(12) United States Patent
`Aksyuk et al.
`
`([10) Patent No.:
`(45) Date of Patent:
`
`US 6,204,946 B1
`Mar. 20, 2001
`
`US006204946B1
`
`RECONFIGURABLE VVAVELENGTH
`DIVISION MUL’I‘IPLEX ADD/DROP DEVICE
`USING MICROMIRRORS
`
`Inventors: Vladimir A. Aksyuk, Piscataway;
`David J. Bishop, Summit; Joseph E.
`Ford, Oakhurst; James A. Walker,
`Howell, all of NJ (US)
`
`Lucent Technologies Inc., Murray Hill,
`NJ (US)
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Appl. No; 08/968,935
`Filed:
`Nov. 12, 1997
`
`Related U.S. Application Data
`Provisional application No. 60/056,482, filed on Aug. 21,
`1997.
`
`Int. Cl.7 ...................................................... H04J 14/02
`
`U.S. Cl.
`
`.......................... 359/131; 359/124; 359/129;
`385/24
`
`Field of Search
`
`359/124, 129-131,
`359/128; 385/24
`
`/10
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3/1998 Chawki etal.
`5,726,785 ’*
`9/1998 Bendellietal.
`5.812291 *
`7/199‘) Miyakawa et al.
`5,926,300 *
`* cited by examiner
`Primary Examiner4Kinfe—Michael Negash
`(57)
`ABSTRACT
`
`...........
`
`359/130
`359/129
`................ .. 35‘)/124
`
`AWDM add/drop device for use in an optic communications
`system for adding and dropping optical wavelengths from a
`m1Iltiple—wavelengtli optical system. The device includes a
`set of lenses, a planar grating wavelength multiplexer and a
`mieromirror array switchable for individual wavelengths of
`the multiple—Wavelength signal between a transmit mode and
`a refieet mode. The grating angularly demultiplexes a
`multiple-wavelength optical signal in a first direction and the
`individual wavelengths are processed by the micromirror
`array and directed to the grating in a second direction. The
`micromirror array will either refleet select wavelengths to a
`first port or transmit select wavelengths to a second port. In
`a preferred embodiment, ports on a first multiport circulator
`input the multiple-wavelength optical signal to the WDM
`add/drop device and output the multiple-wavelength optical
`signal from the WDM add/drop device. A second multiport
`circulator provides to-be-added wavelengths to the WDM
`add/drop device and removes to-be-dropped Wavelengths
`from the WDM add/drop device.
`
`26 Claims, 2 Drawing Sheets
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-1
`
`

`
`U.S. Patent
`
`Mar. 20, 2001
`
`Sheet 1 0f2
`
`US 6,204,946 B1
`
`FIG.
`
`1
`
`H/0910000091
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-2
`
`

`
`U.S. Patent
`
`Mar. 20, 2001
`
`Sheet 2 of 2
`
`US 6,204,946 B1
`
`FIG. 3
`
`10
`
`I
`won REFLECT/TRANSMIT
`
`°‘R°”““°R 2
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-3
`
`

`
`US 6,204,946 B1
`
`1
`RECONFIGURABLE WAVELENGTH
`DIVISION MULTIPLEX ADD/DROP DEVICE
`USING MICROMIRRORS
`
`RELATED APPLICATION
`
`This application claims priority from U.S. Provisional
`Patent Application Ser. No. 60/056,482 which was filed on
`Aug. 21, 1997.
`BACKGROUND OF THE INVENTION
`
`I. Field of the Invention
`
`This invention relates to optical devices for adding and
`dropping optical signals to an optical fiber carrying existing
`optical signals without interfering with the existing optical
`signals. More particularly, the present invention is directed
`to a wavelength division multiplex add/drop optical device
`using a micromirror array for transmitting and reflecting
`optical signals in an optical communications system.
`II. Description of the Related Art
`In wavelength division multiplexed optical networks it is
`increasingly important to be able to switch multiple inde-
`pendent wavelength signals into and out of a single fiber
`without disturbing the other channels. This task is presently
`accomplished by utilizing an assembly of separate compo-
`nents such as a pair of wavelength demultiplexers and a set
`of N two-by-two bypass exchange switches. As is known,
`one of the wavelength demultiplexers, also known as a
`router, separates a multifrequency optical input data signal
`into N multiple fibers, with each fiber carrying a single ’
`wavelength. The bypass exchange switches accept the added
`and dropped channels. The other wavelength multiplexer
`combines the existing wavelengths with the added wave-
`lengths onto a single fiber for transmission in the commu-
`nications system. Among the drawbacks of such a discrete
`component approach, however, are the cost and size of the
`individual components and the resulting overall cost and
`size of the system.
