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Cu hi 3.1: Cc phng php iu khin trong mng quang .... 2

Cu hi 3.2: Trnh by c ch bo v ng truyn quang

WDM. ...................................................................................... 2

Cu hi 3.3 : V s cu trc ca b khuch i EDFA theo 3

ch bm (thun, ngc v 2 chiu), nu chc nng cc khi

v nguyn tc hot ng............................................................ 5

Nu cc u khuyt im ca khuch i quang si EDFA ......... 5

Cu 3.4: Trnh by cc giai on pht trin IP/ WDM. .............. 9

Cu hi 3.5 : Trnh by cc cu trc mng IP trn WDM phn

loi theo mt bng d liu. ...................................................... 11

Cu hi 3.6: Trnh by cc cu hnh truy nhp FTTx. .............. 15

Cu hi 3.7 : Cu hnh tham chiu v nu cc khi chc nng c

bn ca mng truy nhp quang FTTx. ..................................... 18

Cu hi 3. 8: Trnh by cu trc c bn ca h thng thng tin

quang coherent. ...................................................................... 19

Cu hi 3.9 : Trnh by cu to v gii thch nguyn l hot ng

ca b khuch i Raman. ...................................................... 20

Cu hi 3.10 : Trnh by cu to v gii thch nguyn l hot

ng ca b khuch i quang bn dn SOA. .......................... 23

Cu hi 3.11 : Nu khi nim v ASK, FSK, PSK, v dng sng

tn hiu ti cc u vo v u ra b iu bin trong thng tin

quang Coherent, vi tn hiu u vo b iu bin l tn hiu s

ng vi dy bit 101010101, sng mang quang n sc E=

E0sin(2f0t+/2). .................................................................... 24

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Cu hi 3.1: Cc phng php iu khin trong mng quang

C 3 phng php iu khin trong cc mng IP trn quang:

Phng php iu khin tnh: p dng cho giai on u t chc truyn ti IP/ WDM v vic iu khin gia IP v WDM c thc hin theo mt phng thc cp pht c nh.

Phng php iu khin ng: p dng cho giai on th hai, cc mng WDM c chuyn i t cu trc vng ring hay im-im sang cu trc mesh vi cc h thng DWDM. Trong giai on ny, iu khin WDM thng qua vic cp pht cc bc sng c thc hin bng d liu iu khin nhm m bo tn dng mng mt cch hiu qu.

Phng php iu khin tch hp: Gii php iu khin tch hp s dng trong m hnh gii php mng ngang hng. Trong , mt phng iu khin u dng c mng WDM v IP, ng thi kt ni quang c dn hng bi nh tuyn IP.

Cu hi 3.2: Trnh by c ch bo v ng truyn quang WDM.

Bo v 1 + 1:

- Lu lng truyn dn c bo v l m phng qua hai ng dn song song. Khi hot ng bnh thng, pha ch nhn hai chui lu lng cn bng v s la chn mt trong nhng chui ny. Trong trng hp lu lng trn ng chnh b li, pha ch s chuyn sang ng dn khc cn li.

- Gy lng ph bng thng.

Bo v 1 : 1:

- Hai ng dn song song cng c s dng. Tuy nhin, khi hot ng bnh thng khng c mt lu lng no c truyn qua ng dn d phng. Ch trong trng hp b li, ng dn chnh s chuyn ngun v ch vo ng dn d phng.

Bo v 1: N:

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- Nhng ng truyn dn ca mng chia s mt ng truyn dn d phng.

- iu quan trng l k thut phc hi ny c th lu c mt li ring l.

- Trong trng hp nhiu li, th tc bo hiu phi khng nh chc chn rng ch ng dn ca mng l c bo v ti mt thi im.

a. Bo v ng truyn quang.

- Khi thc hin cu hnh im- im hoc mng vng WDM th thng s dng c ch bo v 1+1 hoc 1:1 cho lp on truyn dn.

- Khi s dng c ch bo v 1+1, ton b tn hiu WDM c bo v bng cch chia thnh hai tn hiu ti nt WDM v truyn dn trn hai si quang ring bit. Ti nt pha thu, c hai tn hiu c so snh v tn hiu c cht lng tt hn s c chn.

