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1. WDM: khi nim, v m hnh, nu u im v khuyt im?Khi nim: La cong nghe ghep kenh trong o cac bc song quang

c ghep lai e truyen i ong thi tren cung mot si quang ma

khong gay anh hng lan nhau

Chc nang cua cac phan t trong he thong WDM:

Phat tn hieu Tx: s dung laser co the thay oi bc song(Tunable Laser, Multiwavelength Laser) co o rong pho hep,

mc cong suat phat nh va bc song phat ra on nh

nam trong gii han cho phep.

MUX: ket hp mot so nguon sang khac nhau thanh motluong tn hieu anh sang tong hp e truyen dan qua si

quang DEMUX: phan chia luong anh sang tong hp thanh cac tn

hieu anh sang rieng re tai moi cong au ra bo tach.

Si quang: truyen dan tn hieu chu s anh hng cuanhieu yeu to : suy hao si quang, tan sac, cac hieu ng

phi tuyen, van e lien quan en khuech i tn hiu

EDFA: khuech ai tn hieu cac che o: khuech ai congsuat, khuech i ng v tin khuych i. Khi dng b khuy ch i

EDFA cho h th ng WDM ta phai am bao cac yeu cau sau : + l i khuy ch i ng u cho t t c cc b c sng ( mc chnhlch khng qu 1 dB).

+ S thay oi so lng kenh bc song lam viec khongc gay anh hng en mc cong suat au ra cua cac

kenh.

+ Co kha nang phat hien s chenh lech mc cong suatau vao e ieu chnh lai cac he so khuech ai nham

am bao ac tuyen khuech ai la bang phang oi vi tat

ca cac kenh.

Tx1

MUX

Tx2

TxN

DEMUX

Rx1

Rx2

RxNEDFA

1

2

3.

N

1

2

N

1

2

NEDFA

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Thu tn hieu Rx: s dung cac bo tach song quang nh tronghe thong thong tin quang thong thng : PIN, APD.

u im, nhc im WDMu im Nhc im

- Tn dng ti nguyn di tn rt rng ca si

quang

- Cha khai thc ht bng tn si quang (mi SD

bng C v L)- Tn trong sut, truyn ng thi nhiu t/h c

dng khc nhau- Chu nh hng ca tn sc th, tn sc phncc mode & tsPT

- Truyn dn 2 chiu trn 1 si quang - khai thc bo dng phc tp- Nhiu ng dng khc nhau nh:+ Mng ng trc, ng di

+ Mng qun b, LAN, NGN

- Phi s dng cng c tin tin: Laser, lcquang, K quang

- Kh nng m rng d dng- Tit kim u t, ng truyn( si quang) ..

Phn b bc sng:

Hai vung bc song co suy hao thap: 1300nm va 1550nm Bc song hoat ong trong WDM phu thuoc vao vung bc song

cong tac cua khuech ai quang:

+ C band: 1530nm -1565nm (khuyech ai quang si EDFA)+ L band: 1570nm 1625nm (khuyech ai Raman)

Tan so tham khao (G.692): 193,1 THz (1552,52 nm) Khoang cach kenh (Channel Spacing):

+ o chenh lech tan so tieu chuan gia cac kenh ke nhau+ eu hoac khong eu nhau han che hieu ng tron 4 bc

song (Four Wave Mixing) trong si quang G.652

+ G.692: 50GHz (0.4nm), 100GHz (0.8nm), 200GHz (1.6nm)1. So snh DWDM, CWDM?

CWDM DWDM

- Khong cch knh rng (20nm) - Khong cch knh hp(4nm)- S dng cc bng S,C, L Bng tn hot ng: Bng C (1530,3 nm 1565nm)

- B lc knh ln, chnh xc thp - B lc knh nh, chnh xc cao- Dung lng knh t - Dung lng knh ln- Dng trong mng FFTx - S dng trong mng ng trc- Gi r - Gi t

2. Cc yu t nh hng n h thng WDM

Suy hao:

Suy hao do hap thu (Absorption)+ Hap thu tap chat kim loai: o suy hao phu thuoc vao tp cht,nng tp cht, bc sng nh sng.

