Ulllted States Patent [19]
`Bishop et al.
`
`US005936752A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,936,752
`Aug. 10, 1999
`
`[54] WDM SOURCE FOR ACCESS
`
`5,500,761
`
`3/1996 Goossen et a1. ...................... .. 359/290
`
`APPLICATIONS
`
`[75] Inventors: David J. Bishop, Summit; Joseph E.
`Ford, Oakhurst; James A. Walker,
`Howell, an of Ni
`
`[73] Assignee: Lucent Technologies, Inc., Murray
`Hill, N1
`
`[21] Appl.No.: 08/778,120
`
`[22]
`
`Filed:
`
`Jan. 2, 1997
`
`Related US. Application Data
`Provlslonal apphcanon NO' 6O/018’417’ May 28’ 1996'
`[60]
`[51] Int. Cl.6 .................................................... .. H04J 14/02
`[52] U_S_ C]_ ________________ __
`_ 359/124; 359/130; 359/290
`[58] Field of Search ................................... .. 359/124, 130,
`359090, 291; 385/52
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,526,155
`5,745,271
`
`6/1996 Knox et al. . . . . .
`. . . .. 359/130
`4/1998 Ford etal. ............................ .. 359/130
`
`_
`_
`Primary Exammer—Thomas Mullen
`
`ABSTRACT
`[57]
`The present invention provides an apparatus and method for
`a single-source Wavelength division multiplexed (WDM)
`signal. According to the invention, light from a broad
`Wavelength bandwidth or multiWavelength source is
`delivered, over one or more input optical ?bers, to a device
`for spatially separating the light into a plurality of spectral
`components each having a different Wavelength. The device
`further directs the spectral components along separate opti
`cal paths. A modulator array is provided containing a plu
`rality of optical modulators spaced to each receive one of the
`different Spectral Components Information is encoded on
`each spectral component through the action of each modu
`lator. The encoded spectral components originating from a
`given input ?ber are combined to generate a multiplexed
`optical signal.
`
`5,450,510
`
`9/1995 Boord et a1. ...................... .. 359/130 X
`
`21 Claims, 6 Drawing Sheets
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-1
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 1 of6
`
`5,936,752
`
`252:8
`>32
`
`55¢
`
`25mm
`
`zocéfmm
`
`@2688
`
`H53
`
`Z
`
`$523.60
`
`55c
`
`M853
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-2
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 2 of6
`
`5,936,752
`
`N 65%
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-3
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 3 of6
`
`5,936,752
`
`FIG. 3
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-4
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 4 of6
`
`5,936,752
`
`119
`
`FIG. 5 1
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-5
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 5 of6
`
`5,936,752
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-6
`
`

`
`U.S. Patent
`
`Aug. 10,1999
`
`Sheet 6 of6
`
`5,936,752
`
`E58“
`51
`
`E x
`
`5.522%:
`
`A 65%
`
`~55:
`
`12
`
`é \ m2
`5. \
`
`NEEEZE =5:
`
`
`£38
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-7
`
`

`
`1
`WDM SOURCE FOR ACCESS
`APPLICATIONS
`
`STATEMENT OF RELATED CASES
`
`5,936,752
`
`2
`nents originating from a given input ?ber. In this manner, a
`multiplexed optical signal is generated from a single light
`source.
`
`This is a Provisional Application Ser. No. 60/018,417
`?led May 28, 1996 and US. Pat. No. 5,745,271 issued Apr.
`28, 1998.
`
`FIELD OF THE INVENTION
`
`The present application relates to optical communications
`using Wavelength division multiplexing. More particularly,
`the invention relates an improved source for a Wavelength
`division multiplexed-based optical communications system.
`
`BACKGROUND OF THE INVENTION
`Wavelength division multiplexed (WDM) optical ?ber
`communications systems transmit data on several optical
`carrier signals having different Wavelengths. Typical prior
`art WDM systems use a separate optical signal source for
`generating each carrier signal. For example, a 1><N array of
`laser diode signal sources may be used to provide N carrier
`signals having different Wavelengths. The carrier signal
`Wavelengths are typically evenly spaced apart Within the
`bandWidth of the optical ?ber in Which the signals are
`transmitted. Each laser diode is modulated by a different
`data stream so that N independent channels of information
`are provided.
