0001
`
`Capella 2014
`Cisco v. Capella
`IPR2014-00894
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 1 of 6
`
`US 6,657,770 B2
`
`FIG.
`
`1
`
`PRIOR ART
`
`
`
`FIG. 2
`
`PRIOR ART
`
`
`
`0002
`0002
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 2 of 6
`
`US 6,657,770 B2
`
`FIG. 3(A)
`
`FIG. 3(3)
`
`
`
`
`320
`
`PROGRAMMABLE
`
`330
`
`
`
`
`PROGRAMMABLE
`DEMUX
`
`360
`
`FIG. 4
`
`WAVELENGTH
`
`SWITCH
`
`0003
`0003
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 3 of 6
`
`US 6,657,770 B2
`
`FIG.5
`
`
`
`CONTROLSIGNAL 580
`
`
`
`0004
`0004
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 4 of 6
`
`US 6,657,770 B2
`
`FIG.6
`
`
`
`CONTROLSIGNAL 570
`
`0005
`0005
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 5 of 6
`
`US 6,657,770 B2
`
`0006
`0006
`
`

`
`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 6 of 6
`
`US 6,657,770 B2
`
`FIG. 8
`
`PROGRAMMABLE
`
`DEMUX
`
`'
`
`DEMUX
`
`PROGRAMMABLE
`
`DEMUX
`
`PROGRAMMABLE
`
`PROGRAMMABLE
`
`DEMUX
`
`840—K—1
`
`840—K-2
`
`840—K—3
`
`840-K—K
`
`0007
`0007
`
`

`
`US 6,657,770 B2
`
`1
`PROGRAMMABLE OPTICAL
`MUIfl‘!PLEXI§Rr"|)l£MULTII’I.EXER
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`'l'his application claims priority of Provisional Applica-
`tion Ser. No. 6Ui’3UU,272 filed on Jun. 22, 2001.
`
`TECIINICAL FIELD
`
`The present invention relates to fiber optic networks, and
`more particularly to fiber optic wavelength division multi-
`plexers and demultiplexers.
`BACKGROUND OF THE INVENTION
`
`The transmission capacity of fiber-optic communication
`systems has increased significantly by use of wavelength
`division multiplexing (WDM) techniques. In a WDM com-
`ntunication system, multiple channels, where each channel
`is differentiated by using a unique wavelength of light, carry
`modulated optical signals in a single optical fiber between a
`transmitter and a receiver. The transmitter uses an optical
`multiplexer to combine multiple channels into the fiber for
`transmission. and the receiver uses an optical demultiplexer
`to separate the optical channels for detection. FIG. 1 illus-
`trates a typical optical dernultiplexer (demux) 120 contain-
`ing a single input port 110 and multiple output ports 130-1
`through 130-N, where each optical channel from the input
`port is mapped to a unique output port in sequential order
`(channel
`1 will exit from port 130-1, channel 2 from port
`130-2, etc.}. Optical multiplexers are simply demultiplexers
`operated in the reverse direction, where a specific wave-
`length has to be supplied to the correct input port to emerge
`at the output port as a multiplexed signal.
`It is expected that in the foreseeable future, communica-
`tion systems will evolve to communication nctworlo: con-
`sisting of multiple access nodes, each containing a WDM
`transmitter andior receiver, that are interconnected in some
`prescribed fashion (e.g., ring or bus) or arbitrarily {e.g.,
`mesh). Information How between two access nodes will be
`carried on an available optical wavelength that is assigned
`by a protocol according to network availability. The trans.-
`mitting node will have to employ a bank of lasers at different
`wavelengths as available sources. all connected properly to
`the multiplexers ports, utilizing only a small fraction of the
`lasers at any given time for communication. This is clearly
`an expensive solution, as most of the hardware is lying idle.
`Alternatively, wavelength tunable lasers can be used.
`However, tunable lasers cannot be Connected directly to the
`optical multiplexer, as the multiplexer's input ports can only
`accept the correct wavelength to function properly.
`FIG. 2 illustrates a possible solution, consisting of a
`switching matrix 220 added to the node, whose role is to
`route the tunable lasers's signals 210-1 through 210-M to the
`correct input ports 230-1 through 230-N of multiplexer 240.
`This added hardware is again costly.
`It is clear that
`the
`receiving node will also have to address the same issues for
`the demultiplexing and detection task.
