Acoustooptic Cell Array (AOCA) System for DWDM Application in Optical Communication

Transcription

1 596 Acoustooptc Cell Arry (AOCA) System for DWDM Applcto Optcl Commucto ml S. Rwt*, Mocef. Tyh, Sumth R. Ktkur d Vdy Nll Deprtmet of Electrcl Egeerg Uversty of Nevd, Reo, NV 89557, U.S.A. Tel: ; Fx: ; E-Ml: rwt@ee.ur.edu Abstrct- The property of dffrcto of optcl bem by cousto-optc cell rry (AOCA) system depedg o the wvelegth d coustc frequecy hs bee vestgted for DWDM pplcto optcl commucto. The pplcto s MUX/DEMUX d cross-coect to vod fber bedg losses s the m focus of ths pper. The pper presets the bsc cocept, lyss d performce of two- d threedmesol rry system. The modfed rgg codtos, deflecto gle d dffrcto effcecy hve lso bee lyzed. Idex Terms- Acoustooptc, rgg, deflecto, dffrcto, MUX/DEMUX. I. INTROUDUCTION The tercto betwee surfce coustc wve d optcl sgl c be used for MUX/DEMUX pplcto wth the dvtges of low drve power, polrzto sestvty d rrow bdwdth [-]. I cousto-optc (AO) cell, the rf frequecy sgl s coverted to coustc surfce wve by trsducer whch tur dffrcts lght bem due to perodc modulto of the refrctve dex v elsto-optcl effect the mterl. The dffrcto effcecy of sgle cousto-optc cell s qute low d cot provde suffcet deflecto of optcl bem to mtch the fber loctos t the output of MUX/DEMUX. The effcecy s cresed by cosderg the phsed rry system of AO cells. The coustooptc dffrcto s hghly desrble s the drectos of the deflected lght bems d testy c be cotrolled by vryg the drve sgl frequecy d power, respectvely. I ths pper we hve lyzed two- d three dmesol AO cell rrys for pplcto s MUX/DEMUX s well s cross-coects whch re mportt for formto processg DWDM etworks. Three dmesol deflectos (x, y, z) re obted by pssg the coustc wve the secod stge cells z-drecto wheres the cdet gle s kept s fucto of x, y drectos. The modfed rgg codtos, deflecto gles d dffrcto effceces for both the systems hve bee obted. II. ASIC THEORY AND ANALYSIS I order to uderstd the bsc cocept of AOCA system, we hve to strt wth sgle cell d oe-dmesol rry. Ths system hs bee thoroughly vestgted by Rwt et. l []. The covetol rgg codto for sgle cell s gve by k. f s = = () k v. d the resultg deflecto gle s obted s f s = s () d v where s the rgg gle, k s the coustc wve umber, k cdet wve umber, s the cdet wvelegth, v s the velocty of the coustc wve d s the cdet gle. The geometrc cofgurto d xs coveto of smple AOCA system s show Fg.

2 597.. for the frst wvelegth L X Y Trsducer s d Fg.. Geometrc cofgurto of sgle AOCA ry The cdet lght trvels postve x-drecto d the coustc wve trvels postve y- drecto. The rgg codto for ths rry s gve by [] ψ k k m s t = = () ks k π d the rgg gle for the rry s obted s ψ m = = t ry () ks where s the rotto gle of the coustooptc wve frot correspodg to wvelegth, s s the physcl seprto betwee two cosecutve cells, ψ s the phse shft betwee m two cosecutve trsducers d d s legth of the cell. A. Two Dmesol Arry I order to obt suffcet deflecto of the bem d for hgher dffrcto effcecy the cocept s exteded to two dmesol rry s show Fg.. I ths lyss t s ssumed tht the rgg codto s stsfed t every stge d ll the cells re detcl. We hve cosdered both the cses () whe the phse chge betwee two dcet trsducers of stge d s dfferet d () whe the phse chge betwee two dcet trsducers of stge d s sme. For the frst cse the rgg codto to be stsfed t the secod stge for ech wvelegth s gve s [] ϕ k s ( ) = rct s = (5) k s k Stge Stge Stge Fg.. A seres of two-dmesol AOCA s ( + ) s s ϕ = rct + rct = ks k s k φ k Stge (6).for the secod wvelegth Smlrly we c get the rgg codtos for rd d th wvelegths. Flly the geerlzed rgg codto for four wvelegth -stge AOCA s obted s s + s s ( + ) ϕ ϕ( + ) = s rct + rct (7) ks ks k = k where ϕ ϕϕ d ϕ re phse shfts betwee,,, y two cosecutve trsducers t tht AOCA, respectvely. For the secod cse whe the phse chge betwee two dcet trsducers of stge d