`There are a number of draWbacks associated With such
`multi-source systems. For example, each optical source
`typically requires active Wavelength stabiliZation in order to
`prevent cross-talk or overlap betWeen adjacent channel
`signals. Additional hardWare and processing may be
`required for such stabiliZation. Furthermore, the complexity
`of individually-stabilized laser diode sources currently lim
`its practical laser diode arrays to about 10 to 20 diodes.
`Additionally, the most ef?cient currently available photonic
`integrated circuits can be formed With only about four laser
`sources on a single chip. Packaging and source complexity
`constraints therefore represent a signi?cant problem in
`present multi-source WDM applications. The complexity of
`each source also substantially increases the overall optical
`system cost. Although a large number of sources may permit
`large numbers of channels in principle, the aforementioned
`practical considerations presently limit the channel density
`of WDM systems to about 20 channels.
`As such, a need exists for a single-source WDM system
`that avoids the cost, complexity and stabiliZation problems
`of the prior art.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides an apparatus and method
`for a single-source Wavelength division multiplexed (WDM)
`signal. According to the invention, light from a broad
`Wavelength bandWidth or multiple Wavelength source is
`delivered, over one or more input optical ?bers, to a device
`for spatially resolving the light delivered by each input ?ber
`into a plurality of spectral components each having a dif
`ferent Wavelength. The device further directs the spectral
`components along separate optical paths. A modulator array
`is provided containing a plurality of optical modulators
`spaced to receive one of the different spectral components.
`Information is encoded on each spectral component
`through the action of each modulator. In preferred
`embodiments, the encoded spectral components are then
`directed to a device that combines all the spectral compo
`
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The aforementioned and other features of the invention
`Will become more apparent, and a better understanding of
`the present invention gained, from the folloWing detailed
`description of speci?c embodiments thereof When read in
`conjunction With the accompanying draWings, in Which:
`FIG. 1 is a schematic vieW of a ?rst illustrative embodi
`ment of a single-source WDM transmitter according to the
`present invention;
`FIG. 2 illustrates the orientation of lenses and a grating
`used in an exemplary embodiment of the present invention;
`FIG. 3 is a schematic vieW of a second illustrative
`embodiment of a single-source WDM transmitter according
`to the present invention;
`FIG. 4 is a schematic vieW of a Dragone router;
`FIG. 5 is a schematic vieW of a third illustrative embodi
`ment of a single-source WDM transmitter according to the
`present invention;
`FIG. 6 is a schematic vieW of a fourth illustrative embodi
`ment of a single-source WDM transmitter according to the
`present invention; and
`FIG. 7 is an illustrative embodiment of an optical com
`munications netWork utiliZing a WDM transmitter according
`to the present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`A ?rst exemplary single-source WDM transmitter 1a
`according to the present invention is illustrated in FIG. 1. A
`broad Wavelength bandWidth or multiWavelength light
`source 3 capable of producing light having a broad range of
`spectral components, i.e., Wavelengths, provides one or
`more optical signals to the transmitter 1a. Suitable exem
`plary light sources include, Without limitation, a multi
`frequency laser operated either pulsed or continuous Wave
`and Without data modulation, a broad spectrum light emit
`ting diode, and an arc lamp appropriately ?ltered and
`ampli?ed.
`Light from the source 3 is received by each ?ber 9i of a
`one-dimensional (1-D) array 10 of N input optical ?bers 9.
`Each of the N input ?bers 9 thus supports transmission of an
`optical signal 5i comprising a plurality of spectral compo
`nents 71'M.
`In the ?rst exemplary embodiment of the WDM trans
`mitter 1a, a collimating device 11, such as a lens or a curved
`mirror, is in optical communication With the array 10 of
`input optical ?bers. Each input optical ?ber 9i is brought to
`a ?ush termination, Wherein the optical signal 5i carried by
`the ?ber 9i is emitted toWard the ?rst collimating device 11.
`The collimating device 11 focuses all the spectral compo
`nents 71'M emitted by each input ?ber 9i at substantially
`in?nite conjugates, thereby substantially collimating all the
`spectral components of each optical signal 5i.
`A device 13 for spatially separating each spectral com
`ponent 7 from every other spectral component of each
`signal Si is in optical communication With the collimating
`device 11. In an exemplary embodiment, the device 13 is a
`blaZed diffraction grating. The collimated optical signals
`exiting the collimating device 11 impinge upon the diffrac
`tion grating causing each spectral component 7 to disperse
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-8
`
`

`
`3
`at an angle approximately proportional to its Wavelength.
