(19) United States
`c12) Reissued Patent
`Chen et al.
`
`I IIIII
`
`11111111
`
`1111111111111111111111111111111111111111111111
`USOORE42368E
`
`US RE42,368 E
`(10) Patent Number:
`May 17,2011
`(45) Date of Reissued Patent:
`
`(54) RECONFIGURABLE OPTICAL ADD-DROP
`MULTIPLEXERS WITH SERVO CONTROL
`AND DYNAMIC SPECTRAL POWER
`MANAGEMENT CAPABILITIES
`
`(75)
`
`Inventors: Tai Chen, San Jose, CA (US); Jeffrey P.
`Wilde, Morgan Hill, CA (US); Joseph
`E. Davis, Morgan Hill, CA (US)
`
`(73) Assignee: Capella Photonics, Inc., San Jose, CA
`(US)
`
`(21) Appl. No.: 12/816,084
`
`(22) Filed:
`
`Jun.15,2010
`
`Related U.S. Patent Documents
`
`6,879,750
`Apr. 12, 2005
`10/745,364
`Dec. 22, 2003
`
`Reissue of:
`(64) Patent No.:
`Issued:
`Appl. No.:
`Filed:
`U.S. Applications:
`(63) Continuation of application No. 10/005,714, filed on
`Nov. 7, 2001, now Pat. No. 6,687,431, which is a
`continuation of application No. 09/938,426, filed on
`Aug. 23, 2001, now Pat. No. 6,625,346.
`
`(60) Provisional application No. 60/277,217, filed on Mar.
`19, 2001.
`
`(51)
`
`Int. Cl.
`G02B 6128
`(2006.01)
`H04J 14102
`(2006.01)
`(52) U.S. Cl. ................ 385/24; 385/10; 385/33; 385/37;
`398/83
`(58) Field of Classification Search .................... 385/24,
`385/11, 10, 37, 34, 33; 398/79, 82, 83, 84,
`398/88, 87
`See application file for complete search history.
`
`100
`~
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5/1995 Patel et al.
`5,414,540 A
`5,629,790 A
`5/1997 Neukermans eta!.
`4/1998 Ford eta!.
`5,745,271 A
`5,835,458 A
`1111998 Bischel et a!.
`9/1999 Tomlinson
`5,960,133 A
`10/1999 Aksyuk eta!.
`5,974,207 A
`212000 Michalicek eta!.
`6,028,689 A
`6,204,946 B1
`3/2001 Aksyuk eta!.
`6,205,269 B1
`3/2001 Morton
`4/2001 Riza
`6,222,954 B1
`7/2001 Jin eta!.
`6,256,430 B1
`6,263,135 B1
`7/2001 Wade
`6,289,155 B1
`9/2001 Wade
`6,307,657 B1
`10/2001 Ford
`6,418,250 B1
`7/2002 Corbosiero eta!.
`12/2002 Bouevitch et al.
`6,498,872 B2
`(Continued)
`
`Primary Examiner- Brian M Healy
`(74) Attorney, Agent, or Firm- Barry N. Young
`
`ABSTRACT
`(57)
`This invention provides a novel wavelength-separating-rout(cid:173)
`ing (WSR) apparatus that uses a diffraction grating to sepa(cid:173)
`rate a multi-wavelength optical signal by wavelength into
`multiple spectral channels, which are then focused onto an
`array of corresponding channel micromirrors. The channel
`micromirrors 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 spectral channels on a channel-by-channel basis
`and coupling any spectral channel into any one of the output
`ports. The WSR apparatus of the present invention may be
`further equipped with servo-control and spectral power-man(cid:173)
`agement capabilities, thereby maintaining the coupling effi(cid:173)
`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 of dynamically recon(cid:173)
`figurable optical add-drop multiplexers (OADMs) for WDM
`optical networking applications.
`
`22 Claims, 12 Drawing Sheets
`
`Cisco Systems, Inc.
`Exhibit 1001, Page 1
`
`