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+ Hap thu ion OH-: o suy hao phu thuoc vao nng ion, bc sng nhsng

+ Hap thu t ngoai va hong ngoai:+ Suy hao do uon cong

+Suy hao do tan xa Rayleigh (Rayleigh Scattering)

Khi song ien t truyen trong moi trng ien moi gap

nhng cho khong ong nhat (co kch thc cua khoang 1/10

bc song) se xay ra hien tng tan xa.

Nhng cho khong ong nhat:

Tn sc: Tan sac la hien tng khi cho mot xung anh sang hepchieu vao au si quang th thu c mot xung anh sang rong hn

cuoi si quang

Anh hng cua tan sac:+ Tn hieu tng t: meo dang tn hieu+ Tn hieu so: chong lap gia cac bit

han che dung lng va c ly truyen cua tuyen quang

- Hiu ng phi tuyn xy ra trong si quang: c 5 hiu ng phi tuynHiu ng tn x (SBS): Nng lng t mt sng nh sng c chuyn sang mt sng nh sng khc c bc sng di

hn (hoc nng lng thp hn). Nng lng mt i b hp th bi cc dao ng phn t hoc cc

phonon, cc phonon lin quan n s tn x l cc phonon m hc v s tng tc ny l xy ra ditn hp bng 20MHz bc sng 1550nm. Sng bm v sng stroke truyn theo 2 hng ngc nhau.

Do SBS khng gy ra bt k tc ng qua li no gia cc bc sng khc nhau khi m khong

cch bc sng ln hn 20MHz. V vy SBS s khng nh hng n WDM do khong cch knh t

hng GHz tr ln.

Tuy nhin, SBS cng c th to nn mo kh quan trng trong mt knh n l. SBS to ra li theo hng ngc li vi hng lan truyn tn hiu. Ni cch khc l hng v ngun. v vy, n

lm suy gim tn hiu c truyn cng nh to ra mt tn hiu c cng c cng mnh v pha

pht nn phi dng mt b cch ly bo v.Hiu ng tn x do kch thch Raman (SRS):

L gy ra s chuyn nng lng t cc knh c bc sng thp sang cc knh c bc sngsao tng ng vi vic sinh ra cc photon nng lng thp t cc photon nng lng cao hn. V y

l hiu ng bng rng. N s gy tc ng khi khong cch knh l 15Hz (125nm). SRS s gy nh

hng trn c hng truyn v hng ngc li.

Hiu ng 4 bc sng FWM Hiu ng trn 4 bc sng l s t hp ca cc tn s tn hiu to ra tn s mi, do hiu

ng FWM s lm gim cng sut knh tn hiu trong WDM. V nu khong cch knh trong WDM l

u nhau th tn s mi to ra c trng vi knh tn hiu gy ra nhiu xuyn knh.

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nh hng ca FWM cng ln khi khong cch gia cc knh cng nh cng nh cng nh

khong cch truyn dn v cng sut mi knh ln. V vy hiu ng FWM s lm hn ch dung lng

v c ly truyn dn cc h thng FWM.

c im:Gy nhiu xuyn knh

Ph thuc vo khong cch knh: khong cch knh cng nh th FWM nh hng cng ln.

Tn sc mu ca si cng gim thi FWM nh hng cng ln

- nh hng ca FWM: lm hn ch dung lng v c ly truyn dn ca cc h thng WDM

Hiu ng t iu pha (SPM): L s thay i tn s xy ra do s dch pha gy ra bi chnh xung nh sng. Trong tn sc sc

mu, cc bc sng khc nhau (cc tn s) lan truyn theo cc vn tc khc nhau. Nh vy xung mang

cc tn s khc nhau khi lan truyn s gin ra. Nh vy SPM gy ra gin xung thng qua tn sc mu.

Khng c u im: khi cng sut lan truyn cao, khong u si quang, SPM c th nixung c th s dng hin tng ny b tn sc.

