Optical Amplifier Handouts

11/27/2014

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B KHUCH I QUANG

TRNG I HC KHOA HC T NHINKHOA iN T - ViN THNG

Nguyn Th Hng Th

10/2012

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TRNG I HC KHOA HC T NHINKHOA iN T ViN THNG

Ni dung:1. Gii thiu chung2. Mt s b thu quang c bn.3. Cc thng s c bn4. ng dng ca b thu quang.

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Nhng nhn t nh hng n tn hiu quang trnng truyn l g?

Tc dng ca b khuch i quang?

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1. Gii thiu chung

Hnh 1: Trm lp quang in

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- Nhc im ca trm lp quang in l ch p dngc cho truyn dn n bc sng => h thng WDM cns dng rt nhiu trm lp quang in => khc phc bngcch s dng cc b khuch i quang.- Phn loi: Theo ng dng: C 3 loi(classes) khuch i quang:khuch i trn ng truyn, khuch i cng sut v tinkhuch i. Theo cu to: SOA, DFAs, RA

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1. Gii thiu chung

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B khuch i cng sut: c t ngay sau thit b pht hoct trn ng truyn nhm tng khong cch truyn dn tn hiu.Yu cu: cng sut ra cc i.

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1. Gii thiu chung

10/2012Hnh 2. V tr b khuch i cng sut quang


Khuch i trn ng truyn: l cc b khuch ic lp t trn tuyn ng truyn quang nhm b cngsut mt mt bi suy hao trn ng truyn.

Yu cu: gi n nh trn ton di thng, gi nhiu mc cc tiu, thc hin vic trao i tn hiu vi si quangtt.

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1. Gii thiu chung

10/2012Hnh 3. V tr b khuch i quang trn ng truyn


Tin khuch i: c t ngay trc b thu quang,nhm khuch i tn hiu trc khi a tn hiu nphotodetectors.

Yu cu: nhy ln, li ln v nhiu thp.

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1. Gii thiu chung

10/2012Hnh 4. V tr b tin khuch i

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Cu to c bn b khuch i: b khuch i hot ngda trn hin tng pht x kch thch. Qu trnh khuch idin ra vng tch cc, ph thuc vo nng lng cangun bm.

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1. Gii thiu chung

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Hnh 5. Cu to c bn bkhuch i quang


SOA(semiconductor optical amplifier): l b khuch iquang c vng tch cc c to ra t vt liu bn dn.

DFAs(Doped Fiber Amplifiers): l b khuch i c vngtch cc l si quang c pha t him. Mt s loi DFAs tiubiu: EDFA(Erbium DFA), PDFA (Praseodymium DFA),TDFA(Thulium DFA), NDFA(Neodymium DFA).

RA(Raman amplifier): l b khuch i hot ng da trnnguyn l ca hin tng phi tuyn tn x Raman.

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1. Gii thiu chung

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SOA c th chia thnh 2 loi da vo h s phn x camt tch cc. Loi c cng hng l khuch i Fabry Perot(FPA) v loi khng c cng hng l khuch i sngchy TWA(traveling wave amplifier).

FPA: H s phn x cao, ln ti 32%, cu trc tng tlaser Fabry Perot, nhng hot ng vi dng phn cc Ibias< Ith

FPA c li cao, nhng ph li nhp nh, khngu => gim bng thng ca b khuch i.

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2. Mt s b khuch i quang

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B khuch i quang bn dn SOA:


TWA: Cu trc ca TWA tng t ca FPA ngoi tr 2 lp chng phn x c t ti 2 u ca vng tch cc => tn hiu nh sng ch c khuch i mt ln trong TWA.

TWA c bng thng b khuch i ln, cng sut ra boha cao, nhy phn cc thp =>TWA c s dng phbin hn FPA.

TWA c th khuch i bc sng quang ca s1310nm v chuyn bc sng sang vng 1510nm do cth dng lm b bin i bc sng.

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Dng bm: SOA hot ng trn c ch bm dngbn ngoi vo vng tch cc to ra hin tng nghcho mt (population inversion), tng t nh cchhot ng ca laser diodes.

Mt in t n(t) c cho bi phng trnh tc (rate equation) nh sau:

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Mt s c tnh ca b SOA:

( ) ( )( ) ( )p stp

n t n tR t R tn

=

(1)


Vi: Rp (t) l tc bm t mt dng bm J(t).Vng tch cc c dy d, p l thi gian sng ca photon.

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Mt s c tnh ca b SOA :( )( )p

J tR tqd

=Trong :

( ) ( )st g th ph g phR t av n n N gv N= L tc pht x kch thch, vi vg l vn tc nhm ca nh

sng ti, l confinement factor, a l hng s li, nth l mt ngng, Nph l mt photon, g l li trn n v chiu di

(2)

(3)


Vi vng tch cc c rng w v dy d, tn hiuquang c cng sut Ps , photon c nng lng hv v vntc nhm l vg th mt photon c tnh nh sau:

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( )(w )s

phg

PNv hv d

= (4)


V d:

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p n: 1.56*1016 photon/m3

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T (1) ta c:

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( ) / 0n t t = trng thi bn vng(steady state), p st

p

nR R

= +

T (2), (3) v (5) ta c li bn vng trong mt n v thi gian:

0

1/ ( ) 1 / ,

th

p

g ph p ph ph

nJqd gg

v N a N N sat

= =

+ +

(5)

(6)


Trong Nph,sat l mt photon bo ha c tnhnh sau:

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1,ph

g p

N satav

=

g0 l li khuch i tn hiu nh.

