(12)
`
`United States Patent
`
`McLaughlin et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,676,126 B2
`Mar. 9, 2010
`
`US00'7'6'7'6126B2
`
`............. .. 335717
`372000 Solgazudetal.
`1272002 13505011535131.
`..
`335724
`472003 13515575151.
`335724
`972003 13371511
`.. 3357140
`372004 0055111575131.
`335717
`972004 Smith etal.
`335713
`1072004 51151155151.
`.35574.01
`1072004 05054151. .................. .. 335724
`1272005 Basavarnhallyetal.
`335713
`472005 13055111515151.
`335724
`1172005 Walteretal.
`335713
`572007 1171515151
`.. 3357140
`1072007 3501555151..
`.. 3357140
`172003 135051711511 .... ..
`335724
`1172005 1355511157
`335713
`77200-7 Wuetal.
`335724
`
`
`
`5,097,359 .4
`5,493,372 132
`5,549,599 132
`5,514,932 132*
`5,707,959 32
`5,793,941 132
`5,301,305 132*
`5,310,159 132
`5,975,733 132
`7,027,534 132
`7,142,744 B2
`7,212,721 132
`7,235,743 132-7
`200370021525 711*
`200570245535 .41
`200770150321 711+
`
`200770242953 .41
`
`1072007 Keywortbetal.
`
`........... .. 393743
`
`(54)
`
`OPTICAL DEVICE WI'TH NON-EQUALLY
`SPACED OUTPUT PORTS
`
`(75)
`
`(73)
`
`Inventors: Sheldon McLaughlin, Ottawa (CA);
`Pierre D. Wall, Ottawa (CA)
`
`Assignee: JDS Uniphase Corporation, Milpitas,
`CA (US)
`
`(“')
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(0) by 0 days.
`
`(21)
`
`App]. No.: 121’332,604
`
`(22)
`
`Filed:
`
`Dec. 1], 2008
`
`Prior Publication Data
`
`(65)
`
`(60)
`
`(51)
`
`(52)
`(53)
`
`(56)
`
`US 20091’0l54874 A1
`
`Jun. 18, 2009
`
`* cited by examiner
`
`Related U.S. Application Data
`
`Provisional application No. 6l7'0l2,960, filed on Dec.
`12, 2007.
`
`(2006.01)
`(2006.01)
`
`Int. Cl.
`G02B 6/00
`G02B 636
`385718; 3351140
`U.S. Cl.
`Field of Classification Search ........... .. 3857'] 5-20,
`335727, 31, 37, 129, 140
`See application file for complete search history.
`References Cited
`
`U.S. PATENT DOCUMENTS
`811995 Lambert, Jr.
`5,440,654 A
`
`Primary Exa7m'ner—Akm E Ullah
`(74) Atromey, Agent, or .F'ir'm—Teitelbaum & MacLean; Neil
`Teitelbaum; Doug MacLean
`
`(57)
`
`ABSTRACT
`
`The invention relates to multiport routing devices for routing
`optical signals which also provide beam attenuation by
`imparting a controllable offset between an optical beam and a
`selected optical port. A multiport optical routing device ofthe
`present invention has a plurality of non-equally spaced opti-
`cal ports disposed in a row to enable beam ofiset for attenu-
`ation witbout substantially increasing optical crosstalk
`between adjacent ports in a compact port arrangement.
