(12) United States Patent
`Marom et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006657770B2
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,657, 770 B2
`Dcc.2,2003
`
`(54)
`
`l'ROGRAMMABLE OJ>TlCAL
`MULTIPLEXEH/DEM ULTIPLEXEH
`
`(56)
`
`References C ited
`U.S. PJITENT DOCUMENTS
`
`(75)
`
`inventors: Dan Mark Marom, Howell, NJ (US);
`David T homas Neilson, Old Bridge, NJ
`(US)
`
`(73)
`
`As.5ig nee: Lucent Technologies [nc., Murray Hill,
`NJ (US)
`
`( . )
`
`Notice:
`
`Subject to any disclaimer, tbe term o[ tbis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 54 days.
`
`(21)
`
`Appl. No.: 09/944,800
`
`(22)
`
`Filed:
`
`A ug. 31, 2001
`
`(65)
`
`J>dor Publication Data
`
`US 2002/0196520 Al Dec. 26, 2002
`
`(60)
`
`(51)
`(52)
`(58)
`
`Helated U.S. Application Data
`Provisional application No. 60/300,272, filed on Jun. 22,
`2001.
`lnt. C l.7
`................................................ G02B 26/00
`U.S. C l . ........................ 359/290; 359/115; 359/291
`Field of Search ......................... 359/115-119, 124,
`359/127-133, 298, 290-291, 558, 618,
`619, 652, 641-42, 644
`
`5,960,133 A • 9/1999 Tomlinson ................... 385/ 18
`6,268,952 Bl • 7/2001 God.il el aJ ................. 359/291
`2002/0131687 A1 • 9/2002 Wilde .................... ...... 385/24
`* cited by examiner
`Primary Examiner- Jordan M. Schwartz
`Assisram Examiner-Jessica Stultz
`(74) Allorney, Agent, or Firm--...:.f3arry H. Freedman; David
`A. Sasso
`(57)
`
`ABSTRACT
`
`A programmable optical demultiplexer can independently
`assign every input optical channe l in a WDM optical com(cid:173)
`munications signal to depart from any desired output pori.
`The demultiplexer device can al5o be operated in ihe reverse
`direction, and tbus achieve programmable optical multi(cid:173)
`plexer functionali ty, by accepting different wavelengths a!
`eacb of multiple input ports and efficiently combining tbe
`wavelength channels at tbe muJtiplexer output pori. The
`programmable multiplexer/demultiplexer device bas an
`optical arrangement for spatially dispersing the optical
`wavelengths, and tunable micro-mirrors for beam steering
`each channel independently. Controlling the beam reflection
`direction determines tbe connectivity between !be input and
`output ports at tbc wavelength level.
`
`32 Claims, 6 Drawing Sheets
`
`640
`
`' '
`P6- 1
`
`0001
`
`Capella 2014
`Ciena/Coriant/Fujitsu v. Capella
`IPR2015-00816
`
`
`
`
`
`

`

`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 1 of 6
`
`US 6,657,770 B2
`
`FIG. 1
`PRIOR ART
`
`£ 110
`----'----+~ DEMUX
`
`130- 1
`130-2
`130-3
`•
`•
`130-N
`
`FIG. 2
`PRIOR ART
`
`230-1
`230-2
`230-3
`•
`•
`230-N
`
`210-1
`210-2
`210-3
`•
`•
`210- M
`
`SWITCHING
`MATRIX
`
`220
`
`0002
`
`MUX
`
`250
`
`