- Khi s dng c ch bo v 1:1, tn hiu WDM ch c pht trn mt si quang. Nu si lm vic c s c, tn hiu WDM s c chuyn mch ti si bo v.

Bo v ng truyn quang theo c ch 1 + 1

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Bo v ng truyn quang theo c ch 1:1

b. Bo v on ghp knh quang

- Phn ln c ch bo v on ghp knh quang thng s dng cc c ch bo v SDH.

- Cc thit b ghp knh xen/r WDM c th ti cu hnh li s a ra s phn phi knh bc sng ng v chuyn mch bo v cc knh quang khi mng c s c.

c. Bo v knh quang

- Lin quan n knh hot ng v knh bo v ti kt cui WDM cung cp c ch bo v 1:1 cho cc knh quang. Khi bo v gm phn pht v phn thu

- Pha pht, tn hiu quang t khch hng n s c chia bi coupler 3 dB v sau gi ti b chuyn pht ca thit b kt cui hot ng v bo v.

- Pha thu, cc tn hiu quang ti t tuyn hot ng v bo v s

c a vo khi chuyn mch quang 12 la chn trong trng hp khi c s c trong lp quang. Knh c la chn sau s c gi ti khch hng.

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Bo v knh quang theo c ch 1:1

Cu hi 3.3 : V s cu trc ca b khuch i EDFA theo 3 ch

bm (thun, ngc v 2 chiu), nu chc nng cc khi v nguyn tc hot ng.

Nu cc u khuyt im ca khuch i quang si EDFA u:

+Ngun laser bm bn dn c tin cy cao, gn v cng sut cao.

+Cu hnh n gin, h gi thnh ca h thng.

+Cu trc nh gn: c th lp t nhiu EDFA trong cng 1 trm, d vn chuyn, thay th.

+ Cng sut ngun nui nh: thun li cho p dng cc tuyn thng tin quang vt bin.

+Ko c nhiu xuyn knh khi K cc tn hiu WDM nh b K quang bn dn.

+ Hu nh ko ph thuc vo phn cc ca tn hiu

Nhc:

+Ph K ca EDFA ko bng phng

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+Bng tn hin nay b gii hn trong bng C v L

+Nhiu c tch ly qua nhiu chng gy hn ch c ly truyn.

a. Ch bm thun:

- Bm thun vi bc sng bm 980nm.

b. Ch bm ngc

- Bm bc sng 1480nm

c. Ch bm 2 hng

- S dng c 2 ngun bm (980nm v 1480nm ngc chiu nhau).

Chc nng cc khi:

- Si quang pha ion t him Erbium (EDF):

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+ nng pha tp 100 2000 ppm, l mi trng K, to ra trng thi nghch o nng .

+ Vng li trung tm c ng knh t 3 -6 m c pha trn ion Er3+ l ni c cng sng bm. L ni xy ra qu trnh khuch i (vng tch cc) ca EDFA.

+ Lp bc c chit sut thp hn bao quanh vng li, Lp v bo v

bao quanh si quang to bn knh si quang tng l 250 m.

+ Trong gin phn b nng lng, cc ion Er3+ c th tn ti nhiu vng nng lng khc nhau c k hiu: 4I15/2 ,

4I13/2 ,

4I11/2,

4I9/2,

4F9/2,

4S9/2,

2H11/2.

- Laser bm:

+ Cung cp nng lng nh sng to ra trng thi nghch o nng trong vng tch cc. Laser bm pht ra nh sng c bc sng 980nm hoc 1480nm.

- WDM Coupler:

+ Ghp tn hiu quang cn khuch i v nh sng t laser bm vo trong si quang. Loi coupler c s dng l WDM coupler cho php ghp cc tn hiu c bc sng 980/1550nm hoc 1480/1550nm.

- B cch ly quang:

+ Ngn khng cho tn hiu quang phn x ngc v pha u pht hoc cc tn hiu quang trn ng truyn phn x ngc v EDFA.

