`Bishop et al.
`
`US006507421B1
`
`(10) Patent No.: US 6,507,421 B1
`(45) Date of Patent: Jan. 14, 2003
`
`(54) OPTICAL
`
`MONITORING FOR OXC FABRIC
`
`(75) Inventors:
`
`David John Bishop, Summit, NJ (US);
`Randy Clinton Giles, Whippany, NJ
`(US); David Thomas Neilson,
`Plainsboro, NJ (US)
`
`6,292,281 B1 " 9/2001 Bala et al ................... 359/110
`6,301,402 B1 " 10/2001 Bhalla et al .................. 386/’16
`6,330,380 B1 ~ 12;/2001 Young et al .................. 385/’17
`6,363,182 B2 ~ 3,/2002 Milles ct al .................. 385/’17
`6,366,716 BI = 4,/2002 Graves ........................ 385/’17
`6,396,975 B1 ~ 5,/2002 Wood et al ................... 385/’18
`
`(73) Assignees:
`
`Lucent Technologies Inc., Murray Hill,
`NJ (US); Agerc Systems Guardian
`Corp., Orlando, FL (US)
`
`cited by examiner
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/414,621
`
`(22) Filed:
`
`Oct. 8, 1999
`
`Int. CI.~ ................................................. H04J 14/00
`(51)
`(52) U.S. Cl ........................ 359/117; 359/128; 359/110;
`359/124; 359/’127; 359/130; 359/159; 385/17;
`385/18
`
`(58) Field of Search ................................. 359/117, 128,
`359/110, 124, 127, 130, 139, 159; 385/17,
`18, 16, 24, 19, 20, 21, 22, 23
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`Primary Examiner~eslie Pascal
`Assistant ExaminerM Ianh Phan
`(74) Attorney; Agent, or Firm~ohen, Pontani, l,ieberman
`& Pavane
`
`(57)
`
`ABSTRACT
`
`An optical crossconnect (OXC) fabric including an array of
`tiltable mirrors, a reflector and a plurality of optical fibers
`controls the position of the mirrors to optimize the transfer
`of a signal between an input optical fiber and an output
`optical fiber by monitoring the optical signal at an optical
`translation unit in each of the input optical fiber and the
`output optical fiber. The optical translation units are operable
`for regenerating the optical signals transmitted through the
`fibers.
`
`5 436 986 A *
`
`7,/1995 Tsai ............................ 385/’16
`
`11 Claims, 2 Drawing Sheets
`
`200e 14c
`
`100
`
`14o
`
`20¢a
`
`"
`
`206
`
`2~4
`
`202
`
`I
`
`I
`
`OXC FABRIC
`
`l CONTROLLER
`
`50
`
`/~200b
`OTO I
`
`204 202
`
`206 [
`
`I
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-1
`
`
`
`U.S. Patent
`
`Jan. 14, 2003 Sheet 1 of 2
`
`US 6,507,421 B1
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-2
`
`
`
`U.S. Patent
`
`Jan. 14, 2003 Sheet 2 of 2
`
`US 6,507,421 B1
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-3
`
`
`
`US 6,507,421
`
`B1
`
`1
`OPTICAL MONITORING FOR OXC FABRIC
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`’lhe present invention relates to an Optical Crossconnect
`(OXC) fabric for connecting an optical signal in an input
`fiber to an output fiber and that includes an array of I/O
`fibers, an array of tiltable mirrors, and a reflector.
`2. Description of thc Related Art
`An Optical Crossconnect (OXC) device comprises an
`array of lenses, a corresponding array of mirrors, and a
`reflector. An array of 1/O fibers which corresponds to the
`array of lenses is received in the device so that the array of
`mirrors corresponds to the array of I/O fibers. Each of the
`mirrors is tiltablc about 2 axcs for dirceting an input signal
`received from its corresponding I/O fiber (i.e. an inpnt fiber)
`against the reflector to another mirror and to an output one
`of the 1/O libers, thereby signally connecting the input fiber
`to the output fiber and functioning as a switch.