`
`14 Claims, 10 Drawing Sheets
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`‘K
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`" 222
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`Ca
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`IP
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`Capella 2033
`JDS Uniphase v. Capella
`IPR2015-00731
`
`1
`
`

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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 1 of 10
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`US 7,676,126 B2
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` FIG.1(PRIORART)
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`2
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 2 of 10
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`US 7,676,126 B2
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`/"‘“122
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`010
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`.-._.-.-.4-"11
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`01B
`FIG.2(PRIORART)
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` /
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`132C
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`132D
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`Ex. IIIITIITIII
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`132B
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`3
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 3 of 10
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`Us 7,676,126 B2
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`QMADE
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`om.©E
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`mm.05
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`<m.03
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`4
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`

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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 4 of 10
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`US 7,676,126 B2
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`EN
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`5
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 5 of 10
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`US 7,676,126 B2
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`C)
`C\I
`\-
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`V‘:
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`(Dr—1
`LT-4
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`ON
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`132A
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`(V
`(‘'3
`1-
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`132C
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`6
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 6 of 10
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`Us 7,676,126 B2
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`7
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 7 of 10
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`Us 7,676,126 B2
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`8
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 8 of 10
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`Us 7,676,126 B2
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`301
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`FIG. 8A
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`FIG. 8B
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`U.S. Patent
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`Mar. 9, 2010
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`Sheet 10 or 10
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`FIG. 10A
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`FIG. 10B
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`US 7,676,126 B2
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`1
`OPTICAL DEVICE WITH NON-EQUALLY
`SPACED OUTPUT PORTS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`The present invention claims priority from U.S. Provi-
`sional Patent Application No. 6lt'0l 2,960 filed Dec. 12, 2001'‘,
`entitled “Non-equal port spacing in WSS", which is incorpo-
`rated herein by reference for all purposes.
`
`TECHNICAL FIELD
`
`The present invention relates to optical devices for routing
`and modifying optical signals, and in particular to optical
`devices providing variable beam attenuation with non-
`equally spaced output ports.
`
`BACKGROUND OF THE INVENTION
`
`Optical routing devices such as optical switches and, in
`particular wavelength selective switches (WSS), are used in
`optical communications and optical measurement applica-
`tions. Conventional optical routing devices, such as those
`disclosed in U.S. Pat. No. 6,097,859 issued Aug. 1, 2000 to
`Solgaard et al; U.S. Pat. No. 6,498,822 issued Dec. 24, 2002
`to Bouevitch et al; U.S. Pat. No. 6,707,959 issued Mar. 16,
`2004 to Ducellier et al; U.S. Pat. No. 6,810,169 issued Oct.
`26, 2004 to Bouevitch, and U. S. Pat. Publication No. 2007/
`0242953 published Oct. 18, 200? to Keyworth et al, which are
`incorporated herein by reference, separate a multiplexed opti-
`cal beam into constituent wavelengths with a dispersive ele-
`ment, and then direct individual wavelengths or groups of
`wavelengths, which may or may not have been modified, back
`through the device to a desired output port.
`In a typical WSS the input andoutput optical ports are faces
`of optical fibers that are arranged in an array wherein fibers
`are equally spaced and held in position in a fiber array unit
`(FAU). The front end of the device may further include a
`polarization diversity unit for ensuring the beam of light
`routed within the device has a single state ofpolarization. The
`back end of the device typically includes a switching engine,
`also referred to herein as a beam director, wherein individu-
`ally controllable devices are used to redirect selected wave-
`lengths back to one of several output ports.
`An optical beam emerging from the FAU is transformed by
`the WSS optics into multiple beams according to the wave-
`length, and made to converge at the switching engine. The
`WSS optics is effective in mapping the optical fiber position
`in the FAU to a beam angle at the switching engine. The
`switching engine operates by imparting a controllable tilt to
`an incoming beam, to redirect it to an output port. Possible
`switching engine technologies include tiltable micro—mirrors
`of a micro electromechanical switch (MEMS) and liquid
`crystal on silicon (LCoS) phase arrays. The switching engine
`is typically voltage controlled, with the amount of tilt gener-
`ally increases with the applied voltage.
`In addition to switching between parts, it may be desirable
`for the switching engine to attenuate optical signals. This
`variable attenuation may be accomplished by tilting the beam
`slightly away from an angle corresponding to an optimal
`optical alignment with a selected output fiber port, such that
`the beam impinges thereupon with some controllable olfset
`and suffers a coupling loss into the output fiber. Optical
`switches wherein signals are variably attenuated by tilting
`micro-minors away from the optimal optical alignment with
`a target optical port are disclosed for example in U.S. Pat. No.
