(12) United States Patent
`Marom
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,950,609 B2
`Sep. 27, 2005
`
`US006950609B2
`
`(54) TUNABLE, MULTI-PORT OPTICALADD-
`DROP MULTIPLEXER
`
`(75) Inventor: Dan Mark Marom, Howell, NJ (US)
`
`(73) Assignee: Lucent Technologies Inc., Murray Hill,
`NJ (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 628 days.
`
`(21) Appl. N0.: 09/944,802
`(22) Filed:
`Aug. 31, 2001
`(65)
`Prior Publication Data
`
`US 2002/0196493 A1 Dec. 26, 2002
`
`Related US. Application Data
`(60) Provisional application No. 60/300,272, ?led on Jun. 22,
`2001.
`
`(51) Int. Cl.7 ............................................... .. H04J 14/02
`(52) us. Cl. ........................... .. 398/83; 398/79; 398/82;
`398/84; 398/45; 385/24; 385/37
`(58) Field of Search ............................ .. 398/83, 84, 82,
`398/79, 45, 87, 88; 385/24, 37, 18, 31,
`16, 17, 15, 27
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`
`6,243,179 131 * 6/2001 Thompson et al. .......... .. 398/9
`6,493,117 131 * 12/2002 Milton et al. ............ .. 398/49
`
`6,657,770 B2 * 12/2003 Marom et al. ............ .. 359/290
`
`* cited by examiner
`
`Primary Examiner—Hanh Phan
`(74) Attorney, Agent, or Firm—B. H. Freedman; D. A.
`Sasso
`
`(57)
`
`ABSTRACT
`
`A tunable (recon?gurable) OADM provides multiple drop
`ports and multiple add ports by Which desired channels can
`be removed from, or added to, a composite optical signal. In
`one embodiment, a programmable demultiplexer is arranged
`to receive an input signal containing components at X
`different Wavelengths from an optical input port, and dis
`tribute the input signal components among K output ports.
`K-l of the output ports are the “drop” ports of the OADM,
`and cumulatively contain W different Wavelengths. The
`remaining port, Which is the “through port” that carries the
`Z Wavelengths not dropped from the original input signal, is
`connected to the ?rst port of an M port programmable
`multiplexer having M-1 other input ports. The remaining
`M-1 ports are the “add” ports of the OADM, Which cumu
`latively receive v different Wavelengths to be added by the
`OADM.
`
`5,960,133 A * 9/1999 Tomlinson ................. .. 385/18
`
`9 Claims, 4 Drawing Sheets
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 1
`
`

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`U.S. Patent
`
`Sep. 27, 2005
`
`Sheet 1 0f 4
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`US 6,950,609 B2
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`FIG. 1
`PRIOR ART
`
`C 120
`
`/ 1 10
`
`C 140
`
`130 \A
`
`L 150
`
`FIG. 2
`PRIOR ART
`
`[220
`
`[210-1
`
`[240‘
`
`[210-
`
`[260
`
`23O—1\.l_v
`
`250-11
`
`|:‘230—2
`
`l-r 250-2
`
`FIG. 3
`PRIOR ART
`
`C 20
`
`340
`
`330 -
`
`f 350
`
`360
`
`370
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 2
`
`

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`U.S. Patent
`
`Sep. 27,2005
`
`Sheet 2 0f 4
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`US 6,950,609 B2
`
`FIG. 4(A)
`
`FIG. 4(B)
`
`420
`
`400
`
`410-1
`
`410-2
`
`410-3
`
`460-1 _
`
`460-2 '
`
`460-3 _
`
`E
`
`470
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 3
`
`

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`U.S. Patent
`
`Sep. 27,2005
`
`Sheet 3 0f 4
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`US 6,950,609 B2
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 4
`
`

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`U.S. Patent
`
`Sep. 27,2005
`
`Sheet 4 0f 4
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`US 6,950,609 B2
`
`FIG. 7
`760
`
`740-K
`
`742-K
`743-K
`
`741-K
`
`740-2
`
`740-1
`
`742-3
`743-3
`
`742-2
`
`743-2
`
`742-1
`743-1
`
`741-3
`
`741-2
`
`741-1
`
`850-1
`
`850-2
`
`WAVELENGTH SWITCH
`
`830
`
`840-1
`
`840 2
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 5
`
`

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`US 6,950,609 B2
`
`1
`TUNABLE, MULTI-PORT OPTICAL ADD
`DROP MULTIPLEXER
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application claims priority of Provisional Applica
`tion Ser. No. 60/300,272 Which Was ?led on Jun. 22, 2001.