`To ensure proper positioning of the mirrors for optimizing
`the connection of the optical signal from the input I/O fiber
`to the output I/O fiber, optical taps arc formed in each of the
`I/O fibers for monitoring the optical signals and ensuring
`that the output signal approximates the input signal. If a
`difference between the input and output signals exceeds a
`threshold value, the mirror positions are adjusted to opfimize
`the output signal. Aproblem xvith this arrangement is that the
`optical taps direct a portion of the optical signal away from
`the I/O fibcr. Furthcrmore, OXCs typically ineludc arrays of
`approximately 256 fibers and mirrors. Accordingly, the
`optical taps add considerable cost to the OXC because they
`are required for each of the I/O fibers.
`
`SUMMARY OF THE INVENTION
`
`The present invention uses signals present in an optical
`translation unit to monitor the mirror position and maintain
`optimal performance of an optical erosseonncct (OXC)
`device. After an optical signal is transmitted from its source
`to the OXC device, it is generally degraded Ii’om its original
`form and amplitude due to attenuation and other losses
`and/or disturbances that it may receive or that are present
`along its path. For this reason, each I/O fiber includes an
`optical translation unit (OTU) which detects the incoming
`signal and regeneratcs the signal to its propcr intensity and
`form. To accomplish this task, the OTU converts the optical
`signal to an electrical signal, performs the regeneration on
`the electrical signal, and transforms the regenerated electri-
`cal signal into an optical signal for continued transmission of
`the optical signal to the OXC fabric. Although the OTU is
`not a part of the OXC fabric and is typically controlled
`separately therefrom, the electrical signal present in the
`OTU can be used instead of an optical tap connected to the
`optical fiber to control the mirror position, because that
`electrical signal in the OTU represents the optical signal that
`is transmitted to the OXC fabric. Since the presence of an
`OTU in the fibers is required to ensure signal quality, the use
`of thc OTU for control of thc mirror position rcduccs the
`number of required parts for the OXC and thereby does not
`significantly add to the cost of manufaclure.
`Other objects and features of the present invention will
`become apparent from the following detailed description
`considered in conjunction with the accompanying drawings.
`It is to be understood, however, that the drawings are
`designed solely for puq~oses of ilhJstration and not as a
`
`2
`definition of the limits of the invention, for which reference
`should be made to the appended claims. It should be further
`undcrstood that thc draxvings arc not necessarily drawn to
`scalc and that, unless otherwise indicated, thcy arc merely
`s intended to conceptually illustrate the structures and proce-
`dures described herein.
`
`BRIEF DESCRIPTION OF TIlE DRAWINGS
`
`In the drawings, wherein like reference characters denote
`10 similar elements throughout the several views:
`
`FIG. 1 is an clcvatcd pcrspcctivc view of an Optical
`Crossconncct (OXC) according to thc prcscnt invcntion; and
`FIG. 2 is a block diagram showing the control arrange-
`merit for the present invention.
`
`15
`
`DETAILED DESCRIPTION OF THE
`CURRENTLY PREFERRED EMBODIMENTS
`
`Referring to FIG. 1, an Optical Crossconnect (OXC)
`20 fabric 100 comprises an array of imaging lenses 10, a mirror
`array 20, and a reflector 30. The OXC 100 is typically
`formcd using Micro Electro-Mechanical Systems (MEMS)
`technology. The array of imaging lenses 10 comprises lenses
`12a-12d respectively aligned with I/O fibers 14~-14d. The
`2s mirror array 20 includes a plurality of mirrors 22a~2d
`respectively corresponding to the 1/O fibers 14a-14d. The
`lenses 12a-12d respectively correspond to the I/O fibers
`14a-14d for focussing the optical signals transmitted
`between the I/O fibers 14a-14d and the respective mirrors
`3o 22a-22d of the mirror array 20. To simplify the drawing and
`for ease of explanalion of its operafion, lhe OXC fabric 100
`of FIG. 1 is shown as having four I/O fiber and mirrors.