`SUMMARY OF THE INVENTION
`
`_ ,
`
`A wavelength division multiplexed (WDM) transmit/
`reflect unit is disclosed for transmitting and reflecting select
`wavelengths of a multiwavelength optical signal onto optic
`fibers in an optic communications network. The transmit_/
`reflect unit includes a lens positioned at a first port and a
`second port for directing the incoriiirig optical signal to a
`planar grating wavelength multiplexer which angularly dis-
`perses the wavelengths in the signal. Afocusing lens focuses
`the angularly dispersed wavelengths for receipt by a micro-
`mirror array switchable between a transmitting mode and a
`reflecting mode. The transmitting mode directs select wave-
`lengths of the incoming signal from one port to the other port
`and the reflecting mode directs an incoming signal from the
`first port back to the first port.
`Areconfigurable WDM add/drop device is also disclosed. H
`The add/drop device employs a WDM transmit/reflect unit,
`of the type described above, which is disposed between first
`and second 3-port circulators. The first circulator interfaces
`with one port on the transmit/reflect unit and receives, from
`an input port, an input multiwavelength optical signal and
`outputs, to an output port, a multiwavelength optical signal.
`The second circulator interfaces with another port on the
`transmit/reflect unit. The second circulator receives, froiu.
`an add port, a wavelength to be added to the multiwave-
`length signal, and transmits, to a drop port, a wavelength to
`be dropped from the multiwavelength signal.
`
`2
`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 purposes of illustration and not as a
`definition of the limits of the invention, for which reference
`should be made to the appended clairris.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings, wherein like reference numerals denote
`similar elements throughout the several views:
`FIG. 1 is a diagrammatic representation of an optical
`transmit/reflect unit in accordance with the present inven-
`tion;
`FIG. 2 depicts a single column micromirror array;
`IIIG. 3 is a block diagram of a WDM add/drop device in
`accordance with the present invention; and
`FIG. 4 depicts a dual column micromirror array.
`DETAILED DESCRIPTION OF THE
`PRESENTLY PREFERRED EMBODIMENTS
`
`The present invention utilizes a modified attenuation unit
`10 as shown in FIG. 1, which is the subject of U.S. patent
`application Ser. No. 08/690,696 filed on Jul. 31, 1996
`entitled “Attenuation Device For Wavelength Multiplexed
`Optical Fiber Communications”, the entirety of which is
`incorporated by reference herein. As shown, unit 10 includes
`_ a planar grating wavelength multiplexer 12 and a modulator
`array 14. Unit 10 has a first port 16 which receives optical
`signals from an optical fiber 5 carrying multiple wave-
`lengths. The light from the optical fiber 5 input at port 16 is
`collimated by a collimating lens 18 and is then diffracted by
`the planar grating 12 so that each wavelength in the optical
`signal provided to port 16 is dispersed,
`i.e.
`the various
`wavelengths leave the grating 12 at different angles from
`each other. The dispersed light is then focused by a lens 20
`onto the modulator array 14 to produce a column of spots,
`with each spot position in the column of spots corresponding
`to a particular wavelength in the input signal.
`As explained more fully in the aforementioned US.
`patent application Ser. No. 08/690,696, modulator array 14
`has a reflective surface and includes a column of variable
`attenuators positioned to coincide with the location of spots
`in the column of spots. The attenuators are reflective micro-
`mechanical devices whose reflectivity can be electrically
`controlled. Each spot corresponding to each wavelength in
`the focused signal is incident on a different attenuator, thus
`allowing individual control of the transmitted intensity for
`each wavelength. The modulator 14 is placed with its
`reflective surface normal to the optical axis of the unit 10 so
`that the attenuated light reflected from the modulator 14 can
`be collected and collimated by a second pass through
`focusing and collimating lens 20. Lens 20 is positioned such
`that the original incident beam (the beam travelling in the
`direction of arrows/\and B) illuminates a different region of
`the surface of lens 20 than the surface illuriiiriated by the
`reflected beam (the beam travelling in the direction of
`arrows C and D). In other words, there is no spatial over-
`lapping of the reflective beam with the incident beam on lens
`20.
