Multistage Optical System for Broadcasting and Switching Information

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Multistage optical system forbroadcasting and switching information

David Mendlovic, Bruce Leibner, and Nadav Cohen

Conventional switching systems connect each input channel to one output channel. Broadcastingsystems permit the connection of each input channel to more than a single output. A broadcast 2 3 2switch is presented. This switch is an extension of the standard bypass–exchange switch. It allows forthe broadcasting of the inputs in addition to the conventional modes. Multistage interconnection net-works can be constructed with this switch as the basic building block. Such networks will extend theircapabilities, allowing for broadcasting features. Three implementations of this type are described, andexperimental results for the 2 3 2 switch are also presented. © 1999 Optical Society of America

OCIS codes: 060.1810, 200.4650.

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1. Introduction

Conventional switching systems connect each inputchannel to one output. Broadcasting switches, onthe other hand, can connect each input channel toseveral output channels. The broadcasting capabil-ities of switches are determined by two main criteria:~a! the number of outputs that each input can beconnected to and ~b! the connectivity restrictions ofhe switching matrix. With the growth and devel-pment of communication systems the demand forroadcasting switches is increasing rapidly. Thesewitches are used in everyday life for many videopplications such as cable TV, videoconferences,losed-circuit TV’s, etc. In addition, the broadcast-ng property exists in almost every communicationnit for backup or for connection of active transmis-ions to test points for parallel monitoring.Several conventional all-optical switch designs

ave been proposed that are based on the crossbarrchitecture,1–5 the three-stage ~or the five-stage!

Clos network,6,7 and multistage interconnection net-work ~MIN! architectures, such as the Omega, Ban-yan, Clos, Cantor, and others.8–12 Opticalbroadcasting switches have been proposed only forcrossbar implementations and for Clos networks thatuse crossbar switches as subelements. One of the

The authors are with the Department of Physical Electronics,Faculty of Engineering, Tel Aviv University, 69978 Tel Aviv,Israel. D. Mendlovic’s e-mail address is [email protected].

Received 1 March 1999.0003-6935y99y296103-08$15.00y0© 1999 Optical Society of America

main problems in implementing an all-optical broad-casting switch is the need to divide the input signalamong the broadcast outputs. Most optical crossbarimplementations can easily be adapted to broadcast-ing systems. For example, the N 3 N optical cross-ar consisting of two-dimensional N 3 N array ofptical shutters placed between two orthogonal cylin-rical lenses1 can broadcast by means of simply open-

ing two or more shutters along a column. In thissystem the light intensity of the each output, regard-less of whether it is broadcast, is equal to 1yN.

Another example of crossbar broadcasting was pre-sented by Wu et al.5 Their conventional crossbarimplementation is a polarization-based system thatuses cascaded stages of a vector of ly2 switchableretarders placed between two birefringent calcitecrystals. Activating and inactivating the retardersin the different stages deviates or leaves untouched,respectively, the optical path propagation of each in-put, hence enabling the steering and the connectingof each input to the wanted output. Their suggestedbroadcasting crossbar is implemented by the replace-ment of all the ly2 retarders in the conventionalswitch with ly4 switchable retarders and the addi-tion of an extra stage. On activating a ly4 retarderthe signal obtains a circular polarization and is splitby the calcite crystal into its two orthogonal-polarization components. One of the components,which contains half of the beam energy, is deflectedby the calcite crystal after the retarder and continuesto propagate through the calcite crystals in the stagesthat follow toward the wanted output. The secondpolarization continues to the next stage—the follow-ing ly4 retarder—enabling the signal to be broadcast

10 October 1999 y Vol. 38, No. 29 y APPLIED OPTICS 6103

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to the following output as well or to continue to theadjacent output. In this manner the input signalcan be broadcast to all the outputs. It is clear that,in this setup, the intensity is not divided equallyamong the broadcast outputs. The first output re-ceives half of the intensity of the incoming input, thesecond broadcast output receives one fourth, and soon. In general, the light intensity of the nth broad-cast output is given by 1y2n of the input intensity.Furthermore, conventional switching, which con-nects one input to one output, in this system will beaccompanied by the loss of half of the input intensity.