`

`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 2 of 6
`
`US 6,657,770 B2
`
`FIG. 3(A)
`
`FIG. 3(B)
`
`310-1
`310-2
`310-3
`
`• •
`
`310-K
`
`PROGRAMMABLE
`MUX
`
`330
`
`350
`
`PROGRAMMABLE
`DEMUX
`
`I
`I
`I
`
`340./: I
`
`I
`
`I
`I
`I
`
`!\..380
`I
`I
`
`370-1
`370-2
`370-3
`•
`•
`370-K
`
`FIG. 4
`
`WAVELENGTH
`SWITCH
`
`430-1
`430-2
`430-3
`•
`•
`
`430-s
`
`410-1
`410-2
`410-3
`
`•
`•
`410-r
`
`/
`420
`
`'
`
`I
`I
`I
`
`!\..440
`I
`I
`
`0003
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 2, 2003
`Dec. 2, 2003
`
`Sheet 3 0f 6
`Sheet 3 of 6
`
`US 6,657,770 B2
`US 6,657,770 B2
`
`I./)
`
`0 v
`
`I./)
`
`FIG.5
`
`lC
`•
`~
`~
`
`SIGNAL
`
`_.J < :z
`
`CONTROL
`
`(.!)
`(/)0
`_.J ex:>
`Ql.l")
`0::
`1-:z
`0
`(...)
`
`--- ----- -------- J.,
`a..
`
`N
`
`N
`i
`I
`I
`,.._
`,.._
`o
`a
`C.) C)
`PH
`PH
`U3
`U3
`l.l")
`l.l")
`
`0
`..(cid:173)
`l.l")
`
`CD
`PK
`U?
`
`0004
`0004
`
`

`

`U.S. Patent
`
`Dec. 2, 2003
`Dec. 2, 2M3
`
`Sheet 4 of 6
`Sheet 4 0f 5
`
`US 6455737“ 132
`US 6,657,770 B2
`
`I
`f6
`
`tD
`
`
`
`~
`
`---- -----tb Q..
`
`0005
`0005
`
`

`

`~ •
`rJJ. •
`~
`~
`f"'f'
`
`~ = f"'f'
`
`~
`~
`!">
`"N
`N
`
`0 s
`
`00 =(cid:173)~
`~ ....
`
`Ul
`0 .....
`
`C\
`
`e V1
`
`C\
`~
`Ul
`-...l
`~
`-...l
`~
`t:=
`N
`
`
`
`Jflawd'S'I]
`
`€002‘Z'39“
`
`730
`
`9J”5139115
`
`w0LL‘LS9‘9sn
`
`I
`
`FIG. 7(A)
`
`
`
`I :1
`.. J
`
`y
`L~O, 770
`
`FIG. 7(A)
`
`0006
`
`T
`
`710, 770
`
`780'i
`
`I 740
`
`'-,, : L..
`
`IlL='
`
`1
`
`FIG. 7(B)
`
`P7-1
`
`

`

`U.S. Patent
`
`Dec. 2, 2003
`
`Sheet 6 of 6
`
`US 6,657,770 B2
`
`FIG. 8
`
`PROGRAMMABLE
`DEMUX
`r---+~
`
`810
`
`PROGRAMMABLE
`DEMUX
`
`830-1
`830-2
`830-3
`•
`•
`830-K
`
`PROGRAMMABLE
`DEMUX
`
`PROGRAMMABLE
`DEMUX
`1..----~
`
`0007
`
`840-1-1
`840-1-2
`840-1-3
`
`•
`
`•
`840-1-K
`
`840-2-1 ...
`
`840-2-2
`840-2-3
`•
`•
`840- 2-K
`
`•
`•
`840-K-1
`840-K-2
`840-K-3
`•
`•
`840-K-K
`
`