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Nguyn tc hot ng:

- Khi bm nh sng cho laser:

+ Khi s dng ngun bm laser 980nm, cc ion Er3+ vng nn s hp th nng lng t cc photon (c nng lng Ephoton =1.27eV) v chuyn ln trng thi nng lng cao hn vng bm (1).

+ Ti vng bm, cc ion Er3+ phn r khng bc x rt nhanh (khong

1s) v chuyn xung vng gi bn (2).

Khi s dng ngun bm laser 1480nm, cc ion Er3+ vng nn s hp th nng lng t cc photon (c nng lng Ephoton =0.841eV) v chuyn sang trng thi nng lng cao hn nh ca vng gi bn (3).

+ Cc ion Er3+

trong vng gi bn lun c khuynh hng chuyn xung vng nng lng thp (4).

+ Sau khong thi gian sng (khong 10ms), nu khng c kch thch bi cc photon c nng lng thch hp cc ion Er3+ s chuyn sang trng thi nng lng thp hn vng nn v pht x ra photon (pht x t pht) (5).

- Khi cho tn hiu nh sng i vo EDFA, c 2 qu trnh:

+ Cc photon tn hiu b hp th bi cc ion Er3+ vng nn (6). Tn hiu nh sng b suy hao

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+ Cc photon tn hiu kch thch cc ion Er3+ vng gi bn (7). Hin tng pht x kch thch xy ra => EDFA khuch i tn hiu nh sng ti.

- K tn hiu nh sng ti:

+ Cc ion Er3+

vng gi bn ang trng thi kch thch nh ngun bm (7) nhn c kch thch t tn hiu nh sng ti s chuyn trng thi nng lng t mc nng lng cao vng gi bn xung mc nng lng thp vng nn v pht x ra photon mi c cng hng truyn, cng phn cc, cng pha v cng bc sng.

=> Tn hiu nh sng c khuch i.

Cu 3.4: Trnh by cc giai on pht trin IP/ WDM.

a. Giai on IP/ATM/SDH/WDM

- y l giai on u tin trong cng ngh truyn ti IP trn quang.

- Trong giai on ny, cc IP datagram trc khi a vo mng truyn ti quang phi thc hin chia ct thnh cc t bo ATM c th i t ngun ti ch

- Ti chuyn mch ATM cui cng, cc IP datagram mi c khi phc li t cc t bo.

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- y l giai on c y cc tng IP, ATM v SDH, do chi ph lp t, vn hnh v bo dng tn km nht. Tuy nhin, khi cng ngh cc router cn nhiu hn ch v mt tc , dung lng th vic x l truyn dn IP trn quang thng qua ATM v SDH vn c li v mt kinh t.

b. Giai on IP/SDH/WDM

- Giai on ny, tng ATM b loi b v cc IP datagram c chuyn trc tip xung tng SDH. Thay vo , ngi ta s dng cng ngh router vi nhng u im vt tri so vi chuyn mch ATM v mt tnh nng, dung lng v v router IP l phng tin truyn dn u vit cho cng ngh IP datagram.

- Ngoi ra, vic c thm k thut MPLS b sung vo tng IP s to ra hai kh nng mi:

- Th nht, n cho php thc hin k thut lu lng nh vo kh nng thit lp knh o VC.

- Th hai, MPLS tch ring mt iu khin ra khi mt nh hng nn cho php giao thc iu khin IP qun l trng thi thit b m khng yu cu xc nh r bin gii ca cc IP datagram.

- Nh vy, c th d dng x l i vi cc IP datagram c di thay i.

c. Giai on IP/WDM

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- Trong giai on ny, tng SDH cng b loi b v IP datagram c chuyn trc tip xung tng quang.

- Gii php ny cho php truyn trc tip IP datagram trn h thng WDM, mi giao thc s c mt bc sng tng ng.

- Vic loi b tng ATM v tng SDH ng ngha vi vic c t phn t mng phi qun l hn v vic x l cng t hn (vic x l y thc hin theo tng lung quang).