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`6,798,941 to Smith et al and U.S. Pat. No. 7,142,744 to Walter
`et al, which are incorporated herein by reference.
`Unfortunately, when an output optical beam is offset from
`its optimal alignment with a target output optical port in a
`multiport routing device, the beam may come into a partial
`alignment with an adjacent optical port,
`increasing the
`amount of light lking into the non-selected adjacent port,
`resulting in an undesirable optical crosstalk between adjacent
`optical ports in the array.
`
`SUMIUIARY OF THE INVENTION
`
`Accordingly, an object of the present invention is to over-
`come the shortcomings of the prior art by providing an
`improved optical routing device wherein variable attenuation
`of routed optical signals is aflected without inducing optical
`crosstalk between adjacent output ports andwithout adding to
`the device complexity.
`In accordance with the invention, there is provided a mul-
`tiport optical routing device for routing and modifying an
`optical signal, comprising an input optical port for receiving
`the optical signal, a plurality of output optical ports disposed
`in a row comprising first, second and third consecutive optical
`ports, and a beam director optically coupled to the input port
`for receiving at least a portion of the optical signal therefrom
`and for clirezting said at least a portion of the optical signal as
`a light beam at a controllable angle for coupling into one of
`the output optical ports, wherein the first, second and third
`consecutive optical ports are non-uniformly spaced with a
`first distance cl, between the first and second output optical
`ports that differs from a second distance dz between the sec-
`ond and third output optical ports by at least 10%.
`In accordance with one aspect of this invention, each three
`consecutive optical ports from the plurality of output optical
`ports are non-equally spaced with inter-port distances
`between adjacent ports difi"ering by at least 10%.
`In accordance with one aspect of the invention, the beam
`director is adjustable to direct the light beam along an optical
`path towards the second output optical port for coupling
`thereinto, and is further adjustable to at 1st partially shift the
`light beam away from an alignment with the second optical
`output port towards one of the first and third output optical
`ports that is distanced farther away from the second optical
`port so as to provide a controllable optical loss for light
`coupled into the second optical port without causing light of
`the light beam to leak into adjacent optical ports.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention will be described in greater detail with ref-
`erence to the accompanying drawings which represent pre-
`ferred embodiments thereof, in which like elements are indi-
`cated with like reference numerals, and wherein:
`FIG. 1 is a schematic representation of a top view of one
`conventional multiport optical routing device with a disper-
`sive element;
`FIG. 2 is a schematic side view ofa prior-art front-end unit
`of the device shown in FIG. 1;
`FIGS. 3A and 3B are end-on views of three consecutive
`
`equally spaced optical ports in a multi-port optical routing
`device without a provision for beam offset for attenuation
`illustrating beam-port alignment without and with an offset;
`FIG. 3C is an end-on view of three consecutive equally
`spaced optical ports in a multi-port optical routing device
`with an increased inter-port spacing providing for a beam
`oifset for attenuation;
`
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`12
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`US 7,676,126 B2
`
`3
`FIG. 3D is an end-on view of three consecutive non-
`equally spaced optical ports in a multi-port optical routing
`device according to one embodiment the present invention;
`FIG. 4 is a schematic side view of a front-end unit of a
`multiport optical routing device having non-equally spaced
`ports according to one embodiment of the present invention;
`FIG. 5 is a schematic side view of one embodiment of a
`
`multiport optical routing device having non-equally spaced
`ports according to the present invention;
`FIG. 6 is a schematic top view of the multiport optical
`routing device shown in FIG. 5 incorporating the front-end
`unit with non-equally spaced optical ports;
`FIG. 7 is a schematic side view of another embodiment of
`a multiport optical routing device having non-equally spaced
`ports according to the present invention;
`FIGS. 8A and 8B are end-on views of exemplary 9-port
`fiber array units with non-equal and equal port spacing,
`respectively, for use in multiport optical routing devices pro-
`viding for variable optical signal attenuation by beam offset;
`FIG. 9 is a is a schematic perspective view of a multiport
`optical routing device with optical ports forming a two-d.i-
`mensional array;
`FIGS. 10A and 10B are a schematic representations of
`end-on and side views of one embodiment of a front-end unit
`
`having non-equally spaced optical ports arranged in a two-
`dimensional array for use in the multiport optical routing
`device platform illustrated in FIG. 9.