`

`US 6,657,770 B2
`
`1
`PROGRAMMABLE OPTICAL
`M ULTII'LEXER!DEM ULTlPLEXER
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`"Jhis application claims priority of Provisional Applica(cid:173)
`tion Ser. No. 60/300,272 filed on Jun. 22, 2001.
`
`TECHNICAL FIELD
`l11e present invent ion relates to fiber optic networks, and
`more particularly to fiber optic wavelength division multi(cid:173)
`plexers and demultiplexers.
`
`13/\CKGROUND OF THE INVENTION
`'lbe transmission capacity of ftber-opl ic communication
`systems has increased signiftcan tly by use of wavelength
`division multiplexing (WDM) techniques. ln a WDM com(cid:173)
`munication system, multiple channels, where eacb channel
`is dillcrentiatccl by using a unique wavelength of light, carry
`modulated optical signals in a single optical fiber between a
`transmiller and a receiver. The transmitter uses an optical
`multiplexer to combine multiple channels into tbe fiber for
`transmission, and the receiver uses an optical demultiplexer
`10 separate the optical channels for detection. FIG. 1 iUus(cid:173)
`trates a typical optical demultiplexer (demux) 120 contain(cid:173)
`ing a single input pon llO and multiple output ports 130-1
`through 130-N, where each optical cbaooel from tbe input
`port is mapped to a unique output port in sequential order
`(channel I will exit from port 130-1, cbaooel 2 from port
`130-2, etc.). Optical multiplexers are simply demultiplexers
`operated in the reverse direction, where a specific wave(cid:173)
`length has to be supplied to tbc correct input pon to emerge
`at the output port as a multiplexed signal.
`It is expected lhat in the foreseeable future, communica(cid:173)
`tion systems will evolve to communication oel\vorks con(cid:173)
`sisting of multiple access nodes, each containing a WDM
`transmiller and/or receiver, that are interconnected in some
`prescribed fashion (e.g., ring or bus) or arbitrarily (e.g.,
`mesh). Information llow between two acces.s nodes will be
`carried on an available optical wavelength tbat is assigned
`by a protocol according to network availability. The irans(cid:173)
`mitting node will have to employ a bank of lasers at different
`wavelengths as available sources, all connected properly to
`tbe multiplexer's ports, uli.lizing only a small fraction of tbe
`lasers at any given time for communication. This is clearly
`ao expensive solution, as most of the hardware is lying idle.
`1\lteroatively, wavelength tunable lasers can be used.
`llowever, 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 tbrougb 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 tbe
`receiving node will also have to address the same issues for
`tbe demultiplexing and detection task.
`
`SUMMARY OF THE INVENTION
`In accordance with the present invention, a programmable
`optical muhiplexer/demuJtiplexer can establish a reconfig(cid:173)
`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(cid:173)
`mable demultiplexer is arranged to receive ao input signal
`
`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 microlcns array, which lens is aligned to
`s tbe input port. The microleos array contains K additional
`lenses that arc aJjgncd to the K output ports. The resultant
`collimated beam originating from the input pon is then made
`incident on a diffraction grating, which angularly disperses
`the composite optical signal according to wavelength,
`10 thereby forming N separate beams baving different wave(cid:173)
`lengths and distinct propagation angles. Each of the N
`separate beams propagates to a single lens tbat is arranged
`to collecl all the beams and provide, for each wavelength, a
`converging beam focused onto a particular micro-mirror in
`J5 an array containing N micro-mirrors. Each mirror in the
`array is individually controlled to reflect tbe iocideot beam
`(representing a corresponding wavelength) in a desired
`direction, such that it will (a) re-enter the Ieos, (b) be
`collimalecl by the lens and redirected to a different location
`20 on the diiTraction grating, and (c) be eventually couplccl
`from the diffraction grating through a particular Ieos io the
`micro-lens array to a desired output port (Lbe particular
`micro-lens is aligned to tbe desired output port). Generally,