The above drawbacks come in addition to the in-herent disadvantage of the crossbar architecture ingeneral. Crossbar systems tend to grow rapidly asthe number of input–output channels grows. Spe-cifically, for N input–output channels a crossbar-based system will require N2 switching elements,whereas a MIN-based system will require only N1.5

elements. Therefore MIN systems are advanta-geous for large systems.

This paper proposes a new, to our knowledge, all-optical switch that makes possible four modes: twoconventional modes ~bypass–exchange! and twobroadcasting modes. In Section 2 the proposedbroadcast-switching element is described. This ele-ment can serve as a building block for constructingbroadcast MIN’s with relatively high light efficiency,easy alignment, a fewer number of active cells ~forlarge-scale systems! compared with crossbar imple-mentation, and a homogeneous intensity distributionamong broadcast outputs. Various implementa-tions can be designed by use of this powerful basicelement. Three implementation examples are de-tailed in Section 3. We conclude this report withpreliminary experimental demonstrations ~Section4!, followed by a discussion and conclusions.

2. 2 3 2 All-Optical Broadcasting Switch

The proposed 2 3 2 all-optical broadcasting switch isdesigned to perform four different tasks, as shown inFig. 1. The first two are conventional bypass–exchange switching. The other two are the broad-casting options that permit the connection of eachinput to the two outputs.

One of the most promising approaches for achiev-ing conventional bypass–exchange switching is byuse of polarization-coded inputs that are controlleddynamically with electrically controlled ly2plates.9–12 The design of the proposed system isbased on a controlled ly2 plate that is placed betweentwo birefringent calcite crystals that act as beam-displacement plates10–14 ~BDP’s!. This approachhas been demonstrated for 2 3 2 and 4 3 4 opticalswitches.12,13 The basic structure of this switch ishown in Fig. 2.In this system the two incomming signals A and B

are orthogonally polarized ~for example, by use of aly2 plate in the entrance plane of signal B!. Theyare combined by a calcite crystal ~BDP1!, driventhrough a controlled ly2 ferroelectric liquid-crystal~FLC! pixel, and reopened by a second calcite crystal

104 APPLIED OPTICS y Vol. 38, No. 29 y 10 October 1999

~BDP2!. When the proper voltage is applied to theFLC pixel, it acts as a ly2 pixel, and the polarizationsof signals A and B interchange, thus exchanging theinputs in the output plane ~exchange mode!. Other-wise, the FLC is transparent to the incoming signals,and the output is identical to the input ~bypassmode!. The last ly2 plate in the output plane ad-justs the output polarization of the second beam.

Now, on the basis of a similar approach, we proposea 2 3 2 broadcasting switch, which is shown in Fig. 3.By replacing the controlled ly2 FLC pixel betweenthe two calcite crystals with two controlled ly4 FLCpixels in cascade, we obtain the four possible states ofthe broadcasting switch, as shown in Fig. 1.

The exchange mode is achieved by the activation of

Fig. 1. The four possibilities of the 2 3 2 broadcasting switch.~a! Bypass mode. ~b! Exchange mode. ~c! Upper broadcastingmode. ~d! Lower broadcasting mode.

Fig. 2. Diagram of a 2 3 2 bypass–exchange switch based onpolarization coding with bifringent calcite crystals as BDPs and aFLC ly2 retarder switch.

Fig. 3. Proposed setup for the 2 3 2 broadcasting switch.

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Table 1. The Four States of the 2 3 2 Broadcasting Switch

the two ly4 FLC pixels, which is equivalent to acti-ating the single ly2 FLC pixel shown in Fig. 2. The

bypass mode is acheived by the disactivation of thetwo ly4 FLC pixels, which causes the pixels to betransparent.

The two new broadcasting modes are achieved bythe activation of only one of the ly4 FLC pixels andare illustrated in Fig. 4. The upper broadcastingmode @Fig. 4~a!# is achieved when only signal A entersthe system. Signal A propagates through calcitecrystal BDP1 untouched and continues through thecontrolled ly4 FLC pixels. The activated ly4 FLCpixel changes the linear polarization of the signal tocircular polarization ~denoted as “o”!. The secondcalcite crystal ~BDP2! splits the circularly polarizedsignal into two linear orthogonally polarized beams ofequal intensity. One beam continues to propagatealong the axis, and the second is displaced by thecalcite crystal.