`After the attenuated signals from modulator array 14 are
`colliriiated by lens 20, the collimated signals propagate back
`towards the grating 12 which then diffracts the light
`to
`combine all of the wavelengths of the collimated signals into
`the same angle and redirects the light towards the input
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-4
`
`

`
`US 6,204,946 Bl
`
`3
`collimating lens 18. Since, as discussed above, the reflected
`light is laterally displaced as a result of the position of lens
`20, a fold mirror 22 may be introduced to direct only the
`attenuated reflected light into an output collimating lens 24
`which is used to focus the light onto a separate output fiber
`7 positioned at a second port 26. In such a configuration, the
`multiple wavelength attenuator unit 10 can be used as a
`functionally transmissive component. In other words, light
`entering fro111 one fiber 5 through first port 16 is aifected by
`the modulator 14 and continues into a separate and distinct
`output fiber 7 positioned at the second port 26.
`In accordance with the present invention, the attenuation
`unit 10 of FIG. 1 is modified by replacing the modulator
`array 14 with a micromechanical mirror array; the somodi—
`fied unit 10 can then be used as a WDM transmit/reflect
`switch operable in a reflective mode and in a transmissive
`mode. In the transmissive mode, select wavelengths are
`directed or transmitted from first port 16 to second port 26.
`In the reflective mode, select wavelengths input at first port
`16 are reflected back to that same port. In particular, and
`with reference to FIG. 2, a micromechanical mirror array 30
`having a plurality of micromirror plates 32 arranged in a
`single column is shown. Mirror array 30 is designed so that
`each incoming optical wavelength—which, as explained
`above,
`is represented by a spot
`in a column of spots—
`illuminates a separate micromirror plate 32 in the micro-
`mirror array. Each micromirror plate 32 can be electrically
`controlled to toggle between two or more angular states so
`that each micromirror plate will orient its corresponding
`reflected wavelength into one of two or more directions.
`In a preferred embodiment, the micromirror array 30 is
`designed with an appropriate micromirror plate pitch, tilt
`angle, and tilt axis such that in one state (“off”) the reflected
`hght is directed to the output collimating lens 24 and second
`port 26, and in the other mirror state (“on") the light is
`reflected back onto the same path by which it entered the
`micromirror so that the light is returned to the first colli-
`mating lens 18 and directed back to the input fiber through
`first port 16.
`Thus, as explained above, by replacing modulator 14 in
`the attenuation unit 10 of FIG. 1 with mirror array 30, there
`is formed a WDM transmit/rcflcct unit that can operate in a
`transmissive mode and in a reflective mode. The VVDM
`switch may be placed in an optical fiber path carrying
`multiple wavelengths to selectively reflect or transmit each
`individual wavelength, depending on a set of electrical
`control signals applied to the mirror array plates 32. The
`response time of the WDM switch is determined by the
`mirror array 30, i.e. by the toggle time for the individual
`micromirror plates 32.
`In general, it is possible for the VVDM switch 10 to operate
`in three states, namely
`to reflect a signal input at port 16
`back to port 16, (ii) to transmit a signal input at port 16 to
`port 26 and vice versa; and (iii) to reflect a signal input at
`port 26 back to port 26. In the transmissive mode wherein ..
`the mirror array 30 is set to transmit a particular wavelength
`from one port to the other, light at the particular wavelength
`which enters fiber port 16 will be carried to fiber port 26.
`Similarly, and because of the symmetrical property of the
`optical path, light at that particular wavelength which enters
`fiber port 26 will be transmitted to fiber port 16. In a
`refiective mode, however,
`the reversible property of the
`optical path is not present because the angle of the micro-
`mirror which reflects one incident beam will cause light
`from the other port. to be reflected at an angle of twice the
`original incident angle. Therefore, when the WDM transmit/
`reflect unit of FIG. 1 operates in a reflective mode to reflect
`
`_
`
`4
`a particular wavelength, light at the particular wavelength
`which enters fiber port 16 will be reflected back to fiber port
`16, i.e. will not be transmitted to fiber port 26. When, on the
`other hand, light at the particular wavelength enters fiber
`port 26, the signal will not reflect back to fiber port 26.