`the number of output ports K and optical wavelength com-
`25 pooeots N arc independent. Tbe demultiplexer can be
`designed to operate in the regime where K~N, so that each
`wavelength component can be assigned to aoy output port.
`The invention can also be operated in a mode where K<N,
`in which case more than ooe wavelength Ls applied to ao
`30 output port, or in a mode where K>N, in which case one or
`more output pons arc not used. In aoy event, tbe present
`invention enables as.-;ignmeot of any wavelength to any
`output port.
`The embodiment just described can be operated in the
`35 "reverse'' direction, in order to act as a programmable
`multiplexer, rather than as a demultiplexer. In tbe mulli(cid:173)
`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
`40 available at a single output port. The K input signals
`cumulat ively conta in a tota l of N different wavelengths, or,
`stated different ly, 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 io
`45 a microlcns array that contains K+l lenses. Ooe Ieos is
`aligned with the output port, while lbe remaining lenses are
`aligned each to a corresponding input port. Tbe resuJtaot
`collimated beam originating from each input pori is then
`made incident on a diffraction grating, which diffracts the
`so optical signal as a function of its wavelength. The diffraction
`grating is arranged such that all of the separate beams, wbicb
`have diO'erent wavelengths and therefore distinct propaga(cid:173)
`tion angles, propagate to a single lens that collects aU ~be
`beams and provides, for each wavelength, a coovcrgmg
`ss beam focused onto a particular micro-mirror in an array.
`Each mirror in the array is individually controlled to reflect
`the incident beam (representing a corresponding
`wavelength) in the desired direction, such that it will (a)
`re-enter the Ieos, (b) be collimated by tbe lens and redirected
`60 to a single location on the diffraction grating, and (c) be
`eventually coupled from the diffraction grating to tbe output
`port through the particular Ieos in the micro-lens array tbat
`is aligned with the output port. Here again, in general, tbe
`number of inpul porL<> K and optical wavelength components
`65 N arc independent. The multiplexer can be designed to
`operate in the regime where KaN, so that each wavelength
`component can originate at any input port. The invention can
`
`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 pons are not
`used. In any event, the present invention enables multiplex(cid:173)
`ing (combining) of all input wavelengths originating at the
`K input ports to the output port.
`
`BRIEF DESCRIP'110N OF THE DRAWINGS
`
`The present invention will be more fully appreciated by
`consideration of the following detailed description, which
`shou ld be read in light of the drawing in which:
`FIG.1 is an illustration of the operation of a conventional
`optical wavelength demulliplexer;
`FIG. 2 is an illustration of the conventional required
`hardware for multiplexing multiple channels with tunable
`wavelength sources;
`FIG. 3(o) is an illustration of the general operation of the
`present invention, when operating as a programmable opti(cid:173)
`cal wavelength multiplexer, while FIG. 3(b) is an illustration
`of the genera l operation of a the present invention, when
`operating as a programmable optical wavelength demulti(cid:173)
`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 ao illustration of an alternative embodiment of
`the present invention using tilting micro-mirrors and func(cid:173)
`tioning as a programmable demultiplexer;
`FIGS. 7(o) and 7(b) are diJierent views of yet another
`embodiment of the present invention using shift-inducing
`micro-prisms and functioning as a programmable demul ti(cid:173)
`plexer; and
`FIG. 8 is an illustration of a cascade of programmable
`demultiplexers for increasing the output channel count.
`
`DETAlLED DESCRIPTION
`
`The programmable optical multiplexer/demultiplexer in
`accordance wi th the present invention provides for wave(cid:173)
`length routing between the input and output ports. It is
`designed for selectively multiplexing, demultiplexiog and
`switching of optical channels in dense wavelength division
`multiplexed (DWDM) communication systems. In this