- Cc bc sng khc nhau c th xen/r hoc chuyn i bc sng cc nt khc nhau nh cc thit b nh: OXC, OADM, b nh tuyn bc sng quang.

S kt hp IP phin bn mi vi kh nng khi phc ca tng quang, cc thit b OAM&P v chc nng nh tuyn phn b to ra kh nng phc hi, pht hin

Cu hi 3.5 : Trnh by cc cu trc mng IP trn WDM phn loi

theo mt bng d liu. Gm 3 m hnh:

- IP/WDM im im

- IP/WDM cu hnh li

- IP/WDM chuyn mch

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a. IP/WDM im im

- Vi cu trc ny, cc tuyn quang WDM im - im c s dng cung cp cc dch v truyn ti cho lu lng IP.

- Cc thit b WDM, chng hn nh OADM t chng khng hnh thnh mt mng. Thay vo , chng ch cung cp tuyn lp vt l gia cc b nh tuyn IP. SONET/SDH c th c s dng cho truyn khung trn cc knh WDM.

- Cc gi IP c ng gi trong cc khung SONET/ SDH khi s dng cc phng thc ng gi trn SONET/ SDH.

- Kin trc IP trn WDM im-im cn c b nh tuyn IP kt ni nh hng ti cc b nh tuyn IP khc qua cc tuyn si quang trn cc bc sng khc nhau.

- i vi IP trn WDM im- im, cu trc mng hon ton tnh.

- Cc h thng qun l i vi cc mng ny u c tp trung ha, c tng tc ln nhau gia cc lp IP v WDM.

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b. IP/WDM cu hnh li

- Trong cu trc IP/WDM cu hnh li, giao in cc b nh tuyn IP c kt ni ti cc giao din pha khch hng ca mng WDM.

- Cc giao din kt ni cho WDM v xen/r t kt ni trong mng WDM. V vy, mng WDM t c cc tp vt l v tp tuyn quang. Tp vt l WDM gm cc cc phn t mng kt ni vi nhau qua si quang; tp tuyn quang c thc hin nh kt ni knh bc sng.

- Trong IP/WDM cu hnh li, qu trnh thit lp v hy b knh bc sng c iu khin cc giai on ring bit.

- Chuyn mch lu lng IP v chuyn mch bc sng khng bao gi hot ng trong cng lp ca mng ca IP/WDM cu hnh li.

- Cc tuyn quang trong mng WDM c thit k ph hp vi tp IP. Nh kt ni cho WDM cu hnh thch hp, giao din b nh tuyn nh c th ni ti giao din b nh tuyn bt k khc.

c. IP/WDM chuyn mch

- C s h tng WDM c kh nng h tr trc tip chuyn mch gi.

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- C 3 phng php chuyn mch gi c bn:

+ Chuyn mch burst quang (OBS).

+ Chuyn mch nhn quang (OLS).

+ Chuyn mch gi quang (OPS).

- OBS v OLS s dng m hnh chuyn mch gi c ln/lung nn khc vi nh tuyn gi IP thng thng. OBS v OLS khng hiu cc mo u gi IP v v vy khng th chuyn tip cc gi IP.

- OPR i din cho thc hin quang ca nh tuyn IP nn n h tr y cc chc nng IP.

- Cc h thng WDM chuyn mch l khng nh m, v cc cng ngh x l logic quang v nh m d liu quang hin nay vn cha chn mui. Cc ng dy tr quang c s dng m phng cc b m quang. Cc dng dy tr ny t phc tp hn nhiu so vi b nh truy nhp ngu nhin.

- Cng nh vy, cc h thng WDM chuyn mch da vo x l in t ca mo u gi iu khin cc hot ng chuyn mch => OPR khng chn mui bng OBS. B sung vo cc b m quang s gy nh hng n thng mi ho ca OPR bao gm tc chuyn mch, tin cy v suy gim tn hiu ca c cu chuyn mch.

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- OBS v OLS c m t nh OLSR (Optical Label Switching Router). Khc nhau ch yu gia OBS v OLS l OBS s dng chuyn mch gi nhanh, nhng OLS chuyn mch lung. OLS thng s dng bc sng mang ph trong bng truyn thng tin iu khin (mo u lung).