`In accordance with the present invention, the modified
`two state transmit/reflect unit 10 is used as an element of a
`WDM add/drop device 40, as illustrated, by way of example,
`in FIG. 3. As there shown, the WDM transmit/reflect unit 10,
`i.e. the attenuator shown in FIG. 1 with mirror array 30 (FIG.
`2) substituted for modulator 14, is placed between a first and
`a second 3-port optical circulator 42, 44. A 3-port optical
`circulator is a commercially available device which transfers
`an input signal at port C1 to port C2, and which transfers an
`input signal at port C2 to port C3. The first circulator 42
`receives a VVDM input data stream 46 and passes it to port
`1 (corresponding to the first port 16 in FIG. 1) on the WDM
`transmit/reflect unit 10. For wavelengths which are to be
`carried without change (i.e. wavelengths neither added nor
`dropped), the corresponding micromirrors in switch 10 are
`set to reflect first port 16, i.e. to reflect those wavelengths
`back to first port 16. The reflected signals enter circulator 42
`through port C2 and are carried by the circulator to port C3,
`where they continue in the optical network as a W'DM output
`data stream 48.
`In the transmissive mode, the inventive WDM add/drop
`device 40 is configured to add a wavelength to the WDM
`input 46 only when a wavelength is dropped. Thus, in the
`transmissive mode, unit 10 is activated to pass or transmit
`through its second port the Wavelength to be dropped to
`circulator 44 and to pass or transmit the wavelength to he
`added from circulator 44 to circulator 42. In particular, the
`transmitted (to-be-dropped) wavelength leaves unit 10
`through its fiber port 2 and enters the second circulator 44
`through its port C2, and leaves the circulator through a fiber
`connected to circulator port C3. A router 50 connected to
`port C3 can be included for WDM demultiplexing so that the
`dropped wavelength may be directed into separate fibers, as
`is known in the art
`to, for example, direct
`the dropped
`wavelength to downstream optical network units. Wave-
`lengths that are to be added are provided to an input router
`52 which multiplexes the wavelengths to a single fiber
`connected to port C1 of circulator 44. The incoming (to—be—
`added) wavelengths at port CI of circulator 44 will be
`transmitted by device 10, i.e. by activating the mirror plate
`32 corresponding to the added wavelength to transmit the
`added wavelength. The transmitted added wavelength is
`then combined onto the WDM output signal 48.
`With reference now to FIG. 4, a preferred embodiment of
`the micromirror array 30 is depicted. As shown, the micro-
`mirror array has two columns of mirrors 32' separated by
`low rellectivity surround 33. The mirrors are deposited on
`plates suspended between pivots 34 so as to enable them to
`tilt about an axis. In the preferred embodiment, the tilt axis
`is chosen so as to provide n1axir11ur11 coupling and minimum
`crosstalk. The mirror position is controlled by a voltage
`applied to electrodes 35 connected to individually addressed
`electrical pads (not shown) located below the mirrors. An
`electrostatic force that is generated by the applied voltage
`between the pads and the mirrors 32‘ deflects the addressed
`mirror to one of the two angular states.
`The WDM add/drop device 40 can be used to simulta-
`neously process more than one multifrequency optical sig-
`nal. For example, and again with reference to FIG. 1,
`multiple fibers each carrying a multifrequency signal can be
`coupled to ports 16 and 26. As will be readily apparent from
`the foregoing discussion, each optical signal carried by each
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-5
`
`

`
`US 6,204,946 B1
`
`5
`optical fiber will produce a corresponding column of spots,
`with the position of each spot in each column corresponding
`to a particular wavelength. Thus, a pair of input fibers placed
`side-by-side will create two parallel rows of spots at the
`miciomeehanical iiiirior array 30. By configuring iriicroiiie-
`chanical mirror array 30 so that it contains multiple columns
`of mirrors as for example shown in FIG. 4, i.e. a mirror
`column for each column of spots, multiple optical signals
`can be siriiiiltaneously processed by the niicroniechaiiical
`mirror array 30 through a single WDM add/drop device 40.
`In other words, a single set of lenses 18, 20 and 24, and a
`single planar grating 12, all sharing a common alignment,
`can be used in accordance with the invention to simulta-
`neously process multiple multifrequency optical signals.