The lower broadcasting mode @Fig. 4~b!# is achievedwhen only signal B enters the system. Signal B isproperly polarized by the ly2 pixel in the entranceand is deviated by calcite crystal BDP1. It is driventhrough the activated ly4 FLC pixel, which changesthe linear polarization of the signal to circular polar-ization. From this point on the advancement of thesignal is identical to that described for the upperbroadcasting mode. Table 1 summarizes the fourstates of the system.

We note that this system can also be implementedwith one ly2 pixel and one ly4 pixel, instead of thetwo ly4 pixels, between the two calcite crystals. Inthis case the bypass mode is achieved by disactivationof both pixels. The exchange mode is achieved by

Fig. 4. The two broadcasting modes. ~a! The upper broadcastingmode. ~b! The lower broadcasting mode.

the activation of the ly2 pixel solely, and the broad-casting mode is achieved by the activation of only thely4 pixel. Also, the use of 3ly4 instead of ly4 re-tarders can be considered.

As opposed to most of the broadcasting architec-tures suggested to date, this one fully encompassesthe properties of the conventional switch. Thereforethis architecture can implement a much wider rangeof applications.

Another important and unique property of thisproposed switching system is the division of thebroadcast input signal into two energy-equivalentoutput signals. Thus in MIN systems that consistof several such 2 3 2 broadcasting switches activat-ing the broadcasting state in the proper switcheswill divide the energy of the input signal among theconnected outputs evenly ~for an even pair of out-puts!. In other broadcasting systems the inputlight intensity is inappropriately divided among thebroadcast outputs. In some cases the input lightintensity is divided into 1yN ~N is the number ofoutputs! for each of the broadcast outputs, regard-less of their number.1 In other cases the light in-tensity is divided among the broadcast outputs sothat the nth broadcast signal receives 1y2n of theinput intensity.5 Therefore the proposed architec-ture allows each input to be connected to a largernumber of outputs, while it requires a lower detec-tor sensitivity at the output plane.

One more important property of the proposed 2 3broadcasting switch is that changing the state ofsingle signal from the bypass or the exchangeode to the broadcasting mode does not interfereith the original output signal; it only reduces its

ntensity. In the opposite process in which theroadcast signal is returned to one signal in theypass or the exchange mode, the altered signal isot harmed, but its intensity is amplified. Thusne can change the state of a switch with a singlenput to the broadcasting mode and back withoutarming the preliminary output information.urthermore, the 2 3 2 broadcast switch is simple,

is easily cascadable, and offers a relatively highlight efficiency. All these advantages provide theproperties that make the proposed 2 3 2 broadcast-ing switch an attractive and powerful basic unit fordesigning general broadcasting MIN switches andtailored broadcasting implementations.

3. Broadcast-System Implementations

Various MIN’s consisting of 2 3 2 conventionalswitches have been suggested.8–12 Simply replacing

Inputs

FLC State

Output state1 2

Both A and B Off Off BypassBoth A and B On On ExchangeA Off On Upper broadcastB Off On Lower broadcast


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the 2 3 2 conventional switches with the 2 3 2 broad-asting switches adds broadcasting capabilities to thenterconnection system. In this section three broad-asting implementations of the 2 3 2 broadcastingwitch are presented. The first is a general perfect-huffle ~PS! MIN with 2 3 2 broadcasting switcheshat is capable of fully connecting one input to all theutputs. In the second, we introduce a reconfigu-able backup system that is a more specific imple-entation of the 2 3 2 broadcasting switch. In the

third, we introduce a test access implementation forparallel monitoring of incoming signals in a recon-figurable interconnection network.

A. Perfect-Shuffle Multistage Interconnection NetworkBroadcasting Systems

One of the major advantages of the MIN configura-tion is the wide range of switching architectures,routing algorithms, and connectivity capabilitiesfrom wide-sense and rearrangable nonblockingswitches to fully and partially connected switches.14

One of the most familiar MIN’s is the PS MIN shown

Fig. 5. Fully connected PS MIN for 16 input channels.