Hiu ng ny ch nh hng n h thng c tc caoHiu ng iu chng xuyn pha (CPM):

Trong h thng a knh dch pha ca mt knh khng nhng ph thuc vo cng (cng sut) ca chnh knh m cn ph thuc vo nhng knh cn li gy ra chirp v tn sc mu.

Hiu ng ny ch nh hng n h thng c tc cao.

3. Cc linh kin quang trong h thng WDM

Cac linh kien thu thu ong (Passive Component): Coupler, Splitter, Tap Isolator, Circulator Optical Filter Optcial Multiplexer and Demultiplexer

Coupler (b ghp/tch tn hiu) Coupler l b dng kt hp (combiner) hoc phn chia (splitter) nh sng. Coupler nh hng (directional coupler): cho nh sng qua theo 1 hng.

Coupler song hng (bidirectional coupler): cho nh sng qua theo hai hng ngc nhau Cc ng dng ca coupler: B coupler vi t s ghp 1 c dng trch mt phn nh tn hiu quang, phc v

cho mc ch gim st.

Coupler cn l b phn c bn to nn cc thnh phn quang khc, chng hn nh: cc

b chuyn mch tnh, cc b iu ch, b giao thoa Mach-Zehnder MZI... MZI c th

c ch to hot ng nh b lc, MUX/DEMUX, chuyn mch v b chuyn i bc

sng.

Thc hin ghp/tch bc sng trn si quang. Nh iu chnh chiu di ghp thch hp

khi ch to, coupler 2 x 2 ghp 50:50 phn b cng sut nh sng t mt u vo ra lm 2

phn bng nhau 2 ng ra. Coupler ny cn c gi l coupler 3 dB, ng dng ph bin

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nht. T coupler 3 dB, c th to nn b coupler n x n ghp n tn hiu khc nhau vo mt

si quang.

Optical filter(b lc quang) B lc l thit b ch cho php mt knh bc sng i qua, kha i vi tt c cc knh bc

sng khc

B lc quang c chia lm hai loi: b lc c nh (fixed filter) v b lc iu chnh c(tunable filter)

B ghp/tch knh bc sng: Nguyn l hot ng ca b MUX/DEMUX cng tng t nh b Coupler. Tuy nhin, b

Coupler/Splitter thc hin ghp tch tn hiu c cng bc sng, cn b MUX/DEMUX thc

hin ghp tch tn hiu cc bc sng khc nhau.

Isolator(b cch ly): Isolator l thit b khng thun ngc.N ch truyn nh sang qua n theo mt chiu v

ngn khng cho truyn theo chiu ngc li.Isolator c dng ti u ra ca cc thit b

quang (b khuch i, ngun pht laser) ngn qu trnh phn x ngc li cc thit b ,

gy nhiu v h hi thit b.

B circulator c dng nh mt b phn ch to phn t xen rt quang OADM. Si quang:

Cac yeu to anh hng en chat lng cua si quang

N21 ...,,, )Nk1(,k Bolock

Boloc ieu

chnh c

1 2 N )Nm1(m

(a) (b)

(a) B lc c nh bc sng k. (b) B lc c th iu chnh bc sng c trong khang .

1

2

n

n21,...,,

n21,...,,

1

2

n

MUX DEMUX

(a) (b)

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+ Tan sac mode, tan sac sac the, tan sac phan ccmode (polarization mode dispersion)

+ Cac hieu hng phi tuyen: Shelf-Phase Modulation (SPM),Cross-Phase Modulation (XPM), Stimulated Raman Scattering

(SRS), Stimulated Brillouin Scattering (SBS), Four-Wave Mixing

(FWM)

Cac loai si quang: Standard SMF, Dispersion-Shifted Fiber (DSF),Non-Zero DSF

Optical Transmitter Laser

Optical Receiver Photodiode

Optical Amplifier:

Khuech ai quang ban dan SOA (Semiconductor Optical

Amplifier) Khuech ai quang si pha chat hiem xDFA (Rare Earth-DopedFiber Amplifier)

Switching Element

Wavelength Convertor

4. Phn bit loi si quang

a. Si quang G.652 (SMF)