`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, a programmable
`optical mulliplcxerldemultiplexer can establish a reconfig-
`urable connection between any two ports from the multiple
`device ports, independently for each optical wavelength that
`is inserted by the input ports.
`In one embodiment of the present invention, a program-
`mable demultiplexer is arranged to receive an input signal
`
`ll!
`
`I5
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`containing components at N different wavelengths from an
`optical input port, and distribute the input signal components
`among K output ports. The input signal is collimated by a
`particular lens in a microlens array, which lens is aligned to
`the input port. The microlens array contains K additional
`lenses that are aligned to the K output ports. The resultant
`collimated beam originating from the input port is then made
`incident on a diffraction grating, which angularly disperses
`the composite optical signal according to wavelength,
`thereby fon'ning N separate beams having different wave-
`lengths and distinct propagation angles. Each of the N
`separate beams propagates to a single lens that is arranged
`to collect all the beams and provide, for each wavelength, a
`converging beam focused onto a particular micro-mirror in
`an array containing N micro-mirrors. Each mirror in the
`array is individually controlled to reflect the incident beam
`(representing a corresponding wavelength]
`in a desired
`direction, such that
`it will (a) re-enter the lens, (b) be
`collimated by the lens and redirected to a dilTerent location
`on the diffraction grating, and (c) be eventually coupled
`from the diffraction grating through a particular lens in the
`micro—lens array to a desired output port (the particular
`micro-lens is aligned to the desired output port). Generally,
`the number of output ports K and optical wavelength com-
`ponents N are independent. The dernultiplexer can be
`designed to operate in the regime where K=N, so that each
`wavelength component can be assigned to any output port.
`The invention can also be operated in a mode where K<N,
`in which case more than one wavelength is applied to an
`output port, or in a mode where K:-N, in which case one or
`more output ports are not used. In any event, the present
`invention enables assignment of any wavelength to any
`output port.
`The embodiment just described can be operated in the
`"reverse" direction,
`in order
`to act as a programmable
`multiplexer, rather than as a demultiplexer. In the multi-
`plexer arrangement, K input signals each containing one or
`more different wavelengths, are received from a plurality of
`K optical input ports and must be combined and made
`available at
`a single output port. The K input signals
`cumulatively contain a total of N different wavelengths, or,
`stated differently, any particular wavelength component can
`exist at only one of the K input ports, or contention will
`occur. Each input signal is collimated by a respective lens in
`a mierolens array that contains K+l
`lenses. One lens is
`aligned with the output port, while the remaining lenses are
`aligned each to a corresponding input port. The resultant
`collimated beam originating from each input port is then
`made incident on a dilIraction grating, which dillracts the
`optical signal as a function of its wavelength. The dilfractiori
`grating is arranged such that all of the separate beams, which
`have different wavelengths and therefore distinct propaga-
`tion angles, propagate to a single lens that collects all the
`beams and provides, for each wavelength, a converging
`beam focused onto a particular micro-mirror in an array.
`Each mirror in the array is individually controlled to rellect
`the incident beam (representing a corresponding
`wavelength) in the desired direction, such that
`it will (a)
`re-enter the lens, (b) be collimated by the lens and redirected
`to a single location on the diffraction grating, and (c) be
`eventually coupled from the diffraction grating to the output
`port through the particular lens in the micro-lens array that
`is aligned with the output port. Here again, in general, the
`number of input ports K and optical wavelength components
`N are independent. The multiplexer can be designed to
`operate in the regime where K=N, so that each wavelength
`component can originate at any input port. The invention can
`
`0008
`0008
`
`

`
`US 6,657,770 B2
`
`3
`also be operated in a mode where K<N, in which case more
`than one wavelength is applied to an input port, or in a mode
`where K:-N, in which case one or more input ports are not
`used. In any event, the present invention enables multiplex-
`ing (combining) of all input wavelengths originating at the
`K input ports to the output port.