`regard, a demultiplexer can be though t of as a lxK wave(cid:173)
`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(o) is a diagram iJJustrating 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(cid:173)
`bined and output from output port 330. Ln accordance wi th
`the invention, it is desired that any optical channel or
`combination of channels can be inserted at any input port
`310-1 through 310-k and emerge at the output pon 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 port.
`Multiplexer 320, as described more fu lly below, is arranged
`sucb tbat it physically prevents the detrimental possibility of
`combining two optical channels operating on the same
`wavelength from two different input ports.
`
`5
`
`10
`
`4
`As shown in FIG. 3(b), when operating in programmable
`demultiplexer mode, multiplexer 320 is operated in the
`reverse direction. A programmable demultiplexer 360 bas
`input port 350 arranged to receive an optical communica-
`tioos signal containing multiple optical wavelengths. The
`individual wavcleogtbs arc tbeo independently assigned to
`the k output ports, 370-1 tbrough 370-k, by the program(cid:173)
`mable demultiplexer, as prescribed by the control signal380.
`Note that the number of input or output ports, k, may be
`equal to or dilierent from the number of DWDM channels.
`FIG. 4 illustrates, in general terms, another operation
`mode wherein the present invention implements a wave(cid:173)
`length switch 420 having mul tiple input ports 410-1througb
`410-r and multiple output ports 43 0-1 through 430-s, where
`15 r and s can be different integers. The different optical
`channels are distributed among the input ports 410-1
`th rough 410-r, whe re each port may carry multiple channels,
`but no channel can appear on two different input ports
`simultaneously. Each optical channel is routed indepen-
`20 dently to its required output destination port, 430-1 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 demultiplexer as was described generally in
`25 connection with FIG. 3(b). Input port 510, typically a single
`mode optical fiber, carries an input optical signal tha t
`contains multiple optical wavelengths f..-1 through A.-N of a
`DWDM communication system. To accomplish the demul(cid:173)
`tiplexer function, it is desired that each of these wavelengths
`30 be assigned to one of tbe various output porLs 570-1 through
`570-k, as instructed by a provided control signal380 of FIG.
`3(b). 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
`35 of wavelengths in tbe input optical signal.
`As shown in FIG. 5, the optical beam 502 emerging from
`input port 510 is rapidly diverging, due to diffraction effects.
`A micro-lens array 520 is aligned with and spaced apart from
`input port 510, as well as with output ports 570-1 through
`40 570-k, such that the ports are at t he 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(cid:173)
`lens. The effect of the individual micro-lens that is aligned
`to the input port 510, is to collimate the diverging beam 502
`45 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 foca l pla ne, denoted as plane P5-2
`by lhe do tted line in the figure. Tile beam then continues io
`50 diverge.
`The diverging beam 508 is collimated by a second Ieos
`540, that is placed such that its front focal plane coincides
`with plane P5-2, resulting in the beam 512 that slill contains
`all of the input optical channels. Beam 5U is directed onto
`ss a reflection diffraction grating 550 that introduces wave(cid:173)
`length dependent diffraction and serves to separate the
`optical channeL<;, so that each channel can be independently
`accessed. An il lustrative diffracted beam 515, propagating at
`a unique direction or angle with respect to grating 550,
`60 contains only a single optical channel at a particular wave(cid:173)
`length f..-j. The diffracted beam 515 propagates back through
`the Ieos 540, which focuses the beam 518 at the lens's front
`focal plane, plane P5-2. There will be N such beams, one for
`each wavelength J..-1 through J..-N, each propagating at a
`65 slightly different direction. It is thus seen thai the optical
`subsystem consisting of the Ieos 540 and diffraction grating
`550 serves to spatially separate the optical channels at plaoe
`
`0009
`
`