`In optical fiber components, it is generally important to
`minimize the polarization dependence loss. However, the
`di raction grating 12 used to separate the wavelengths tends
`to have a different diffraction efficiency for horizontal and
`for vertical input polarization. This variation can be large,
`especially for gratings with a relatively fine spatial fre-
`quency of several hundred lines per millimeter or more. One
`way to minimize the net polarization dependence is to pass
`the polarization dependent element in both directions with a
`90 degree polarization rotation between the passes. In this
`manner,
`the signal on the first pass experiences a first
`polarization loss and the return signal experiences a second
`polarization loss. The result is that any input polarization
`will experience the average loss.
`Any fiber—coupled component can be rendered polariza-
`tion independent iii
`this manner provided that it can be p
`doubled, where the polarization rotation can be accom-
`plished by an appropriate fiber-coiipled device. In the optical
`system of FIG. 1, the grating 12 is the only component that
`is polarization dependent, and it is already double passed in
`that the optical signal
`is reflected from the grating in a
`forward direction as shown by arrows A and B, and in a
`reverse or return direction as shown by arrows C and D. By
`placing a polarization rotating element 56 into the system, as
`for example between the grating 12 and lens 20, the losses
`are averaged in a single round trip through the device 10.
`One such optical element that can accomplish at least an
`approximate 90 degree polarization rotation is, by way of
`example, a quarter wave plate having an appropriate angular
`orientation with respect to the grating 12. With this simple
`addition, the polarization dependent losses of the WDM
`add/drop switch 40 can be reduced.
`Although the preferred embodiments are described here-
`inabove using specific optical elements such as a collimating
`and focusing lens 20 and a dispersion grating 12 to disperse
`and focus wavelengths of a multiple-wavelength optical
`signal, other optical elements can be used to perform this
`function without departing from the scope of the present
`invention. For example, a dilfractive optical element such as
`an off-axis holographic lens can be used to perform both
`imaging and dispersing. For such elements, there is no need ,
`for a collimator lens and a colliinated beam would not be
`required. Alternatively, a sequence of volume holographic
`elements can be used which each element diffracting a single
`wavelength towards the micromirror array 30 at a distinct
`angle. Furthermore, a superimposed volume hologram can
`be used where multiple distinct holograms are recorded in a
`single volume in individually direct distinct wavelengths.
`lastly, a sequence of multilayer dielectric thin film mirrors
`can be employed with each mirror designed to rellect only
`a selected subset of wavelengths into a particular angle.
`Thus, while there have shown and described and pointed
`out fundamental novel features of the invention as applied to
`
`_
`
`,
`
`6
`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 without departing
`from the spirit of the invention. llor example, it is expressly
`intended that all combinations of those elements which
`perform substantially the same function in substantially the
`same way to achieve the same results are within the scope
`of the invention. It is the intention, therefore, to be limited
`only as indicated by the scope of the claims appended
`hereto.
`We claim:
`1. A WDM transmit/reflect unit for selectively transmit-
`ting a select wavelength of a multiple—wavelength optical
`signal from at least one first optic fiber to at least one second
`optic fiber and reflecting the select wavelength from the at
`least one first optic fiber back to the at least one first optic
`fiber, said unit comprising:
`a first port for receiving the multiple-wavelength optical
`signal from the at least one first optic fiber;
`a first
`lens for collimating the received multiple-
`wavelcngth optical signal;
`means for angularly displacing from each other individual
`ones of the multiple wavelengths in the collimated
`multiple-wavelength optical signal when the multiple-
`Vvavelength optical signal
`is travelling in a first
`direction, and for angularly combining the individual
`wavelengths of the niultiple-waveleugtli optical signal
`when the multiple-wavelength optical signal is travel-
`ling in a second direction;
`a second lens for focusing the angularly displaced wave-
`lengths when the multiple-wavelength signal is travel-
`ling in the first direction and for collimating the
`multiple—wavelength signal when the multiple-
`wavelength signal is travelling in the second direction;
`a micromirror array for receiving the multiple-wavelength
`signal from the second lens and selectively switchable
`between a transmission mode for transmitting the select
`wavelength to the at least one second optic fiber and a
`reflection mode for reflecting the select wavelength to
`the at least one first optic fiber;
`a second port connected to the second fiber for receiving
`the deflected angularly combined optical signal from
`said angularly displacing means when the array is in the
`transmit mode; and
`third lens positioned between said grating and said
`second port for focusing the angularly combined
`multiple-wavelength signal onto said second port for
`receipt by the second fiber.