`
`TECHNICAL FIELD
`
`10
`
`The present invention relates to optical communications,
`and more particularly to an arrangement for a tunable,
`multi-port optical add-drop multiplexer (OADM) that can
`add optical channels to, and extract optical channels from,
`an optical signal in a Wavelength division multiplexing
`(WDM) system.
`
`BACKGROUND OF THE INVENTION
`
`The transmission capacity of ?ber-optic communication
`systems has increased signi?cantly by use of the Wavelength
`division multiplexing (WDM) technique. In a WDM system,
`multiple channels, Where each channel is differentiated by
`using a different Wavelength of light, each carry modulated
`optical signals in a single optical ?ber betWeen transmitter
`and receiver nodes. In a typical optical communication
`system, it is desirable to have a feW access nodes along the
`?ber path betWeen the transmitter and receiver end terminals
`that have the ability to add and/or drop one or more optical
`channels. A node having this capability is often referred to
`as an optical add/drop multiplexer (OADM).
`FIG. 1 illustrates a conventional OADM 110 arranged to
`drop and add only a single optical channel. OADM 110 has
`tWo input ports 120 and 130, and tWo output ports 140 and
`150. Input port 120 carries multiplexed optical channels k1
`through KN from the communication line and input port 130
`carries a local optical channel kmdd that is to be added to the
`?ber link. Output port 140 contains all the optical channels
`k1 through KN from the input port 120, except the optical
`channel KMW that has been extracted and essentially
`replaced by kmdd. The dropped optical channel 7»
`i-drop
`emerges from output port 150.
`Some simple OADM’s of the type shoWn in FIG. 1 are
`?xed, in that only a preassigned optical channel can be
`added/dropped; in more sophisticated arrangements, a
`recon?gurable system architecture may be used to imple
`ment a tunable optical channel OADM that is able to change
`the Wavelength that is added and/or dropped.
`A different architecture is conventionally required When
`an access node in an optical communication system has to
`add/drop more than one channel. FIG. 2 illustrates a solution
`based on a cascade of single channel OADMs at the access
`node. The multiplexed optical channels are introduced at
`input port 220 of a ?rst OADM 210-1. The output port 240
`of OADM 210-1 is connected to the input port of a second
`OADM 210-2. The output port 260 of OADM 210-2 carries
`all the multiplexed optical channels to be transmitted on the
`communication channel. OADMs 210-1 and 210-2 have
`channel add ports 230-1 and 230-2 and channel drop ports
`250-1 and 250-2, respectively. Each OADM may be of the
`?xed channel type or tunable channel type.
`While FIG. 2 shoWs, for illustrative purposes, a solution
`With tWo OADMs that can add/drop one channel each, for a
`total of tWo channels, more than tWo OADMs can be
`inserted at the access node using the serial cascade approach.
`The cascading solution, hoWever, suffers from a high
`through loss for the channels that have to pass all the
`
`30
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`35
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`40
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`45
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`55
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`60
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`65
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`2
`OADMs in the cascade from the communication system
`input 220 to the output 260.
`FIG. 3 illustrates another conventional solution based on
`an OADM 310 that can add and drop multiple channels
`Within a single device. An input port 320 carries the multi
`plexed optical channels from the communication line While
`input port 330 carries the multiplexed local optical channels
`that are to be added to the ?ber link. The local channels to
`be added, Which are available from transmitters 380-1
`through 380-N, are combined in a multiplexer 360 and
`applied to input 330. Output port 340 carries multiplexed
`optical channels consisting of all the added optical channels
`from input port 330 and the through channels from the
`system input port 320. The dropped optical channels emerge
`from output port 350 as a group of channels, and must be
`separated in a demultiplexer 370 before being available to
`receivers 390-1 through 390-N.