`However, the OXC fabric may include any number of 1/O
`fibers and mirrors and more typically includes a 16x16 array
`35 of 256 fiber and mirrors.
`Each mirror 22a~2d of the mirror array 20 is connected
`to a controller 50 which controls the tilt of the mirrors for
`routing a signal from one 1/O fiber to another. ’lhe mirrors
`22a-22d are formed using MEMS technology with a two
`4n axis flexure gimbal mount via torsion springs 25 so that each
`mirror 22a-22d can be tilted +/-5 degrees on each axis in
`response to a voltage signal. For example, if an input signal
`on I/O fiber 14a is to be routed to I/O fiber 14c, the mirrors
`22a and 22c are tilted so that the signal is reflected off of
`45 mirror 22a and directed toward reflector 30, reflected off the
`reflector and directed toward nairror 22c, and reflected off of
`mirror 22c and directed to the I!O fiber 14c. This particular
`routing example is depicted in FIG. 1. In this manner, any
`Iwo I/O fibers may be signally connected.
`FIG. 2 is a block diagram showing the connection of the
`I/O fibers 14a-14d to the OXC fabric 100. Each of the I/O
`fibcrs 14a-14d may bc used as cithcr an input fibcr or an
`ontput fiber. However, as a practical matter some are defined
`as input fibers and others as output fibers. In FIG. 2, I/O
`5s fibers 14a and 14b are input libers and the 1/O fibers 14c and
`14d are output fibers. Before entering the OXC Fabric 100,
`each input I/O fiber 14a-14b runs through a respective
`Optical Translation Unit (OTU) 200a-200b which is con-
`neeted to the controller g0. The primary fnnction of the OTU
`~0 200a-200b is to act as a buffer element for the optical signal
`and, more specilically, as a regeneration unit for regenerat-
`ing the optical signal in the fiber. When an optical signal
`travels through a long length of optical fiber, the original
`optical signal is attenuated and may be adversely affected in
`~5 other ways such, for example, as via a phase shift and/or a
`frequency variation due to various external influences.
`Accordingly, the OTU 200a~00b on the input I/O fibers
`
`50
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-4
`
`
`
`US 6,507,421 B1
`
`3
`14a-14b converts the received optical signal into an elec-
`trical signal, regenerates the electrical signal back to its
`original intensity and lbrm, and converts the regenerated
`electrical signal back into an optical signal. The regenerated
`signal is then transmitted to the OXC fabric 100. The ontput
`I/O fibers 14c-14d also have respective OTUs 200c-200d
`which pcrform the same function. If somc degradation of the
`signal occurs in the OXC, the OTU 200c, 200d will clean-up
`the signal by restoring the correct intensity and form before
`the signal is transmittcd cxtcrnally.
`As stated above, the mirror positions are controlled by a
`controller 50 ha response to a routing command 60 from an
`external source. Basically, the routing command instructs
`the controller as to which output fibcr to connect to an input
`fiber. The routing command 60 may be a leading command
`received on an input fiber or may be received from some
`other external source. Upon receipt of the command, the
`controller 50 performs a coarse adjustment of the mirrors to
`put the mirrors into proper position. However, to optimize
`the position of the mirrors so that the optical signal is
`optimally conncctcd bctwccn thc input fibcr and thc output
`fiber, the positions of the mirrors are monitored. This is
`accomplished indirectly by monitoring and comparing the
`optical signals in the input fiber and output fiber. For this
`purpose, the controller 50 is connected to the OTUs
`200a-200d and the controller monitors the signal sent to the
`OXC fabric in the input fiber and the signal exiting the OXC
`fabric in the output fibcr. Morc spccifically, the controller 50
`is connected to the electrical signal present in each OTU
`which represents the optical signal that is sent to, in the case
`of the input fiber 14a-14b, or received from, in the case of
`the output fiber 14c-14d, the OXC 100. The controller 50
`then compares the input signal to the output signal. If the
`difference between the values of the optical signal in the
`output fibcr and thc fuput fiber cxcccds a threshold value, the
`controller $0 a~justs the position of the mirrors in an attempt
`to correct or minimiTe the difference between the signals.