3 598 stge s sme, the rgg codto for the frst wvelegth t the frst cell of the secod stge s gve by ϕ k s ( ) = rct s = (8) k s k Smlrly the rgg codto for the secod wvelegth s obted s ϕ k s ( + ) = s rct s + = (9) ks k Now the geerlzed rgg equto for ths cse s obted s ( ) s + + s ϕ ϕ ( + ) = s rct + rct ks k s ( + ) k = k () Smlrly we c derve the reltoshp for deflecto gle for eve d odd umber of rry s f s ( d ) = ( ) = v () ϕ + ( ) s + rct ks.. for eve umber of stge s d = ( ) = ( ) ϕ + ( ) s + rct ks for odd umber of stge. Three Dmesol Arry f v () For three dmesol rry, the dffrcted output of the frst AOCA s cdet o other two AOCA s show Fg.. The coustc wves to cell rrys A d A re gve z-drecto. I ths rrgemet the deflecto gle of cells A d A s ot the sme xy ple but s fucto of x, y d z s observed from frot vew of the structure show Fgs.. Fg.. Cscded rrgemet of two AOCA The rgg gle for AOCA-A vector form s obted s f = s s rz x v f f s cos rz v cos s s s rz y v Fg.. Frot vew of AOCA rrgemet z () It s evdet from Eq. () tht the gle s fucto of x, y d z. Smlrly the rgg codto for AOCA-A s obted s

4 599 f = s + s s s ry rz x f + cos s s s ry rz y f + s s s s ry rz z () These rgg gles hve bee obted by cosderg tht the phse shft betwee the trsducers of the cells re dfferet. It s observed tht the rgg codto cot be stsfed for the secod stge s t s gle of x, y d z wheres the cdet gle s betwee x d y oly. It mes tht the successve stges re ecessry to deflect the bems the requred drecto d to get optmum dffrcto effcecy. The lyss for more stges s crred out o the bss of sme pheome d rgg gle codto but t becomes more complex. The deflecto gle for the frst OACA s oly betwee x d y drectos cosderg oly the frst order dffrcto. For the ext AOCA (A d A) s the coustc wve psses through z- drecto, the gle of deflecto s betwee z xs d xy ple. Other mportt prmeters for AOCA system re the ormlzed power d dffrcto effcecy [] whch depeds o the cell sze, seprto betwee the cells, umber of cells, cdet gle d oretto of AOCA system. The lyss of these prmeters s beyod the scope ths short pper. III. NUMERICAL RESULTS AND DISCUSSION A plot betwee optcl wvelegth d deflecto gle for two-dmesol rry s show Fg. 5. It s oted tht there s.5 degree chge for the deflecto gle for every oe ometer chge the wvelegth. Also the cdet gle hs to be very close to the rgg gle for mxmum deflecto gle. The reltoshp betwee dffrcto effcecy d optcl Fg. 5. Optcl wvelegth d deflecto gle wvelegth for two-dmesol rry t stge s show Fg.6. It s otced tht the crosstlk of the system becomes very hgh f we select hgher rf frequeces s the dffrcto effcecy s decresed. Three dmesol vrto of deflecto gle wth cdet gle from - to + degrees s Fg.6. Dffrcto effcecy d optcl wvelegth show Fg.7. It s otced tht the deflecto s xyz drectos. Smlrly -D plot of wvelegth versus deflecto gle for cdet gles.8,.5 d degrees s show Fg. 8. Ag the deflecto gle s ll three drectos.

5 6 [] ml S. Rwt, Y. Ncr, H.W. L d J.Le h, Acousto-optclly tued MUX/DEMUX for DWDM pplctos, Jourl of Optcl Commuctos, vol., pp. -5, Jue. [] ml S. Rwt, Sumth R. Ktkur d Mocef. Tyh, Two-dmesol coustooptc cell rry (AOCA) for MUX/DEMUX pplcto DWDM, Proceedgs of SPIE Photocs West-5, Vol. 57, pp. 5-6, Aprl 5. [] Yghu Weg, Smulto d desg of DWDM system usg cousto-optc phsed rry rgg cells wth cross-tlk suppresso, MS Thess, Uversty of Nevd, Reo, August 999. Fg.7. -D plot of cdet gle vs. deflecto gle Fg.8. -D Plot of wvelegth vs. deflecto gle for dfferet cdet gles IV. CONCLUSION The lyss of AOCA system two d three dmesos hve bee preseted. Ths clerly shows tht the AOCA systems wth proper rrgemet d oretto c be used both s MUX/DEMUX d cross-coect for DWDM pplcto optcl commucto. REFERENCES [] Cheu D. Tr, Prcples d Alytcl Applctos of Acousto-Optc Tuble Flters, Elsever Scece, 997.