leaving
`the OADM respectively. And there are not fundamental
`restrictions on the wavelengths to be added or dropped.
`3) The coupling of the spectral channels into the output ports
`is dynamically controlled by a servo—control assembly.
`rendering the OADM less susceptible to environmental
`effects (such as thennal and mechanical disturbances) and
`therefore more robust in performance. By maintaining an
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`optimal optical alignment. the optical losses incurred by
`the spectral channels are also significantly reduced.
`4) The power levels of the spectral channels coupled into the
`output pons can be dynamically managed according to
`demand. or maintained at desired values (cg. . equaliYed at
`a predetermined value) by way 0 f the servo-control assem-
`bly. This spectral power-management capability as an inte-
`gral part of the OADM will be particularly desirable in
`WDM optical networking applications.
`5) The use of free-space optics provides a simple. low loss.
`and cost-effective construction. Moreover. the utilization
`
`of the servo-control assembly effectively relaxes the req-
`uisite fabrication tolerances and the precision of optical
`alignment during initial assembly. enabling the OADM to
`be simpler and more adaptable in structure. lower in cost
`and optical loss.
`6) The underlying OADM architecture allows a multiplicity
`of the OADMs according to the present invention to be
`readily assembled (cg. cascaded) for W[)M optical net-
`working applications.
`The novel features ofthis invention. as well as the invention
`itself. will be best understood from the following drawings
`and detailed description.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`FIGS. lA-ll) show a Iirst embodiment ofa wavelength-
`separating—routing (WSR) apparatus according to the present
`invention. and the modeling results demonstrating the perfor—
`mance of the WSR apparatus:
`PIGS. 2A-2C depict second and third embodiments of a
`WSR apparatus according to the present invention:
`FIG. 3 shows a fourth embodiment of a WSR apparatus
`according to the present invention:
`FIGS. (IA-48 show schematic illustrations oftwo embodi-
`ments of a WSR—S apparatus comprising a WSR apparatus
`and a servo—control assembly. according to the present inven-
`tion:
`FIG. 5 depicts an exemplary embodiment of an optical
`add-drop multiplexer (OADM) according to the present
`invention: and
`FIG. 6 shows an alternative embodiment of an DADM
`according to the present invention.
`
`[)l-E'ILM LED DESCRIPTION
`
`In this specification and appending claims. a “spectral
`channel“ is characterized by a distinct center wavelength and
`associated bandwidth. Each spectral channel may carry a
`unique information signal. as in WDM optical networking
`applications.
`FIG. 1A depicts a first embodiment of a wavelength-sepa-
`rating-muting (WSR) apparatus according to the present
`invention. By way of example to illustrate the general prin-
`ciples and the topological structure ofa wavelength-separat-
`ing-routing (WSR) apparatus of the present invention. the
`WSR apparatus 100 comprises multiple inputfoutput ports
`which may be in the fonn ofan array offiber collimators 110.
`providing an input port 110-1 and a plurality of output ports
`110-2 through lltl-N (N23): a wavelength-separator which
`in one form may be a diffraction grating 101; a beam-focuser
`in the form ofa focusing lens 102: and an array ol‘chaiuiel
`micromirrors 103.
`
`In operation. a multi—wavelength optical signal emerges
`from the input port 110—1. The diffraction grating 101 angu-
`larly separates the multi-wavelength optical signal into mul-
`tiple spectral channels. which are in tum focused by the
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1001, Page 17
`Exhibit 1001, Page 17
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`focusing lens 102 into a spatial array of distinct spectral spots
`(not shown in FIG. 1A) in a one-to-one correspondence. The
`channel micromirrors 103 are positioned in accordance with
`the spatial array formed by the spectral spots. such that each
`channel micromirror receives one of the spectral channels.
`The channel micromirrors 103 are individually controllable
`and movable. e.g.. pivotable [or rotatable) under analog (or
`continuous) control, such that. upon reflection. the spectral
`channels are directed into selected ones of the output ports
`110-2 through llO-N by way of the focusing lens 102 and the
`diffraction grating 10]. As such. each channel micromirror is
`assigned to a specific spectral channel, hence the name “cht
`~
`nel micromirror". Each output port may receive arty number
`of the reflected spectral channels.
`For purposes of illustration and clarity. only a selective few
`(e.g.. three) of the spectra] charms-ls. along with the input
`multi-wavelength optical signal. are graphically illustrated in
`FIG. 1A and the liillowing figures. It should be noted. how-
`ever. that there can be any number of the spectral channels in
`a WSR apparatus of the present invention (so long as the
`number of spectral channels does not exceed the number of
`channel mirrors employed in the system). It should also be
`noted that the optical beams representing the spectral chan-
`nels shown in FIG. 1A and the following figures are provided
`for illustrative purpose only. That is. their sizes and shapes
`may not be drawn according to scale. For instance. the input
`beam and the corresponding diffracted beams generally have
`different cross—sectional shapes. so long as the angle of inci—
`dence upon the diffraction grating is not equal to the angle of
`diffraction. as is known to those skilled in the art.
`In the embodiment of FIG. 1A.
`it is preferable that the
`diffraction grating [01 and the channel microtuirrors 103 are
`placed respectively at the first and second (i.e.. the front and
`back) focal points (on the opposing sides) ofthe focusing lens
`102. Such a telecentric arrangement allows the chief rays of
`the focused beams to be parallel to each other and generally
`parallel to the optical axis. In this application, the telecentr‘ic
`configuration fttrther allows the reflected spectral channels to
`be e llic iently coupled into the respective output ports. thereby
`minimizing various translational walk-00‘ effects that may
`otherwise arise. Moreover. the input multi—wavelength opti—
`cal signal is preferably collimated and circular in cross—sec—
`tion. The corresponding spectral channels diffracted from the
`diffraction grating 101 are generally elliptical in cross-sec-
`tion: they may be of the same size as the input beam in one
`dimension and elongated in the other ditnension.
`[t is known that the diffraction elliciency ofa diffraction
`grating is generally polarization—dependent. That is. the difw
`fraction efiiciency of a grating in a standard mounting con—
`figuration may be considerably higher for P—polarization that
`is perpendicular to the groove lines on the grating than for
`S-polariration that is orthogonal to P-polarivation. especially
`as the number of groove lines (per unit length) increases. To
`mitigate such polurination-sensitive effects. a quarter-wave
`plate 104 may be optically interposed between the diffraction
`grating 101 and the channel micromirrors 103. and preferably
`placed between the diffraction grating 101 and the focusing
`lens 102 as is shown in l-‘IG. 1A. In this way, each spectral
`ehatmel experiences a total of approximately 90-degroe rota-
`tion in polarization upon traversing the quarter-wave plate
`104 twice. (That is, ifa beam oflight has P-polariration when
`first encountering the diffraction grating. it would have pre-
`dominantly (if not all) S—polarization upon the second
`encountering. and vice versa.) This ensures that all the spec—
`tral channels incur nearly the same amount of rotmd-trip
`polarization dependent loss.
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`In the WSR apparatus 100 of FIG. 1A. the diffraction
`grating 10]. by way of example.
`is oriented such that the
`focused spots of the spectral channels fall onto the channel
`micromirrors 103 in a horizontal array. as illustrated in FIG.
`ll}.
`Depicted in FIG. 1B is a close-up view of the channel
`micromirrors 103 shown in the embodiment of FIG. 1A. By
`way of example, the channel micromirrors 103 are arranged
`in a one-dimensional array along the x-axis (i.e._. the horizon-
`tal direction in the figure). so