`For simplicity, the diffraction of a single optical signal 51 is
`illustrated in FIG. 1. The various spectral components
`received by the device 13 are directed toWard a focusing/
`collimating device 15, Which can be a single lens or a curved
`mirror. The device 15 is con?gured so that it receives all the
`spectral components 71'M of each optical signal 51'N along
`a ?rst path 16 that is off center With respect to its optical axis
`A—A. As described later, the off-center ?rst path enables the
`various spectral components to be re?ected back through the
`focusing/collimating device 15 along a second path 18 so as
`to be received by a ID array 25 of N output optical ?bers 26.
`The focusing/collimating device 15 focuses the various
`spectral components 71'M at different locations on a tWo
`dimensional (2D) modulator array 19. For simplicity, FIG. 1
`shoWs the array 19 to be a 1D array receiving the spectral
`components of a single optical signal 51. The second dimen
`sion of the array 19 is “out of the page,” With additional
`columns of modulators 21 receiving the spectral components
`from other input optical signals 52—5N. The 2D modulator
`array 19 preferably contains N><M surface-normal microme
`chanical optical modulators 21, Where M is the number of
`independent Wavelength channels.
`The operating Wavelength and speed of the modulators 21
`are suitably selected as a function of the intended service.
`The modulators can operate in the visible range, or 850
`nanometers (nm) or telecommunication Wavelengths and
`can transmit data at about 1 million bits per second or more.
`Exemplary suitable optical modulators include microme
`chanical modulators such as, Without limitation, those
`described in US. Pat. No. 5,500,761, and US. Pat. Nos.
`5,636,052; 5,654,819; 5,589,974; 5,825,528; 5,751,469 and
`5,659,418. Such modulators include a movable membrane
`suspended above a substrate, de?ning a gap therebetWeen.
`The movable membrane comprises at least one layer of
`material having a refractive index that is approximately
`equal to the refractive index of the substrate. As a voltage is
`applied by a controlled voltage source, the movable mem
`brane moves toWard the substrate, changing the siZe of the
`gap. As the gap siZe changes, modulator re?ectivity changes.
`The change in re?ectivity can be used to modulate an optical
`signal. In other embodiments, other types of micromechani
`cal modulators or semi-conductor optical modulators can be
`used. The aforementioned patent and patent applications, as
`Well as any other patents, patent applications and publica
`tions mentioned in this speci?cation are incorporated by
`reference herein.
`The modulators 21 in the modulator array 19 have a pitch
`spacing selected so that each spectral component 7 of light
`re?ected by the device 13 is focused on a different modulator
`21 Within the N><M modulator array 19 by the focusing/
`collimating device 15. Information can then be encoded on
`each of M spectral components 7 by the action of a
`modulator 21.
`55
`Modulated spectral components 81'M for each of the N
`optical signals are directed to the focusing/collimating
`device 15 and folloW the second path 18 off-center With
`respect to the device’s optical axis A—A. The focusing/
`collimating device 15 directs the modulated spectral com
`ponents 81'M to the device 13, at substantially the same angle
`at Which the spectral components 71'M left the device 13.
`Consequently, the various modulated spectral components
`corresponding to each original optical signal are multiplexed
`into modulated optical signals 61'N by the device 13. FIG. 1
`illustrates the multiplexing of the spectral components 81'M
`into modulated WDM signal 61. Note that When the
`
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`5,936,752
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`10
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`15
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`20
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`30
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`4
`focusing/collimating device 15 receives the spectral com
`ponents 71'M, it focuses them on the modulator array. When
`it receives the spectral components 81'M, hoWever, it colli
`mates them.
`A focusing device 23, such as a lens or curved mirror, is
`in optical communication With the device 13 and a ID array
`25 of N output optical ?bers 26. The device 13 directs
`collimated modulated multiplexed optical signals 61'N to the
`focusing device 23, Which focuses the spectral components
`81'M of each of the N modulated signals 6 onto the ID array
`25 of N output optical ?bers 26. In this manner, a plurality
`of modulated multiplexed data signals are generated from a
`single broad band or multiWavelength optical source and
`coupled into an array of output ?bers.