`

`US 6,657,770 B2
`
`5
`P5-2. One proficient in the field can design the optical
`system to provide the su.Jiicient spatial separation of the
`wavelength channels at this plane. Note tha t FIG. 5 traces
`only the single wavelength A.-j for simplicity.
`A micro-mirror array 560 is placed at plane P5-2, such
`tbat each optical channel is focused on a separate mirror
`element. Each mirror 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 10
`collimated by lens 540, and the collimated beam 525 is
`diffracted off reflective grating 550, resulting in beam 528
`that is propagating back towards the device output ports.
`Leos 540 focuses beam 528, converting 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
`P5-2 and is recollimated by lens 530, resulting in beam 535.
`Beam 535 is focused by one of the micro-lenses of the
`micro-lens array 520, with the focused beam 538 at plane
`P5-1 and coupling to the desired one of the output ports
`570-1 th rough 570-K. The output port is selected for each
`wavelength by the beam propagation direction that is
`imparted by the tilt of the individual mirrors in mirror array
`560.
`By virtue of the arrangement of FIG. 5, each wavelength
`is controlled separately, and it is therefore possible to assign
`each wavelength independently to any output port. In other
`words, the invention allows the input optical wavelength
`channels to emerge on any desired output port. The arrange(cid:173)
`ment just described also advantageously permits one or
`more of the output ports 570-1 through 570-k to receive
`more than one optical beam and consequently more than one
`wavelength. This is because the mirrors in array 560 arc
`arranged to reflect the beams back through the same wave(cid:173)
`length dependent imaging system (consisting of leases 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 simullancously to
`their desired output ports. llowever, it is to be noted that,
`when there is oo 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(cid:173)
`mirror array 560 can be directed back towa rd 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 550. Rather, a person skilled in the art will recognize
`that the tilt imposed by the micro-mirror corresponding to
`wavelength A.-j in array 560 determines to which output port
`that particular wavelength channel will couple, and that
`various dilferent arrangements can be used to direct the
`output of the micro-mirrors to the individual output ports.
`The 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 determined by an electrical
`voltage. Since a unique mirror tilt is required to select the
`output port, there will also be a unique voltage correspond(cid:173)
`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. ln
`operation, a command requests a specific output port for
`each communication channel. The device controller then
`obtains from the da tabase the necessary voltages to set tbe
`mirrors in mirror array 560, and applies the required voltage
`to each mirror.
`While input port 510 and output ports 570-1 through
`570-k in FIG. 5 are shown as a linear (one dimensional)
`
`6
`array, and the individual mirrors in micro-mirror array 560
`have a single rotation axis to reflect the beam in the
`directions tha t correspond to the desired output ports, it is to
`be understood that the input and output ports may also be
`5 arranged io a two-dimensional array, filling the input plane
`more efficiently. Ia 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 progTammable multiplexer, by using ports
`570-1 through 570-k as the input ports and port 510 as the
`output port. Each of the e lements in FIG. 5 then operates in
`a manner that is the "reverse" of that just described.
`15 Specifically, using an input oo port 570-1 as ao example, the
`diverging beam output 538 from that port is collimated by
`particular aligned Ieos in Ieos array 520, and directed
`through lens 530 to lens 540, where the now again diverging
`beam is collimated and applied to grating 550. T he geometry
`20 of the arrangement is such that the reflected beam from
`grating 550 (as well as all of tbe other reflected beams for the
`other input wavelengths and ports) are directed back through
`Ieos 540 to a specific one of the mirrors io array 560. These
`mirrors are arranged, in accordance with the invention, to
`25 reflect the beams back through Ieos 540 to the appropriate
`point on grating 550 such that aU of the beams are reflected
`from the grating through lens 540 and then through Ieos 530,
`finally being all incident on the single output port 510.
`Tbe arrangement of FIG. 5 can also be easily modified to
`30 operate as a wavelength switcb, as previously described for
`tbe functionality illustrated in FIG. 4. Instead of having a
`single input port and k output ports (in the programmable
`demultiplexer case), the k+l device ports are redistributed
`such that there are r input ports and s output ports (where
`35 k+l=r+s). Tbc 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 tbe s output
`ports.
`Ao alternative embodimenl of the present invention is
`40 depicted in FIG. 6, again implementing a programmable
`demultiplexer 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 optica l input
`signal containing multiple optical wavelengths J..-1 througb
`45 A.-N of the DWDM communication system. Eacb 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 670 applied to the micro-mirror array 650. In
`the embodiment of PIG. 6, the input and output ports are
`50 placed at plane P6-l , which coincides wi th the front focal
`plane of the leases in microleos array 620. The output beam
`602 from the input port 610 is collimated by one Ieos in
`microlens array 620. The resultant collimated beam 605 is
`propagated in free space and made incident on diffraction
`ss grating 630, which angularly disperses the optical channels
`according to wavelength. The diffracted beam 608 of a
`wavelength channel A.-j (again, for convenience, only one
`beam for A.-j is shown) propagates to lens 640, and focuses
`the beam 612 at the lens's back focal plane, denoted by plane
`60 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 tbe channel A.-j directs
`the reflected beam 615 in a desired direction, such that it will
`eventually couple to the correct output port. Lens 640
`65 collimates the reflected beam 615 to beam 618, which is
`afterwards di!Iracted from difi'rac tion grating 630. The dif(cid:173)
`fracted beam 622 is propagated in free space aod focused by
`
`0010
`
`

