(12) United States Patent
`US 6,542,655 B1
`(10) Patent N0.:
`(45) Date of Patent:
`Apr. 1, 2003
`Dragone
`
`USOO6542655B1
`
`(54) N><N CROSSCONNECT SWITCH USING
`WAVELENGTH ROUTERS AND SPACE
`SWITCHES
`
`(75)
`
`Inventor: C0rrad0 P. Dragone, Little Silver, NJ
`(US)
`
`(73) Assignee: Lucent Technologies Inc., Murray Hill,
`NJ (US)
`
`*
`
`Notice:
`
`J
`y
`Sub'ect to an disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/653,448
`
`(22)
`
`Filed:
`
`Aug. 31, 2000
`
`(51)
`Int. Cl.7 .............................. G02B 6/26; G02B 6/42
`
`(52) US. Cl. ............................. 385/17; 359/124
`(58) Field of Search .............................. 385/15, 16, 17,
`385/37; 359/124
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`........ 319/123
`5,369,514 A * 11/1994 Eilenberger et a1.
`5,627,925 A *
`5/1997 Alferness et a1.
`............. 385/17
`
`.............. 385/24
`5,745,612 A *
`4/1998 Wang et a1.
`.................... 385/17
`6,335,992 B1 *
`1/2002 Bala et a1.
`OTHER PUBLICATIONS
`
`Bernasconi, P., Doerr, C. R., Dragone, C., Cappuzzo, M.,
`Laskowski, E., and Paunescu, A., “Large N>< Waveguide
`Grating Routers,” Journal of Lightwave Technology System
`
`IEEE Communications Magazine, 18(7): pp. 985—991, Jul.
`2000 May 1987.
`
`Dragone, C., “Optimum Design of a Planar Array of Tapered
`Waveguides,” J. Opt. Soc. Amer. A., vol. 7, No. 11, pp.
`2081—2093, Nov. 1990, Applied Optics, Apr. 26, 1987.
`
`Dragone, C., “An N x N optical multiplexer using a planar
`arrangement of two star couplers,” IEEE Photon. Technol.
`Lett., vol. 3, pp. 812—815, Sep. 1991.
`
`* cited by examiner
`
`Primary Examiner—Cassandra Spyrou
`Assistant Examiner—Alessandro V. Amari
`
`(74) Attorney, Agent, or Firm—John A. Caccuro
`
`(57)
`
`ABSTRACT
`
`An N><N crossconnect switch, for large N, is implemented
`using an arrangement of smaller wavelength routers com-
`bined with space switches. An N><N crossconnect switch is
`constructed in three stages, using a plurality of input space
`switches, a plurality of (N/m)><(N/m) router (whose reduced
`size N/m allows efficient realization in integrated form), and
`a plurality of output space switches.
`In the router,
`the
`number of wavelengths is reduced by a factor m. The input
`and output space switches can be implemented using cross-
`bar or Clos type construction. In one arrangement each
`modulator is combined with a small space switch consisting
`of 2x2 elements. Each space switch can be realized with
`negligible crosstalk by using a dilated arrangement.
`
`21 Claims, 15 Drawing Sheets
`
`TUNABLE
`LASER
`201
`
`MODULATOR
`202
`
`
`
`
`
`
`DATA-N
`
`IN
`
`RECEIVER
`203
`
`V—‘—
`
`NxN
`FIG.
`
`1
`
`
`
`
`
`DATA-1
`R —>
`01
`
`
`
`El
`
`DATA-N0N
`
`Petitioner Huawei - Exhibit 1005, p. l
`
`Petitioner Huawei - Exhibit 1005, p. 1
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 1 0f 15
`
`US 6,542,655 B1
`
`D(
`
`Cf)
`LJJ
`DH
`DLLJ
`1:
`
`><
`
`;'
`
`—2
`
`)
`CL.
`}_
`
`DO Z
`
`mLL]
`QD—1
`DL|_l
`
`D(
`
`><3[
`
`.—
`I)
`D.
`ZH
`Z
`
`
`
`LIJ
`Q7—1
`DLu
`1:
`3
`
`3C
`
`><
`
`N
`
`p...
`a:
`<0
`0r—-<
`Q0:
`Na
`RD.
`
`Petitioner Huawei - Exhibit 1005, p. 2
`
`Petitioner Huawei - Exhibit 1005, p. 2
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 2 0f 15
`
`US 6,542,655 B1
`
`F]C . 2
`
`TUNABLE
`
`LASER
`201
`
`MODULATOR
`202
`
`RECEIVER
`203
`
`
`
`Petitioner Huawei - Exhibit 1005, p. 3
`
`Petitioner Huawei - Exhibit 1005, p. 3
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 3 0f 15
`
`US 6,542,655 B1
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`
`
`Petitioner Huawei - Exhibit 1005, p. 4
`
`Petitioner Huawei - Exhibit 1005, p. 4
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 4 0f 15
`
`US 6,542,655 B1
`
` ROUTER401
`
`WAVELENGTH
`
`
`
`403—1
`
`4
`
`ZIEn::
`
`Petitioner Huawei - Exhibit 1005, p. 5
`
`Petitioner Huawei - Exhibit 1005, p. 5
`
`