`In the ?rst exemplary embodiment of a transmitter 1a
`according to the present invention, an off-center optical
`con?guration is used so that the modulated multiplexed
`signals 61'N are delivered to an array 25 of output ?bers
`distinct from the array 10 of input ?bers. In an alternative
`embodiment, a single array of optical ?bers could be used
`for input and output. In such a case, an off-center optical
`con?guration Within the transmitter is not required. Rather,
`an external ?ber component, such as a 2x2 splitter or an
`optical circulator, is used to separate the modulated output
`signals 6 from the input.
`It Was noted above that the device 13 for spatially
`separating the spectral components of an optical signal may
`be, in one embodiment, a blaZed diffraction grating. In
`presently preferred embodiments, if such a diffraction grat
`ing is used, it is oriented in a “skeW”—LittroW mount as
`shoWn in FIG. 2.
`A LittroW mount is a standard con?guration in spectrom
`eter design. See Born et al., Principles of Optics, Chap. 8,
`Sect. 6 (6th Ed., Pergammon Press 1984). In LittroW
`con?guration, the grating is placed so that diffracted light is
`approximately retrore?ected back toWards the original
`source, except that each color returns at a slightly different
`angle. For compactness, a single lens can be used to colli
`mate incident light, and focus the diffracted output. LittroW
`con?guration offers certain advantages in optical
`performance, including a relatively loW sensitivity to input
`polariZation.
`To spatially separate the diffracted light from the original
`source, it is necessary to tilt the grating slightly aWay from
`perfect or “true” LittroW con?guration. In spectrometers,
`Where the optical paths and the lens focal lengths are large,
`a slight tilt angle is often sufficient. Therefore, the optical
`performance is not signi?cantly affected. In preferred imple
`mentations of the present invention, it is necessary to keep
`the lens focal length short, hence the tilt angle necessary to
`separate the diffracted output can be as large as 45°. In prior
`art applications in Which a short focal length is required, the
`tilt is applied in the same plane as the spread of diffracted
`Wavelengths. Such an approach is the simplest, since the
`optical system remains on a tWo-dimensional surface, mak
`ing it relatively easy to fabricate mounts and align the optics.
`In other Words, a constant beam height about the mount
`plane is retained.
`According to the present invention, the grating 13 is tilted
`in the orthogonal direction, so that the beams are shifted out
`of the plane of diffracted light. Such a con?guration is
`shoWn in FIG. 2. Such a con?guration requires a three
`dimensional layout, and causes the light rays to folloW a
`“skeWed” optical path through the focusing/collimating
`device 15. While historically it Would have been dif?cult to
`design such a skeWed optical system, such designs are noW
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-9
`
`

`
`15
`
`5
`readily handled by computer lens design programs known to
`those skilled in the art.
`The principle advantage of the present con?guration is
`that the deviation from LittroW con?guration is made in the
`orthogonal plane from the plane of diffraction. This alloWs
`a large angle of separation of the diffracted output from the
`input light Without sacri?cing the bene?cial polariZation
`properties of the LittroW con?guration.
`The exemplary embodiment of a WDM transmitter 1a
`described above utiliZes free-space optics. In a second
`exemplary embodiment, a WDM transmitter 1b according to
`the present invention can be implemented advantageously
`using integrated optics, as shoWn in FIG. 3. The various
`collimating and focusing devices used in conjunction With
`the transmitter 1a are not required When using such inte
`grated optics.
`The WDM transmitter 1b includes a routing device 110,
`such as an optical circulator or a 50/50 splitter. The routing
`device 110 receives an optical signal 5 from a broad band
`optical source 3 to Which it is optically coupled, such as by
`a ?ber 107 shoWn in FIG. 3. Suitable optical sources include
`those previously described. The routing device 110 delivers
`the optical signal 5 to an optical ?ber 112, Which is brought
`to a ?ush termination at a device 114 for spatially separating
`each spectral component 7 from other spectral components
`of the optical signal 5. In a transmitter using integrated
`optics, such as the transmitter 1b, the device 114 is an
`arrayed Waveguide such as a Dragone router (also knoWn as
`a Waveguide array router). See Dragone, “An N><N Optical
`Multiplexer Using a Planar Arrangement of TWo Star
`Couplers,” IEEE Photon. Tech. Lett., 3(9), pp. 812—815
`(September 1991); Zirngibl, et al., “Demonstration of a
`15x15 Arrayed Waveguide Multiplexer on InP,” IEEE Phot.