`

`US 6,657,770 B2
`
`7
`a lens in microlens array 620 that is aligned to the desired
`output port. The converging beam 625 focuses at plane P6-1
`where it is coupled to the desired output port (shown as port
`660-k) in the array of output ports 660-l 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-mirrors,
`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 tbe embodiment o[ FIG. 5, by
`"reversing'' the inputs and outpuLs or assigning several ports
`to be input ports and several ports to be output ports,
`respectively.
`An embodiment of a programmable demultiplexer
`arranged in accordance with the principles of the present
`invention, but using micro-walkoff prisms or mirrors, is
`depicted in FIGS. 7(a) and 7(b), in which FrG. ?(a) is a view
`of the embodiment in the y-z plane, and FIG. 7(b) is a view
`of the same embodiment, but in the x-z plane. In this
`embodiment, the input/output ports 710 and 770-1 through
`770-k, respectively, are arranged in a linear array on plane
`P7 -1. 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 A.-1 through A.-N.
`The output beam is collimated by Ieos 720, which is placed
`such that its front focal plane coincides with plane P7-l. The
`collimated beam 705 is incident on a reflective diffraction
`grating 730. The diffraction effect angularly separates the
`optical channels according to their optical wavelengths in
`the y-z plane of the coordinate system. The diffracted beam 30
`708 represents ao arbitrarily chosen optical channel at
`wavelength /..-j and the remaining beams of the other wave(cid:173)
`lengths are not shown, [or simplicity. The beam 712 is
`focused by lens 720 io the back-propagation direction at
`plane P?-1, onto one mirror in the micro-prism array 740.
`The optical channels are separated in space io the y coor(cid:173)
`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 sufficient spatial
`separation of the wavelength channels on the micro-prism
`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 at90 degrees).
`The translation direction is in the x coordinate axis. The
`reflected beam 715, which is spatially sbif1ed from the
`incident beam 712, is collimated by lens 720. The collimated
`beam 718 is incident on tbe diffraction grating 730. The
`diffracted beam 722 is free space propagated to Ieos 720
`which focuses the beam ooto a desired one of the output
`ports 770-lthrougb 770-k. It wiU be further understood by
`a person skilled in the art that the spatial shift imposed by the
`micro-prism corresponding to wavelength f..-j in array 740
`determines to which output port that particu lar wavelength
`channel will couple. Since each wavelength is controlled
`separately, it is possible
`to assign each wavelength
`independently, allowing the input optical wavelength chao(cid:173)
`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 tbe
`same manner as previously explained in connection with the
`embodiment of FIG. 5.
`Ac; the trend of increasing number of optical channels in
`a WOM system continues, it is likely that the number of
`output ports Kin the programmable demultiplexer (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 bas fewer ports relative to a larger number
`
`8
`of channels N (i.e., K«N). To address this situation, it is
`possible to use the programmable demultiplexer (or pro(cid:173)
`grammable multiplexer) as previously described in FIGS. 5
`through 7, in a cascade arrangement or architecture. As
`5 depicted io FIG. 8, an input port 810 carries input optical
`cbanoels A.-I through A.-N to a first programmable demulti(cid:173)
`plexer 820-0. Each output port of that programmable demul(cid:173)
`tiplexer is connected to a ditTerent second stage program(cid:173)
`mable demultiplexer, such tha t output port 830-J
`is
`10 connected to programmable demultiplexer 820- J, port830-2
`to programmable demultiplexer 820-2, etc. The first pro(cid:173)
`grammable demultiplexer 820-0 can assign any K channels
`to each of its output ports. These K channels wi ll be
`separated to individual output ports by the following second
`15 stage programmable demultiplexer. This arc hi tecture
`increases the number of available output ports from K to Kz.
`(Note that the cascaded demul tiplexers are not each requjred
`to have the same number of ports, K; if one demultiplexer
`had K ports and another bad K' ports, then the total ports (or
`20 the cascade arrangement would be K-K'.) If required, the
`cascading approach can be contioued until all channels can
`be assigned to separate output ports. l'be cascading archi(cid:173)
`tecture is also compatible with typical system deployments,
`which begin with few utilized wavelengths out of the N
`25 possible wavelengt