`

`US. Patent
`
`A r. 1 2003
`
`Sheet 5 0f 15
`
`
`
`Petitioner Huawei - Exhibit 1005, p. 6
`
`

`

`US. Patent
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`A r. 1 2003
`
`Sheet 6 0f 15
`
` 9%65%
`
`Petitioner Huawei - Exhibit 1005, p. 7
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 7 0f 15
`
`US 6,542,655 B1
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`
`
`
`
`Petitioner Huawei - Exhibit 1005, p. 8
`
`Petitioner Huawei - Exhibit 1005, p. 8
`
`

`

`US. Patent
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`A r. 1 2003
`
`Sheet 8 0f 15
`
`
`
`Petitioner Huawei - Exhibit 1005, p. 9
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 9 0f 15
`
`US 6,542,655 B1
`
`FIG.4F
`
`Petitioner Huawei - Exhibit 1005, p. 10
`
`Petitioner Huawei - Exhibit 1005, p. 10
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 10 0f 15
`
`US 6,542,655 B1
`
`. .
`.1"
`‘”FIG.4C
`
`Petitioner Huawei - Exhibit 1005, p. 11
`
`Petitioner Huawei - Exhibit 1005, p. 11
`
`

`

`
`
`Petitioner Huawei - Exhibit 1005, p. 12
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 12 0f 15
`
`US 6,542,655 B1
`
`FIG. 5
`
`m=2
`
`2x3
`m=3
`
`Petitioner Huawei - Exhibit 1005, p. 13
`
`Petitioner Huawei - Exhibit 1005, p. 13
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 13 0f 15
`
`US 6,542,655 B1
`
`FIG. 7
`
`m=2, FULLY DILATED
`
`701
`
`705
`
`2m-1
`
`703
`
`707
`
`
`
`Petitioner Huawei - Exhibit 1005, p. 14
`
`Petitioner Huawei - Exhibit 1005, p. 14
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 14 0f 15
`
`US 6,542,655 B1
`
`FIG. 9
`
`DILATED 3 x 3
`
`903
`2m-1
`
`m=3, 22 ELEMENTS, DEPTH=5
`
`Petitioner Huawei - Exhibit 1005, p. 15
`
`Petitioner Huawei - Exhibit 1005, p. 15
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 15 0f 15
`
`US 6,542,655 B1
`
`FIG.
`
`10
`
`m x (2m-1) SWITCH, m=2
`
`(2m—1)=3
`
`LAZER
`
`A
`
`11
`
`m
`
`I2
`INPUT SIGNAL
`
`2X1 SWITCH
`
`FIG.
`
`1 1
`
`m x (2m—1)
`
`2m-1=3
`
`
`
`01
`
`02
`
`m
`
`OUTPUT
`SIGNALS
`
`
`Petitioner Huawei - Exhibit 1005, p. 16
`
`Petitioner Huawei - Exhibit 1005, p. 16
`
`

