CNG CNG NGH TRUYN TI QUANGPhn 1:H thng WDMPhn loi cc h thng WDM
theo khong cch cc knh bc sng s dng trong h thng.(cu 1.13.1) BWDM: H
thng WDM bng tn rng (BWDM Broad passband WDM)+ Ra i sm nht trong
lch s pht trin ca WDM+ Thc hin truyn dn 2 knh bc sng, trong mi knh
bc sng thuc mt ca s truyn dn (vng 850 nm, 1310 nm hoc vng 1550 nm),
khong cch gia cc knh trong h thng ny c vi trm nm.+ Chi ph h thng
thp, tuy nhin dung lng v khong cch truyn dn b gii hn. CWDM: H thng
WDM ghp mt thp (CWDM Coarse WDM)+ Ra i nm 1990, cho php ghp nhiu hn
2 bc sng trn h thng.+ Cc khuyn ngh ITU-T G.694.2 v G.695+ 18 bc sng
t bng O n bng L+ S dng cho cc ng dng mng truy nhp/LAN/MAN+ Khong
cch bc sng rng: 20 nm+ Dung sai dch ph i vi ngun quang rng hn: 2 nm
DWDM:H thng WDM ghp mt cao (DWDM Dense WDM)+ L cc h thng WDM hin ti
ang khai thc trn th gii.+ Khuyn ngh ITU-T G.694.1+ Cho php ghp rt
nhiu cc bc sng trn h thng+ S dng cho cc dch v tc cao MAN/WAN+ Khong
cch knh (bc sng) hp: 200 Ghz, 100Ghz, 50 Ghz, 25 Ghz + Cc ngun
quang i hi nghim ngt n nh nhit v bc sng+ Dung sai dch ph i vi ngun
quang: 0.02 nm (chokhong cch knh 25 GHz)+ Chun G.692 quy nh v khong
cch cc knh, bc sng trung tm ca hthng DWDM nh sau: Khong cch cc knh:
100 GHz Bc sng trung tm: 1552.52 nm Vng bc sng hot ng: Bng S, C, L,
U.S khi v trnh by nguyn l hot ng ca h thng thng tin quang ghp knh
theo bc sng WDM n hng/song hng ( cng Lm b n hng)a.WDM n hng(cu
2.1.1) S khi:bc sng chiu pht trn 1 si v bc sng chiu thu trn 1 si
khc
Chc nng cc khi B pht quang: Bin i tn hiu vo thnh tn hiu nh sng
ghp vo si quang.Qu trnh ny gi l iu bin hay iu ch quang. Si quang:
truyn dn nh sng t ni pht n ni thu B thu quang: Bin i sng ti tr thnh
tn hiu in c dng ging nh tn hiu truyn dn ban u.Trong tn hiu ra c th
c cha tp m v mo km theo(i vi truyn dn analog) hoc li bit(truyn dn
digital).Qu trnh ny gi l qu trnh gii iu ch hay iu bin quang. B ghp
knh quang theo bc sng: ghp tn hiu quang t cc thit b u cui khc nhau
(1-n) thnh tn hiu quang tng ghp vo si quang. B tch knh quang theo
bc sng:Tch tn hiu quang tng t si quang a bc sng thnh cc tn hiu
quang c cc bc sng khc nhau(lamda1-lamda n) a ti cc thit b u cui
quang tng ng. B khuch i quang:+Trong qu trnh truyn nh sng trong si
quang,nh sng b suy hao.C ly truyn dn cng di th nh sng truyn dn cng
b suy hao.Suy hao ca si quang gy nn suy hao tn hiu truyn dn.+Vi cc
tuyn truyn dn di, th nh sng truyn dn u thu b suy gim ln nn ko m bo
b thu khi phc tn hiu truyn dn ban u.+Do , b li suy hao ca si quang,
trn tuyn truyn dn ngi ta s dng cc b khuch i quang. Nguyn l hng i:
Pha pht cc tn hiu in c to ra My pht quang nhn cc tn hiu in s s dng
b bin i in quang =>thnh tn hiu quang c cc bc sng B ghp knh quang
nhn N tn hiu quang ny s thc hin ghp N bc sng ny ln cng mt si quang
Sau khi qua knh truyn dn tn hiu c gi ti pha thu. B tch knh quang s
tch N bc sng quang ra N cc ng khc nhau. Mi ng c gi n mt b thu
quang. Bthu quang nhn c tn hiu quang s chuyn v thnh tn hiu in ban
u. Nguyn l hng v:Tng t nh hng i xong N tn hiu ny s c ghp ln 1 si
khc si hng i song vn gi nguyn bc sng.a.WDM song hng(cu 2.1.2) S
khi:2 bc sng chiu pht v chiu thu trn cng mt si
Chc nng cc khi(ging n hng) Nguyn l hng i(ging n hng) Nguyn l hng
v:Nguyn l hng v tng t hng i song: B pht quang s to ra tn hiu quang
vi cc bc sng . B tch v ghp hng bc sng hng v thc hin ghp bc sng. B
ghp v tch bc sng hng v.