`BRIEF DESCRIPTION 01‘ THE DRAWINGS
`
`The present invention will be more fully appreciated by
`consideration of the following detailed description, which
`should he read in light of the drawing in which:
`FIG. 1 is an illustration of the operation of a conventional
`optical wavelength demultiplexer;
`FIG. 2 is an illustration of the conventional required
`hardware for multiplexing multiple channels with tunable
`wavelength sources;
`FIG. 3(a) is an illustration of the general operation of the
`present invention, when operating as a programmable opti-
`cal wavelength multiplexer, while FIG. 3(b) is an illustration
`of the general operation of a the present invention, when
`operating as a programmable optical wavelength dcmulti~
`plexer;
`FIG. 4 is an illustration of a wavelength switch with
`multiple input ports and multiple output ports;
`FIG. 5 is an illustration of an embodiment of the present
`invention using tilting micro-mirrors and functioning as a
`programmable demultiplexer;
`FIG. 6 is an illustration of an alternative embodiment of
`the present invention using tilting micro-mirrors and func-
`tioning as a programmable demultiplexer;
`FIGS. 7(0) and 7(1)) are lLlilIB]'€l'lI views of yet another
`embodiment of the present invention using shift-inducing
`micro—prisms and functioning as a programmable demulti—
`plexer; and
`FIG. 8 is an illustration of a cascade of programmable
`demttltiplexers for increasing the output channel count.
`DI.-‘.’l‘AILl:".D DESCRIPTION
`
`The programmable optical multiplexcrldemu[tiplexer in
`accordance with the present invention Plovides for wave-
`length routing between the input and output ports.
`It
`is
`designed for selectively multiplexing, demultiplcxing and
`switching of optical channels in dense wavelength division
`multiplexed (DWDM) communication systems.
`In this
`regard, a demultiplexer can be thought of as a 1xK wave-
`length switch (1 input and K outputs). while a multiplexer
`can be thought of as a Kxl wavelength switch (K inputs and
`1 output}.
`FIG. 3(a) is a diagram illustrating the overall functioning
`of the present
`invention when operated in programmable
`multiplexer mode. Programmable multiplexer 320 includes
`a plurality of input ports 310-1 and 310-k which are com-
`bined and output [rom output port 330. In accordance with
`the invention,
`it
`is desired that any optical channel or
`combination of channels can be inserted at any input port
`310-1 through 310-}? and emerge at
`the output port 330.
`Control of the multiplexing process, which is the capability
`that makes the multiplexer "programmable" is achieved by
`virtue of a control
`input 340, which establishes a unique
`pathway in multiplexer 320 for each optical channel
`between any one of its input ports and its output pon.
`Multiplexer 320, as described more fully below, is arranged
`such that it physically prevents the detrimental possibility of
`combining two optical channels operating on the same
`wavelength from two different input ports.
`
`4
`As shown in FIG. 3(3)), when operating in programmable
`demultiplexer mode, multiplexer 320 is operated in the
`reverse direction. A programmable dcmultiplexer 360 has
`input port 350 arranged to receive an optical communica-
`tions signal containing multiple optical wavelengths. The
`individual wavelengths are then independently assigned to
`the k output ports, 370-1 through 370-k, by the program-
`mable demultiplexer, as prescribed by the control signal 380.
`Note that the number of input or output ports, k, may be
`equal to or dillerent from the number of DWDM channels.
`FIG. 4 illustrates,
`in general terms, another operation
`mode wherein the present
`invention implements a wave-
`length switch 420 having multiple input ports 410-1 through
`410-1’ and multiple output ports 430-1 through 430-3, where
`r and s can be different
`integers. The different optical
`channels are distributed among the input ports 410-1
`through 410-1‘, where each port may carry multiple channels,
`but no channel can appear on two different
`input ports
`simultaneously. Each optical channel
`is routed indepen-
`dently to its required output destination port, 4-30-I though
`430-S, as prescribed by the control signal 440.
`FIG. 5 is an illustration of an embodiment of the present
`invention using tilting micro-mirrors and functioning as a
`programmable demultiplcxer as was described generally in
`connection with FIG. 3(1)). Input port 510, typically a single
`mode optical
`fiber, carries an input optical signal
`that
`contains multiple optical wavelengths 3.-1 through }.-N of a
`DWDM communication system. To accomplish the demul-
`tiplexer function, it is desired that each of these wavelengths
`be assigned to one of the various output ports 570-1 through
`5704:, as instructed by a provided control signal 380 of FIG.
`305). Note that it is possible for more than one wavelength
`to be assigned to the same output port, and that the number
`k of output ports does not have to be equal to the number N
`of wavelengths in the input optical signal.
`As shown in FIG. 5, the optical beam 502 emerging from
`input port 510 is rapidly diverging, due to diffraction effects.