`The multiple channel OADM of FIG. 3 eliminates the
`high through loss associated With the cascading solution of
`FIG. 2; hoWever, it requires additional hardWare for multi
`plexing (With multiplexer 360) and demultiplexing (With
`demultiplexer 370) the added and dropped channels. If the
`added and dropped channels are a ?xed subset, then only the
`required subset of optical channel transmitters in transmit
`ters 380-1 through 380-N and subset of optical receivers in
`receivers 390 through 390-N are populated. This is an
`ef?cient solution. HoWever, in a dynamic optical commu
`nication system, the added and dropped channels can change
`over time, according to demand. Complete netWork ?ex
`ibility necessitates full population of all the optical channel
`transmitters 380-1 through 380-N and receivers 390-1
`through 390-N. This is a very expensive solution, as only a
`subset of channels Will typically be used at any given time,
`While the others remain idle. Tunable transmitters and
`receivers cannot be used With the multiplexers and
`demultiplexers, due to the ?xed channel assignment betWeen
`the input and output ports of such devices. Passive combin
`ing and splitting can be used, but the poWer budget for that
`solution is impracticable.
`
`SUMMARY OF THE INVENTION
`
`In accordance With the present invention, architectures for
`implementing an OADM are based upon and use the pro
`grammable optical multiplexer/demultiplexer as described
`in co-pending application Ser. No. 09/944,800 ?led concur
`rently hereWith and assigned to the same assignee as the
`present application. As described in the aforementioned
`co-pending application, a programmable optical demulti
`plexer is arranged to receive a multiplexed optical signal
`containing a plurality of separate channels, each With an
`associated Wavelength, and independently assign each input
`optical channel to a desired output port. Likewise, a pro
`grammable optical multiplexer is arranged to receive a
`plurality of separate optical channels, each With an associ
`ated Wavelength, and combine the different Wavelengths into
`a single multiplexed optical signal that is made available at
`the multiplexer output port.
`The present invention realiZes a tunable (recon?gurable)
`OADM that provides multiple drop ports and multiple add
`ports by Which desired channels can be removed from, or
`added to, a composite optical signal. The channels added to
`and dropped from the optical signal can be individual
`channels (With a single Wavelength per channel) and there
`fore enabled for direct connection to ?xed (or tunable)
`optical transmitters and optical receivers, respectively.
`Alternatively, the channels added to and dropped from the
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 6
`
`

`
`US 6,950,609 B2
`
`3
`optical signal can themselves be multiplexed, enabling more
`advanced features. The OADM of the present invention
`provides a loW loss architecture for all the optical signals
`that traverse through the device, as required for transparent
`optical netWorks.
`In one embodiment of the present invention, a program
`mable demultiplexer is arranged to receive an input signal
`containing components at X different Wavelengths from an
`optical input port, and distribute the input signal components
`among K output ports. K-l of the output ports are the “drop”
`ports of the OADM, and cumulatively contain W different
`Wavelengths. The remaining port, Which is the “through
`port” that carries the Z Wavelengths not dropped from the
`original input signal, is connected to the ?rst port of an M
`port programmable multiplexer having M-1 other input
`15
`ports. The remaining M-1 ports are the “add” ports of the
`OADM, Which cumulatively receive v different Wavelengths
`to be added by the OADM. By appropriately controlling the
`demultiplexer and multiplexer, the OADM can indepen
`dently both drop and add channels to the optical signal,
`resulting in an output signal containing y Wavelengths. In the
`foregoing description, v, W, x, y and Z are integers, Where
`x+v—W=y and Z=x—W=y—v.
`In another embodiment of the present invention, the
`OADM includes additional multiplexers and/or
`demultiplexers, so that (a) the channels to be added are ?rst
`themselves multiplexed before being added to the optical
`signal at the OADM, or (b) the channels to be dropped are
`initially grouped so that multiple channels are dropped at
`once, and the group of dropped channels is then demulti
`plexed to recover individual dropped channels.
`
`25
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`35
`
`40
`
`The present invention Will be more fully appreciated by
`consideration of the folloWing detailed description, Which
`should be read in light of the draWing in Which:
`FIG. 1 is an illustration of a single channel OADM;
`FIG. 2 is an illustration of a cascade of single channel
`OADMs for accessing multiple channels;
`FIG. 3 is an illustration of a multiple channel OADM;
`FIGS. 4(a) and (b) are illustrations of a programmable
`multiplexer and demultiplexer (respectively) that are the
`building blocks of the present invention;
`45
`FIG. 5 is an illustration of an embodiment of an OADM
`arranged in accordance With the principles of the present
`invention and that includes a programmable demultiplexer
`folloWed by a programmable multiplexer;
`FIG. 6 is an illustration of an alternative embodiment of
`the OADM using a cascade of programmable multiplexers
`and demultiplexers for greater channel count;
`FIG. 7 is an illustration of another embodiment of the
`OADM using a single programmable demultiplexer With
`optical circulators; and
`FIG. 8 is an illustration of an alternative embodiment of
`an OADM that uses a Wavelength distribution sWitch With
`several input ports and several output ports, Where optical
`channels do not occur on more than one input port.