Hot ng bc sng 1310nm Khi hot ng 1550nm th suy hao truyn dn nh nhng tn sc lnb. Si quang G.653 (DSF)

Hot ng bc sng 1550nm Thay i s phn b khc x lm cho nh tn sc bng 0 dch t 1310nm n khu vc

1550nm . Lm tng hiu hiu sut cc cc hin tng phi tuyn lm bin dng tn hiu c bit hiu

ng FMW

c. Si quang G.654

Si quang thay i bc sng ct im tn sc bng 0 vn 1310nm, tn sc 1550nm vn cn cao ch yu s dng cp quang

bin

d. Si quang G.655 (NZ-DSF)

im tn sc bng 0 nm 1550nm m dch ti 1570nm hoc gn 1510nm 1520nm do tn sc ti 1550nm khng ln, c ly b hn ch bi tn sc vi trm km.

Lm nh hng ng k nh hng hiu ng trn 4 bc sng FWM

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Non ITU L2

Non ITU L1

SONET

IP ROUTER

SONET

TransponderMUX/DEMUX

ITU L2

ITU L1

ITU L3

L1 L2L3

Loscc

Losc

RECEIVERER

LASER

O/E/O

E/O/E MUX

5. Cc phn t mng (NE) WDMa. B u cui ng quang (OLT)

nh ngha:

B u cui ng quang OLT (Optical Line Terminal) l thit b kh n gin trong mng

truyn dn WDM. OLT c trong cc m hnh mng im-im, thc hin ghp tn hiu u pht

v truyn i trn si quang, gii ghp u thu v chuyn cc tn hiu thnh phn n pha u

cui khch hng. OLT gm c ba khi chc nng chnh: chuyn i tn hiu (Transponder), ghp

bc sng (Wavelength Multiplexer) v khuch i quang (Optical Amplifier) (chc nng khuch

i tn hiu l ty chn OLT v khng c minh ha trn hnh).

B U CUI NG QUANG

S khi ca mt b u cui ng quang (OLT). OLT bao gm b ghp knh/phn knh

bc sng v b chuyn i tn hiu (transponder). B chuyn i tn hiu chuyn i tn hiu n

t ngi s dng thnh tn hiu ph hp cho vic truyn dn trn cc tuyn WDM v ngc li cng

chuyn tn hiu t tuyn WDM thnh tn hiu ph hp cho ngi s dng. Cc b chuyn tip s

khng cn thit nu thit b khch hng c th truyn v nhn trc tip cc tn hiu tng thch vi

tuyn WDM. OLT cng c kh nng kt cui mt knh gim st quang ring l (OSC) dng trn

tuyn quang.

B chuyn i tn hiu thc hin chuyn tn hiu n t mng khch hng vi nhng tc , bcsng v giao thc khc nhau sang thnh tn hiu thuc bc sng chun theo qui nh ca ITU-T.

Vi nhng tn hiu khch hng khc nhau, b chuyn i cung cp cc giao tip khc nhau. Giao

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Laser bmRaman LASER

Chng li Chng li

B tn scBBB

LoscLosc OADM

My thu

tip ny gi l giao tip khch hng. B ghp bc sng ghp cc tn hiu qua b chuyn i

hnh thnh tn hiu WDM, truyn trn mng WDM. Mng WDM c th s dng cc b khuch i

quang khuch i tn hiu truyn i c xa hn.

Cc chc nng Chc nng chuyn i tn hiuB chuyn i tn hiu ti OLT thc hin cc chc nng khc nhau nh:

Chuyn tn hiu sang bc sng, mc cng sut v cc thng s quang cho ph hp vi

yu cu chung ca lp knh quang. B chuyn i tn hiu thc hin chuyn tn hiu quang

sang in ri t in sang quang dng cc b pht laser WDM m ta kho st trn.