Phn 2: Khuch i quang OA Nu cc tham s c bn ca b khuch i quang (cu
2.3 trong ngn hng).Giia. H s khuch i:G = Pout / PinG (dB) = 10 log
(Pout / Pin) Pin va Pout la cng sut u vao va u ra ca b khuch i
quang [mW]. H s khuch i c trng cho kh nng khuch i cng sut nh sng ca
b khuch i. B gii hn bi cc c ch bo ha khuch i. iu ny lm gii hn cng
sut quang ra cc i ca b khuch i. b. rng bng tn khuch i (B0) L p ng
tn s quang ca OA: G(f) khi o h s khuch i G ca cc tn hiu quang cc tn
s khc nhau. rng bng tn khuch i ca b khuch i quang Bo c xc nh bi im
-3dB so vi h s khuch i nh ca b khuch i. Gi tr Bo xc nh bng thng ca
cc tn hiu c th c truyn bi mt b khuch i quang. c. Cng sut ra bo ha
Khi hot ng ch tn hiu nh, cng sut quang u ra s tng tuyn tnh vi cng
sut quang u vo theo h s khuch i G: Pout = G.Pin. Tuy nhin, khi cng
sut u vo Pin tng n mt mc no , h s khuch i G khng tng na m c th khng
i thm ch bt u gim khi tip tc tng cng sut u vo. Khi , b khuch i
quang t trng thi bo ha. Cng sut u ra ti im G gim 3 dB c gi l cng
sut ra bo ha Psat, out.
d. Nhiu b K - H s nhiu NF Cc b khuch i quang u to ra nhiu, gy ra
do pht x t pht, pha ca cc photon pht x t pht l ngu nhin. Nng lng do
pht x t pht to ra cng s c khuch i khi chng truyn qua b khuch i v
pha u ra. Ti u ra ca b khuch i cng sut quang thu c Pout bao gm c
cng sut tn hiu c khuch i - G.Pinv cng sut nhiu pht x t pht c khuch
i (ASE) - PASE.Pout = G.Pin + PASE nh hng ca nhiu i vi b khuch
quang c biu din bi h s nhiu (NF).
SNRin, SNRoutl t s tn hiu trn nhiu ti u vo v u ra ca b khuch i
[mW]. NF ca b khuch i cng nh th cng tt.
u khuyt im ca ca khuch i quang bn dn SOA/ EDFA/ Raman ( 3 cu
1.10, 1.11 v 1.12 trong ngn hng, tc mi 1 im).GiiSOAEDFARaman
u: + H s K cao (25 30dB)+ Kch thc nh, c th tch hp vi cc linh kin
quang bn dn khc.+ Di thng ln, c th ln ti 100nm+ C th thc hin K tn
hiu c 2 ca s a/s 1310nm v 1550nmu:+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 hiuu:+ Tp m nhiu thp.+ Cu trc n gin,
khng cn si c bit.+ D chn bng tn.+ C th t c bng thng rng nh kt hp vi
laser bm.
Nhc:+Cng sut ra bo ha thp (5mW), hn ch kh nng ca SOA khi lm b K
cng sut.+ H s nhiu cao (5-7dB), nh hng n cht lng ca SOA khi lm b
tin K v b K ng dy.+Nhiu xuyn knh ln do cc hiu ng phi tuyn, km n nh
do li chu nh hng ca nhit +Ph khuch i c dng gn sng do tnh khng hon
ho ca lp chng phn x to ra.+Km n nh do h s khuch i chu nh hng ca
nhit .Nhc:+Ph K ca EDFA ko bng phng.+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.Nhc:+Xuyn m gia cc knh tn hiu do tn x Raman kch thch SRS. y l
mt trong cc hiu ng phi tuyn ca si quang c th gy nh hng n cht lng ca
h thng ghp knh theo bc sng WDM.+H s K thp.+ Hiu sut K thp hn so vi
EDFA: K Raman cn 1 cng sut bm ln hn t cng 1 gi tr h s K.