`

`US 6,542,655 B1
`
`1
`N><N CROSSCONNECT SWITCH USING
`WAVELENGTH ROUTERS AND SPACE
`SWITCHES
`
`TECHNICAL FIELD OF THE INVENTION
`
`invention relates to optical crossconnect
`The present
`switches and, more particularly,
`to an N><N crossconnect
`switch implemented using wavelength routers combined
`with space switches.
`BACKGROUND OF THE INVENTION
`
`In high capacity optical networks, an essential device is
`the N><N crossconnect switch. The function of this device is
`
`to provide, at each node, full connectivity among several
`incoming fibers, each carrying several wavelength channels.
`The switch must be nonblocking, and it must be fast and
`efficient. If N is not
`too large,
`these properties can be
`realized by using a single N><N wavelength router combined
`with tunable transmitters capable of producing N wave-
`lengths. However, this technique is only feasible if the size
`N of the router is not
`too large. This is because as N
`increased, the N><N router was difficult to realize in inte-
`grated form with satisfactory performance of low loss and
`low crosstalk, and each transmitter had to provide N wave-
`lengths.
`With the ever-increasing capacity of optical networks
`there is continuing need for even larger N><N crossconnect
`switches.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the apparatus of the present invention,
`the problem of implementing a N><N crossconnect switch,
`for large N, is solved by using an arrangement of smaller
`wavelength routers combined with space switches. In the
`prior art, a large N><N switch implemented using a router
`was difficult to realize in integrated form, with satisfactory
`performance of low loss and low crosstalk, and each trans-
`mitter had to provide N wavelengths. According to the
`present
`invention,
`the number of router wavelengths is
`reduced by a factor In and the N><N crossconnect switch is
`constructed in three stages using space switches and smaller
`routers. The input and output space switches can be imple-
`mented using crossbar or Clos type construction. In the
`crossbar construction, the input and output switches are 1x2
`and 2x1 switches respectively. In the Clos construction, the
`input stage uses m><(2m—1) space switches and the output
`stage uses (2m—1)><m space switches. In both the crossbar or
`Clos type construction, the reduced size of the center stage,
`using (N/m)><(N/m) wavelength routers, allows efficient
`realization in integrated form. Using input space switches
`with tunable transmitters, each with N/m wavelengths, pro-
`vides full non-blocking connectivity of the N><N crosscon-
`nect switch. In one arrangement, the input and output space
`switches are implemented using 2x2, 1x2, and 2x1 switch
`elements. In one input space switch embodiment, a data
`modulator is combined with the 2x2 switch elements and
`
`integrated on a single wafer. Each input and output space
`switch can be realized with negligible crosstalk by using a
`dilated arrangement.
`More particularly, my invention is directed to an N><N
`nonblocking optical switch for providing a connection
`between any of N inlets and any of N outlets, the N><N
`switch comprising
`an input stage including a plurality of input space
`switches, each input of each of the input space switches
`connects to a different one of the N inlets;
`
`10
`
`15
`
`20
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`25
`
`30
`
`35
`
`40
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`45
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`50
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`55
`
`60
`
`65
`
`2
`an output stage including a plurality of output space
`switches, each output of each of the output space
`switches connects to a different one of the N outlets;
`and
`
`a center stage connected between the input stage and the
`output stage, the center stage including a plurality of
`N/m><N/m wavelength routers, wherein a connecting
`link is provided between each N/m><N/m wavelength
`router and each input or output switch, so that each
`N/m><N/m wavelength router connects to each input
`space switch and each output switch.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings,
`FIG. 1 shows a prior art wavelength router consisting of
`a waveguide grating between two free-space regions. The
`input and output waveguides are spaced by a along the input
`and output boundaries of the router;
`FIG. 2 shows a nonblocking cross-connect switch con-
`sisting of a N><N wavelength router combined with N
`tunable lasers, N modulators and N receivers;
`FIG. 3 shows a nonblocking cross-connect switch realized
`in three stages using a crossbar construction. The building
`blocks in the central stage are N/2><N/2 routers;
`FIG. 4a shows an illustrative physical embodiment, and
`FIG. 4b a block diagram, of the invention using a nonblock-
`ing N><N cross-connect switch realized using Clos arrange-
`ment. The building blocks in the center stage are n><n routers
`and,
`in the other two stages, m><(2m—1) and (2m—1)><m
`space switches;
`FIG. 4c shows a router reduction factor of 4, where each
`center stage block of FIG. 4b is realized by using 2x2 routers
`in an arrangement similar to that shown in FIG. 3;
`FIG. 4d shows an arrangement, having a router reduction
`factor of 4, which is derived from Clos arrangement of FIG.
`4b for N=16 and m=2 by realizing each center stage block
`of FIG. 4b using the FIG. 3 arrangement of N/4><N/4 routers;
`FIG. 46 shows an arrangement, having a router reduction
`factor of 4, which is derived from Clos arrangement of FIG.
`4b where each center stage block of FIG. 4b is itself
`implemented by a FIG. 4b arrangement;
`FIG. 4f shows a m><p switch consisting of two stages of
`m1><p1 and m2><p2 switches. Notice that m=m1m2 and
`P=P1p2;
`FIG. 4g shows the arrangement of FIG. 4f with each
`building block realized using the fully dilated 2x3 arrange-
`ment of FIG. 7;
`FIG. 4h shows the arrangement of FIG. 4g with reduced
`depth and reduced switch element count obtained by remov-
`ing redundant switch elements;
`FIG. 5 shows a nonblocking 2x3 arrangement with mini-
`mum number of elements;
`FIG. 6 shows a nonblocking 3x5 arrangement with mini-
`mum number of elements;
`FIG. 7 shows a crossbar input space switch having two
`1x2 input switches,
`two intermediate 1x2 switches, and
`three 2x1 output switches;
`FIG. 8 shows a crossbar input space switch of FIG. 7 as
`a combination of binary trees with two 1x3 input switches
`and three 2x1 output switches;
`FIG. 9 shows a nonblocking 3x5 crossbar arrangement
`with minimum depth;
`FIG. 10 shows a nonblocking 2x3 input space switch
`arrangement including two input modulators; and
`
`Petitioner Huawei - Exhibit 1005, p. 17
`
`Petitioner Huawei - Exhibit 1005, p. 17
`
`