Theo chiu ngc li, thc hin chuyn i tn hiu tng thch vi lp knh quang sang tn

hiu tng thch vi lp khch hng cng qua chuyn i quang-in-quang. Thc t c th ch

thc hin chuyn i theo mt chiu t lp khch hng vo lp knh quang.Thm vo hoc trch ra cc tn hiu mo u c th qun l tn hiu truyn i ngay ti lp

knh quang.

Gim st BER ca tn hiu truyn trong lp khch hng v tn hiu truyn trong lp quang

ti u vo (ingress) v u ra (outgress) ca n.

Hin ti cng c xu hng trin khai b chuyn i tn hiu ti cc thit b u cui khch

hng. iu ny gip gim chi ph, thit b WDM cng bt cng knh v phc tp hn.

Tuy nhin, pha giao din u ra (outgress) ca b chuyn i, thng gi l giao din knh

quang, vn cha c chun ho v khc nhau i vi cc nh cung cp thit b WDM khc nhaunn xu hng cng ngh ny vn cha c trin khai rng ri.

Chc nng ghp bc sngB ghp bc sng thc hin ghp cc tn hiu thuc cc bc sng khc nhau tng thch vi

khuyn ngh ca ITU-T thnh tn hiu truyn i trn mt si quang. Cc k thut ghp bc

sng m ta kho st nh k thut ng dn sng AWG, k thut in mi mng

mng, k thut cch t Bragg, ... u c th c ng dng.

Chc nng khuch i tn hiu

Chc nng khuch i tn hiu l ty chn ti OLT. thc hin c chc nng khuch itn hiu, c th dng hai cu hnh EDFA khc nhau. Cu hnh EDFA khuch i cng sut cho

hng pht (booster amplifier) v cu hnh EDFA tin khuch i (Pramplifier) cho hng thu.

Hin nay, cc nt mng WDM c th hot ng cc bc sng bng C (1530-1565 nm) v bng

L (1565-1625 nm) do b khuch i EDFA hot ng c trn hai bng sng ny.

Ngoi ba chc nng chnh trn, OLT cn c chc nng kt cui (ghp/tch) knh gim st

OSC (Optical Supervisory Channel). Knh gim st c truyn trn mt bc sng khc vi

bc sng truyn tn hiu. Vai tr ca OSC l gim st hot ng ca cc b khuych i quang

dc theo mt lin kt quang v thc hin cc chc nng qun l khc.

b. B khuch i ng quang (OLA)

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Cc b khuch i ng quang OLA (Optical Line Amplifier) c dng gia cc lien kt

quang vi nhng khong cch bng nhau (trn thc t c th khong cch t cc OLA khng

bng nhau nhng phi nh hn mt gi tr khong cch nht nh, thng l khong 100-200 km).

Trn hnh l s khi ca OLA, thnh phn c bn mt hoc nhiu khi li l si EDF

mc ni tip vi nhau, gia cc chng li c th l b b tn sc (dispersion compensasor)

b tn sc tch lu dc theo tuyn quang.

Cc b khuch i ng quang OLA (Optical Line Amplifier) c dng gia cc lin kt

quang vi nhng khong cch bng nhau (trn thc t c th khong cch t cc OLA khng

bng nhau nhng phi nh hn mt gi tr khong cch nht nh, thng l khong 100-200 km).

Trn hnh l s khi ca OLA, thnh phn c bn mt hoc nhiu khi li l si EDF mc

ni tip vi nhau, gia cc chng li c th l b b tn sc (dispersion compensasor) b tn

sc tch lu dc theo tuyn quang.

S khi ca mt b khuych i ng dy quang in. Trn hnh v ch v mt hng. B

khuych i s dng nhiu tng khuych i Erbium v bao gm b b tn sc (ty chn) v cc

OADM gia cc tng khuych i. B bm Raman c th dng cung cp thm khuych i

Raman cho on si quang. OSC c tch ra ti u vo v kt cui, v xen vo ti ng ra.

B OLA cn c cc thit b thc hin chc nng ghp/tch knh gim st OSC. Ti u vo

khi cha qua cc khi li, knh gim st OSC c lc li v a vo u thu OSC. Tip n,

sau khi khuch i cc knh tn hiu thuc cc bc sng khc nhau, knh OSC c ghp chung

vo vi cc knh tn hiu v truyn i. Nh vy, knh OSC khng c khuch i bi cc OLA.