V s cu trc b khuch i EDFA theo 3 ch bm thun/ ngc/ 2 chiu, nu chc
nng cc khi v nguyn tc hot ng. (cu 3.2.2)Gii V s cu trc ca b i EDFA
theo 3 ch bm thun/ ngc/ 2 chiu Ch bm thun:
+Ngun bm c bm cng chiu vi hng truyn tn hiu.+Thng s dng bc sng bm
980nm. Ch bm ngc
+Ngun bm c bm ngc chiu vi hng truyn tn hiu.+Thng s dng bc sng bm
1480nm. Ch bm 2 hng
+S dng hai ngun bm theo hai chiu ngc nhau.+C th s dng c 2 bc sng
bm 980nm v 1480nm.
Chc nng cc khi: Si quang pha ion t him Erbium (EDF):+ nng pha tp
100 2000 ppm, l mi trng K, to ra trng thi nghch o nng . + Vng li
trung tmc 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 bcc chit sut thp
hn bao quanh vng li, Lp v bo vbao quanh si quang to bn knh si quang
tng l 250 m. 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.
Nguyn tc hot ng:-Nguyn l khuch i ca EDFA c da trn hin tng pht x
kch thch. (cu ny c 0.25 im)-Qu trnh khuch i tn hiu quang trong
EDFA:+ Khi s dng ngun bm laser 980nm, cc ion Er3+ vng nn s hp th
nng lng t cc photon v chuyn ln trng thi nng lng cao hn vng bm.+ Ti
vng bm, cc ion Er3+ phn r khng bc x rt nhanh (khong 1s) v chuyn
xung vng gi bn.Khi s dng ngun bm laser 1480nm, cc ion Er3+ vng nn s
hp th nng lng t cc photon v chuyn sang trng thi nng lng cao hn nh
ca vng gi bn.+ Cc ion Er3+ trong vng gi bn lun c khuynh hng chuyn
xung vng nng lng thp.+ 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). 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. Tn hiu nh sng b suy hao.+ Cc photon tn hiu
kch thch cc ion Er3+ vng gi bn. Hin tng pht x kch thch xy ra, 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. => EDFA khuch i tn hiu
nh sng ti.
Trnh by cu to v gii thch nguyn l hot ng ca b khuch i quang
Raman/SOA. (2 cu 3.7 v 3.8 trong ngn hng, tc l mi loi b khuch i s
tng ng vi mt cu 3 im).Giia. 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.+
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:
Khuch i Raman da trn hin tng tn x Raman kch thch (hin tng photon th
cp sinh ra do kch thch t ngun bn ngoi). c c khuch i Raman cn phi to
ra s nghch o nng . 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 iCc cu hnh bm K Raman Bm xui:
Bm ngc:
Bm 2 hng:
b.B khuch i SOA Cu trc v nguyn l hot ng ca b khuch i quan bn dn
SOA tng t nh laser bn dn. Cu to
+ Ngun bm bn ngoi c cung cp bi dng in phn cc.+ Vng tch cc trong
SOA c t gia hai lp bn dn loi n v p, khuch i nh sng u vo nh qu trnh
pht x kch thch. + Gia ni tip xc ca vng hot tnh v cc phn bao bc l mt
phn cch c gi l d tip xc. 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 . + 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.
Phn 3- B tn scTrnh by cc phng php b in/b quang b tn sc trong h
thng thng tin quang Tn sc l hin tng xung quang b dn rng khi truyn
dc theo tuyn si quang. Trong h thng truyn dn tng t, tn sc lm cho tn
hiu quang ti u thu b mo dng so vi tn hiu ban u. Cn i vi truyn dn s,
tn sc gy ra s giao thoa gia cc k hiu (ISI) dn n li ti b thu. B tn
sc c th c thc hin ti my pht,my thu hoc dc theo si quang:Phng trnh
truyn xung nh sng trong si quang
Trong A bin ng bao ca xung.
tn sc bc 2
tn sc bc 3Trong thc t 3 c th b qua khi ln hn 0,1 ps2/km. Gii
phng trnh trong trng hp ring 3 = 0 th nghim l:
Trong l bin i Fourier ca A(0,t).