Fig. 6. Headlight broadcasting features of the 2 3 2 broadcastinnput to all the outputs. ~b!, ~c! Two different patterns of two inp


in Fig. 5. This MIN consists of repeating stages offixed PS interconnections followed by bypass–exchange switch arrays. A fully connected PS MIN~any single input can be connected to any single out-put, but some connections are not possible if otherconnections already exist! is achieved by use of log2 Nstages.

By replacing the conventional 2 3 2 switches withthe new 2 3 2 broadcasting switches in a fully con-nected N 3 N PS MIN, we gain additional broadcast-ing features. One noticeable broadcasting feature ofthis system is that it enables the broadcasting of eachof the inputs to all the outputs, hence acting as abroadcast selector. Figure 6~a! illustrates an exam-ple of such a system in which channel 1 is broadcastto all outputs. In this case all the switches in thepropagation path of the input are activated in thebroadcasting mode ~activating one ly4 pixel!. Thisway the number of connected outputs is multiplied ineach stage, and after log2 N stages the input is broad-ast to the N outputs. Note that, in this configura-ion, there is no need to alter the state of the switcheshen another channel should be broadcast. Any in-

oming input will be broadcast to all the outputs. Inddition, the light intensity is divided equally amonghe outputs, thus requiring the minimum incomingight intensity.

Another broadcasting example is the capacity toroadcast any two inputs each to Ny2 outputs. Inhis case several different possibilities exist. Inigs. 6~b! and 6~c! two of the possible connectionsre shown for a 16 3 16 PS MIN. The state of eachwitch is clearly visible in the figures. In these twoxamples the input light is divided equally as well,hus reducing the required incoming light intensity.

tch in a 16 3 16 fully connected PS MIN. ~a! Broadcasting eachbroadcasted to Ny2 outputs.

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Between these all-broadcasting implementationsand the conventional fully connected switch lies a fullrange of implementations that encompasses the con-ventional switching of some of the inputs togetherwith the broadcasting of several other inputs. Fur-thermore, increasing the number of stages of the PSMIN, as in rearrangable systems, will increase therange of switching possibilities. In the examples de-scribed in Subsection 3.B, we introduce two cases ofPS MIN’s that are used for specific broadcasting andswitching configurations.

B. Reconfigurable Interconnection and Backup Systems

The second demonstration of using the proposed 2 32 broadcasting switch is that of reconfigurable inter-connection and hardware-backup systems. In manycommunication systems backup capability is impor-tant and requires minimum-error-link restoration,i.e., active links should be restored with minimal ef-fect on the end users. One of the main drawbacks ofall the all-optical switches proposed to date is therelatively slow switching time, which usually is lim-ited to several microseconds. These switches cannothandle the fast rates of optical fiber links of severalgigabits per second and thus cannot offer a minimum-error-link backup system.

One of the most common ways to perform effec-tive backups is to broadcast simultaneously the in-formation to the opposite end user through two ormore links ~connections! that could be routed dif-ferently. The information at the opposite end userdestination is restored in all the links simulta-neously, and the selection among alternative links

Fig. 7. Diagram of 4 3 4 reconfigurable interconnection andackup system. Each of the switches S1–S6 represents a 2 3 2roadcasting switch.

Fig. 8. Examples of three types of configurations of the 4 3 4 reconup. ~b! Two links backed up. ~c! A single link double-backed up

is done by electronics, which can switch among thelinks in nanosecond rates. Hence the number oferrors that will appear for the restored link is re-duced enormously. This method transfers theswitching problem back to the electronics, whichare more suitable, in the meantime, for this task.In this situation the all-optical switch is used as ameans of realizing the wanted interconnection con-figuration and the required backup connections.The wanted configuration can be altered, but thatalteration will harm the active channels that areaffected by the change.

As is shown in Fig. 7, we propose such a reconfigu-rable interconnection and backup system with fourinputs and four outputs ~4 3 4!. This system is ahree-stage 4 3 4 PS MIN with 2 3 2 broadcastingwitches. Basically, it is a rearrangable nonblock-ng switch and makes the following configurationsossible:

1. Any interconnection configuration between theour inputs and the four outputs. In this case all thewitches are used as conventional bypass–exchangewitches.2. Any interconnection configuration of three in-

uts and one backup link to the four outputs @Fig.~a!#. In this case a chosen input is broadcasthrough one of the switches.