`
`55
`
`DETAILED DESCRIPTION
`
`The present invention describes neW architectures for
`implementing an OADM that advantageously makes use of
`the programmable optical multiplexer/demultiplexer
`described in applicant’s co-pending application identi?ed
`above. For the purposes of completeness, the functionality
`
`65
`
`4
`of that element is described in connection With FIGS. 4(a)
`and 4(b) herein. As illustrated in FIG. 4(a), a programmable
`optical multiplexer 420 has K input ports 410-1 through
`410-K and a single output port 430. Each of the input ports
`can receive an optical signal containing one or more optical
`channels from the set of }\.-1 through k-N, provided the
`channels of each input port are different. The optical signals
`are combined in the multiplexer, and emerge as a composite
`signal at output port 430 containing all the optical channels
`}\.-1 through k-N. Operationally, multiplexer 420 establishes
`a unique pathWay for each optical channel betWeen any one
`of the input ports 410-1 through 410-K and the output port
`430, as prescribed by a control signal 440, physically
`preventing the detrimental possibility of combining tWo
`optical channels operating on the same Wavelength from tWo
`different input ports.
`The programmable multiplexer of FIG. 4(a) can also be
`operated in the reverse direction and function as a program
`mable demultiplexer 400, as shoWn in FIG. 4(b). A single
`input port 450 receives a multiplexed optical signal contain
`ing a plurality of Wavelengths or channels, and separates the
`signal so that one or more of the channels appears at each of
`the output ports 460-1 through 460-M. The assignment of
`speci?c channels to output ports is independent, and is
`determined by a control signal on input 470. In this
`demultiplexer, note that, if desired, one or more Wavelengths
`applied at input port 450 can be output from that same port,
`instead of being output from one of the other output ports
`460-1 through 460-M. This capability Will be useful in
`connection With the OADM arrangement illustrated in FIG.
`7 and described more fully beloW.
`From the foregoing description, it is seen that the pro
`grammable multiplexer 420 of FIG. 4(a) and the program
`mable demultiplexer 400 of FIG. 4(b) can each be imple
`mented in the same hardWare device (assuming that K=M).
`It is to be noted that the device can be operated so that it
`concurrently acts as a multiplexer and as a demultiplexer.
`Using the demultiplexer of FIG. 4(b) as an example, in
`addition to the processing of Wavelengths as described
`previously, Wavelengths can be introduced into the device
`through ports 460-1 through 460-M at the same time that
`Wavelengths are being output from those ports. HoWever,
`each Wavelength being processed in the device must have a
`unique path betWeen an input port and an output port, Which
`path may be traversed bi-directionally.
`FIG. 5 illustrates an embodiment of an OADM arranged
`in accordance With the present invention, using a program
`mable multiplexer and demultiplexer of FIGS. 4(a) and 4(b).
`An input port 510 carries the multiplexed optical channels
`}\.-1 through k-N of the communication system. A program
`mable demultiplexer 520 assigns the optical channels to the
`various output ports 530-1 through 530-K. The optical
`channels that are transmitted through the OADM (i.e., not
`dropped) are assigned to a ?rst one of the output ports,
`namely output port 530-1. The dropped channels are
`assigned to the remaining ports, namely ports 530-2 through
`530-K. Typically, the dropped channels are detected at the
`drop site, and therefore each drop port 530-2 through 530-K
`is usually terminated by an optical receiver 531-2 through
`531-K. In this operation mode, a single dropped channel is
`assigned to an available drop port, so that up to K-l
`channels can be dropped. (Note that multiple channels can
`be assigned to a drop port, as described more fully beloW.)
`Also note that optical detection may, instead of being
`performed directly at the drop port, be performed at a remote
`location, such as at a customer’s premises. In that case,
`several dropped channels can be assigned to the drop port
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 7
`
`

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`US 6,950,609 B2
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`5
`that leads to the customer for demultiplexing and detection
`of the multiple optical channels.