Gim tn sc ca tn hiu quang nh gim h s pha ca tn hiu quang. Gii
php ny c thc hin ti my pht, ti my thu hoc dc theo si quang. Phng
php b quang: Gii php c s dng b tn sc trn cc ng truyn dn quang.Hin
nay, c rt nhiu k thut c s dng nh: S dng si quang b tn sc (DCF) Phng
php b tn sc bng si c tn sc m. Phng php ny da trn nguyn l sau: Tn sc
ca si n mode ni chung l tng ca tn sc dn sng v tn sc vt liu. Nh vy,
v mt nguyn tc vi mt cu trc thnh phn hp l c th to ra si c tn sc ln,
ngc du ti bc sng cng tc nh trc. Da theo tnh cht ny, trn mi khong lp
t thm mt on si c tn sc m vi di hp l th c th b c phn no tn sc. S dng
cc b lc quang Trong k thut b tn sc bng b lc quang, thng mt b lc
quang c t sau mt chng si di L km. Gi s b lc quang c hm truyn t
H():
Tn hiu truyn qua b lc c biu din nh biu thc
Bng cch khai trin pha ca H() theo chui Taylor v gi s hng bc hai
s c biu thc
S dng cch t si quang(S dng cch t Bragg si chirp )(cau
2.6.1&1.15.1(nu nguyn l hot ng))
-Chit xut trong si thay i theo chu k dc si :
Trong l chu k im bt u ca on cch t
l s thay i tuyn tnh dc theo chiu di ca on cch tTi v tr z trn on
cch t Bragg, mt sng nh sng s b phn x ngc li nu bc sng ca n tha mn
cng thc:
Trong l bc sng Bragg ti v tr z tng ng vi chu k cch t - Cc xung
truyn trong cch t si chirp:c tnh ca quang si cch t Bragg chu k bin
i l ti nhng v tr tng ng vi chu k di hn s phn x nhng nh sng c bc sng
di hn.Khi cc xung tn hiu c cc bc sng di hn i vo u on si cch t c chu
k di s b phn x phn u ca on cch t v nhng bc sng ngn hn s phi i mt
qung ng xa hn ca on cch t sau mi phn x ngc li.
-S phn x ca cc thnh phn tn s khc nhau :Vi s phn x ca nhng thnh
phn tn hiu c cc bc sng di hn phn u ca on cch t v cc thnh phn tn hiu
c nhng bc sng ngn hn s phi i mt qung ng xa hn ca on cch t sau mi
phn x ngc li. Kt qu l mt khong thi gian tr d s c to ra gia thnh phn
bc sng ngn so vi thnh phn bc sng di. Khong cch d c xc nh theo:
d l khong thi gian trneff l chit xut hiu dngL l di on cch t
Braggc l vn tc nh sng trong chn khngc l hiu s gia bc sng b phn x u
on cch t (thnh phn bc sng di nht) so vi bc sng b phn x cui on cch t
(thnh phn ngn nht).-V m hnh v m t b tn sc s dng cch t Bragg si
quang
M hnh c bn ca thit b b tn sc dng cch t Bragg chu k thay i tuyn
tnh Circulator l thit b ghp ni quang ch cho nh sng i ln lt cc cng
1, 2, 3 theo chiu kim ng h. Mt xung b gin rng sau khi c khuch i s i
qua mt circulator ti on cch t Bragg c chu k bin i nh hnh v. S dng k
thut kt hp pha quang Trong h thng quang c li di s dng k thut iu
chnh pha quang (OPC) b tn sc Nguyn l ca OPC l thc hin iu chnh kt hp
pha ca sng nh sng di dng trng phc ca tuyn, kt qu l ti na sau nh hng
ca GVD na u .Phng php ny cn c gi l o ph gia chng . Phng php s dng
thng dng nht cho OPC l FWM trong mi trng phi tuyn , thng chn bc sng
bm trng vi bc sng tn sc khng. B giao thoa Mach- Zehnder
Phn 4:Truyn ti IP/Quang Trnh by cc giai on pht trin IP/ WDM.