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B OLA cng c th c cu hnh gm b khuch i Raman thc hin chc nng khuych i

hn b (distributed amplifier) bng cch cu hnh ti u vo ca n ngun bm Raman c cng

sut quang ln, bm ngc chiu vi chiu tn hiu i vo.

c. B xen rt quang (OADM) nh ngha

B ghp xen/rt quang OADM (Optical Add/Drop Multiplexer) thng c dng trong cc

mng quang th v mng quang ng di v n cho hiu qu kinh t cao, c bit i vi cu

hnh mng tuyn tnh, cu hnh mng vng (Ring).

Chc nng ca b ghp xen/rt quang l n c cu hnh xen/rt mt s knh bc sng,

cc knh bc sng cn li c cu hnh cho i xuyn qua (pass through).

Cc cu trc cho OADM:

Cu trc song song. Cu trc song song theo bng. Cu trc ni tip. Cu trc xen/rt theo bng sng.

6. EDFA: Ngun bm 980nm hoc 1480nm

u im:

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

Thit b n gin nn gi thnh h thng gim. Cu trc nh, c th lp t nhiu EDFA trong cng mt trm, d vn chuyn v thay th Cng cng sut ngun nui nh, thun li khi p dng cho cc tuyn thng tin quang vt

bin

Khng c nhiu xuyn knh khi khuch i cc tn hiu WDM nh b khuch i bn dn.Nhc im:

Ph li ca EDFA khng bng phng Bng tn gii hn trong bng C v L

Nhiu c tch ly qua nhiu chng K nn hn ch c ly truyn

7. Khuch i quang:

Nguyn l hot ng ca khuch i quang:

Da trn hin tng pht x kch thch Khng c s hi tip v cng hng Khuch i quang c th lm tng cng sut tn hiu nh sng c a vo b khuch i nhng

khng th to ra tn hiu quang kt hp ca ring n ng ra

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Cc ng dng ca khuch i quang:

Khuch i cng sut (booster amplifier):+ Khuch i tn hiu c cng sut cao t b pht trc khi a vo trong si

quang

+ Lm tng cng sut tn hiu quang n mc cao nht lm cho khong cchtruyn t cc i

Yu cu: to ra cng sut u ra cc i ch khng phi li cc i v cng sut tn hiu u vob khuych i cng sut ln.

Khuch i ng dy (in-line amplifier):+ Hot ng vi tn hiu tuyn si quang+ B mt mt cng sut gy ra bi suy hao si, kt ni v vic phn phi tn hiu

trong mng

+ C th lp nhiu b khuch i ng dy lin tip+ Yu cu: n nh trn ton b di thng ca h thng WDM, gi nhiu

mc cc tiu v thc hin vic trao i tt tn hiu quang vi si quang truyn dn Tin khuch i (preamplifier):+ Khuch i tn hiu ngay trc khi tn hiu c a vo b thu+ Hot ng vi cng sut tn hiu vo yu+ Yu cu: nhy tt, li ln v nhiu thp+ Nhiu thp l c im quan trng ca b tin khuch i v nhiu ti u thu

cao

+ S dng b tin khuch i gim c yu cu nghim ngt ca nhy mythu v cho php mng vn hnh vi tc bt cao hn.

u im ca khuch i quang:

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+ Khuych i trc tip tn hiu quang khng c mch ti to thi gian, mchphc hi (b bin i E/O hoc O/E)

khuch i quang s tr nn linh hot hn

+ Khng ph thuc vo tc bit v phng thc iu ch tn hiu nng cp h thng n gin hn

+ Khuch i nhiu tn hiu c bc sng khc nhau cng truyn trn mt siquang

Cc c tnh k thut ca khuych i quang:

li tn hiu (Signal Gain):

Bng thng li (Gain Bandwidth)

Cng sut ng ra bo ho (Saturation Output Power)

H s nhiu (Noise Figure):