`2. The WDM transmit/reflect unit of claim 1, wherein
`when said micromirror array is in said transmission mode,
`and when a second multiple—wavelength signal is present at
`said second port, the second multiple—wavelength signal is
`transmitted to said first port.
`3. The WDM transmit/reflect unit of claim 1, wherein said
`micromirror array comprises a plurality of mirror plates,
`with each plate positioned for receiving one of the individual
`wavelengths of said multiple-wavelength signal.
`4. The WDM transmit/reflect unit of claim 3, wherein
`each mirror plate is responsive to an electrical signal for
`selectively activating each plate between the transmission
`mode and the reflection mode.
`5. The WDM transniit/reflect unit of claim 3, wherein
`each mirror plate is responsive to an electrical signal for
`selectively reorienting each plate between the transmission
`mode and the reflection mode.
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-6
`
`

`
`US 6,204,946 Bl
`
`7
`6. The WDM transmit/reflect unit of claim 3, wherein said
`micromirror array has a vertical axis, wherein each mirror
`plate has a vertical axis, and each said mirror plates is
`arranged so that its vertical axis is angularly offset from the
`vertical axis of said minor array.
`7. The WDM transmit/reflect unit of claim 6, wherein
`each said mirror plate of the micromirror array is selectively
`rotatable about its axis to transmit or reflect select wave-
`lengths of the multiple—wavelength optical signal.
`8. The WDM transmit/reflect unit of claim I, wherein said
`angularly displacing means comprises a grating.
`9. The WDM transmit/reflect u11it of claim 3, wherein said
`plural mirror plates are arranged in a column.
`10. The WDM transmit/reflect unit of claim 3, wherein the
`at least one first optic fiber comprises a first plurality of optic
`fibers, each providing a multiple—wavelength optical signal
`to said first port, wherein the at least one second optic fiber
`comprises a second plurality of optic fibers, equal in number
`to the plurality of first optic fibers and each of the second
`optic fibers receiving an angularly combined deflected
`multiple—wavelength signal
`from said second port, and
`wherein said plural mirror plates are arranged to form a
`plurality of columns of said mirror plates equal in number of
`columns to the plurality of optic fibers in the first plurality
`of optic fibers, and wherein each said column of mirror
`plates comprises a plural number of mirror plates at least
`equal to the multiple wavelengths in each multiple wave-
`length optical signal.
`11. The WDM transmit/reflect 11nit of claim 1, further
`comprising a deflecting element positioned between said
`angularly displacing means and said third lens [or defiecting
`the angularly combined multiple—wavelength signal to the at
`least one second optic fiber when the array is in the trans-
`mitting mode.
`I2. The WDM transmit/reflect unit of claim I. further
`comprising a polarization dependent optical component
`positioned between said angularly displacing means and said
`second lens.
`13. The WDM transmit/reflect unit of claim 12, wherein
`said polarization dependent optical component comprises a
`quarter—wave plate.
`14. AWDM add/drop device for adding wavelengths to
`and dropping wavelengths from a multiple—wavelength opti-
`cal signal in an optical communication system, comprising:
`an input port for receiving a WDM multiple—wavelength
`input optical signal from at least one first optic fiber;
`an output port
`for outputting a WDM multiple-
`wavelength output optical signal to at least one second
`optic fiber;
`a WDM add port for receiving as an input an add
`wavelength to be added to the multiple—wavelength
`optical signal;
`a VVDM transmit/reflect unit having a first port and a
`second port for transmitting one of the multiple wave-
`lengths of the multiple-wavelength signal from the first
`port to the second port in a first direction, for trans— ”
`milling the added wavelength from the second port to
`the first port in a second direction, and for reflecting
`one of the multiple wavelengths of the multiple-
`wavelength signal from the first port back to the first
`port;
`a first multiport circulator disposed between said WDM
`input port, said W'DM output port and said first port of
`said WDM transmit/reflect unit, said circulator being
`operable for receiving the WDM multiple—wavelength
`input signal from said input port and providing the
`WDM input signal to said first port of said WDM
`transmit/reflect unit and for receiving the WDM
`
`8
`multiple—wavelength signal reflected by said WDM
`transmit/reflect unit and the added wavelength trans-
`mitted by said WDM transmit/reflect unit and provid-
`ing the received reflected WDM niultiple-wavelength
`signal and added wavelength to said output port;
`a WDM drop port for outputting from the WDM input
`signal, one of the multiple wavelengths dropped from
`the WDM multiple—wavelength optical signal transmit-
`ted by said WDM transmit/reflect unit; and
`a second circulator disposed between said WDM add port,
`said WDM drop port and said second port of said
`WDM transmit/reflect unit for forwarding one of the
`multiple transmitted wavelengths from the WDM
`transmit/reflect unit to said WDM drop port and for
`forwarding the WDM added wavelength from said
`WDM add port to said second port of said WDM
`transmit/reflect unit.