`

`US RE42,368 E
`Page 2
`
`U.S. PATENT DOCUMENTS
`6,567,574 B1
`5/2003 Ma eta!.
`7/2003 Aksyuk eta!.
`6,600,851 B2
`9/2003 Wilde et al.
`6,625,346 B2
`10/2003 Wagener eta!.
`6,631,222 B1
`10/2003 Ford eta!.
`6,634,810 B1
`6,687,431 B2 *
`2/2004 Chen et a!. ...................... 385/24
`10/2004 Bouevitch et al.
`6,810,169 B2
`
`6,879,750 B2 *
`6,898,348 B2
`6,989,921 B2
`7,183,633 B2
`2002/0131691 A1
`2003/0043471 A1
`
`4/2005 Chen et a!. ...................... 385/24
`5/2005 Morozov et a!.
`112006 Bernstein eta!.
`2/2007 Daneman et a!.
`9/2002 Garrett et a!.
`3/2003 Belser et al.
`
`* cited by examiner
`
`Cisco Systems, Inc.
`Exhibit 1001, Page 2
`
`

`

`U.S. Patent
`
`May 17,2011
`
`Sheet 1 of 12
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`US RE42,368 E
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`Exhibit 1001, Page 4
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`

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`

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`May 17,2011
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`Cisco Systems, Inc.
`Exhibit 1001, Page 11
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`

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`May 17,2011
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`Exhibit 1001, Page 12
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`

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`Exhibit 1001, Page 14
`
`

`

`US RE42,368 E
`
`1
`RECONFIGURABLE OPTICAL ADD-DROP
`MULTIPLEXERS WITH 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(cid:173)
`tion; matter printed in italics indicates the additions
`made by reissue.
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of U.S. application Ser.
`No. 10/005,714, filed Nov. 7, 2001 now U.S. Pat. No. 6,687,
`431, which is a continuation of U.S. application Ser. No.
`09/938,426, filed Aug. 23, 2001, now U.S. Pat No. 6,625,346
`which claims the benefit ofU.S. application Ser. No. 60/277,
`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
`(OADMs) for wavelength division multiplexed optical net(cid:173)
`working applications.
`
`BACKGROUND
`
`As fiber-optic communication networks rapidly spread
`into every walk of modern life, there is a growing demand for
`optical components and subsystems that enable the fiber(cid:173)
`optic communications networks to be increasingly scalable,
`versatile, robust, and cost-effective.
`Contemporary fiber-optic communications networks com(cid:173)
`monly employ wavelength division multiplexing (WDM), for
`it allows multiple information (or data) channels to be simul(cid:173)
`taneously transmitted on a single optical fiber by using dif- 40
`ferent wavelengths and thereby significantly enhances the
`information bandwidth of the fiber. The prevalence ofWDM
`technology has made optical add-drop multiplexers indis(cid:173)
`pensable building blocks of modern fiber-optic communica(cid:173)
`tion networks. An optical add-drop multiplexer (OADM)
`serves to selectively remove (or drop) one or more wave(cid:173)
`lengths from a multiplicity of wavelengths on an optical fiber,
`hence taking away one or more data channels from the traffic
`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(cid:173)
`terized by a distinct wavelength) onto and from an optical
`fiber respectively, without disrupting the overall traffic flow
`along the fiber. Indeed, careful placement of the OADMs can
`dramatically improve an optical communication network's
`flexibility and robustness, while providing significant cost
`advantages.
`Conventional OADMs in the art typically employ multi(cid:173)