- OLSR thng c trin khai trong mt cm. Bn trong cm, ch c OLSR bin yu cu b sung y ngn xp giao thc IP. OLSR bin cng cung cp m in t nn cc gi IP i n c th xp hng ch i ti bin trong trng hp thit lp LSP ng.

- Cc OLSR c kt ni nh cc si quang khi h tr cc knh bc sng.

- OPR c th c trin khai ng nh cc b nh tuyn IP in t, tuy nhin OPR c nhiu giao din hn. Trong thc t, giao din dnh sn l mt trong cc b iu khin chnh pha sau OPR trn b nh tuyn IP in.

Cu hi 3.6: Trnh by cc cu hnh truy nhp FTTx.

Si quang ti vng dn c (FTTC).

Si quang ti c quan (FTTO).

Si quang ti ta nh (FTTB).

Si quang ti tn nh (FTTH).

- Phng thc FTTC:

+ si quang c ko ti ONU t ti va h.

+ Mt hoc nhiu ta nh kt ni n ONU bng cp ng, khong cch t ONU ti thu bao khong 100m.

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+ Phng thc FTTC c khuyn ngh s dng cho cc vng dn c c mt dn tng i cao, c bit l nhng ni c th s dng li mng cp ng, hoc nhng ni kh lp t cp quang.

+ y cng l mt phng thc truy nhp ph hp cho cc khch hng c nhu cu i vi cc dch v VoIP, truy nhp internet tc cao.

- Phng thc FTTB:

+ Si c ko ti mt ONU t trong ta nh.

+ Cc khch hng c th truy nhp internet theo cc kt ni n ONU thng qua LAN.

+ Chiu di + ca phn cp ng thng khng ln hn 10m.

+ Cu hnh h thng truy nhp FTTB:

+ tn dng hiu qu cc ngun ti nguyn c th phng thc FTTB+LAN c xem l c th tit kim ti a chi ph xy dng mng.

+ Hn na, khong cch ngn gia ONU v thit b u cui thu bao cng cho php pht trin tng bc t FTTB+LAN sang FTTH/FTTO.

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+ M hnh FTTB ph hp vi cc ta nh c mt ln cc khch hng l doanh nghip v h c nhu cu c bit ln v bng tn, c bit cc ta nh ny u c LAN.

- Phng thc FTTO/FTTH

+ si quang c ko ti c quan hoc h gia nh, trong mt ONT c t ti thu bao.

+ ONT l im phn pht dch v cho php cc nh khai thc cung cp cc dch v s liu, thoi v hnh nh trn cng mt si.

+ Cu hnh h thng truy nhp FTTO/FTTHH:

+ FTTO/H c kh nng cung cp bng tn rt ln, tuy nhin chi ph cho vic xy dng mng li rt cao, cn phi xem xt c th khi thit k.

+ Nhn chung, tin ti phng n FTTO/H cn c chin lc pht trin mng v k hoch trin khai c th c c cc bc thc hin v u t hp l .

+ Phng thc ny c bit ph hp khi cn phi lp t cc mng cp mi hoc phi thay th mng cp c.

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Cu hi 3.7 : Cu hnh tham chiu v nu cc khi chc nng c

bn ca mng truy nhp quang FTTx.

Cc khi chc nng c bn ca mng truy nhp FTTx

- Khi chc nng OLT

+ Khi u cui ng quang OLT cung cp giao din quang pha mng vi ODN, ng thi cng cung cp t nht mt giao din pha mng dch v.

OLT c th chia thnh dch v chuyn mch v dch v khng chuyn mch.

OLT cng qun l bo hiu v thng tin gim st iu khin n t ONU, t cung cp chc nng bo dng cho ONU. OLT c th lp t tng i ni ht hoc mt v tr xa.

- Khi chc nng ONU/ONT:

+ Khi mng quang ONU/ONT t gia ODN v thu bao.

Pha mng ca ONU c giao din quang, cn pha thu bao l giao din in.

