I.GiithiuHthngTTQIMDDHthngTTQIMDDlg?

Cc H Thng Thng Tin Quang

Msc.Eng.NghimXunAnh

s dng iu bin cng (IMIntensity Modulation),v tchsngtrctipDD(DirectDetector) thngtinvphacatnhiukhngngvaitrquan trng(khcbitvihthngTTQCoherent)

H thng TTQ IMDD ra i u tin, v ang c s dng rng ri trong mng quang ti Vit namvnhiunckhc.Tchinnayt(2,5 10Gb/s(STM4,STM16)2/26/2007 OpticCommunicationSystems 3

NhngnidungchnhI. II.

I.1NguynlhthngIMDD

HthngthngtinquangIMDD Hthngthngtinquangcoherent

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4

I.1.1.PhaMyPhtPha pht thc hin bin i tn hiu in uvo thnh tn hiu quang tng ng v pht tn hiu quang ny vo si quang thc hin vic truyn thngtin. [My pht thc hin iu ch ngun quang (LED hoc LD) bng dng tn hiu in (digital hoc analog)cntruyn].Tcl,cngsutquangratl tuyn tnhvi dng iu bin Kiu iuch ny giliuchcngIM(IntensityModulation).

I.1.2.TruyntintrnsiquangCngsut tnhiu b tn haotrong qu trnh truyn nhsngdctheochiudicasi(dohpthca tpcht,cabnthnvt liu,hpthint, suy haodouncong,tnxvv) Lengthlimitted! Suyhaocngsut(suyhaoxen)doccphnttrn tuyn(bni, mi ni, mi hn,ccb ghp/xenr knh,ccbchuyni) Lengthlimitted! Mo(dnxung)tnhiudotnsc(tnscgiacc mode,tnscmode(tnscvntcnhm),tnsc dn sng, tn sc vt liu, tn sc phn cc mode vv... Bitratelimitted!.2/26/2007 OpticCommunicationSystems 7

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Intensitymodulation

I.1.3.PhaMyThuSngtnhiuquangcphtitphaphtsaukhi ti b thu quang c bin i thnh tn hiu in (nhphotodiode),ckhuchivkhiphcthnh tnhiucdngnhuvothitbphtquang. Photodiode (O/E) thc hin tch sng theo lut bnh phngvnbinicngsutquangthuctrc tipthnhdngin(dngphoto)tiuracan. bthukiunycgilbthutchsngtrctip (DD).CcphotodiodecthlpinhocAPD. Tch sngtrctipcbiuhinl mythuquang,tn hiu c tch ra trc tip bng gc m khngc btkxlhocbinino.

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I.2.TstnhiutrnnhiuSNRTstnhiu/nhiu(SNR)lthamsrtquantrng trong b tch sng quang. N xc nh cht lng ca b thu quang tng t v l yu t ch yu quytnhnhycabthuquangs. Saukhitnhiuquanglantruynquamtclydi, cng sut ca n rt thp. Do cn c b thu quang tt, b tch sng quang v cc mch in khuchisaunphikthptiuchoraSNR cao.Tcl:Btchsngquangcnchiusutlngtcaopht racngsuttnhiuln,v

SNR(continued.)Tronggiihnnhiunhit(ss > sT)th RP h P in in SNR pin = = (*) 2eB 2 nB h e e Note: Trong cc b thu quang thc t s dng tch sngpin,nhiutrilnhiunhit(dobtchsng c intr titchsng nnn sinhra dngnhiu nhitkhlntoranhiunhit.)2/26/2007 OpticCommunicationSystems 11

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SNR(continued)Nhiucabtchsngquangvbkhuchiinphi cngthpcngtt.

SNR(continued.)Trong nhiu b thu quang, dng nhiu nhit hiu dng ln gp khong 20 ln dng nhiu lng t hiudngvkhong100lndngtihiudng. Tngt,tsSNRcabthuquangdngAPDl(MRP )2 in SNRAPD = 2 2 e(RP + Id ) F + 2 eIl + ( kBT /R )F B eB M A eB 4 in L n e

T stnhiutrnnhiucaphotodiodecxcnh lIp Cngsut tn hiu t dng photo SNR = = 2 Cng sut nhiu b tch sng + Cng sut nhiu b khuch i s2

T sSNRcabthuphotodiodepincvitl:SNRpin = R P 2 e(RP + Id + Il)+ ( kBT /R ) nB eB 4 in L F e2 2 in