`
`DETAILED DESCRIPTION
`
`The present invention relates to multiport optical routing
`devices for routing and modifying optical signals, which uti-
`lize beam offset or beam misalignment at optical ports for
`affecting variable attenuation of output optical signals; it
`provides an improvement according to which at least some of
`the optical ports of the device are disposed in a row forming
`a one dimensional (ID) array of optical ports with non-equal
`port spacing, so that there is three consecutive optical ports
`for which a center optical port is disposed substantially closer
`to one of its neighbors than to the other, thereby providing
`room for offsetting or shifiing an incoming optical beam
`slightly away from an optimal alignment with the center port
`to provide variable optical coupling thereinto without causing
`undesirable leaking of the beam light into adjacent optical
`ports.
`The invention can be utilized in a variety of routing device
`platforms wherein the direction of the beam offset for optical
`signal attenuation coincides with, or at least has a projection
`upon, a beam switching direction, i.e. the direction in which
`the beam moves when it is switched to another output port, so
`that offsetting a beam for the purpose of attenuation moves
`the beam closer to an adjacent output port.
`Embodiments of the invention will now be described with
`
`reference to wavelength dispersive optical routing devices,
`also referred to as wavelength selective switches (WSS)
`wherein the optical ports are in the form of optical
`waveguides such as optical fibers arranged in a 1D optical
`fiber array.
`FIG. 1 illustrates a top view of one typical WSS platform
`100 in which the output signals may be attenuated by ofl'set-
`ting beams in the switching direction. The WSS 100 is dis-
`closed in U.S. Pat. No. 6,707,959 to Ducellier et al, which is
`assigned to the assignee of the instant application and is
`incorporated herein by reference. In the WSS 100, a light
`redirecting element having optical power in the form of a
`spherical reflector 120 receives a beam of light from a front-
`and unit 122. The spherical reflector 120 reflects the beam of
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`light to a diffraction grating 124, which disperses the beam of
`light into its constituent wavelength channels. The wave-
`length channels are again redirected by the spherical minor
`120 to a backend unit 126, which is also referred to herein as
`a beam director.
`
`The front end unit 126 according to prior an is illustrated in
`FIG. 2 in firrther detail and includes equally spaced input!
`output optical ports 132A to 132D disposed in a row, each of
`which may have a corresponding lens 134A to 134D, respec-
`tively, forming a lens array 134; although four ports are
`shown, a WSS may have any number ofports greater that two.
`An angle to offset lens 136, also referred to herein as the
`switching lens, converts the lateral offset of the inputfoutput
`ports 132A to 132D relative to an optical axis 111 into an
`angular beam offset at a point 138, which is imaged by the
`spherical reflector 120 onto the beam director 126. The lens
`array 134 is optional and can be absent in some embodiments.
`The optical ports 132A-C may be coupled to a 1D fiber array,
`and may be ends ofsingle mode optical fibers laid out in a row
`in equally spaced parallel v-groves in a fiber array unit (FAU)
`132.
`
`The beam director 126 may include an actuation array of
`bm deflecting elements, which may be in the form of a
`micro-electro-mechanical (MEMS) array of tilting miners
`which can be used to steer each ofthe demultiplexed beams to
`one of several positions corresponding to a desired output
`port 132. The beam angle introduced at the back end unit 126
`is then transformed by the switching lens 136 to a lateral
`offset corresponding to the desired inputfoutput fiber 132A to
`132D. Alternatively, a liquid crystal phased array (LC or
`LCoS, if incorporated on a silicon driver substrate) can be
`used as the beam director 126 to redirect the light, as
`described for example in U.S. Pat. No. 6,707,959 that is
`incorporated herein by reference.