`plexers/demultiplexers (e.g, waveguide grating routers or
`arrayed-waveguide gratings),
`tunable
`filters,
`optical
`switches, and optical circulators in a parallel or serial archi(cid:173)
`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 65
`separates a multi-wavelength signal into its constituent spec(cid:173)
`tral components. A wavelength switching/routing means
`
`2
`(e.g., a combination of optical switches and optical circula(cid:173)
`tors) then serves to drop selective wavelengths and add others.
`Finally, a multiplexer combines the remaining (i.e., the pass(cid:173)
`through) wavelengths into an output multi-wavelength opti-
`5 cal signal. In the serial architecture, as exemplified in U.S.
`Pat. No. 6,205,269, tunable filters (e.g., Bragg fiber gratings)
`in combination with optical circulators are used to separate
`the drop wavelengths from the pass-through wavelengths and
`subsequently launch the add channels into the pass-through
`10 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(cid:173)
`lying architecture, the OADMs currently in the art are char-
`15 acteristically high in cost, and prone to significant optical loss
`accumulation. Moreover, the designs of these OADMs are
`such that it is inherently difficult to reconfigure them in a
`dynamic fashion.
`U.S. Pat. No. 6,204,946 to Askyuk et a!. discloses an
`20 OADM that makes use of free-space optics in a parallel con(cid:173)
`struction. In this case, a multi-wavelength optical signal
`emerging from an input port is incident onto a ruled diffrac(cid:173)
`tion grating. The constituent spectral channels thus separated
`are then focused by a focusing lens onto a linear array of
`25 binary micromachined mirrors. Each micromirror is config(cid:173)
`ured to operate between two discrete states, such that it either
`retroreflects 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
`30 pass-through signal (i.e., the combined pass-through chan(cid:173)
`nels) shares the same 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
`35 additional optical circulator 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-through signal by way
`of the diffraction grating and the binary micromirrors.
`Although the aforementioned OADM disclosed by Askyuk
`eta!. has the advantage of performing 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 port/fiber as the input
`45 signal. An optical circulator therefore has to be implemented,
`to provide necessary routing of these 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-
`so vided to multiplex the add channels before entering the sys(cid:173)
`tem and to demultiplex the drop channels after exiting the
`system. This additional multiplexing/demultiplexing require(cid:173)
`ment adds more cost and complexity that can restrict the
`versatility of the OADM thus-constructed. Second, the opti-
`55 cal circulators implemented in this OADM for various rout(cid:173)
`ing purposes introduce additional optical losses, which can
`accumulate to a substantial amount. Third, the constituent
`optical components must be in a precise alignn1ent, in order
`for the system to achieve its intended purpose. There are,
`60 however, no provisions provided for maintaining the requisite
`alignment; and no mechanisms implemented for overcoming
`degradation in the alignment owing to environmental effects
`such as thermal and mechanical disturbances over the course
`of operation.
`U.S. Pat. No. 5,906,133 to Tomlinson discloses an OADM
`that makes use of a design similar to that of Aksyuk et a!.
`There are input, output, drop and add ports implemented in
`
`Cisco Systems, Inc.
`Exhibit 1001, Page 15
`
`