`

`US 6,542,655 B1
`
`3
`FIG. 11 shows a nonblocking 3x2 output space switch
`arrangement including two receivers.
`In the following description, identical element designa-
`tions in different figures represent identical elements. Addi-
`tionally in the element designations, the first digit refers to
`the figure in which that element is first located (e.g., 102 is
`first located in FIG. 1).
`
`DETAILED DESCRIPTION
`
`A nonblocking N><N switch is realized using wavelength
`routers as building blocks. Each router [1,2] is a strictly
`nonblocking switch, which allows the destination of each
`input signal to be changed by simply changing the signal
`wavelength.
`(Note in this specification, a reference to
`another document is designated by a number in brackets to
`identify its location in a list of references found in the
`Appendix B) With reference to FIG. 1, there is shown a prior
`art wavelength router consisting of a waveguide grating 101
`between two free-space ‘slab’ regions, 102 and 103. The
`input and output waveguides are spaced by a along the input
`and output boundaries of the router and the waveguide
`grating arms 101 are spaced by b along the slab regions. In
`a well-known manner, changing the wavelength of a signal
`on any of the N input waveguides changes to which of the
`N output waveguides the signal is switched.
`Shown in FIG. 2, is a nonblocking cross-connect switch
`consisting of a N><N wavelength router of FIG. 1 combined
`with N tunable lasers 201, N modulators 202 and N receivers
`203. When N is not too large, the arrangement of FIG. 1 or
`FIG. 2 can be realized by using a single router. Then, each
`input signal must be produced by a multiwavelength laser
`capable of N wavelengths [1], and each input signal can be
`transmitted to any particular output port by simply selecting
`the appropriate laser wavelength. Thus, at any of the inputs
`Il—IN, by changing the wavelength of the associated laser,
`the data signals Data-1 through Data-N can be switched to
`any of the outputs Ol—ON. Illustratively, the Data-1 signal
`on input 11 is shown switched to output ON, while the
`Data-N signal is switched to output 01.
`However for large values of N>64, this type of cross-
`connect switches is difficult to realize using this technique,
`as discussed in Appendix A. This is because each laser
`would then have to be capable of a large number of
`wavelengths, and also because the router would be difficult
`to realize in integrated form with satisfactory performance
`of low loss and low crosstalk for large N. In accordance with
`the present invention, this problem is solved for large N by
`realizing the N><N switch by using an arrangement of smaller
`routers. To this purpose an arrangement of (N/m)><(N/m)
`wavelength routers is combined with input and output stages
`S consisting of space switches as shown in FIGS. 3 and 4a.
`In FIG. 3, the N><N switch arrangement is realized with
`minimum loss and crosstalk by using a crossbar construction
`[3]. On the other hand, it may be desirable to reduce the
`number of routers by using a Clos arrangement[4], shown in
`FIG. 4a, in which case it is generally desirable to reduce
`loss, crosstalk and waveguides crossings must be minimized
`as shown here. A property of the FIG. 3 and FIG. 4a
`arrangements is that each signal traverses only one router. As
`a consequence, the prior art problems of constructing a large
`N><N switch are eliminated, since the number of wave-
`lengths is reduced by a factor m, and the size of each router
`is also reduced by the same factor.
`1. Optimum Arrangements
`Returning to FIG. 1, there is shown a N><N router [5—7]
`consisting of N input waveguides, N output waveguides, two