3. Any interconnection configuration of two in-uts and their two backup links to the four outputsFig. 8~b!#. In this case both inputs are broadcasthrough one of the switches.

4. Any interconnection configuration of two in-uts in which one link is backed up twice to the fourutputs @Fig. 8~c!#. In this case a selected input isroadcast through two switches.5. Any broadcasting interconnection of one of the

nputs to the four outputs.

C. Noninterrupting Link-Monitoring Capability inInterconnection Networks

One important property required in communicationinterconnection systems is the ability to monitor ac-

able interconnection and backup system. ~a! A single link backed
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tive communication links without disturbing them.The 2 3 2 broadcasting switch enables the design of

IN’s with this property by use of the broadcastingode. This capacity is due to the fact that a change

n the state of a switch with a single input to theroadcasting mode and back does not harm the pre-iminary output information. In Fig. 9 such a sys-em is shown for three inputs, three outputs, and theonitoring output ~MO!.The system shown in Fig. 9 is a four-stage 4 3 4 PSIN in which all the switches ~S1–S8! are 2 3 2

roadcasting switches. The three inputs and thehree outputs are listed as A–C, and the last output ishe MO. Each of the channels for signals A–C can be

monitored at the MO port by means of changing asingle switch to the broadcasting mode. In that wayafter an interconnection state has been achievedmonitoring any channel does not interfere with theconnection. Instead, it simply reduces the moni-tored channel’s light intensity.

In the configuration presented in Fig. 9 switchesS1, S3, and S7 are in constant-bypass mode.Switches S6 and S8 are in constant-exchange mode.Switches S2, S4, and S5 have only one input and areused to broadcast the wanted input to the MO. Intheir nonbroadcasting states, S2 and S5 are in thebypass mode, and S4 is in the exchange mode.Broadcasting signal C to the MO is performed by

eans of changing only switch S2 from the bypassode to the broadcasting mode. Removing signal C

rom the MO is accomplished by means of reinstatinghe position of switch S2 from the broadcasting modeo the bypass mode. In the same manner, signal A isroadcast to the MO by means of changing onlywitch S5 from the bypass mode to the broadcastingode, and broadcasting signal B to the MO is main-

ained by use of only switch S4. Note that in thisesign only one signal can be broadcast to the MO.n other designs, one can add several MO’s and in-rease the possibilities.

Figure 10 shows two more interconnection config-rations of the three inputs and the three outputsith the MO. Note that, in each configuration, the

tates of the switches differ and at least three of thewitches have one input. These switches performhe requested signal broadcasting to the MO. Inig. 10~a! the active switches should be S2, S5, and S8

or signals C, B, and A, respectively. In Fig. 10~b!the active switches are S2, S6, and S8 for signals C,A, and B, respectively.

This system can also be designed as an N:1 backupsystem. That is, the MO can be used as a shared-backup output to any of the N inputs without the

Fig. 9. Diagram of a 3 3 3 interconnection network with nonin-terrupting link monitoring.


need to reconfigure the active channels on choosingthe wanted backed-up input.

4. Experimental Results

A preliminary experimental demonstration of the 2 32 broadcasting switch was carried out for the setupillustrated in Fig. 3. The purpose of the experimentwas to show the four possible modes of the 2 3 2broadcasting switch with respect to the values listedin Table 1. As shown in Fig. 11, the input planeconsisted of two signals ~represented by a triangleand a circle! illuminated by a collimated beam of 630nm. The results of the four states are shown in Fig.11.