Ngoi 4 thng s k thut chnh c nu trn cc b khuch i quang cn c nh gi da trn

cc thng s sau:

nhy phn cc (Polarization sensitivity): s ph thuc ca li ca b khuch i vophn cc ca tn hiu

nh hng ca nht i vi li v bng thng li Xuyn nhiu (crosstalk)8. K Raman

Cu to:

Pin

Signal gain

3dB

Pin,sat

Pin

Pout

Psat

Pin,sat

( / )

( / )in

out

S NNF

S N=

10log mWdBmW

PoutG

Pin

=

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- Si quang: l ni xy ra qu trnh khuch i. Si quang ny cng l si quang truyn tn hiunh si SMF, DSF Trong khuch i quang Raman khng cn s dng si quang c bit

(si c pha trn ion Er3+) nh b khuch i EFDA.

- B ghp(Coupler): dng ghp bc sng tn hiu vo vi sng bm.

- Laser bm(Pump laser): 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 .

- B cch ly(Isolator): 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 (Stimulated Raman Scattering).

Tn x Raman kch thch l hin tng mt nguyn t hp th nng lng ca mt photon, sau to

ra mt photon c nng lng khc. V vy, tn x Raman kch thch c nh ngha l hin tng

photon th cp c sinh ra do kch thch t ngun bn ngoi.

c khuch i Raman th phi to ra s nghch o nng . iu ny t c bng cch cung

cp nng lng cho cc nguyn t ca si quang t mt laser bm c bc sng thp hn bc sngca tn hiu. Khi , cc nguyn t ca si quang s hp th nng lng bm c nng lng cao

(bc sng ngn) v chuyn ln mc nng lng cao hn. Khi c tn hiu n, 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

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Hnh 2.1 S chuyn nng lng trong khuch i Raman

Ngun bm t 1430-1460nm H s khuch i Raman tng hu nh tuyn tnh vi trn lch bc song gia tn hiu v

ngun bm v t nh ti 1060 nm v gim nhanh chng sau .

Bng thng li c th t 45-50nm Nu di tn cc tn hiu cn K raman ln hn bng thng li cc K raman (gi s40nm) cn phi s dng nhiu ngun bm khc nhau. Mi ngun bm c bc sng khc nhau

40nm.

Hiu sut li ca K raman khng cao, t h s khuch i ln cn phi s dng cngsut tng i cao.

u im:

Tp m nhiu thp Cu trc n gin khng cn si quang c bit D chn bng tn

C th t c bng thng rng nh kt hp ci laser bmNhc im: Xuyn m gia cc knh tn hiu do hin tng tn x raman kch thch SRS H s khuch i thp, cn mt cng sut bm ln t cng li vi EDFAng dng: Trong mng thng tin quang c ly di v cc di

9. B khuch i quang si EDFA:

Cu to EDFA:

Mt on si quang silic n mode c pha thm nguyn t t him erbium Er3+

mi trngdin ra qu trnh khuych i

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Ngun bm (laser) c ghp vi on si quang qua mt coupler cung cp nng lng choqu trnh khuych i

Ngun bm c bc sng 980 nm hoc1480 nm Isolator: ch cho php nh sng truyn theo mt hng

Nguyn l hot ng ca EDFA:

Khi s dng bc sng 1480nm th khng gii thch, v v ng 1 v 2.

Coupler

Laser bm

Isolator Isolator

Er3+- doped

fiber

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Khi s dng ngun bm laser 980nm, cc photon (Ephoton =1.27eV) s kch thch in t

t vng nn ln vng kch thch (1) Ti vng kch thch, cc in t phn r khng bc x rt nhanh (khong 1s) xungvng nng gi bn (2) Khi s dng ngun bm laser 1480nm, cc photon (Ephoton= 0.841eV) s kch thch in

t t vng nn ln nh ca vng gi bn (3)

Cc in t trong vng gi bn lun c khuynh hng chuyn xung vng nng lngthp (vng c mt in t cao) (4)