`Still referring to FIG. 5, output 530-1 is called a “through
`route”, and contains one or more of the optical channels that
`Were present in the input signal on line 510, but of course
`does not include the channels that Were dropped. The
`through route on output 530-1 is connected to the input port
`540-1 of a programmable multiplexer 550, that has an
`additional M-l input ports 540-2 through 540-M to Which
`the “add channels” are introduced. Typically, a tunable
`optical channel transmitter 541-2 through 541-M is con
`nected to each add input port and arranged to provide a
`signal containing a single optical Wavelength. HoWever, it is
`possible to add several multiplexed optical channels at each
`port 540-2 through 540-M, Which may, for example, origi
`nate from a remote site, such as a customer’s premise.
`Output port 560 carries the multiplexed optical channels,
`comprised of the through channels and the added channels.
`A control signal 570 directs the programmable demulti
`plexer 520 and multiplexer 550 to carry out the Wavelength
`add and drop to and from the proper ports. In this
`embodiment, the add and drop channels are processed by
`tWo different devices, namely programmable demultiplexer
`520 and programmable multiplexer 550, enabling the add
`channel Wavelengths to either be different from the drop
`channels Wavelengths or alternatively, have some drop chan
`nel Wavelengths in common With the add channel Wave
`lengths.
`If the number of added and dropped channels exceeds the
`number of available add ports M-1 and drop ports K-l of
`the embodiment of FIG. 5, it is possible to cascade the
`programmable multiplexers and demultiplexers, as shoWn in
`FIG. 6. The input optical channels at the OADM are
`introduced at port 610, and enter the ?rst programmable
`demultiplexer 620. The through channels exit at port 630-1,
`Which is connected to input port 640-1 of programmable
`multiplexer 670, and emerge at the output port 695. The
`signal path of the through channels is identical to the signal
`path of the through channels in the embodiment of FIG. 5.
`Drop channels exit programmable demultiplexer 620 at
`one of the other ports 630-2 through 630-K, and one or more
`of the outputs can contain multiple channels. For example,
`as shoWn in FIG. 6, outputs 630-3 and 630-2 each contain
`multiple channels, and are accordingly each connected to a
`second programmable demultiplexer 650-3 and 650-2,
`respectively. The second programmable demultiplexer
`increases the number of available drop ports. Such an
`arrangement is possible due to the ability of the program
`mable demultiplexer 620 to direct more than one channel to
`one or more of the output ports 630. In this embodiment, it
`is assumed that the second programmable demultiplexers
`650-3 and 650-2 each direct a single the channel to a distinct
`output port for detection. HoWever, it is possible to again
`iterate (i.e., nest) the process, if yet additional ports are
`needed.
`Still referring to FIG. 6, an example of the path taken by
`a dropped channel is as folloWs: ?rst, the channel exits
`programmable demultiplexer 620 from port 630-3, as part of
`a group of dropped channels. Port 630-3 is connected to
`second programmable demultiplexer 650-3, Where the group
`of dropped channels is then demultiplexed, so that the
`dropped channel may illustratively exit from port 660-3-1.
`By connecting each of K-l ports 630-2 through 630-K to a
`second programmable demultiplexer (650-2 through 650-K)
`that has K output ports, the total number of available drop
`ports can therefore increase up to K(K—1). Note hoWever,
`that the OADM of FIG. 6 may also be implemented such that
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`6
`programmable demultiplexers 650-2 through 650-K having
`different characteristics than the ?rst programmable demul
`tiplexer 620, e.g., a greater or lesser number of ports.
`In the arrangement of FIG. 6, the same cascading solution
`is implemented for the add channels as for the drop
`channels, just described. In particular, a series of multiplex
`ers 690-2 through 690-M are each arranged to receive a
`plurality of add channels. For example, multiplexer 690-2
`receives add channels 690-2-1 through 690-2-M, multi
`plexer 690-3 receives add channels 690-3-1 through 690-3
`M, and so on. An example of the path of an added channel
`is as folloWs: the added channel is introduced at port
`680-2-1, Which is connected to programmable multiplexer
`690-2, Which is subsequently connected to input port 640-2
`of programmable multiplexer 670, Which leads to the output
`port 695. By virtue of the arrangement of FIG. 6, the number
`of available add ports can therefore increase up to M(M—1).
`As With the embodiment of FIG. 5, the OADM of FIG. 6
`may drop and add different channels. Note that While
`programmable multiplexers 690-2 through 690-M can be the
`same as programmable multiplexer 670, they do not have to
`be. For example, if desired, some or all of the multiplexers
`690-2 through 690-M can be ?xed rather than
`programmable, in order to reduce cost. Likewise, program
`mable demultiplexers 650-2 through 650-K are not required
`to be the same as programmable demultiplexer 620. In FIG.