`In operation, an optical multiplexed signal is launched into
`the front-end unit 122 and optionally passes through a polar-
`ization beam splitter and a waveplate (not shown) to provide
`two beams of light having the same state ofpolarization. Each
`of the two beams of light is transmitted to the spherical
`reflector 120 and are reflected therefrom towards the diffrac-
`
`tion grating 124. The diffraction grating 124 separates each of
`the two polarized beams into a plurality ofchannel sub-beams
`of light having different central wavelength, each channel
`sub-beam formed of a diflerent spectral portion of the input
`optical signal, and disperses them in a dispersion plane,
`which is in the plane of, or parallel to or at an acute angle to
`the plane of, FIG. 1. In a preferred embodiment the dispersion
`plane is generally perpendicular to the plane of FIG. 2 in
`which the optical fiber ports 132A-132D are spread out, also
`referred to herein as the switching plane, to make switching
`between different ports less wavelength dependent, although
`dispersing the wavelengths in the plane of FIG. 2, i.e. the
`switching plane, is also possible. The plurality of channel
`sub-beams are transmitted to the spherical reflector 120,
`which redirects them to the MEMS 126, where they are inci-
`dent upon respective micro-mirrors as spatially separated
`spots corresponding to individual spectral channels.
`Each channel sub-beam can be reflected by a respective
`minor or a group of DC cells of the beam director 126 back-
`wards along the same path or a different path, which extends
`into or out of the page in FIG. 1 to the array of fibers 132,
`which would extend into the page generally normally to the
`dispersion plane. Alternatively, each channel sub-beam can
`be reflected backwards along the same path or a different
`path, which extends in the plane of the page of FIG. 1. The
`sub-beams of light are transmitted, from the beam director
`126, back to the spherical reflector 120 and are redirected to
`
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`US 7,676,126 B2
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`the diffraction grating 124, where they are recombined and
`transmitted back to the spherical reflector 120 to be transmit-
`ted to a predetermined inputfoutput port 132A, B, C or D
`shown in FIG. 2.
`Referring to FIGS. 1 and 2, each ofthe micro-mirrors ofthe 5
`bm director 126 is rotatable to reflect the channel sub-beam
`incident thereupon at a controllable angle, so as to direct it,
`with the aid ofthe spherical mirror 120 and the switching lens
`136, to a selected one of the output optical ports 132A-D, as
`illustrated by beams 201A-201D that are shown to couple in
`or out respective output ports 122A-122C. By tilting a micro-
`mirror so as to tilt a respective channel sub-beam slightly
`away from an angle corresponding to an optimal alignment
`with the selected one of the optical ports 132A-D, an optical
`coupling of a sub-beam into a respective selected port can be
`reduced, as the channel sub-beam will impinge upon the
`selected port with an oflset, thereby providing a controllable
`attenuation to light coupled into the selected port.
`in an embodiment wherein the switching plane is orthogo-
`nal to the dispersion plane it may be preferable that the attenu-
`ation is achieved by tilting the beam in the switching plane,
`i.e. in the plane of FIG. 2, which coincides with or is parallel
`to the plane of the port array 132. However, in this case tilting
`the channel sub-beam away from the selected port will move
`it towards an adjacent optical port. This is illustrated in FIGS.
`3A and 3B, which are face-on depictions of a portion of the
`FAU 132 showing the three consecutive optical ports 132A-C
`disposed in a row with equal spacing, or distance, d, therebe-
`tween; also schematically shown is a cross-section of the
`bin 201B at a beam entrance plane of the FAU 132. Note
`that in the context of this specification, the tenns “distance
`between ports" and “spacing between ports” are used inter-
`changeably to mean a distance between optical axes of adja-
`cent optical ports.
`FIG. 3A illustrate the optimal alignment of the beam 201B
`with the selected optical port 132B of the FAU 132, with the
`optimal alignment corresponding to a substantially zero cit"-
`set between optical axes thereof, so that substantially all light
`of the bm 210B is coupled into the selected output port
`132B.