Sau khong thi gian sng (khong 10ms), nu khng c kch thch bi cc photonc nng lng thch hp (pht x kch thch) cc in t s chuyn xung vng nn v pht x ra

photon (pht x t pht) (5)

nhiu ASE (Amplified Spontaneous Emission)

Khi cho tn hiu nh sng i vo EDFA, s ng thi xy ra hai trng hp sau:+ Cc photon tn hiu b hp th bi cc in t vng nn (6) tn hiu b suy hao+ Cc photon tn hiu kch thch cc in t vng gi bn xung vng nn v to ra mt

photon mi c cng bc sng, cng pha, cng phn cc vi photon tn hiu (pht x kch

thch) (7) tn hiu c khuch i rng gia vng gi bn v vng nn cho php s pht x kch thch (khuch i)

xy ra trong khong bc sng 1530nm 1560nm vng bc sng hot ng ca EDFA

li khuch i gim nhanh chng tai cc bc sng > 1560nm v bng 0dB ti 1616

nm.Nhng yu t nh hng n cc c tnh ( li, di thng, cng sut ra bo ho, nhiu) ca

EDFA:

Chiu di on si quang pha Erbium Nng ion Er3+

Bc sng bm: 980nm hay 1480nm Cng sut bm Chiu bm ca ngun bm so vi tn hiu:

+ Cng chiu (codirectional pumping)+ Ngc chiu (counterdirectional pumping)+ Hai chiu (dual-pumping)

Nhiu (Noise):

Cc lai nhiu: Nhiu ASE: thnh phn nhiu chnh Hiu ng phi tuyn Nhiu pha

H s nhiu Figure Noise (FN) ca EDFA ph thuc vo: Chiu di ca si quang

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Cng sut bm

u im ca EDFA:

Ngun bm laser bn dn c tin cy cao, gn v cng sut cao Thit b n gin h gi thnh ca h thng Cu trc nh c th lp t nhiu EDFA trong cng 1 trm, d vn chuyn v thay

th Cng sut ngun nui nh thun li khi p dng cho cc tuyn thng tin quang vt

bin

Khng c nhiu xuyn knh khi khuych i cc tn hiu WDM nh b khuych iquang bn dn

Nhc im ca EDFA:

Ph li ca EDFA khng bng phng Bng tn hin nay b gii hn trong bng C v bng L Nhiu c tch lu qua nhiu chng khuch i hn ch c ly truyn.

ng dng: ty theo mc ch s dng EDFA c th l b khuch i cng

Sut, tin khuch i hay khuch i ng truyn(trm lp).

10.SOA (KHUCH I QUANG BN DN)u im:

- li cao (25 30dB).

- Kch thc nh, c th tch hp vi cc linh kin quang bn dn khc.- Gii thng ln c th ln ti 100nm, rng hn so vi EDFA.

- C th thc hin khuch i 2 ca s nh sang 1300-1550nm.

Nhc im:

Cng sut ra bo ha thp (khong 5mw) hn ch kh nng ca SOA khi c s dnglm b khuch i cng sut.

H s nhiu cao (5-7dB) nh hng n cht lng ca SOA khi c s dng lm btin khuch i v khuch i ng dy.

Ph thuc vo phn cc c tn hiu quang ti. Nhiu xuyn knh ln do cc hiu ng phi tuyn: hiu ng trn 4 bc sng FWM v

hiu ng bo ha li cho.

Ph li c dng gn sng do s khng hon ho ca lp chng phn x to nn. Km n nh do li chu nh hng ca nhit .

ng dng:

Vi cc c tnh k thut trn, SOA c nhiu khuyt im so vi EDFA khi c dng lm

khuch i quang. Do cho d SOA c nghin cu v ch to t trc EDFA, nhng SOA

khng c s dng lm b khuch i trong h thng WDM cng nh cc h thng truyn dn

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quang khc hin nay. Thay vo , da trn cc hiu ng phi tuyn p ng nhanh ca SOA, SOA

c dng lm cc ng dng khc ca h thng tin quang nh: b bin i bc sng, phc hi

xung ng h v cc ng dng x l tn hiu quang.