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`dielectric slabs 102 and 103, and a waveguide grating 101
`connected between the two slabs. The input and output
`waveguides are connected to the two slabs, and the
`waveguides (arms) of the grating 101 between the two slabs
`are characterized by a constant path-length difference. As a
`consequence each transmission coefficient from a particular
`input waveguide to a particular output waveguide is essen-
`tially characterized by periodic behavior, with equally
`spaced peaks, and each peak is produced by a particular
`order of the grating.
`Ideally one would like to realize a switch by using a single
`N><N wavelength router characterized as in [5,7] by a comb
`of N wavelengths such that the transmission coefficient from
`any input port (waveguide) to any output port has a trans-
`mission peak at one of the above wavelengths. In reality, if
`the router of [5] is designed to produce the above property
`for a particular input port, for instance the central port, one
`finds that the above property only approximately applies to
`the other ports. As a consequence, it is shown in Appendix
`A that
`the router is afflicted by wavelength errors that
`increase with N. Because of these errors, some of the
`wavelengths of maximum transmission deviate from the
`above comb of N wavelengths. In order to keep the resulting
`losses below 1 dB, one must require
`
`N < 36
`
`100GHZ I
`
`GHz being the channel spacing in GHz. For instance, for
`a channel spacing of 50 GHz, one must require N<52. This
`value can be increased by a factor 1.25 by modifying the
`router, by widening its passband as in [6], but this technique
`also increases loss and crosstalk by about 3 dB.
`The above restriction only arises because here we specify
`the same comb of N wavelength for all input ports. By
`allowing a different comb of wavelengths for each input
`port, the above restriction would be eliminated [2], but a
`total of N different combs (including a total of 2N—1
`wavelengths) would then be required in order to provide
`maximum transmission from all input ports. This would
`make the arrangement more difficult to realize since each
`laser would have to produce a different comb, centered at a
`different wavelength.
`The above considerations give one reason for which small
`values of N are desirable in FIG. 1. As pointed out earlier,
`additional reasons are 1) that it is generally desirable to
`simplify the laser design by reducing the number of wave-
`lengths required from each laser and 2) that a router with
`large N>64 is difficult to design in integrated form with
`satisfactory values of loss and crosstalk.
`In view of the above difficulties it is advantageous for
`large N to realize the N><N switch by using, instead of a
`single N><N router, a combination of smaller n><n routers
`where n=N/m and the reduction factor In is a suitable
`integer. Thus a N><N switch is realized in three stages,
`consisting of a central stage of n><n routers combined with
`input and output stages of nonblocking space switches as
`shown in FIGS. 3 and 4. A well-known property of these
`arrangements is that they are nonblocking in the wide sense
`if the routers are replaced by nonblocking space switches,
`and a large enough number of such switches is used. Then,
`if any particular input port and any particular output port are
`idle, one obtains the following nonblocking property: It is
`possible to simultaneously establish input and output paths
`from the above ports to a particular switch in the central
`stage without disturbing any of the other active paths. That
`is, none of the existing connections need be disturbed.
`
`Petitioner Huawei - Exhibit 1005, p. 18
`
`Petitioner Huawei - Exhibit 1005, p. 18
`
`