`Amicro-lens array 520 is aligned with and spaced apart from
`input port 510, as well as with output ports 570-1 through
`5704:, such that the ports are at the micro-lens front focal
`plane, denoted as plane P5-1 by the dotted line in the figure,
`and each port is on the optical axis of its matching micro-
`lens. The effect of the individual micro—lcns that is aligned
`to the input port 510, is to collimate the diverging beam 502
`to a wide beam 505, whose diffraction effects are greatly
`reduced. A high numerical aperture lens 530, whose clear
`aperture contains all the micro-lenses in array 520, focuses
`the beam 505 at its back focal plane, denoted as plane P5-2
`by the dotted line in the Iigure. The beam then continues to
`diverge.
`The diverging beam 508 is collimated by a second lens
`540, that is placed such that its front focal plane coincides
`with plane P5-2, resulting in the beam 512 that still contains
`all of the input optical channels. Beam 512 is directed onto
`a reflection dillraction grating 550 that introduces wave-
`length dependent diffraction and serves to separate the
`optical channels, so that each channel can be independently
`accessed. An illustrative diffracted beam 515, propagating at
`a unique direction or angle with respect
`to grating 550,
`contains only a single optical channel at a particular wave-
`length ?.-j. The diffracted beam 515 propagates back through
`the lens 540, which focuses the beam 518 at the lcns's front
`focal plane, plane P5—2. There will be N such beams, one for
`each wavelength ).-1 through l.-N, each propagating at a
`slightly dilferent direction. It
`is thus seen that the optical
`subsystem consisting of the lens 54-0 and diffraction grating
`550 serves to spatially separate the optical channels at plane
`
`ill
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`0009
`0009
`
`

`
`US 6,657,770 B2
`
`5
`in the field can design the optical
`P5-2. One prolicient
`system to provide the sullicient spatial separation of the
`wavelength channels at this plane. Note that FIG. 5 traces
`only the single wavelength }‘.-j for simplicity.
`A micro—mirror array 560 is placed at plane P5—2, such
`that each optical channel
`is focused on a separate mirror
`element. Each rnirror can be tilted by an electrical control
`signal 580, such that the reflected beam 522, now diverging,
`is propagating at a new, desired direction.
`In the arrangement of FIG. 5, diverging beam 522 is
`collimated by lens 540, and the oollimated beam 525 is
`diffracted olf reflective grating 550, resulting in beam 528
`that
`is propagating back towards the device output ports.
`Lens 540 focuses beam 528, convening it to a converging
`beam 532 which focuses the beam at plane P5-2 (front focal
`plane of lens 540). Beam 532 diverges after passing plane
`I-"5-2 and is recollimated by lens 530, resulting in beam 535.
`Beam 535 is focused by one of the micro-lenses of the
`rnicro-lens array 520, with the focused beam 538 at plane
`P5-1 and coupling to the desired one of the output ports
`570-1 through 570-K. The output port is selected for each
`wavelength by the beam propagation direction that
`is
`imparted by the tilt ofthe individual mirrors in mirror array
`560.
`
`ll!
`
`15
`
`6
`array, and the individual mirrors in micro-mirror array 560
`have a single rotation axis to rellect
`the beam in the
`directions that correspond to the desired output ports, it is to
`be understood that the input and output ports may also be
`arranged in a two—dimensional array, filling the input plane
`more eficiently. In this case, the individual mirrors in the
`micro-mirror array 560 must have two orthogonal rotation
`axes to reflect the beam in the directions that correspond to
`the desired output ports.
`The programmable demultiplexer depicted in FIG. 5 can
`be operated as a programmable multiplexer, by using ports
`570-1 through 570-k as the input ports and port 510 as the
`output port. Each of the elements in FIG. 5 then operates in
`a manner
`that
`is the "reverse" of that
`just described.
`Specifically, using an input on port 570-1 as an example, the
`diverging beam output 538 from that port is collimated by
`particular aligned lens in lens array 520, and directed
`through lens 530 to lens 540, where the now again diverging
`beam is collirrtated and applied to grating 550. The geometry
`of the arrangement
`is such that
`the reflected beam from
`grating 550(as well as all of the other reflected beams for the
`other input wavelengths and ports) are directed back through
`lens 540 to a specific one of the mirrors in array 560. These
`mirrors are arranged, in accordance with the invention, to
`reflcct the beams back through lens 540 to the appropriate
`point on grating 550 such that all of the beams are reflected
`from the grating through lens 540 and then through lens 530,
`finally being all incident on the single output port 510.