`Tech. Lett., 4(11), pp. 1250—1253 (November 1992).
`The Dragone router, shoWn in FIG. 4, consists of an input
`array 201 of Waveguides 202 connected to a ?rst planar free
`space region 203, an output array 211 of Waveguides 212
`connected to a second planar free space region 209, and a
`Waveguide grating 205 connecting the ?rst and the second
`free space region. The Waveguide grating 205 consists of a
`plurality of unequal length Waveguides or grating arms 207.
`Typically, the input array 201 contains the same number
`of Waveguides as the output array 211, Which is usually in
`the range of from about 4 to 16 Waveguides. There is a
`one-to-one correspondence betWeen the number of
`Waveguides 212 in the output array 211 and the number of
`spectral components in the optical signal being demulti
`plexed. Only one of the Waveguides 202 in the input array
`201 is active, i.e., the optical ?ber 112 is connected to only
`one of such Waveguides. In other Words, the Dragone router
`processes a single multi-Wavelength input signal 5 at a time.
`With continuing reference to FIG. 3, the optical signal 5
`delivered from the one active Waveguide 202 expands in the
`?rst planar free space region 203 and couples to the grating
`arms. A constant path length difference betWeen adjacent
`gratings causes a Wavelength dependent phase shift. This
`linear phase progression affects the propagation direction of
`the converging Wave radiated in the second free space region
`209 toWards the output array 211. Consequently, various
`spectral components 71'M having differing Wavelengths
`couple to different Waveguides 212 in the output array 211.
`A 1-D array 116 of modulators 21 is attached to the
`arrayed Waveguide 114. Each modulator 21 in the array 116
`is optically aligned With one of the Waveguides 212. Infor
`mation can then be encoded on the spectral component 7
`65
`delivered to a particular modulator 21 by the action of the
`modulator.
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`5,936,752
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`A modulated spectral component Si is returned from each
`modulator 21. Modulated spectral components 81'M travel
`back through the second planar free space region 209, the
`Waveguide grating 205 and the ?rst planar free space region
`203 and are multiplexed forming a modulated optical signal
`6i travelling back through the optical ?ber 112. The modu
`lated optical signal is separated into a distinct output ?ber
`113 by a second pass through the routing device 110.
`It should be appreciated that While the transmitter 1a can
`deliver a plurality of modulated WDM signals, the trans
`mitter 1b can deliver only a single modulated WDM signal
`at a time.
`In the exemplary embodiments of the transmitters 1a and
`1b described above, the modulators 21 operate in a re?ective
`mode, Wherein the modulated spectral components are
`re?ected aWay from the modulators. In alternate
`embodiments, the re?ective modulators 21 can be replaced
`With transmissive modulators 22. Transmissive modulators
`vary the amount of signal passed through the modulator. A
`preferred design for a transmissive modulator is disclosed in
`US. patent application Ser. No. 08/775,910 ?led Jan. 2,
`1997.
`A ?rst alternative embodiment of a transmitter 1c using
`transmissive modulators is shoWn in FIG. 5. The transmitter
`1c is formed by replacing the array 116 of re?ective modu
`lators 21 shoWn in FIG. 3 With an array 118 of transmissive
`modulators 22 and coupling an output ?ber 122 from an
`array 120 of such output ?bers to each modulator 22. Thus,
`a different modulated spectral component Si is carried by
`each ?ber 122 in the array.
`The transmitter 1c does not multiplex the modulated
`spectral components 81'M. FIG. 6 shoWs a second alternative
`embodiment of a transmitter 1d according to the present
`invention, in Which the modulated spectral components are
`multiplexed onto a single ?ber 213. In the illustrative
`embodiment of a transmitter 1d shoWn in FIG. 6, a second
`arrayed Waveguide 214 is used for such multiplexing.
`As shoWn in FIG. 6, the spectral components 71'M of an
`optical signal 5 are spatially separated and delivered to the
`array 118 of transmissive modulators 22 by the ?rst arrayed
`Waveguide 114. The modulated spectral components 81'M
`are delivered to an input array 301 of Waveguides 302
`belonging to the second arrayed Waveguide 214. The second
`arrayed Waveguide 214 combines the modulated spectral
`components into a WDM optical signal 6, Which is delivered
`to the ?ber 213.