`

`US RE42,368 E
`
`3
`this case. By positioning the four ports in a specific arrange(cid:173)
`ment, eachmicromirror, notwithstanding switchable between
`two discrete positions, either reflects its corresponding chan(cid:173)
`nel (coming from the input port) to the output port, or con(cid:173)
`comitantly reflects its channel to the drop port and an incident
`add channel to the output port. As such, this OADM 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 a!.). However, because a
`single drop port is designated for all the drop channels and a 10
`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 demuti(cid:173)
`plexed upon exiting from the drop port. Moreover, as in the
`case of Askyuk et a!., there are no provisions provided for 15
`maintaining requisite optical alignment in the system, and no
`mechanisms implemented for combating degradation in the
`alignment due to environmental effects over the course of
`operation.
`As such, the prevailing drawbacks suffered by the OADMs 20
`currently in the art are summarized as follows:
`1) The wavelength routing is intrinsically static, rendering it
`difficult to dynamically reconfigure these OADMs.
`2) Add and/or drop channels often need to be multiplexed
`and/or demultiplexed, thereby imposing additional com- 25
`plexity 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(cid:173)
`ronmental effects such as thermal and mechanical distur- 30
`bances over the course of operation.
`4) In an optical communication network, OADMs are typi(cid:173)
`cally in a ring or cascaded configuration. In order to miti(cid:173)
`gate the interference amongst OADMs, which often
`adversely affects the overall performance of the network, it
`is essential that the power levels of spectral channels enter(cid:173)
`ing and exiting each OADM be managed in a systematic
`way, for instance, by introducing power (or gain) equaliza(cid:173)
`tion at each stage. Such a power equalization capability is
`also needed for compensating for non-uniform gain caused
`by optical amplifiers (e.g., erbium doped fiber amplifiers)
`in the network. There lacks, however, a systematic and
`dynamic management of the power levels of various spec(cid:173)
`tral channels in these OADMs.
`5) The inherent high cost and heavy optical loss further 45
`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(cid:173)
`mentioned shortcomings in a simple, effective, and economi(cid:173)
`cal construction.
`
`SUMMARY
`
`The present invention provides a wavelength-separating(cid:173)
`routing (WSR) apparatus and method which employ an array
`of fiber collimators serving as an input port and a plurality of
`output ports; a wavelength-separator; a beam-focuser; and an
`array of channel micromirrors.
`In operation, a multi-wavelength optical signal emerges
`from the input port. The wavelength-separator separates the
`multi-wavelength optical signal into multiple spectral chan(cid:173)
`nels, each characterized by a distinct center wavelength and
`associated bandwidth. The beam-focuser focuses the spectral
`channels into corresponding spectral spots. The channel
`micromirrors are positioned such that each channel micro(cid:173)
`mirror receives one of the spectral channels. The channel
`micromirrors are individually controllable and movable, e.g.,
`
`4
`continuously pivotable (or rotatable), so as to reflect the spec(cid:173)
`tral channels into selected ones of the output ports. As such,
`each channel micromirror is assigned to a specific spectral
`channel, hence the name "channel micromirror". And each
`output port may receive any number of the 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(cid:173)
`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(cid:173)
`length-separator may be provided by a ruled diffraction grat(cid:173)
`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(cid:173)
`focusing means known in the art. The channel micromirrors
`may be provided by silicon micromachined mirrors, reflec(cid:173)
`tive rib bans (or membranes), or other types of beam -deflect-
`ing means known in the art. And each channel micromirror
`may be pivotable about one or two axes. The fiber collimators
`serving as the input and output ports may be arranged in a
`one-dimensional 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-alignment mirrors, in optical
`communication with the wavelength-separator and the fiber
`collimators, for adjusting the alignment of the input multi(cid:173)
`wavelength signal and directing the spectral channels into the
`35 selected output ports by way of angular control of the calli(cid:173)
`mated beams. Each collimator-alignment mirror may be
`rotatable about one or two axes. The collimator-alignment
`mirrors may be arranged in a one-dimensional or two-dimen(cid:173)
`sional array. First and second arrays of imaging lenses may
`40 additionally be optically interposed between the collimator(cid:173)
`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 communication 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
`50 control of the channel micro mirrors on an individual basis, so
`as to maintain a predetermined coupling efficiency of each
`spectral channel in one of the output ports. As such, the
`servo-control assembly provides dynamic control of the cou(cid:173)
`pling of the spectral channels into the respective output ports
`55 and actively manages the power levels of the spectral chan(cid:173)
`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(cid:173)
`ally provide dynamic control of the collimator-alignment
`60 mirrors.) Moreover, the utilization of such a servo-control
`assembly effectively relaxes the requisite fabrication toler(cid:173)
`ances and the precision of optical alignment during assembly
`of a WSR apparatus of the present invention, and further
`enables the system to correct for shift in optical alignment
`65 over the course of operation. A WSR apparatus incorporating
`a servo-control assembly thus described is termed a WSR-S
`apparatus, thereinafter in the present invention.
`
`Cisco Systems, Inc.
`Exhibit 1001, Page 16
`
`