`The arrangement ofFlG. 5 can also be easily modified to
`operate as a wavelength switch, as previously described for
`the functionality illustrated in FIG. 4. Instead of having a
`single input port and k output ports (in the programmable
`dernultiplexer case), the k+1 device pons are redistributed
`such that there are r input ports and s output ports (where
`k+l-r+s). The micro-mirrors in array 560 can establish an
`independent connection for every input wavelength that
`appears on one of the r input ports to any one of the soutput
`ports.
`An alternative embodiment of the present invention is
`depicted in FIG. 6, again implementing a programmable
`dernultiplexer in which one or more wavelengths contained
`in the input signal can be directed to each of multiple output
`ports. In FIG. 6, input port 610 carries the optical
`input
`signal containing multiple optical wavelengths }.-1 through
`?t—N of the DWDM communication system. Each of these
`wavelengths is to be assigned to one of the various output
`ports 660-1 through 660-k, as instructed by an electrical
`control signal 67'!) applied to the micro-mirror array 650. In
`the embodiment of FIG. 6, the input and output ports are
`placed at plane P6-1, which coincides with the front focal
`plane of the lenses in microlens array 620. The output beam
`602 from the input port 610 is collimated by one lens in
`microlens array 620. The resultant collimated beam 605 is
`propagated in free space and made incident on diffraction
`grating 630, which angularly disperses the optical channels
`according to wavelength. The diflracted beam 608 of a
`wavelength channel 7-.-j (again, for convenience, only one
`beam for 1.-j is shown) propagates to lens 640, and focuses
`the beam 612 at the Iens's back focal plane, denoted by plane
`P6—2. A micro—mirror array 650 is placed at plane P6—2, with
`one mirror for each optical wavelength for a total of N
`mirrors. The mirror corresponding to the channel }.—j directs
`the reflected beam 615 in a desired direction, such that it will
`evcntu ally couple to the correct output port. Lens 640
`collimates the reflected beam 615 to beam 618, which is
`afterwards diffracted from diffraction grating 630. The dif-
`fracted beam 622 is propagated in free space and focused by
`
`30
`
`35
`
`40
`
`By vinue of the arrangement of FIG. 5, each wavelength
`is controlled separately, and it is therefore possible to assign _
`each wavelength independently to any output pon. In other
`words, the invention allows the input optical wavelength
`channels to emerge on any desired output port. The arrange-
`ment just described also advantageously permits one or
`more of the output ports 570-1 through 570-Ir to receive
`more than one optical beam and consequently more than one
`wavelength. This is because the mirrors in array 560 are
`arranged to reflect the beams back through the same wave-
`length dependent imaging system (consisting of lenses 540,
`530, 520 and grating 550) and the imaging system is
`designed to convert
`the propagation directions of all
`reflected beams off the micro—mirror array simultaneously to
`their desired output ports. However,
`it is to be noted that,
`when there is no need to have more than one optical beam
`received at a single output port,
`the spatially separated
`wavelengths reflected by the individual mirrors in micro-
`mirror array 560 can be directed back toward output ports
`570-1 through 570—k in other imaging arrangements in
`addition to the arrangement of FIG. 5.
`In such other
`arrangement,
`it
`is not essential that
`the paths include a
`second passage through lens 540 nor a second incidence on
`grating 50. Rather, a person skilled in the art will recognize
`that the tilt imposed by the micro-mirror corresponding to
`wavelength }-.-j in array 560 determines to which output port
`that particular wavelength channel will couple. and that
`various different arrangements can be used to direct the
`output of the micro—mirrors to the individual output ports.
`'lhe ability to tilt each of the individual mirrors in mirror
`array 560 to one of multiple states may be imposed by
`various techniques, most often detennined by an electrical
`voltage. Since a unique mirror tilt is required to select the
`output port, there will also be a unique voltage correspond-
`ing to this tilt and port. The necessary voltage to control each
`output port for every wavelength component of the WDM
`system can be measured and stored in a database.
`In
`operation, a command requests a specific output port
`for
`each communication channel. The device controller then
`obtains from the database the necessary voltages to set the
`mirrors in mirror array 560, and applies the required voltage
`to each mirror.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`While input port 510 and output ports 570-1 through
`570-}: in FIG. 5 are shown as a linear {one dimensional)
`
`0010
`0010
`
`

`
`US 6,657,770 B2
`
`ll!