`It Will be appreciated that a routing device, such as the
`routing device 110 appearing in FIG. 3 is not required in the
`transmitters 1c or 1d.
`In both of the transmitters 1c and 1d, the modulators 22
`Will typically be located on either a ?rst surface of the
`substrate 119 nearest the arrayed Waveguide 114, or on a
`second surface nearest the output ?ber array 122 (transmitter
`1c) or the second arrayed Waveguide 214 (transmitter 1d). If
`the modulators are located on the ?rst surface, the
`Waveguides 211 in the output array 212 can be butt coupled
`to the modulators 22. The thickness of the substrate 119,
`hoWever, prevents butt coupling the other array of
`Waveguides, i.e., the array 122 for the transmitter 1c or the
`array 302 of the second arrayed Waveguide 214 for the
`transmitter 1d, to the modulators. Alternatively, if the modu
`lators 22 are located on the second surface of the substrate
`119, the Waveguides in the array 122 or 302, depending upon
`the embodiment, can be butt coupled the modulators. In such
`embodiments, hoWever, the thickness of the substrate 119
`Will prevent butt coupling the Waveguides in the output array
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-10
`
`

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`7
`212 of the arrayed Waveguide 114 to the modulators. As
`such, a lenslet array can be used to relay image the optical
`“spots” to the appropriate destination, i.e., either to the
`modulators 22 or to the array 122 (transmitter 1c) or the
`array 302 (transmitter 1d).
`The lenslets, Which can be fabricated by methods known
`to those skilled in the art, can be located on the substrate 119
`on the surface opposite to the surface on Which the modu
`lators 22 reside. Alternatively, the lenslets can be disposed
`on a separate substrate. In either case, the lenslets are placed
`betWeen the modulators 22 and Which ever array is not butt
`coupled to such modulators.
`As an alternative to using lenslets, ?ber alignment/
`receiving regions, not shoWn, may be formed in the substrate
`119 on the surface opposite to the surface on Which the
`transmissive modulators 22 reside. Such regions function to
`align each Waveguide With a respective transmissive modu
`lator 22 and further facilitate placing each Waveguide in
`close proximity to a modulator 22. The ?ber alignment/
`receiving regions can be formed using a timed crystallo
`graphic etch. Such ?ber alignment/receiving regions are
`described in detail in the aforereferenced application Ser.
`No. 08/775,910 and US. Pat. No. 5,815,616.
`Among other applications, a WDM transmitter according
`to the present invention can be used advantageously in a
`WDM optical communications netWork. An exemplary pas
`sive optical netWork using a WDM transmitter according to
`the present invention is illustrated in FIG. 7.
`The netWork 400 includes a central of?ce or head end
`terminal 471 having a broad band or multiWavelength opti
`cal source 403 and a WDM transmitter 401 according to the
`present invention, such as the transmitters 1a—1d. The WDM
`transmitter 401, in conjunction With the optical source 403,
`is operable to provide one or more information-encoded
`multiplexed optical signals 406 or (information-encoded
`demultipleXed optical signals). The one or more optical
`signals 406 are distributed to a plurality of optical netWork
`units (ONUs) 479. Each ONU 479 receives information
`intended for it on a prescribed Wavelength. A Wavelength
`routing device 414, such as a Dragone router, demultipleXes
`the optical signal 406 into its spectral components 4081'M,
`and routes each of such spectral components to the appro
`priate ONU 479, i.e., the spectral component having a
`Wavelength matching the prescribed Wavelength of the ONU
`45
`is routed thereto.
`Each ONU 479 may include a receiver 481, such as a
`photodetector, and a transmitter 483, such as a modulator. A
`?rst portion of the optical energy of the spectral component
`received by the ONU 479 is routed to the receiver 481,
`Which converts the received portion to an electrical signal.
`The electrical signal is then routed to processing electronics,
`not shoWn, for decoding of information content contained
`therein.
`A second portion of the optical energy of the spectral
`component is routed to the transmitter 483. The transmitter
`is operable to encode information onto the second portion,
`returning information-carrying spectral component 485i.