`As mcutioncd above, the OTUs 200a-200d arc required
`components in an OXC 1011 for assuring signal quality.
`Accordingly, connecting the controller 5!1 to the OTU to
`provide the control signal for determining the correct mirror
`position does not require the addition of any further com-
`ponents to the OXC fabric 1110.
`FIG. 2 additionally shows a detailed view of OTU 200b
`on the input fiber 14b of the 1/O fibers and a detailed view
`of OTU 200d on the output fiber 14d. Each OTU 200a-200d
`includes an Optical-to-Electrical converter 202, a regenera-
`tion device 204, and an Electrical-to-Optical converter 206.
`The connection in the OTUs 200a-200b of the input fibers
`14a, 14b is made at the point at which the electrical signal
`is connected to the Electrical-to-Optical converter 206. An
`electrical connection in the OTUs 200c-200d of the output
`fiber 14c, 14d is made at the point at which the electrical
`signal is connected to the Optical-to-Electrical converter
`202. The electrical signals are thereby connected to the
`controller 50 and monitored for each IiO fiber. Accordingly,
`when an optical signal is being transmitted from one fiber to
`another in the OXC, the controller 50 monitors the signals
`in the input and output fibers to determine if the signal is
`being optimally transmitted and to adjust the mirrors accord-
`ingly.
`qt~us, while there have shown and described and pointed
`out fundamental novel features of the invention as applied to
`preferred embodiments thereof, it will be understood that
`various omissions and substitutions and changes in the form
`and details of the devices illustrated, and in their operation,
`may be made by those skilled in the art withmlt departing
`
`30
`
`4
`from the spirit of the invention. For example, it is expressly
`intended that all combinations of those elements and/or
`method steps which perform substantially the same function
`in substantially the same way to achieve the same results are
`s within the scope of the inveution. Moreover, it should be
`recognized that structures and/or elements and/or method
`steps shown and/or dcscribcd in conncction with any dis-
`closed form or embodiment of the invention may be incor-
`porated in any other disclosed or described or suggested
`form or embodiment as a general matter of design choice. It
`1{3 .
`~s the intention, therefore, to be funited only as indicated by
`the scope of the claims appended hereto.
`We claim:
`1. An optical crossconncct dcvicc, comprising:
`an input fiber;
`an output fiber;
`an array of tiltable mirrors comprising a plurality of
`mirrors, each mirror being tillable about at least one
`tilting axis for directing a signal received from said
`input fiber to said output fiber;
`a controller operatively connected to said array of tiltable
`mirrors for positioning said mirror of said array of
`tillable mirrors about said at least one tilting axis so that
`an input signal received from said input fiber is directed
`toward said output fiber; and
`an input buffer connected to said input fiber and an output
`buffer connected to said output fiber, said controller
`being connected to said input buffer and to said output
`buffer for monitoring an input optical signal transmitted
`from said input fiber to said array of mirrors and for
`monitoring an output optical signal rcccivcd by said
`output fiber from said array of mirrors, and said con-
`troller being operatively connected to said array of
`mirrors for operatively adjusting a position of said
`mirror of said array of mirrors ha response to a moni-
`tored difference between said input optical signal in
`said input buffer and said output optical signal in said
`output buffer.
`2. The device of claim 1, wherein said input buffer
`4n comprises an input optical translation unit connected to said
`input fiber for regenerating an optical signal in said input
`fiber and said output buffer comprises an output optical
`translation unit for regenerating an optical signal in said
`output fiber.