`
`15
`
`30
`
`35
`
`40
`
`45
`
`7
`a lens in microlens array 620 that is aligned to the desired
`otttput port. The converging beam 625 focuses at plane P6-I
`where it is coupled to the desired output port (shown as port
`6604:) in the array of output porLs 660-1 through 660-k. Note
`that, as with the arrangement of FIG. 5, the device ports can
`be arranged in a linear array with single axis micro—mirr0rs,
`or in a two-dimensional array with two axis micro-mirrors.
`The embodiment of FIG. 6 can be converted to operate as
`either a programmable multiplexer or a wavelength switch,
`as previously explained for the ernbodinient of FIG. 5. by
`"reversing" the inputs and outputs or assigning several ports
`to be input ports and several ports to be output ports,
`respectively.
`An embodiment of a programmable dcmultiplexer
`arranged in accordance with the principles of the present
`invention, but using micro-walkofi" prisms or mirrors,
`is
`depicted in FIGS. '.-‘((1) and 7(b), in which FIG. 7(a) is a view
`ofthe embodiment in the y-2 plane, and FIG. 7(b) is a view
`of the same embodiment, but
`in the x-7. plane.
`In this
`embodiment, the inputfoutput ports 710 and 770-1 through
`7704:, respectively, are arranged in a linear array on plane
`l’7~l. The ports are aligned along the x coordinate axis of the
`system. The output beam 702 of the input port 710 contains
`multiple optical channels at wavelengths }-.-I through it-N.
`The output beam is collimated by lens 720, which is placed _
`such that its front focal plane coincides with plane P7-1. The
`collimated beam 705 is incident on a reflective diflraction
`grating 730. The diffraction effect angularly separates the
`optical channels according to their optical wavelengths in
`the y-7, plane of the coordinate system. The diffracted beam
`708 represents an arbitrarily chosen optical channel at
`wavelength I.-j and the remaining beams of the other wave-
`lengths are not shown, for simplicity. The beam ‘F12 is
`focused by lens 720 in the back-propagation direction at
`plane P7-1, onto one mirror in the micro-prism array 740.
`The optical channels are separated in space in the y coor-
`dinate axis direction, and micro prism array 740 provides a
`separate prism for each wavelength. A person skilled in the
`art can design the optical system to provide suflicicnt spatial
`separation of the wavelength channels on the micro-prisrtt
`array. In this embodiment, each micro-prism element can
`provide a tunable beam walkoff or shift, which is achieved
`by translation of a rooftop prism (two mirrors at 90 degrees).
`The translation direction is in the x coordinate axis. The
`reflected beam 715, which is spatially shifted front
`the
`incident beam 712, is collimated by lens 720. The collimated
`beam 718 is incident on the dilfraction grating 730. The
`diffracted beam 722 is free space propagated to lens 720
`which focuses the beam onto a desired one of the output
`ports 770-1 through 770-k. It will be further understood by
`a person skilled in the art that the spatial shift imposed by the
`micro—prism corresponding to wavelength l.—j
`in array 740
`determines to which output port that particular wavelength
`channel will couple. Since each wavelength is controlled
`separately,
`it
`is possible to assign each wavelength
`independently, allowing the input optical wavelength chan-
`nels to emerge on any desired output port.
`The embodiment of FIG. 7 can be converted to operate as
`a programmable multiplexer or a wavelength switch in the
`same manner as previously explained in connection with the
`embodiment of FIG. 5.
`
`50
`
`55
`
`60
`
`As the trend of increasing nu mbcr of optical channels in
`a WDM system continues,
`it is likely that the number of
`output ports K in the programmable demultiplcxcr (or input
`ports in programmable multiplexer mode) will not continue
`to increase at the same rate, resulting in a desire to have an
`arrangement that has fewer ports relative to a larger number
`
`65
`
`0011
`0011
`
`8
`it is
`of channeLs N (i.e., K-c-:N). To address this situation,
`possible to use the programmable demultiplexer (or pro-
`grammablc multiplexer) as previously described in FIGS. 5
`through 7,
`in a cascade arrangement or architecture. As
`depicted in FIG. 8, an input port 810 carries input optical
`channels 3»-1 through }.-N to a first programmable demulti-
`ptexcr 820-0. Each output port of that programmable demul-
`tiplexer is connected to a different second stage program-
`mable demultiplexer, such that output port 830-l
`is
`connected to programmable demultiplexer 820-1, port 830-2
`to programmable demultiplexer 820-2, etc. The first pro-
`grammable demultiplexer 820-[I can assign any K channels
`to each of its output ports. These K channels will be
`separated to individual output ports by the following second
`stage programmable demultiplexer. This architecture
`increases the number of available output ports from K to K”.