`The receiver 481 and transmitter 482 in each ONU 479
`can be con?gured and packaged in a variety of Ways, such
`as those disclosed in US. Pat. Nos. 5,767,997; 5,784,187
`and 5,815,616; and patent application Ser. No. 08/970,690
`?led Nov. 14, 1997; patent application Ser. No. 08/712,530
`?led Sep. 11, 1996 now US. Pat. No. 5,857,048, and patent
`application Ser. No. 08/775,910 ?led Jan. 2, 1997.
`The information-carrying spectral components 485i are
`delivered to the Wavelength routing device 414, Which,
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`5,936,752
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`8
`operating in reverse, multiplexes information-carrying spec
`tral components 485 received from the ONUs 479 into a
`multiplexed optical signal 487, Which is routed to a receiver
`489 in the central of?ce 471.
`Although several speci?c embodiments of this invention
`have been shoWn and described herein, it is to be understood
`that such embodiments are merely illustrative of the many
`possible speci?c arrangements that can be devised in appli
`cation of the principles of this invention. Numerous and
`varied other arrangements can be devised in accordance With
`these principles by those of ordinary skill in the art Without
`departing from the scope and spirit of the invention.
`We claim:
`1. A transmitter suitable for providing a Wavelength
`division multiplexed (WDM) information-encoded optical
`signal from a single broad Wavelength bandWidth or multi
`Wavelength optical source capable of generating an optical
`signal having a plurality of spectral components, compris
`ing:
`at least one input ?ber optically coupled to the optical
`source for receiving a ?rst optical signal therefrom, the
`?rst optical signal having a plurality of spectral com
`ponents;
`a device operable to spatially separate each spectral
`component of an optical signal, Wherein the device is
`optically coupled to the input ?ber so as to receive the
`?rst optical signal and spatially separate each of its
`spectral components, and further Wherein the device is
`operable to combine spatially separated spectral com
`ponents it receives into a WDM signal; and
`an array of modulators, each of Which modulators is
`operable to encode information onto a spectral
`component, Wherein each modulator of the array
`receives a different one of the spatially separated spec
`tral components; Wherein,
`the modulated spectral components are delivered to one of
`either the device or a second device by Which the
`modulated spectral components are combined into a
`WDM information-encoded optical signal.
`2. The transmitter of claim 1 Wherein the device operable
`to spatially separate each spectral component is optically
`coupled to the input ?ber via free space optics.
`3. The transmitter of claim 2 Wherein the device operable
`to spatially separate each spectral component is a diffraction
`grating.
`4. The transmitter of claim 3 Wherein the diffraction
`grating is oriented in a skeW-LittroW con?guration.
`5. The transmitter of claim 3 further comprising a colli
`mating device optically coupled to the at least one input
`?ber, the collimating device operable to focus all the spectral
`components of the ?rst optical signal at substantially in?nite
`conjugates.
`6. The transmitter of claim 5 further comprising a
`focusing/collimating device that receives the spatially
`separated spectral components from the diffraction grating
`and delivers a different one of the spatially-separated spec
`tral components to each modulator in the array.
`7. The transmitter of claim 6 Wherein the focusing/
`collimating device is spatially oriented so that spatially
`separated spectral components are received along a ?rst path
`that is off center With respect to the optical aXis of the
`focusing/collimating device.
`8. The transmitter of claim 7 Wherein the modulators
`operate in a re?ective mode Wherein the modulated
`spatially-separated spectral components are directed
`toWards and received by the focusing/collimating device,
`
`Petitioner Ciena Corp. et al.
`Exhibit 1012-11
`
`

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`5,936,752
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`10
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`25
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`Which collimates and directs them to the diffraction grating
`for multiplexing into a co-propagating modulated WDM
`optical signal.
`9. The transmitter of claim 8 further comprising a focus
`ing lens that receives the modulated WDM signal from the
`diffraction grating and focuses all the spectral components
`of the modulated WDM signal onto at least one output ?ber
`so that the modulated WDM signal is coupled to the at least
`one output ?ber.
`10. The transmitter of claim 1 Wherein the at least one
`input ?ber is one of a plurality of input ?bers comprising a
`1-D array of input ?bers.
`11. The transmitter of claim 10 Wherein the modulator
`array is a 2-D array arranged into roWs and columns for
`receiving and modulating the spectral components from the
`?rst and a second optical signal.
`12. The transmitter of claim 1 Wherein the device operable
`to spatially separate each spectral component is optically
`coupled to the input ?ber via integra