5. Discussion: System Design Improvements

After presenting the 2 3 2 broadcasting switch andseveral applications, we devote this section to intro-ducing some aspects of the 2 3 2 broadcast-switchingsystems. The first deals with filtering out the sec-ond input signal in switches that are in the broad-casting mode. As explained in Section 2, the 2 3 2broadcasting switch requires only one input in thebroadcasting mode. A second input will be broad-cast together with the original broadcast signal, caus-ing undesired interference ~in most applications!.To eliminate this problem in MIN’s, one should blockthe signals on the inactive inputs in the first stage ofthe system. By blocking these signals, we drive onlythe wanted signals through the system, avoiding theunwanted situation of two inputs in a broadcastingswitch. This task can be accomplished in threeways: The first and most familiar way is by use ofmechanical light shutters in the entrance of eachinput. Two other methods that are more compatiblewith the suggested system are presented in Figs.12~a! and 12~b!. Figure 12~a! shows two polarizersthat are introduced after the ly2 retarders in theentrance plane. In this case eliminating the un-wanted input signal is achieved by means of settingits polarization ~by use of the ly2 retarders! so thatthe polarizers will block it. Figure 12~b! shows the

Fig. 10. Two additional MIN configurations with a noninterrupt-ing monitoring link.

first calcite crystal as partially masked. The un-wanted input signals are eliminated by means of set-ting them to the proper polarizations so that the firstcalcite crystal will direct them toward the maskedzones.

The second issue that should be addressed is thecross talk caused by imperfect optical elements.These undesired signals propagate throughout thesystem, increase with each stage, and join the desiredsignals, causing noise. One way to eliminate suchnoise is to try to block it out in each switch in thesystem. The method shown in Fig. 12~a! does notaddress this problem. The technique shown in Fig.12~b!, on the other hand, enables us to eclipse some ofthis noise while eliminating unwanted input to thebroadcasting switches. Of course, not all the noisecan be eliminated in this way. Even after this mod-ification is implemented, noise will accumulate in theconventional modes because of the imperfections ofthe switching retarders and the second calcite crys-tal. In the broadcasting mode noise is contributed

Fig. 11. The four states of the 2 3 2 broadcasting switch. ~a! BLower broadcasting mode.

Fig. 12. Methods of eliminating unwanted signals. ~a! Un-wanted signals eliminated by use of polarization. ~b! Unwantedsignals eliminated by means of polarization and masking.

by the residue of the incorrectly polarized light of theunwanted signal after the front ly2 retarder.

One more aspect that we note here is the reducedoutput-signal intensity caused by the broadcastingmode. To overcome this problem, one can assemblethe MIN outputs ~the outputs of the last-stage switch-es! with optical amplifiers to equalize the output-signal intensities.

The suggested 2 3 2 broadcasting switch can bealtered to achieve various ratios of broadcasting sig-nals. Introducing, between the two calcite crystals,two different switchable retarders whose sum isequivalent to a ly2 retarder yields a set of six stages.Table 2 shows the possibilities for two retarders ofly8 and 3ly8.

This concept can be expanded and can providemore than two broadcasting ratios by the introduc-tion of more than two retarders between the calcitecrystals, e.g., by use of three retarders, ly8, ly8, andly4. In general, with n different retarders, as manyas 2n broadcasting modes can be obtained for eachinput signal in addition to the bypass and the ex-change modes. Furthermore, a nonbinary retardercan be introduced to generate a continuous range ofratios in the broadcasting mode. One step further isto abolish the constraint that the sum of the retardersbe a ly2-equivalent retarder and also to enable thebroadcasting of both input signals simultaneously.In this way, one can achieve a system that performsall that is described above and, in addition, can real-

mode. ~b! Exchange mode. ~c! Upper broadcasting mode. ~d!

Table 2. The Different Modes of a 2 3 2 Broadcasting Switch with TwoDifferent Retarders

InputSignals

FLC 1~ly8!

FLC 2~3ly8!

OutputSignals

Broadcast-Intensity

Ratioa

A and B Off Off Bypass —A and B On On Exchange —A On Off Broadcast 0.171A Off On Broadcast 5.842B On Off Broadcast 5.842B Off On Broadcast 0.171

aThe broadcast intensity ratio is defined as the upper-broadcasting-system output divided by the lower-broadcasting-system output.

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ize the accomplishment of weighted addition of thetwo input signals. In general, this 2 3 2 element can

erform various additions of the two input signals, ashown in Fig. 13. The input signals are A and B,nd the output signals are X*A 1 Y*B and X*B 1

Y*A. For example, the values of X 5 0 and Y 5 1and of X 5 1 and Y 5 0 yield the bypass and theexchange modes, respectively. For values of X 51y2 and Y 5 1y2 and when one of the input signals isblocked, the broadcasting mode is obtained. Usingdifferent retarders allows different dependent valuesof X and Y to be obtained, providing a whole range offurther implementations.