Tronggiihnnhiunhit(ss > sT ),lc nytac

nhythusthamchiuTrong thng tin quang s, nhy thu lun b rng buc bi t s li bit BER. nhy c th hin bng mt cng sut quang ti thiu c th c th mbotslibitBERcho.(Thngcxc nhtimtimthamchiutrcbnithuR)Khimypht C (Bnipht) TX S Khimythu Siquang C (bnithu) RX

SNR APD =

RP h in P in = 2eB F 2 nB F h e A e A

Vtrongtrnghpny,tstnhiutrnnhiuSNR cabthudngphotodiodeAPDlibgim ibih snhiutriF sovibthuphotodiode pin. A TrongFAcxcnhbngthcnghimxpxl FA Mx Vixlphntgam,=0.3viphotodiodethcSilic,= 0.7/vInGaAs,=1viGermanium.2/26/2007 OpticCommunicationSystems 13

R2/26/2007 OpticCommunicationSystems 15

I.3.nhycabthuquang nhy thu l tham s quan trng nht nh gi khnngvchtlngcaHTTTQ. nhycaothhinkhnngthucmccng sutquangrtthp. nhythucaochophpthitkcccHTTTQ ctccaovclyxa.Nb tcngtrc tip bitsSNRcabtchsngquang.TclSNR cngcaothnhycngcao. eSNR ch nh gi cht lng tn hiu thu trong truyn dn analog c p ng tiu chun rahaykhng,cn2/26/2007 OpticCommunicationSystems 14

nhythuccimthamchiuSlimthamchiutrnsiquangngaysaubni phtC ,cnRlimthamchiutrnsiquang TX ngaytrcbnithuC . RX Cc thng s ti cc im tham chiu xc nh c linquantimctiuthitkontruyndnquang ctslibitBER. 6 12 BERthngnmtrongdi10 10

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nhythucckhuynnghNh vy nhy ca b thu quang l cng sut trungbnhnhnhtcthchpnhnctiim R t c t s li bit BER (Khuyn ngh ca ITUT)nhsau:6 9 10 10 ivicchthngPDH, 10 10 i vi cc h thng SDH STM1, STM4 v STM16mkhngckhuch iquang, 12 v 10 i vi h thng n knh quang v nhiu knhquangcsdngkhuchiquangtiSTM64

BER(continued.)Do tn hiu sau tch sng rt yu nn n cn phi ckhuchi,clc,saucsosnhvi mcngngtimchquytnh thucxung mongmun(bit1hoc0)trongkhethigiancan. Trong trng hp khng li th khi 1 c thu th u ra V (t) phi cao hn in p ngng, v khi out 0cthuthV (t)phinhhnngng. out Trongthct,dotcngcaccloinhiukhc nhauvsgiaothoagiaccxunglncncth gy ra s trch khi gi tr trung bnh ca V (t)v out gyrali.2/26/2007 OpticCommunicationSystems 19

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I.4.Tsbtli(BER)trongbthuquangBthuquangtronghthngthngtinquangsIM DDgmmtbtchsngquang,btinkhuchi, b khuch i in, mch cn bng (lc) v quyt nh.

BERxcnhtllixyratacthdngcchchia cc xung li N cho tng s cc xung N trong e t khongthigiantcho.Ncgiltslibit BERvcvitnhsau:

BER =

Ne N t

xcnhBERtibthu,sphnbxcsuttn hiuuracamchcnbnglrtquantrngv iu quyt nh xem bit 1 hay 0 c pht n. Do , ta xt vn ny thng qua h thng thngtinsviccxung0v1.2/26/2007 OpticCommunicationSystems 18 2/26/2007 OpticCommunicationSystems 20

BER(continued.)

BER(continued.)LixyrakhiII chobit0. D Chaikiulitrncthgplibngvicnhngha xcsutlibitnhsau

BER = p 0 P 1/0 + p 1 P 0/1 ( ) ( ) ( ) ( )TrongP(1/0)lxcsutquytnhnhmbit1khi bit 0 c gi n. P(0/1) l xc sut quyt nh nhmbit0khibit1cgin. p(0) v p(1) l xc sut nhn ng cc bit 0 v 1 tngng.21 2/26/2007 OpticCommunicationSystems 23

Mtxcsutp(I)

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BER(continued.)Hnh trn ch ra tn hiu dao ng nhn c bi mch quyt nh, mch ny ly mu ti thi im quytnht xcnhthngquaskhiphcxung D ngh. GitrlymuIbinngtbitsangbitquanhgi tr trung bnh I hoc I , ty theo bit tng ng 1 0 vibit1haybit0tronglungbit. Mch quyt nh so snh gi tr ly mu vi mc ngngI vginlbit1nuI> I hocbit0 D D nuI2 )th p(0) p(1) 0,5.Khi