Giai on 1: 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. 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.Giai on 2 :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:+ N cho php thc
hin k thut lu lng nh vo kh nng thit lp knh o VC.+ 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.Giai on 3 : Giai on
IP/DWDM
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 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 li v gim st nhanh.Phn
5:Mng truy nhp quang FTTx Nu khi nim v nu cc u khuyt im ca FTTx.Khi
nim: y l mt hnh thc truy nhp trong mng truy nhp si quang, a dch v
ti khch hng.FTTx bao gm cc h thng truy nhp: 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).u im: Dung lng ln C ly on lp di Tnh cch in tt
Tnh bo mt cao tin cy cao v d bo dng Tnh linh hot ln Tnh m rng
caoNhc im: Mc d si quang rt r nhng chi ph cho lp t, bo dng, thit b
u cui l rt ln. Do thit b u cui cn kh t nn khng phi lc no h thng mng
FTTx cng ph hp. i vi nhng ng dng thng thng, khng i hi bng thng ln
nh lt Web, Check mailth cp ng vn c tin dng. Do cng ngy ngi ta cng
cn phi u t nghin cu gim cc chi ph . Cho bit cc cng nghca mng quang
thng PON(Cu 1.8.4) Mng quang th ng (PON) l mt kin trc mng im-a im,
s dng cc b chia quang th ng (khng c ngun cung cp) chia cng sut
quang t mt si quang ti cc si quang cung cp cho nhiu khch hng. u im
:khng cn ngun cung cp nn khng b nh hng bi nhiu ngun, c tin cy cao v
khng cn phi bo dng nh i vi cc phn t tch cc. Cc cng ngh PON: Cng ngh
ATM PON: c ban hnh thnh tiu chun trong G983.1 ca ITU. Trn c s ny xy
dng PON bng rng (B-PON) chun ITU-T G983. Mt mng APON/BPON in hnh
cung cp 622Mbt/s bng thng ng xung v 155 Mbit/s ng ln. Cng ngh GPON:
Chun ITU-T G984 m t s gia tng trong c bng thng v hiu sut s dng bng
thng nh s dng gi ln, c di thay i. Hn na chun G984 cho php vi s la
chn tc bt, c bn s dng tc 2,488 Mbit/s cho lung xung v tc 1,244
Mbit/s cho lung ln. Phng thc gi tng hp GPON (GPON Encapsulation
Methed- GEM) cho php ng gi lu lng d liu ngi dng rt hiu qu, vi s phn
on khung cho php m bo cht lng dch v QoS cao hn phc v cc lu lng nhy
cm (dch v thi gian thc yu cu tr thp) nh truyn thoi v lung video.
Cng ngh: EPON/GEPON+ Chun IEEE 802.3 Ethernet PON (EPON hay GEPON)
c hon thnh nm 2004, nh mt phn ca d n Ethernet First Mile. + EPON
chun IEEE 802.3 s dng khung Ethernet i xng 1,24 Gbit/s tc lung ln v
lung xung.+ EPON c th ng dng cho cc mng trung tm d liu, cng nh cc
mng dch v b ba thoi, d liu v video.+ Gn y, bt u t nm 2006, tip tc
thc hin chun EPON tc cc cao 10Gigabit/s (chun XEPON hay 10- GEPON).
WDM-PON : s dng ghp knh phn chia theo bc sng Cu hnh tham chiu v nu
cc khi chc nng c bn ca mng truy nhp quang FTTx. Cu hnh tham
chiu:
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.+ 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.PHN 6:Qun l v
iu khin mng quang Trnh by cc phng php iu khin mng quang( cu 1.5.3)
C 3 phng php iu khin trong mng quang1. Phng php iu khin tnh: p dng
cho giai oan u t chc truyn ti IP/WDM v vic iu khin gia IP v WDM c
thc hin theo phng php cp c nh2. Phng php iu khin ng: p dng cho giai
on th hai cc mng WDM c chuyn i t cu trc mng ring hay im im sang cu
trc mesh vi cc h thng WDM . 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 1
cch hiu qu3. 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. Phng php
bo v trong mng vng (ring) quang Bo v UPSR/2PHN 7:Mt s cng ngh, k
thut v xu hng nghin cu trong mng truyn ti Nu khi nim v ASK, FSK,
PSK, v dng song tn hiu ti u vo v u ra b iu ch trong h thng thong
tin quang coherent, vi tn hiu u vo b iu bin l tn hiu s ng vi dy bit