6. Conclusion

An all-optical 2 3 2 broadcasting switch that uses twocascaded FLC ly4 pixels and polarizing beam dis-placers, such as calcite crystals, has been proposed.A preliminary experimental demonstration has beenperformed that proved the feasibility of the suggestedidea. This switch constitutes a new concept thatpermits the generation of a whole new family ofMIN’s with broadcasting properties. Several exam-ples of these capabilities have been introduced anddemonstrated by the replacement of the conventional2 3 2 switch with 2 3 2 broadcasting switches.These capabilities include the properties of a fullyconnected PS MIN, a reconfigurable interconnectionand backup system, and a noninterrupting link mon-itor in a MIN.

These switches can be used in all MIN’s thatconsist of 2 3 2 switches, such as the Banyan, thecrossover, the Cantor, etc., to produce various imple-mentations. Furthermore, the compact nature, easyalignment, and cascadability of the proposed config-uration offer an easy means of implementing large-

Fig. 13. Generalized 2 3 2 broadcasting and switching system.


scale broadcasting MIN’s and two-dimensionalbroadcast-switching architectures.

This project is supported by the European Commu-nity ESPRIT program under grant 22613-RODCI.N. Cohen acknowledges the Eshcol Foundation andthe Israeli Ministry of Science and Technology forfinancial support.

References1. A. A. Sawchuk, B. K. Jenkins, C. S. Raghavendra, and A.

Varma, “Optical crossbar network,” Computer 20~6!, 50–60~1987!.

2. D. O. Harris, “Multichannel acousto-optic crossbar switch,”Appl. Opt. 33, 1734–1741 ~1994!.

3. H. Yamazaki and S. Fukushima, “Holographic switch with aferroelectric liquid-crystal spatial light modulator for a largescale switch,” Appl. Opt. 34, 8137–8143 ~1995!.

4. A. R. Dias, R. F. Kalman, J. W. Goodman, and A. A. Sawchuk,“Fiber optic crossbar switch with broadcast capabilities,” Opt.Eng. 27, 955–960 ~1988!.

5. Y. Wu, L. Liu, and Z. Wang, “Optical crossbar elements usedfor switching networks,” Appl. Opt. 33, 175–178 ~1994!.

6. S.-H. Lin, T. F. Krille, and J. Walkup, “Two-dimensional opti-cal Clos interconnection network and it’s uses,” Appl. Opt. 27,1734–1741 ~1988!.

7. M. Hossain, S. Ghanta, and M. Guizani, “Optical realization ofa Clos nonblocking broadcast switching network with constanttime network control algorithm,” Appl. Opt. 32, 665–673~1993!.

8. K. Hogari, K. Noguchi, and T. Matsumoto, “Two-dimensionalmultichannel optical switch,” Appl. Opt. 30, 3277–3278 ~1991!.

9. K. M. Johnson, M. R. Surette, and J. Shamir, “Optical inter-connection network using polarization based ferroelectric liq-uid crystal,” Appl. Opt. 27, 1727–1733 ~1988!.

10. N. Wang, L. Liu, and Y. Yin, “Cantor network, control algo-rithm, two-dimensional compact structure and it’s optical im-plementation,” Appl. Opt. 34, 8176–8181 ~1995!.

11. D. Marom and D. Mendlovic, “Compact, all optical bypass–exchange switch,” Appl. Opt. 35, 248–253 ~1996!.

12. D. Marom and D. Mendlovic, “All-optical reduced state 4 by 4switch,” Opt. Photon. News 7~2!, 43 ~1996!.

13. T. Stone and J. M. Battiato, “Optical array generation andinterconnection using birefringent slabs,” Appl. Opt. 33, 182–190 ~1994!.

14. J. E. Midwinter, Photonics in Switching ~Academic, New York,1993!, Vols. 1 and 2.

Multistage Optical System for Broadcasting and Switching Information

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