`

`US 6,542,655 B1
`
`5
`It should be noted that in the prior art, large N><N switch
`arrangements were realized previously by using space
`switches,
`in which case their nonblocking properties are
`well known. Here, however, we use a combination of routers
`and switches in which case the nonblocking properties are
`only retained if no signal passes through more than one
`router. This condition is sufficient to insure that the signal
`can be transferred to the appropriate output port of the router
`by properly choosing the signal wavelength. Clearly one
`would like all routers to be characterized by the same comb
`of wavelengths, and the above conditions can be satisfied in
`FIGS. 3,4 in different ways. The simplest and most impor-
`tant arrangements are obtained by using the constructions of
`FIGS. 3,4 with n><n routers characterized by n=N/m, where
`m is a suitable reduction factor. The purpose of the input and
`output stages in this case is to produce the appropriate
`reduction factor m, and one finds that the two constructions
`of FIGS. 3,4 have different advantages and disadvantages.
`For m=2, the crossbar construction of FIG. 3 is attractive for
`the simplicity of its input 301 and output 303 stages, and it
`has the advantage of minimizing loss and crosstalk. As
`shown in FIG. 3, the central stages are (N/2)><(N/2) routers,
`i.e., 4 x4, when N=8 and m=2. Larger m can be realized by
`repeated application of the same construction. For m=4,
`N=16, for instance, one can replace each (N/2)><(N/2) router
`in FIG. 3 with a crossbar arrangement of (N/4)><(N/4)
`routers. By this procedure, each switch in the central stage
`is realized by the same construction of FIG. 3, but with N
`replaced everywhere by N/2. More generally, by repeated
`application of the above construction, higher powers of 2 for
`N can be realized by increasing the reduction factor In by
`factors of 2. Thus, for any N and m equal to a power of 2,
`the central stage consists of n><n routers with n=N/m and
`m=25 where s is a suitable integer.
`Shown in FIG. 4a is the physical arrangement of a Clos
`construction and FIG. 4b shows the equivalent block dia-
`gram thereof. The Clos construction, e.g., FIG. 4a, has the
`advantage, over the crossbar construction, e.g., FIG. 3, of
`requiring, for m=2, only three routers 401 instead of four.
`The Clos construction requires, however,
`larger building
`blocks for the input 402 and output 403 stages, as discussed
`later. Clearly, by repeated application of either construction,
`any power of 2 can be realized for the reduction factor In As
`shown in FIG. 4a, for the generalized case, the number of
`input 402 or output 403 switches, m><(2m—1) or (2m—1)><m,
`is equal to n=N/m, the number of n><n routers utilized is
`equal to (2m—1), where N is the number of input ports and
`m is the reduction factor. Thus, for the example shown in
`FIG. 4a, where N=8, m=2, we have n=4 input 402 and
`output 403 switches and (2m—1)=3 routers 401 of size 4><4.
`As shown, each input switch is connected to each of the 3
`routers 401, and therefore either one of the m=2 inputs 404
`to an input switch, e.g., 402-1, can be switched to a
`particular input, input 1, of each of the 3 routers 401. The
`control leads C1 .
`.
`. Ci to input stage, e.g., 402-1, determine
`which input is switched to which router 401. At each of the
`3 routers 401, the selection of wavelengths by the input
`stages 402 determines which router input (inlet) is switched
`to which router output (outlet), At the router output side, the
`same respective output, e.g., output 1, of each of the 3
`routers 401 is connected to a different input of one of the 4
`output stages, e.g., 403-1. At the output stage, e.g., 403-1,
`only 2 signals are transmitted to outlets 1 of the 3 routers 401
`and these two signals are switched to become the 2 outputs
`405. Again the control leads C1 .
`.
`. C’i to output stage, e.g.,
`403-1, determine which input is switched to which output.
`Note that the construction of the of input switches 402,
`m><(2m—1), is the mirror image of the output switches 403,
`(2m—1)><m.
`