`45 3. Thc dcvicc of claim 2, whcrcin each of said input
`optical translation device and said output optical translation
`device comprises an optical-to-electrical converter for con-
`verting an optical signal to an electrical signal, a regenera-
`tion unit for receiving the electrical signal and regenerating
`50 the electrical signal, and an electrical-to-optical converter to
`converting the regenerated signal back to an optical signal.
`4. The dcvicc of claim 3, whcrcin said controllcr is
`connected to said electrical signal in said input optical
`translation device between said regeneration unit and said
`5s electrical-to-optical converter and said controller is con-
`nected to said electrical signal in said output optical trans-
`lation device between said optical-to-electrical converter
`and said regeneration unit.
`5. The device of claim 1, wherein said input fiber com-
`6~ prisesanarrayofinpntfibersand said mltpnt fiber comprises
`an array of output fibers.
`6. The device of claim 1, wherein said array of tiltable
`mirrors comprises a plurality of tiltable mirrors, each of said
`tiltable mirrors being rotatable about two relatively perpen-
`65 dicular axes.
`7. The device of claim 1, wherein said controller is
`connected for receiving a ronring command and inclndes
`
`35
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-5
`
`
`
`US 6,507,421 B1
`
`5
`means for coarsely adjusting said nrirrors of said array of
`mirrors in response to said routing command and for finely
`adjusting a position of said mirrors of said array of mirrors
`in response to thc monitored diffcrcncc bctwccn said input
`optical signal in said input buffer and said output optical
`signal in said output buffer.
`8. The device of claim 1, further comprising a reflector,
`wherein said tiltable mirrors are positionable so that the
`input signal received from said input fiber is directed toward
`said output fibcr via said rcflcctor.
`9. A mcthod of controlling a mirror position in a optical
`crossconnect fabric comprising an array of tiltable mirrors,
`said optical crossconnect fabric receiving a plurality of I!O
`fibers each including an optical translation unit for regen-
`erating an optical signal, wherein said tiltable mirrors are
`operable for directing the optical signal from an input one of
`the plurality of I/O fibcrs to an output one of thc plurality of
`I/O fibers, said method of controlling a mirror position
`comprising the steps of:
`monitoring a level of an optical signal being transmitted
`to the array of tiltable mirrors in the optical translation
`unit from the input one of the plurality of fibers;
`monitoring a level of an optical signal directed from the
`array of tiltablc mirrors in the optical translation unit to
`the outpnt one of the plnrality of fibers;
`comparing the monitored input optical signal to the moni-
`tored output optical signal to calculate a difference
`between the monitored input optical signal and the
`monitored output optical signal;
`
`6
`detemrining whether the calculated difference between
`the monitored input optical signal and the monitored
`output optical signal is grcatcr than a prcdctcrmincd
`threshold level; and
`adjusting the array of mirrors to minimize the calculated
`diffcrcncc between the monitored input optical signal
`and the monitored output optical signal if it is deter-
`mined in said step of determining that the calculated
`diffcrcncc between the monitored input optical signal
`and the monitored output optical signal is greater than
`the threshold level.
`10. Thc method of claim 9, whcrcin the optical translation
`units each include an optical-to-electrical converter for
`converting the optical signal into an electrical signal, and
`whcrcin each of said steps of monitoring a lcvcl of an optical
`signal from the input one of the plurality of fibers and of
`monitoring a level of an optical signal directed to the ontput
`one of the plurality of fibers includes monitoring the elec-
`trical signal in the optical translation units.
`11. The method of claim 9, wherein said step of adjusting
`the array of mirrors comprises coarsely adjusting the array
`of mirrors in response to an external routing command and
`finely adjusting said array of mirrors in response to the
`calculated difference between the monitored input optical
`signal and the monitored output optical signal.
`
`Petitioner Ciena Corp. et al.
`Exhibit 1007-6