Do , ONU c chc nng bin i quang/in. ng thi c th thc hin chc nng x l v qun l bo dng cc loi tn hiu in.

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ONU c th t pha khch hng (FTTH/B) hoc ngoi tri (FTTC).

- Khi chc nng ODN:

+ Khi mng phn phi quang ODN t gia ONU vi OLT.

Chc nng ca n l phn phi cng sut tn hiu quang.

ODN ch yu l linh kin quang khng ngun v si quang to thnh mng phn phi quang th ng.

Nu ODN c thay th bng b ghp knh quang th tr thnh mng phn phi quang hnh sao tch cc.

Cu hi 3. 8: Trnh by cu trc c bn ca h thng thng tin

quang coherent.

Trong s hnh khi c t trong hnh ch nht c ng t nt l nhng phn t chnh phn bit s khc bit gia h thng coherent v h thng IM/DD. Chc nng cc khi: DE (Drive Electronic): khi ny thc hin khuch i tn hiu ng vo nhm to tn hiu c mc ph hp vi cc khi pha sau. CWL (Continuous Wave Laser): y l b dao ng quang s dng laser bn dn c rng ph hp pht ra nh sng lin tc c bc sng

1. LC (laser control): khi ny nhm n nh bc sng pht ra ca b dao ng quang.

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MOD (Modulator): y l khi iu ch quang, s dng k thut iu ch ngoi to ra tn hiu iu ch dng ASK, FSK, PSK hay PolSK

LLO (Laser Local Oscillator): y l b dao ng ni ti b thu s

dng laser bn dn to ra tn hiu quang c bc sng 2. DEC (Detector): khi ny thc hin hai tnh nng, u tin s dng

coupler FBT cng tn hiu thu c (1) v tn hiu ti ch (2). Sau a tn hiu tng ti photodiode thc hin tch sng trc trip theo qui lut bnh phng. thc hin ng vi ngha tch sng coherent th coupler quang phi t hp cc tn hiu quang c phn cc ging nhau.

LOC (Local Oscillator control): khi ny nhm iu khin pha v tn s ca tn hiu dao ng ni n nh. AMP (Amplifier): khi ny khuch i tn hiu in sau khi tch sng quang.

DEMOD (Demodulator): khi ny ch cn thit khi b thu hot ng ch heterodyne.

Cu hi 3.9 : Trnh by cu to v gii thch nguyn l hot ng

ca b khuch i Raman.

- Cu to:

+ Si quang: ni xy ra qu trnh khuch i, l si quang thng truyn tn hiu nh si SMF, DSF..... Trong khuch i Raman, khng cn s dng si quang c bit nh EDFA.

+ Coupler: dng ghp bc sng tn hiu vo vi bc sng bm.

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+ Laser bm c tn s p: dng cung cp nng lng cho cc nguyn t ca si quang chuyn ln trng thi kch thch, gip to ra s nghch o nng . Laser pht ra nh sng c bc sng thch hp ty thuc vo vng bc sng cn khuch i. y l mt u im quan trng ca khuch i Raman so vi EDFA (ch khuch i c cc bc sng bng C).

+ B lc (hoc b cch ly): t hai u ca b khuch i quang ngn chn tn hiu phn x hai u b khuch i. ng thi n cng gip loi tr nhiu ASE theo hng ngc v pha u vo c th gy nh hng n tn hiu u vo.

Nguyn l hot ng:

- Lung nh sng bm c tn s p v nh sng tn hiu tn

sscng c a vo si quang thng qua mt coupler quang. Nng lng s c truyn t nh sng bm sang nh sng tn hiu thng quang hiu ng SRS trong si quang. C th:

- nh sng bm t mt laser bm c bc sng thp hn bc sng ca tn hiucung cp nng lng cho cc nguyn t ca si quang. Khi , cc nguyn t ca si quang s hp th nng lng nh sng bm v chuyn ln mc cao hn (mc khch thch) to ra s o ln nng

- Khi c tn hiu nh sng ti, n s kch thch cc nguyn t ang mc nng lng cao chuyn sang trng thi nng lng thp hn v gii phng ra mt nng lng di dng photon nh sng c cng bc sng (di hn bc sng bm) v cng pha vi tn hiu n. Do , tn hiu c khuch i

Cc cu hnh bm K Raman

- Bm xui:

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- Bm ngc:

- Bm 2 hng:

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Cu hi 3.10 : Trnh by cu to v gii thch nguyn l hot ng

ca b khuch i quang bn dn SOA. - Cu to

+ SOA c iu khin bi dng in,

+ Vng tch cc trong SOA khuch i nh sng u vo nh qu trnh pht x kch thch.