BER =

P 1/0 + P 0/1 ( ) ( ) 2

(*)

Hnh trn cho thy P(0/1) v P(1/0) ph thuc vo hm mtp(I)cagitrlymuI.Dnghmp(I)phthuc vothngkccngunnhiugyraccbinngdng.Nhiu nhit i v nhiu bn c xp x bng phn b T Gaussian,do tng ca chng (gi tr c ly mu I) cnglbinngunhinGaussiancphngsail2 s 2 = s s2 + s T2/26/2007 OpticCommunicationSystems 24

BER(continued.)2 e I Vis s = 2 ( p + I ) e cn sT = d B

BER(continued.)4 BTB k e F n R L Vi

2

Gitrtrungbnhvphngsaicabit1vbit 0khcnhaudoI tngngviI hocI ,ty p 1 0 theobit nhnc.Nu s12 v s02 lccphng saitng ngth xcsutc iukin trn c chobi

Q = Q = Q 0 1 I - I I - I Q = 1 D vQ = D 0 1 0 s s 0 1

s I + s I Nhvy,dngquyt (*) ID = 1 0 0 1 nhtiul s1 + s 0 Khi s1 s0 = ,thI =(I +I )/2tngngvingngquyt D 1 0 nhnmgia.Trnghpnypdngchohuht ccbthupindonhiucanchyulnhiunhit (sT>>sS )vclpvidngtrungbnh. TrongccbthuAPDthI cttheobt(*). D2/26/2007 OpticCommunicationSystems 27

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BER(continued.)Trongerfclhmlib,cnhnghal Khi

BER(continued.)Nh vy BER vi gi tr ngng ti u (I ) ph Dopt. thucvothamsQnhsau(*)

TrongthamsQcxcnhl Phng trnh trn cho thy BER ph thuc vo ngngquytnhI .Trongthct, I ctiu D D nhm ti thiu BER. BER t c khi I c min. D chnsaocho2/26/2007 OpticCommunicationSystems 26

(**)

HnhsauchothysbinthincaBERtheoQnh thno.2/26/2007 OpticCommunicationSystems 28

BER(continued.)N c v da trn biu thc gn ng v kh chnhxckhiQ>3.12 BERcithinkhiQtngvtrnnnhhn10 vi Q>7. nhy thu tng ng vi cng sut quang trung 9 bnhcQ6scBER10 ,.

I.5.nhythuPINphotodiodeGi thit bit 0 khng mang cng sut quang saochoP =0,tcI =0. 0 0 NugilcngsutquangTBthucth rec lgitrtrungbnhcaccbit1v0vkhi P + P 1 0P = rec 2

P clinquan ti I trongbtchsngpinnh 1 1 sau

I =RP = 2 P (vi P0 = 0) R rec 1 1

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BERvs.Q

PINnhythus1 v s0 bao gm cc thnh phn ca c nhiu lng t v nhiu nhit, v vy chng c th c vitnhsau: s 1 = s s 2 + s T2 v s 0 = s T B qua thnh phn dng ti, phng sai nhiu tr thnh s s2 = 2 (2 P ) e e R rec B

s T2 =

4 BTB k e F n R L

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PINnhythuKhihsQcvitnhsau

I.6.nhythuAPDphotodiodeTngtnhivitrnghpPIN, githitcc bit0khngmangcngsut(P =0hayI =0). 0 0 Vi R =MR th cng sut ng vi cc bit 1 lin APD quanviI trongbthuAPDnhsau: 1

Q =

2 R P I rec 1 = 2 2 s 1 + s 0 s S + s T + s T

KhichnhBERthQcxcnhtheobt.BER (trang 28), ri t bt. trn tm c nhy thu cabthuquangnhsau: rec

I =R P = MRP = 2 MR P (do P0 = 0) 1 APD 1 1 recB qua cc thnh phn dng ti, phng sai nhiu cabthuAPDtrthnh 2 s s = 2 2RF (2 P ) e eM A rec B2 s T =

Prec

= pin

Q (eBQ+ s T ) e R33

4 BTB k e F n R L35

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PINnhythuNhnxt: nhy thu ph thucvoccthams b thu.ivi bthuquang PINth nhiunhit sT thngltri,vkhicthcvitdi rec dngnginnhsau: Q T s

APDnhythuKhiQcxcnhl

Q =

P rec

pin

=

2 MR P I rec 1 = 2