`15. The WDM add/drop device of claim 14, wherein said
`WDM transmit/reflect unit further comprises a micromirror
`array having a plurality of mirror plates, with each plate
`positioned for receiving one of the wavelengths of said
`multiple—wavelength input optical signal, and means for
`optical wavelength demultiplexing of the multiple wave-
`length signal onto said plurality of mirror plates.
`16. The WDM add/drop device of claim 15, wherein each
`mirror plate in said micromirror array is responsive to an
`electrical signal for selectively activating each plate between
`transmission and reflection modes of the WDM transmit/
`reflect unit.
`17. The WDM add/drop device of claim 15, wherein each
`_ mirror plate in said micromirror array is responsive to an
`electrical signal for selectively reorienting each plate
`between a transmission mode and a reflection mode.
`18. The WDM add/drop device of claim 15, wherein said
`micromirror array has a vertical axis, wherein each mirror
`plate has a vertical axis, and wherein each said mirror plate
`is arranged so that its vertical axis is angularly offset from
`the vertical axis of said mirror array.
`19. The WDM add/drop device of claim 15, wherein each
`said mirror plates of the micromirror array is selectively
`rotatable about its axis to transmit or reflect select wave-
`lengths of the multiple—wavelength optical signal.
`20. The WDM add/drop device of claim 15, wherein said
`plural mirror plates are arranged in a column.
`21. The WDM add/drop device of claim 15, wherein said
`first port comprises a first port on a multiple port circulator
`and said second port comprises a second port on said
`multiple port circulator, wherein the at least one first optic
`fiber comprises a first plurality of optic fibers, each provid-
`ing a multiple—wavelength optical signal to said first port,
`wherein the at least one second optic fiber comprises a
`second plurality of optic fibers, equal
`in number to the
`plurality of first optic fibers and each of the second optic
`fibers receiving an output multiple—wavelength optical sig-
`nal from said second port, and wherein said plural mirror
`plates are arranged to form a plurality of columns of said
`mirror plates equal in number of columns to the plurality of
`optic fibers in the first plurality of optic fibers, and wherein
`each said column of mirror plates comprises a plural number
`of mirror plates at least equal to the multiple wavelengths in
`each multiple—wavelength optical signal.
`22. AW'DM transmit/refiect unit for selectively transmit-
`ting a select wavelength of a multiple—wavelength optical
`signal from a first optic fiber to a second optic fiber and
`reflecting the select Wavelength from the first optic fiber
`back to the first optic fiber, said unit comprising:
`a first port for receiving the multiple—wavelength optical
`signal from the first fiber;
`
`Petitioner Ciena Corp. et al.
`Exhibit 1027-7
`
`

`
`US 6,204,946 Bl
`
`9
`means for angularly displacing from each other individual
`ones of the multiple wavelengths in the miiltiple-
`wavelength optical signal when the multiple-
`wavelength optical signal
`is travelling in a first
`direction, and for angularly combining the individual
`wavelengths of the miiltiple—wavelength optical signal
`when the multiple-wavelength optical signal is travel-
`ling in a second direction;
`first means for imaging the angularly displaced multiple-
`wavelcngth optical signal to form an image;
`a riiicromirror array for receiving the image from said first
`imaging means, said micromirror array being selec-
`tively switchable between a transmission mode for
`transmitting the select wavelength to the second fiber
`and a reflection mode for reflecting the select wave-
`length to the first fiber;
`said first imaging means operatively imaging the reflected
`select wav