+ Tn hiu u ra bao gm c tn hiu truyn dn v nhiu pht x t pht c khuch i (ASE) do qu trnh khuch i gy ra.

- Nguyn l hot ng:

+Da trn c ch pht x kch thch ca lp tip gip PN.

+ Khi c dng in iu khin, cc in t trng thi nng lng E1 c kch thch bi dng iu khin s nhy ln mc NL cao hn E2 v to nn s nghch o nng .

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+ Khi c nh sng ti kch thch cc in t ang trng thi kch thch E2. Cc in t ny hp th nng lng nh sng tr v trng thi E1 n s gii phng ra mt nng lng ST mi di dng nh sng c nng lng ln hn E2 E1.

+ Qu trnh kch thch cc in t trng thi E2 tip tc din ra, khi tn hiu nh sng c K.

+ Cng c 1 s in t trng thi E2 khng nhn c nng lng ca nh sng ti cng tr v trng thi E1 v pht x ra cc photon. Qu trnh pht x ny gi l pht x t pht.

Cu hi 3.11 : Nu khi nim v ASK, FSK, PSK, v dng sng tn

hiu ti cc u vo v u ra b iu bin trong thng tin quang

Coherent, vi tn hiu u vo b iu bin l tn hiu s ng vi

dy bit 101010101, sng mang quang n sc E= E0sin(2f0t+/2).

Cc dng tn hiu iu ch

ASK (Amplitude Shitf Keying): gi l iu ch s theo bin tn

hiu. Tn hiu ASK c dng sng dao ng c tn s f, mi bit c trng bi bin khc nhau ca tn hiu.

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V d: tn hiu ASK c tn s 100 KHz, bin tn hiu = 1 cho bit 0 v bin tn hiu = -1 cho bit 1.

FSK (Frequency Shitf Keying): gi l iu ch s theo tn s tn hiu. Tn hiu FSK c dng sng dao ng c tn s khc nhau, mi bit c trng bi tn s khc nhau ny ca tn hiu. u im ca iu ch ny l d ch to nhng li hay mc li khi truyn

V d: f = 100Khz cho bit 0 v f' = 200Khz cho bit 1.

PSK (Phase Shitf Keying): gi l iu ch s theo pha tn hiu. Tn

hiu PSK c dng sng dao ng c tn s f, mi bit c trng bi gc pha khc nhau ca tn hiu.

V d: pha= 90 cho bit 0 v pha = -90 cho bit 1.

Tn hiu s u vo 110100101

Sng mang quang E = E0Sin(2f0t+/2)

*vi iu ch ASK tn hiu sau khi iu ch c dng

S(t)= d(t).E = d(t).E0Sin(2f0t+/2) vi d(t) l tn hiu s u vo

S(t)= E0Sin(2f0t+/2) vi bit 1

0 vi bit 0

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*vi iu ch FSK tn hiu sau khi iu ch c dng

S(t)= E0Sin(2f0t+/2) vi bit 1

E0Sin(f0t+/2) vi bit 0

Bit 1 c iu ch vi sng mang c fc=f0

Bit 0 c iu ch vi sng mang c fc=f0/2

d(t)

E V nh trn

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*vi iu ch PSK tn hiu sau khi iu ch c dng

S(t)= E0Sin(2f0t + /2) vi bit 1

E0Sin(2f0t - /2) vi bit 0

Bit 1 c iu ch vi sng mang c 0= /2

Bit 0 c iu ch vi sng mang c 0= - /2

d(t)

E V nh trn