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`In FIG. 3B, the beam 21 0B is shown witha slight olfset 128
`from the port 132B so as to reduce a traction of the light
`coupled into the selected port 132B and provide a desired
`degree of attenuation for the coupled light. However, the
`bm 210B is thereby moved closer to the adjacent port 132A
`so that a portion of light of the beam 210B may now be
`coupled into the adjacent port, resulting in an undesirable
`leaking ofthe optical signal directed to the port 132A into the
`adjacent port 132B, and an optical crosstalk between the
`ports.
`Referring now to FIG. 3C, the distance between ports
`132A-C is increased to a largervalue d2 in a FAU 232, so as to
`reduce or eliminate this undesirable optical crosstalk between
`ports when the beam is oflset for attenuation. Here, dz should
`be suificiently large to prevent light of the beam 201B from
`coupling into the adjacent port 132A beyond a pre-defined
`small value at maximum target attenuation. The distance
`between ports can be expressed in term of the radius 0;) of the
`optical beam 201 at the entrance to the respective port; if the
`bm intensity profile is approximately Gaussian, the beam 60
`radius may be measure at the lie: intensity level. By way of
`example, the ports may be separated by d,=4tu with no pro-
`vision for attenuation, and by Cl2=6(t] with a provision for a
`maximum attenuation by 15 dB and a condition that the
`inter-port crosstalk must not exceed -35 dB.
`However, increasing ofthe inter-port distance has an unde-
`sirable consequence of increasing the overall size of the port
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`array 232, i.e. the distance between ports at the opposite ends
`ofthe array 232, resulting in a larger required tilt angle of the
`micro-mirrors of the beam director 126, and a larger required
`maximum switching voltage that have to be applied to the
`MEMS mirrors.
`
`Therefore, one aspect of the present invention provides a
`FAU 332 having non-equally spaced optical ports as shown in
`FIG. 3D, and a front-end unit 222 shown in FIG. 4 utilizing
`the FAU 332. In the FAU 332, the three consecutive ports
`132A- 13 2C are disposed ina row and are separated liom each
`other by two non-equal distances d2 and d 1, wherein one of
`these distances is greater than the other by at least 10%, and
`preferably by about 20% or more depending on the desired
`maximum attenuation and a diameter of the beam. In the
`shown example, the first port 132A and the second, or middle
`port 132B are disposed at the distance dz from each other,
`which is greater than the distance d, between the middle port
`132A and the third port 132B. The greater of the two dis-
`tances, which is d.2 in the shown embodiment, should be
`sufficiently large so that the beam 201B is not coupled into the
`next adjacent port 132A when the beam offset 128 corre-
`sponds to a maximum desired attenuation of the beam
`coupled into the port 132B. In some embodiments, the dis-
`tance dz may be selected so that the ratio dgfdl is between 1.2
`and 1.6.
`
`In operation, when the optical signal into the port 132B
`needs to be attenuated, the beam 201 at the entrance to the
`FAU 332 is moved towards the adjacent port 132A that is
`disposed farther away than the opposite adjacent port 132C,
`as indicated by the arrow 21], i.e. the beam is moved into the
`larger of two inter-port spacings separating the selected
`middle port 13 2B from the two adjacent ports 132A, C closest
`thereto. Accordingly, the distance cl, between the middle port
`132B and its other adjacent port 132C can be chosen without
`allowance for attenuation.
`
`By way of example, in one embodiment the first inter-port
`distances cl, is between 100 nm and 150 um, and the second
`larger inter-port distance d, is between 150 and 300 pm. In
`another embodiment,
`the first
`inter-port distances d,
`is
`between 200 mm and 300 pm, and the second larger inter-port
`distance d2 is between 300 and 600 pm.