`6, individual control signals to the programmable demulti
`plexers and programmable multiplexers are not explicitly
`shoWn, in order to reduce complexity of the draWing.
`FIG. 7 illustrates another embodiment of an OADM in
`accordance With the present invention, this embodiment
`utiliZing a single programmable multiplexer/demultiplexer
`730 operating in a bi-directional mode, as described
`previously, and a plurality of circulators for separating the
`add and drop channels. An input port 710 carrying the input
`multiplexed WDM channels is connected to a ?rst optical
`circulator 715, Which directs the input channels to input port
`720 of the programmable demultiplexer 730. The control
`signal 760 applied to programmable demultiplexer 730 is
`arranged so that each channel to be dropped is directed to
`any available one of the output ports 740-1 through 740-K
`of demultiplexer 730. Each output port 740-1 through 740-K
`is attached to a corresponding optical circulator 741-1
`through 741-K that directs the dropped channel to the
`corresponding drop port 742-1 through 742-K. An example
`of a drop path is from the input 710, via circulator 715 to
`input port 720 of programmable demultiplexer 730, to a
`demultiplexed output port 740-2 and via optical circulator
`741-2 to drop port 743-2.
`In the arrangement of FIG. 7, added channels are intro
`duced from add ports 743-1 through 743-K, and are con
`nected to respective ports 740-1 through 740-K of program
`mable multiplexer 730 via the corresponding optical
`circulators 741-1 through 741-K. The added channels
`emerge from port 720 Where they are directed to output
`multiplexed port 750 via optical circulator 715.
`Through channels enter programmable demultiplexer 730
`via port 720 and are routed in programmable demultiplexer
`to emerge back on the input port 720. Optical circulator 715
`directs the through channel traffic returning from the pro
`grammable demultiplexer 730 to the output multiplexed port
`750.
`As previously described, programmable demultiplexer
`730, When operating in a bi-directional mode, must be
`arranged such that each Wavelength being processed in the
`device has a unique path betWeen an input port and an output
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 8
`
`

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`US 6,950,609 B2
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`10
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`15
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`25
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`7
`port. Thus, the embodiment of FIG. 7 requires that each
`added Wavelength be introduced at the same port at Which
`the same Wavelength is dropped.
`FIG. 8 illustrates another OADM embodiment operated
`Without Wavelength contention, utilizing the Wavelength
`sWitch shoWn in FIG. 4 of the above-mentioned co-pending
`application. The Wavelength sWitch shoWn in the co-pending
`application has r input ports and s output ports, and is
`arranged so that any particular Wavelength can enter the
`sWitch at one of the input ports and emerge from any one of
`the output ports. In FIG. 8, OADM 820 con?gures the
`Wavelength sWitch to have a plurality of input ports 810 and
`850-1 through 850-P (so that P+1=r), and a plurality of
`output ports 830 and 840-1 through 840-M (so that M+1=s).
`Input port 810 carries the WDM input from a communica
`tion system, and input ports 850-1 through 850-P are the add
`ports. Output port 830 carries the WDM output to the
`communication system and the remaining output ports
`840-1 through 840-M are the drop ports. Control signal 860
`determines the pathWay taken Within OADM 820 for each
`Wavelength, betWeen an input port and an output port. In this
`embodiment, any single input optical Wavelength channel
`may appear at only one input port, preventing a particular
`optical channel from being both dropped and added concur
`rently by the OADM. This is because any Wavelength to be
`dropped must inherently have been introduced into the
`OADM via input port 810, and that same Wavelength cannot
`also be concurrently introduced at one of the add ports 850-1
`through 850-P.
`The path of a dropped channel is from the input port 810
`through the programmable demultiplexer 820, to an avail
`able drop port of 840-1 through 840-M. The path of the
`through channels is from input port 810 through program
`mable demultiplexer 820 to output port 830. The path of the
`added channels is from an available input port 850-1 through
`850-P through programmable demultiplexer 820 to output
`port 830.
`Although the present invention has been described in
`accordance With the embodiments shoWn, one of ordinary
`skill in the art Will readily recogniZe that there could be
`variations to the embodiments and those variations Would be
`Within the spirit and scope of the present invention.