`

`US RE42,368 E
`
`6
`optimal optical alignment, the optical losses incurred by
`the spectral channels are also significantly reduced.
`4) The power levels of the spectral charmels coupled into the
`output ports can be dynamically managed according to
`demand, or maintained at desired values (e.g., equalized at
`a predetermined value) by way of the servo-control assem(cid:173)
`bly. This spectral power-management capability as an inte(cid:173)
`gral part of the OADM will be particularly desirable in
`WDM optical networking applications.
`10 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(cid:173)
`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 (e.g., cascaded) for WDM optical net(cid:173)
`working applications.
`The novel features of this invention, as well as the invention
`itself, will be best understood from the following drawings
`and detailed description.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`5
`Accordingly, the WSR-S (or WSR) apparatus of the
`present invention may be used to construct a variety of optical
`devices, including a novel class of dynamically reconfig(cid:173)
`urable optical add-drop multiplexers (OADMs), as exempli(cid:173)
`fied in the following embodiments.
`One embodiment of an OADM of the present invention
`comprises an aforementioned WSR-S (or WSR) apparatus
`and an optical combiner. The output ports of the WSR-S
`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 of the system. The optical combiner may be an
`Nxl (N~2) broadband fiber-optic coupler, for instance, 15
`which also serves the purpose of multiplexing a multiplicity
`of add spectral channels to be coupled into the system.
`In another embodiment of an OADM of the present inven(cid:173)
`tion, a first WSR-S (or WSR) apparatus is cascaded with a
`second WSR-S (or WSR) apparatus. The output ports of the 20
`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 charmels
`from the first WSR -S apparatus and one or more add charmels 25
`are directed into the input ports of the second WSR-S appa(cid:173)
`ratus, and consequently multiplexed into an output multi(cid:173)
`wavelength optical signal directed into the exiting port of the
`second WSR-S apparatus. That is to say that in this embodi(cid:173)
`ment, one WSR-S apparatus (e.g., the first one) effectively 30
`performs a dynamic drop function, whereas the other WSR -S
`apparatus (e.g., the second one) carries out a dynamic add
`function. And there are essentially no fundamental restric(cid:173)
`tions on the wavelengths that can be added or dropped, other
`than those imposed by the overall communication system. 35
`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(cid:173)
`tioned embodiments provide only two of many embodiments
`of a dynamically reconfigurable OADM according to the
`present invention. Various changes, substitutions, and alter(cid:173)
`nations can be made herein, without departing from the prin- 45
`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(cid:173)
`mirrors that are individually and continuously control(cid:173)
`lable, an OADM of the present invention is capable of
`routing the spectral channels on a charmel-by-channel
`basis and directing any spectral charmel into any one of the 55
`output ports. As such, its underlying operation is dynami(cid:173)
`cally reconfigurable, and its underlying architecture is
`intrinsically scalable to a large number of channel connts.
`2) The add and drop spectral channels need not be multi(cid:173)
`plexed and demultiplexed before entering and after leaving 60
`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 65
`effects (such as thermal and mechanical disturbances) and
`therefore more robust in performance. By maintaining an
`
`FIGS. 1A-1D show a first embodiment of a wavelength(cid:173)
`separating-routing (WSR) apparatus according to the present
`invention, and the modeling results demonstrating the perfor(cid:173)
`mance of the WSR apparatus;
`FIGS. 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. 4A-4B show schematic illustrations of two embodi(cid:173)
`ments of a WSR-S apparatus comprising a WSR apparatus
`and a servo-control assembly, according to the present inven(cid:173)
`tion;
`FIG. 5 depicts an exemplary embodiment of an optical
`40 add-drop multiplexer (OADM) according to the present
`invention; and
`FIG. 6 shows an alternative embodiment of an OADM
`according to the present invention.
`
`DETAILED 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
`50 unique information signal, as in WDM optical networking
`applications.
`FIG. 1A depicts a first embodiment of a wavelength-sepa-
`rating-routing (WSR) apparatus according to the present
`invention. By way of example to illustrate the general prin(cid:173)
`ciples and the topological structure of a wavelength-separat(cid:173)
`ing-routing (WSR) apparatus of the present invention, the
`WSR apparatus 100 comprises multiple input/output ports
`which may be in the form of an array of fiber collimators 110,
`providing an input port 110-1 and a plurality of output ports
`110-2 through 110-N (N~3); a wavelength-separator which
`in one form may be a diffraction grating 101; a beam-focuser
`in the form of a focusing lens 102; and an array of channel
`micromirrors 103.
`In operation, a multi-wavelength optical signal emerges
`from the input port 110-1. The diffraction grating 101 angu(cid:173)
`larly separates the multi-wavelength optical signal into mul(cid:173)
`tiple spectral channels, which are in turn focused by the
`
`Cisco Systems, Inc.
`Exhibit 1001, Page 17
`
`

`

`US RE42,368 E
`
`7
`focusing lens 102 into a spatial array of distinct spectral spots
`(not shown in FIG. lA) 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 110-N by way of the focusing lens 102 and the 10
`diffraction grating 101. As such, each channel micro mirror is
`assigned to a specific spectral channel, hence the name "chan(cid:173)
`nel micromirror". Each output port may receive any number
`of the reflected spectral channels.
`For purposes of illustration and clarity, only a selective few
`(e.g., three) of the spectral channels, along with the input
`multi-wavelength optical signal, are graphically illustrated in
`FIG. lA and the following figures. It should be noted, how(cid:173)
`ever, that there can be any number of the spectral channels in 20
`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(cid:173)
`nels shown in FIG. lA and the following figures are provided 25
`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(cid:173)
`dence upon the diffraction grating is not equal to the angle of 30
`diffraction, as is known to those skilled in the art.
`In the embodiment of FIG. lA, it is preferable that the
`diffraction grating 101 and the channel micromirrors 103 are
`placed respectively at the first and second (i.e., the front and
`back) focal points (on the opposing sides) of the focusing lens 35
`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 telecentric
`configuration further allows the reflected spectral channels to
`be efficiently coupled into the respective output ports, thereby 40
`minimizing various translational walk-off effects that may
`otherwise arise. Moreover, the input multi-wavelength opti-
`cal signal is preferably collimated and circular in cross-