`With reference to FIG. 4, the front-end unit 222 that utilizes
`the FAU 332 of the present invention may include a micro-
`lens array 234 wherein the micro-lenses 13 4A-1 34D are non-
`equally spaced so as to be aligned with respective optical
`ports of tire FAU 332, but is otherwise similar to the front-end
`unit 122 shown in FIG. 2. Optical bea.ms 201B and 201B‘ are
`shown by way of example to illustrate optimal beam-port
`alignment, and an alignment with a beam offset for attenua-
`tion, respectively.
`FIGS. 5 and 6 provide an example of a multiport routing
`device 200 according to one embodiment of the present
`invention. The multiport routing device 200 may be similar to
`the WSS 100 in all respects except that it utilizes the front-end
`unit 222 with non-equally spaced optical ports in place of the
`front-end unit 122 described hereinabove with reference to
`FIG. 2.
`Specifically, FIG. 5 shows the side view of the device 200,
`with only a single MEMS micro-mirror 126A of the beam
`director 126 shown for illustration. The FAU 332 includes the
`
`three consecutive output ports 132A, 132B and 132C, which
`are referred to herein as the first, second, and third optical
`ports, respectively, and are disposed in a row in the plane of
`FIG. 5, which coincides with or is parallel to the switching
`plane of the device. The difliaction grating 124 and the
`MEMS micro-mirror 126A are preferably disposed in the
`focal plane of the spherical mirror 120, but are shown with a
`
`14
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`14
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`7
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`US 7,676,126 B2
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`slight offset therefrom for clarity. In FIG. 5, the beam director
`126 is adjustable to orient the MEMS Inicro-Inirror 126A to
`deflect a beam 201B at a controllable angle 141 so as to direct
`it to couple into any of the ports 132 alter twice reflecting
`from the spherical mirror 120 and once—from the grating 5
`124. By way of example, the beam director 126 is shown to
`direct the beam 201B along an optical path shown by a
`respectively labeled solid line for coupling into the port 132B,
`which is selected by the chosen orientation of the micro-
`mirror 126A. The orientation of the micro-mirror 126A may
`be firrther adjusted to at lst partially tilt the light bm 201B
`away fiom an alignment with the second optical output port
`towards one the adjacent optical ports that is distanced farther
`away from the selected second optical port 132B, so as to
`affect a variable optical loss for light passing through the
`second optical port 132B without causing light of the light
`but 201B to leak into any ofthe adjacent optical ports. Light
`bm 201B can be tilted to impinge upon the selected port
`132B with an offset, as illustrated by the beam 201B‘ shown
`with a dashed line. In the shown example, the micro-mirror
`126A of the beam director 126 is tilted clock—wise which is
`suitable to move the beam 201B at the FAU 332 towards the
`
`10
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`15
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`20
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`FIG. 7 illustrates an optical path of a de-multiplexed beam
`311 that is directed by a corresponding MEMS mirror of the
`beam director 20 to align with the second optical port 132B
`disposed between the first optical port 132A and the third
`optical port 132C at the non-equal distances dz and d1 there-
`from, respectively. By tilting the respective mirror of the
`MEMS beam director 20 clock-wise, the beam 311 may be
`made to follow a slightly difierent optical path so as to arrive
`at the FAU 332 with a slight offset with respect to the target
`port 132B, as illustrated by a dashed line in FIG. 7, so at to
`provide a desired degree of attenuation for light coupled into
`the port 13213. Since the beam is offset towards the port 132A
`that is positioned farther apart from the target port 132B,
`substantially no light of the beam 201B is leaked into the
`adjacent port. It will be appreciated that while offsetting the
`but 201B in the direction of the first ports 132A is accom-
`plished in the shown example by tilting the MEMS mirror 20
`clock-wise, beams ofdifferent wavelength may require tilting
`a respective minor of the beam director 20 counter-clock-
`wise in order to move the respective beam towards the larger
`inter-port spacing. It will be fiirther appreciated that although
`only 5 optical ports 132 are shown, the FAU 332 may include
`any number of optical ports greater than 2.