`6
`In FIGS. 4a and 4b, changing the reduction factor m can
`change the size of the routers and input and output stages.
`Thus, for a given N, increasing In by a factor of 2 reduces
`the size, n=N/m, of each router by a factor 2 and clearly this
`technique can be used with either the crossbar or Clos
`construction. As shown in FIG. 4c, for instance, is a switch
`arrangement where the router size used in each of the center
`stages 401 is further reduced by a factor of 2, and hence
`implemented using N4><N/4 routers. Thus FIG. 46 illustrates
`a router reduction factor of 4, where each center stage block
`401 of FIG. 4b is realized by using 2><2 routers in an
`arrangement similar to that shown in of FIG. 3. In FIG. 4c,
`the input stage 411 includes the 2x3 switches 402 and the
`1x2 switch elements 413,
`the central stage includes the
`N4><N/4 (i.e., 2x2) routers 410, and the output stage 412
`includes the 2x1 switches 414 and the 3x2 switch elements
`
`403. Note that while FIG. 4b is a Clos construction (i.e., each
`input stage 402 can access each center stage router 401), the
`arrangement of FIG. 4c is a non-Clos arrangement. Shown
`in FIG. 4d is a switch where N=16 and the reduction factor
`
`is m=4. In FIG. 4d, the switch is realized by the arrangement
`of FIG. 4a, with each building block 401 in the central stage
`realized by using the arrangement of FIG. 3 with N replaced
`by N/2. Then each central stage building block becomes a
`combination of 4 (N/4)><(N/4) routers as shown in FIG. 4d.
`The resulting arrangement consists of a central stage of 12
`(N/4)><(N/4)
`routers 420. The twenty-four
`1><2 space
`switches 423 together with the eight 2><3 space switches 424
`would then become the input stage 421. The twenty-four
`2><1 space switches 425 together with the eight 3><2 space
`switches 426 would then become the output stage 422. In
`this arrangement each signal at one of the 16 inlets, 427, is
`transferred by the input stage 421 to a particular (N/4)><(N/4)
`router, 420, and switched by the output stage to a particular
`one of the 16 outlets, 428. Therefore by properly choosing
`a signal wavelength, M .
`.
`. All, the signal at a switch inlet
`427 can be switched via input stage 421 and router 420 to an
`appropriate outlet of the router, using a total of only n=N/4
`wavelengths (4 in our example of N=16). Thus, each input
`signal laser (e.g., 1003 of FIG. 10) needs only to provide 4
`wavelengths. At the output side of routers 420, the signal is
`then transferred by the output stage 422 to the appropriate
`switch outlet.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`Shown in FIG. 46 is a Clos switch arrangement derived
`from FIG. 4a where the routers used in each of the blocks
`
`401 of the center stage are further reduced in size by a factor
`of 2, and hence implemented using N4><N/4 routers. Note
`that FIG. 46 is a Clos construction since each switch inlet
`
`431 and outlet 437 can access each center stage router 432.
`Thus FIG. 46 illustrates a router reduction factor of 4, where
`each center block 401 is realized by using 2><2 routers in an
`arrangement similar to that shown in of FIG. 3. In FIG. 46,
`the input stage 433 includes the switches 402 and 434, the
`central stage includes the N4><N/4 routers 432, and the
`output stage 435 includes the switches 436 and 403.
`2. Clos Arrangement with Wavelength Routers in the Central
`Stage
`As pointed out earlier Clos arrangement minimizes the
`number of n><n wavelength routers in the central stage. On
`the other hand,
`it requires nonblocking m><(2m—1) and
`(2m—1)><m space switches in the input 402 and output 403
`stages as shown in FIG. 4a and, for this reason, the arrange-
`ment is found to have higher loss and higher crosstalk than
`the crossbar arrangement of FIG. 3. It is therefore important
`to optimize the input and output switches as shown next.
`Notice FIG. 4a requires in general 2m—1 routers and, in the
`special case m=2, it requires only three routers. Since m=2
`
`50
`
`55
`
`60
`
`65
`
`Petitioner Huawei - Exhibit 1005, p. 19
`
`Petitioner Huawei - Exhibit 1005, p. 19
`
`