`(Note that the cascaded demultiplexers are not each required
`to have the same number of ports, K; if one demultiplexcr
`had K ports and another had K" ports, then the total ports for
`the cascade arrangement would be K-K'.] If required, the
`cascading approach can be continued until all channels can
`be assigned to separate output ports. The cascading archi-
`tecture is also compatible with typical system deployments,
`which begin with few utilized wavelengths out of the N
`possible wavelengths. Initially, a few programmable dcmulw
`tiplexers may be deployed; as the number of operating
`wavelengths grows, more programmable dernultiplexers can
`later be inserted. This solution provides a low system
`roll-out price with a "pay as you grow” architecture.
`Based on the foregoing,
`it
`is seen that a programmable
`optical mu ltiplexcrrtdemultiplexcr module, which can estab-
`lish any connect ion between the input and output ports of the
`module for each wavelength independently, has been
`described. The programmable multiplexerldemultiplexer
`device has an optical arrangement for spatially dispersing
`the optical wavelengths, and tunable (or tilting) micro-
`mirrors for beam steering each channel independently. Con-
`trolling the beam reflection direction determines the con-
`ncctivity between the input and output ports at
`the
`wavelength level. The functionality alforded by the present
`invention may become of utmost
`importance as optical
`networks with wavelength reconfiguration emerge.
`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. For
`example, an important concept in the present invention is the
`ability to modify the propagation parameters of optical
`beams of different wavelengths to one of many states, such
`that
`the beams can be directed to desired locations. The
`embodiments disclosed in the present invention described
`tilting mirrors and shiftable rooftop prisms as exemplary
`elements that can modify the propagation parameters of an
`incident beam. Other beam modifying elements may be
`substituted, such as spatial light modulators (based on liquid
`crystal, acousto-optic, electro-optic devices, etc.), other mir-
`ror combinations, switched volume holograms or photonic
`crystals, etc. As another example, while the tilting mirror
`arrays and micro—walkotf prism arrays were previously
`described as each controlling the beam propagation of a
`single wavelength or channel, it
`is to be understood that
`these elements can each control
`the beam propagation of
`groups of multiple channels that are contiguous in the
`wavelength domain. Accordingly, for example, in the pro-
`grammable demultiplexer embodiment of F IG. 7, the device
`can process N separate wavelengths in wavelength contigu-
`
`

`
`US 6,657,770 B2
`
`9
`ous groups, using a prism array containing less than N
`mirrors, to independently assign each group to any one of
`the K device output ports. Many other modifications may be
`made by one of ordinary skill in the art without departing
`from the spirit and scope of the appended claims.
`I;’We claim:
`1. A programmable multiplexer in which K input signals
`each containing one or more diiferent wavelengths, said K
`input signals cumulatively containing a total of N dilTerent
`wavelengths, are received from a plurality of K optical input
`ports and combined at a single output port, comprising
`a microlens array that contains K+l lenses, wherein (a)
`one lens is aligned with the output port, while the
`remaining lenses are aligned each to a corresponding
`input pon, and wherein (b) each input signal is colli-
`mated by a respective lens in said microlens array,
`a micro-mirror array containing N tilting micro-mirrors
`means for directing the resultant collimated beam origi-
`nating from each input port to be incident on a dilIrac-
`lion grating, which dilfracts the optical signal as a
`function of its wavelength, said diffraction grating
`being arranged such that each of the separate beams,
`which has a unique wavelength and therefore distinct
`propagation angle, propagates to a particular micro-
`mirror in said rnicro-mirror array, and
`means for individually controlling each mirror in the array
`to rellect the incident beam representing a correspond-
`ing wavelength in a desired direction, such that it will
`be redirected to a single location on the ditfraction
`grating, and coupled from the diffraction grating to the
`output port through the particular lens in the micro—lens
`array that is aligned with the output port.
`2. The invention defined in claim I wherein the number of
`input posts K and optical wavelength components N are
`indep