110100101, song mang quang n sc E = E0sin(2*pi*f0t+pi/2).(cu 3.7)
iu ch ASK: thc hin iu ch bin P ca sng mang quang p(t) l sng nh sng
pht x ca LD vi tn hiu cn truyn dn i(t).Cn tn s i vi iu ch nh phn
tng t ,P ly mt trong hai gi tr c nh trong tng thi k bit,ph thuc vo
bit 1 hay bit 0 c truyn dn.Biu thc tn hiu tng qut:+sng nh sng p(t)
ca LD c dng: p(t)=Pcos(+tn hiu iu bin quang c dng: + iu ch FSK: thc
hin iu ch tn s f ca sng mang quang p(t) l sng nh sng pht x ca LD vi
tn hiu cn truyn dn i(t).Cn bin P v pha ca sng mang quang p(t) khng
thay i.Biu thc tn hiu tng qut:+sng nh sng p(t) ca LD c dng:
p(t)=Pcos(+tn hiu iu tn quang c dng:
iu ch PSK: thc hin iu ch phaca sng mang quang p(t) l sng nh sng
pht x ca LD vi tn hiu cn truyn i(t).Cn bin P v tn s ca sng mang
quang p(t) khng thay i.i vi PSK nh phn, pha ly hai gi tr thng chn l
0 v pi.Biu thc tn hiu tng qut:+sng nh sng p(t) ca LD c dng:
p(t)=Pcos(t+)+tn hiu iu tn quang c dng:
Trnh by k thut chuyn mch burst quang v chuyn mch gi quanga.Chuyn
mch burst quang(cu 2.8.3)
c im: + Thng tin c bn trong chuyn mch burst quang l burst.+ Thng
tin iu khin thng c truyn trc burst mt khong thi gian gi l offset
time cu hnh cc chuyn mch trong sut ng i t ngun ti ch. Thi gian
offset ny bng tng thi gian tr x l ca cc gi tin iu khin ti tt cc cc
nut.+ Cc burst thng tin c chuyn tip end-to-end t ngun n ch m khng
thc hin nh m (buffering) cc node trung chuyn. Nguyn tc hot ng Trong
chuyn mch burst quang, mo u iu khin burst c truyn dc tuyn iu khin v
pht trc burst mt khong thi gian. Nh vy, mo u iu khin s n cc nt
chuyn mch trung gian trc, cho php mi nt chuyn mch thc hin cc tnh
ton chuyn mch v tin hnh ci t kt ni cho chuyn mch ng thi im trc khi
burst d liu n. Theo cch ny, burst d liu quang c th c gn vo ng i ca
n qua mng t u vo n u ra. Tr gia mo u iu khin v burst tng khi s lng
cc chng v tr x ly ti cc nt chuyn mch trung gian tng. Chuyn mch
burst quang dnh sn mt ng gi yu cu thit lp v sau gi burst m khng cn
i xc nhn thit lp. S d nh vy l v thi gian truyn burst l tng i
nh.
b.Chuyn mch gi quang
c im+ Thng tin c bn trong chuyn mch gi quang lpacket.+ Thng tin
iu khin gi tin nm tiu gi tin v truyn ng thi cng lc c gi tin.+ S dng
c ch nh m v chuyn tip (buffering and forwarding) Nguyn tc hot ng
Trong chuyn mch gi quang, mo u iu khin gi cng c th c x l nh nhn v c
gi cng vi gi d liu dc theo cng tuyn. Xt n thi gian cn thit tnh ton
quyt nh chuyn mch, gi d liu thng c nh tuyn qua ng dy tr quang lc n
chuyn mch trung gian. Gi tr tr c chn sao cho khi gi d liu c pht hin
t ng dy tr th ci t kt ni cho quang c thc hin. Gi tr tr ny l cc b v
khng i ti mi nt chuyn mch trung gian v c lp vi cc tuyn ring bit m
cc gi chim c. Cc gi trong mng quang c chiu di c nh hoc thay i. Gi c
chiu di c nh ging nh t bo ATM v mt th d ca gi c di thay i l gi IP.
Gi c chiu di thay i tim thng tin iu khin vo mng nn c hiu qu hn. Tuy
nhin, kch c gi chiu di thay i khng th qu ln hoc ti thiu phi nh hn
dung lng ca ng dy tr quang. V vy, gi kch c ln cn c phn on truyn.
Chn chiu di gi da trn ng dng v cc c tnh lu lng. C hai h chuyn tip
trong chuyn mch gi quang: datagram v mch o. Trong chuyn tip
datagram, m u gi truyn trong bng hoc ngoi bng c kim tra ti mi nt
trung gian v khng c thi gian lch v ti trng v m u c chuyn ti cng
nhau. Cch ny c s dng trong IP. Trong chuyn tip mch o, cc mch o c
thit lp trc khi cc gi c gi i trn cc mch o. Mch ny l o vi ngha l
khng dnh sn rng bng tn bt k. Mch o c cng i vo trong bng chuyn mch.
Cng vo phi hp s th t nhn dng mch o i vo vi mt cng ra. Cc mch o thit
lp c s dng trong khi chuyn tip.
Coupler
Laser bm
Si quang thng
Isolator