`

`US 6,542,655 B1
`
`7
`is simplest to realize, and it can be used to realize any higher
`power of 2, it is the most important case in practice, and each
`m><(2m—1) switch can then be realized as in FIG. 5 by using
`an arrangement of elements without waveguides crossings.
`With reference to FIG. 5, there is shown a nonblocking 2><3
`arrangement implemented with a minimum number 3 of 2x2
`switching elements. Each of the 2x2 switching elements
`operate under control of a control signal C which controls
`whether the element is in a bar state, e.g., 501 and 503, or
`a cross state, e.g., 502. Note that none of the waveguides,
`e.g., 504, that interconnect the 3 elements 501—503 cross
`each other. Notice the ‘depth’ is generally defined as the total
`number of elements along the path of a particular signal, and
`it
`is an important parameter that determines loss and
`crosstalk. Thus, the depth of the 2x3 arrangement is two
`since a signal at an input port must pass through at most two
`elements to reach an output port.
`For m=3, on the other hand, one finds that a total of ten
`2><2 elements is required and the optimum m><(2m—1)
`arrangement with minimum depth is shown in FIG. 6. As
`shown, 3 elements are used as 1><2 elements, 3 elements
`form a 3x2 arrangement, and 4 elements form a 3x3
`arrangement. However, a disadvantage of Clos arrangement
`of FIG. 4a as compared to the crossbar arrangement of FIG.
`3 is that it has higher crosstalk. Indeed, in FIG. 3, each input
`and output element receives only one signal and, as a
`consequence, negligible crosstalk is caused by the element
`extinction ratio. In comparison in FIGS. 5 and 6, some of the
`elements, e.g., 501 and 503 of FIG. 5 simultaneously receive
`two signals, and appreciable crosstalk is then caused by the
`elements’ extinction ratio. An attractive solution to this
`
`problem is to modify the arrangements of FIGS. 5 and 6 so
`as to insure that each element is traversed by only one signal,
`e.g.,
`like 502 of FIG. 5. We have derived for m=2 the
`arrangement of FIG. 7, which is referred to as a fully dilated
`2><3 arrangement. This is the optimum arrangement satisfy-
`ing the above condition with minimum number of elements
`and minimum depth. It is a crossbar arrangement of binary
`trees, and it consists of two 1><3 input switches (701,702 and
`703,704 form separate 1><3 switches) combined with three
`2><1 output switches, 705—707, as shown in FIG. 8. As
`shown, the arrangement includes 7 elements, and it has only
`one waveguide crossing 708. Similarly for m=3 the optimum
`m><(2m—1) dilated arrangement is realized with minimum
`depth, of 5, by using 22 elements forming a crossbar
`arrangement of input and output binary trees, as shown in
`FIG. 9. Three 2><2 elements 901 are used as 1><2 elements,
`7 elements form a 3x2 element 902, and 12 elements form
`a 3x3 element 903. Each 2><2 element in the above dilated
`
`arrangements is used as a 1x2 or 2x1 element, and hence it
`is traversed by only one signal, and therefore high extinction
`ratio is not required for the various elements. On the other
`hand, the arrangements of FIGS. 5 and 6 are clearly simpler,
`and these are the preferred arrangements if the 2x2 elements
`have high extinction ratios.
`As previously noted, the depth is generally defined as the
`total number of elements along the path of a particular
`signal, and it is an important parameter that determines loss
`and crosstalk. Also important in general is the depth given
`by the total number of columns formed by the various
`elements, since it determines the wafer size when the
`arrangement is realized integrated form a single wafer. The
`arrangement of FIG. 3 has the lowest depth. On the other
`hand, if only three routers are used in the central stage (FIG.
`4a), then the arrangements of FIGS. 5 and 6 minimize depth,
`number of elements, and waveguides crossings.
`As pointed out earlier, repeated application of Clos con-
`struction produces an arrangement with reduction factor
`
`8
`equal to the product of the individual factors. For instance
`two successive applications of Clos construction with fac-
`tors m1 and m2 produce m=m1m2, and the result is an input
`stage arrangement similar to that of FIG. 4b, as shown in
`FIG. 4f. The only difference is that the input stage is now
`made up of m><p switches, instead of m><(2m—1) switches,
`and similarly the output stage consists of p><m switches, with
`m=m1m2 and p=p1p2 with p1=2m1—1 and p2=2m2—1. Each
`FIG. 4f switch now consists of two stages respectively made
`up of m1><p1 and m2><p2 switches. The input and output
`switches are now characterized by p>2m—1 and, therefore,
`the number of center blocks can be reduced by realizing the
`N><N arrangement in a single step, by using the arrangement
`of FIG. 4b with m=m1m2 and using m><(2m—1) and (2m—
`1)><m input and output switches. On the other hand simpler
`input and output switches are obtained by using the arrange-
`ment of FIG. 4d obtained with two applications of Clos
`construction. In particular, from the arrangement of FIG. 4f,
`one can realize for m=4 a fully dilated arrangement with
`m1=m2=2 by using for each block in FIG. 4f the arrangement
`of FIG. 7. In this case one finds that each connection 450
`
`between two stages in FIG. 4f involves a 2x1 element
`directly connected to a 1x2 element, as shown by 451 in
`FIG. 4g. Therefore each pair of elements 451 of FIG. 4g can
`be replaced by a single 2><2 element 452 and the final result
`is the arrangement of FIG. 4h, which is attractive because it
`is simple to realize in integrated form and it has negligible
`first-order crosstalk. Notice the above result, the occurrence
`for each connection between two blocks in FIG. 4f of a 2x1
`element directly connected to a 1x2 element, is a general
`property of FIG. 4f whenever each building block is fully
`dilated. T