`For example, FIG. 8A illustrates an embodiment of the
`FAU 332 having 9 optical ports disposed in a row shown in a
`vertical orientation, including three non-equally spaced con-
`secutive ports 432A, 432B and 432C, of which first two
`adjacent ports 432A and 432B are spaced apart by the dis-
`tanoe dz that is greater than the distance (11 separating the
`second two adjacent ports 432B and 432C. In the shown
`embodiment, each optical port is spaced apart from two near-
`est adjacent optical ports by two non-equal distances that
`differ by at least 10%, and preferably by between 20 and 60%.
`The direction of beam offset for attenuation for each port is
`indicated by thick arrows 211. FIG. 8B provides for compari-
`son a FAU 232 having the same number of optical ports that
`are equally spaced according to the prior art, with inter-port
`distances dz selected to allow a similarbeam offset for attenu-
`ation without port cross-coupling.
`Advantageously, the non-equally spaced optical ports of
`the present invention enable to reduce the port array size and
`the maximum beam switching distance, which is indicated in
`FIGS. 8A,B with arrows 401 and 301, respectively. By way of
`example, cl,
`is 100 pm, dz is 150 um, and the maximum
`switching distance between opposite edge ports is reduced in
`an optical routing device such as WSS 200 utilizing the FAU
`332 by 200 pm or about 15% compared to a similar optical
`routing device utilizing the FAU 232, advantageously result-
`ing in a reduction of a maximum switching voltage, or
`enabling adding another port within the angular range of FAU
`232. Reducing the total switching angle range required to
`switch over a given number of ports is advantageous also
`because the angle range achievable from a beam director such
`as a MEMS mirror is limited. As a further advantage, reduc-
`ing the switching angle reduces the numerical aperture of the
`optical system in the switching direction, which helps to
`reduce the effect of aberrations and the overall size of the
`optics.
`Although the embodiments described hereinabove are
`shown with a single one-dimensional array of non-equally
`spaced optical ports, other or the same embodiments may
`utilize two-dimensional port arrays. According to the inven-
`tion, such two-dimensional arrays of ports include one or
`more rows of in which at least three consecutive ports are
`non-equally spaced, with a middle optical port located closer
`to one of adjacent ports in the respective row than to the other
`
`port 132A, which is the farthest fi'om the selected port of the
`two closest adjacent ports 132A and 132C.
`F'lG. 6 shows a top view ofthe device 200; which is similar
`to the top view of the WSS 100 shown in FIG. 1, except for the
`front-end unit 222 shown to replace the prior-art front unit
`122 in accordance with the present invention.
`FIGS. 5, 6 illustrate just one particular embodiment of the
`multi-port routing device of the present invention with non- 30
`equal port spacing. It will be appreciated that other types of
`multi-port optical routing devices, which provide variable
`optical attenuation by moving a beam of light directed to a
`selected optical port closer to an adjacent output port, will
`benefit from the use of non-equal spacing of the optical ports
`as described hereinabove.
`
`35
`
`For example, FIG. 7 shows a WSS 300 according to
`another exemplary embodiment of the invention. The WSS
`300 is based on a known switching platform that is described
`for example in U.S. Patent Application No 2006r'0245685 to
`Ducellier et al, which is incorporated herein by reference.
`However, while the device described in the ’685 application
`has evenly-spaced ports, the WSS 300 utilizes the front-end
`unit 222 with N non-equally spaced ports 232 disposed in a
`row. In the shown example the WSS 300 is configured as a
`1x5 switch with a MEMS-based beam director 20, a diffrac-
`tion grating 14, and a coupling lens 18 having an optical
`power for optically coupling the optical ports 18, the grating
`14 and the beam director 20. One difierence between the WSS
`300 and WSS 200 described hereinabove is that in the WSS
`
`300 the switching and dispersion planes are substantially
`parallel coinciding with the plane of FIG. 7.
`An optical port 232:’ is aligned with an optical axis of the
`WSS 300 and may be used as an input port, while the 4 others
`may be used as output ports. In operation, an input wave-
`length-multiplexed optical signal 301 from the input optical
`port 232:‘ is passed to the grating 14,