`Accordingly, many modi?cations may be made by one of
`ordinary skill in the art Without departing from the spirit and
`scope of the appended claims.
`What is claimed is:
`1. An optical add/drop multiplexer (OADM) arranged to
`add v optical channels to, and remove W optical channels
`from, an input Wavelength division multiplexed optical
`communication signal containing X optical channels, in
`order to generate an output Wavelength division multiplexed
`optical communication signal containing y optical channels,
`said OADM comprising
`a programmable demultiplexer having an input port and K
`55
`output ports, said programmable demultiplexer
`arranged to receive said input signal containing said x
`optical channels on said input port and distribute one or
`more of said channels to each of said K output ports,
`Wherein one of said K output ports is a through port
`containing Z optical channels and Wherein the remain
`ing K-1 of said output ports are the drop ports of said
`OADM, and Wherein said K-1 output ports cumula
`tively contain said W optical channels,
`a programmable multiplexer having M input ports and a
`single output port, said programmable multiplexer
`arranged to receive said Z optical channels on one of
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`40
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`65
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`8
`said input ports and said v optical channels on the
`remaining M-1 of said input ports, and combine all of
`said channels on said M input ports onto said output
`port, to generate said output Wavelength division mul
`tiplexed optical communication signal containing said
`y optical channels, and
`means for controlling (a) said demultiplexer to route
`desired drop and through channels from said input port
`of said OADM to said K output ports and (b) said
`multiplexer to route desired add and through channels
`from said M input ports to said output port of said
`OADM,
`Wherein M and K are integers equal to or greater than 2
`and Wherein v, W, x, y and Z are integers.
`2. The invention de?ned in claim 1 Wherein each channel
`from said W optical channels are distributed to a unique one
`of said K-1 output ports of said programmable demulti
`plexer.
`3. The invention de?ned in claim 1 Wherein each channel
`from said v optical channels is received by a unique one of
`said M-1 input ports of said programmable multiplexer.
`4. The invention de?ned in claim 1 Wherein more than one
`channel from said W optical channels is distributed to at least
`one of said K-1 output ports of said programmable demul
`tiplexer.
`5. The invention de?ned in claim 1 Wherein more than one
`channel from said v optical channels is received by at least
`one of said M-1 input ports of said programmable multi
`plexer.
`6. The invention de?ned in claim 4 Wherein one or more
`of said K-1 output ports that contains more than one channel
`are each applied to a respective additional demultiplexer.
`7. The invention de?ned in claim 5 Wherein one or more
`of said M-1 input ports that contains more than one channel
`are each received from a respective additional multiplexer.
`8. An optical add/drop multiplexer (OADM) arranged to
`add a ?rst group of one or more optical channels to, and
`remove a second group of one or more optical channels
`from, an input Wavelength division multiplexed optical
`communication signal containing a third group of one or
`more optical channels, in order to generate an output Wave
`length division multiplexed optical communication signal
`containing a fourth group of one or more optical channels,
`said OADM comprising
`a programmable Wavelength sWitch having (a) a primary
`input port, (b) M-1 additional input ports constituting
`the add ports of said OADM, (c) a primary output port,
`and (d) K-1 additional output ports constituting the
`drop ports of said OADM, said programmable sWitch
`arranged to
`receive said input signal containing said
`third group of optical channels on said primary input
`port and distribute one or more of said channels to each
`of said K-1 additional output ports, Wherein said K-1
`output ports cumulatively contain said second group of
`optical channels, and (ii) combine all of said channels
`on said M-1 additional input ports onto said primary
`output port, to generate said output Wavelength division
`multiplexed optical communication signal containing
`said fourth group of optical channels, and
`means for controlling (a) a demultiplexer to route desired
`drop and through channels from said input port of said
`OADM to said K output ports and (b) a multiplexer to
`route desired add and through channels from said M
`input ports to said output port of said OADM,
`Wherein M and K are integers equal to or greater than 2.
`9. An optical add/drop multiplexer (OADM) arranged to
`add a ?rst plurality of optical channels to, and remove a
`
`Cisco Systems, Inc.
`Exhibit 1051
`Page 9
`
`

`
`US 6,950,609 B2
`
`second plurality of optical channels from, an input Wave
`length division multiplexed optical communication signal in
`order to generate an output Wavelength division multiplexed
`optical communication signal, said OADM comprising
`a programmable demultiplexer having an input port and K
`output ports, said programmable demultiplex