0 ( )thpp

nJg aqd

=

(7)

(8)


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Tnh Rp v g0 ?


li khuch i: li ca b khuch i c tnh theo cng thc:

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,

,

s out

s in

PG

P=

Trong Ps,out v Ps,in ln lt l cng sut vo vcng sut ra.

(9)

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li khuch i:Ngoi ra, li khuch i c th c tnh nh sau:

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Trong , gm l h s li ca vt liu, l h shp th ca vt liu, L l chiu di si quang, g(z) l li ton phn trn n v chiu di.

exp[( ( ) ] exp[ ( ) ]mG g L g z L= (10)


Trong g0 l li cha bo ha, Pd (z) l cngsut tn hiu quang ti im z, Pamp,sat l cng sut quangbo ha.

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B khuch i quang bn dn SOA: li khuch i:

0

,

( ) ( )1 damp sat

gg z P zP

=

+

Vi:

t:0 0exp( )G g L=

(11)

(12)


li khuch i:

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B khuch i quang bn dn SOA:0,1 ln( )

,

GPamp satGPs in G

= + (13)

Hnh 6. S thay i li b khuchi theo cng sut ng vo


B khuch i EDFA c chiu di t 10-30m, c phatp cht Erbium vo vng tch cc, c th hot ng ctrong vng 1531 n 1616 nm.

Cu trc mt b EDFA nh sau:

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B khuch i quang EDFA:

Hnh 7. Cu trc b khuch i EDFA

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Laser bm: hot ng bc sng 1480nm hoc980nm, cung cp nng lng nh sng to ra trng thinghch o nng vng tch cc.

WDM Coupler: Ghp tn hiu quang cn khuch i vnh sng t laser bm vo trong si quang.

B cch ly quang(isolator): ngn khng cho tn hiuquang c khuch i phn x ngc v pha u pht hoccc tn hiu quang trn ng truyn phn x ngc vEDFA.

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Cc vng nng lng caEr3+

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Hnh 7: Gin phn b nng lng ca Er3+


Cc vng nng lng ca Er3+ :- Vng 4I15/2 c gi l vng nn, c nng lng thpnht.- Vng 4I13/2 l vng gi bn v iron c thi gian sng y lu nht, khong 10ms.- Cc vng cn li l vng c nng lng cao, cn gi lvng kch thch, hay vng bm.

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chnh lch nng lng gia vng gi bn v vngnn:

- T y vng gi bn n nh ca vng nn: 0,775eV(1600nm)- T y vng gi bn n y vng nn 0,814eV(1527nm).- T nh vng gi bn n y vng nn 0,814eV(1477nm).

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C ch hot ng ca b EDFA:

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Hnh 9: Qu trnhchuyn i nnglng trong bEDFA


C ch hot ng ca b EDFA:Khi s dng ngun bm l laser c bc sng 980nm,

nng lng ca photon bm l 1,27eV.- Cc iron Er3+ s hp th nng lng photon bm vchuyn ln vng bm.(1)- Ti vng bm, iron s phn r khng bc x v chuynxung vng gi bn (2).

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- Cc photon vng gi bn c khuynh hng chuynxung vng nng lng thp hn, c mt in t cao (4).- Nu photon vng gi bn sau 10ms khng nhn ckch thch ca photon nh sng, iron Er3+ s t ng chuynxung vng nn v pht x photon (pht x t pht) (5).

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B khuch i quang EDFA: C ch hot ng ca b EDFA:


Photon nh sng khi vo trong si EDFA nu b hp thbi cc iron Er3+ vng nn s lm suy hao tn hiu. (6)- Sau khong 10ms, nu iron nhn c nng lng caphoton kch thch (photon ca nh sng cn khuch i), ironEr3+ s chuyn xung vng nn v pht x photon c cnghng, cng phn cc, cng pha vi photon nh sng yl qu trnh khuch i nh sng. (7)

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Khi s dng ngun bm c bc sng 1480 nm, c nnglng photon l 0.841eV, cc iron Er3+ vng nn s hpth nng lng ca photon v chuyn ln trng nh cavng gi bn(trng thi nng lng cao hn) (3).

Cc bc tip theo khuch i tn hiu khi s dngngun bm c bc sng 1480nm tng t nh ca ngunbm c bc sng 980 nm. (4)(5)(6)(7)

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So snh 2 bc sng 980nm v 1480nm:

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Cng sut ng ra b khuch i:

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B khuch i quang EDFA: Hiu sut chuyn i nng lng v li

, , ,

ps out s in p in

s

P P P +

Trong : Pp,in l cng sut ca ngun bm, p v s l bc sng bm v bc sng tn hiu.

(14)


Hiu sut chuyn i nng lng c tnh nh sau:

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, , ,

, ,

1ps out s in s outp in p in s

P P PPCE

P P

=

Cng thc tnh li khuch i:

,,

, ,

1 p p ins outs in s s in

PPG

P P= +

(15)

(16)

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B khuch i quang EDFA s dng bc sng bm980nm, vi cng sut bm l 30mW, khuch i bcsng 1550nm l 20dB. Vy cng sut vo cc i l baonhiu? Cng sut ra cc i l bao nhiu?

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P s,in 190mPs,out =12,8dBm


Nhiu trong b khuch i:Nhiu chnh trong b khuch i quang l nhiu gy ra

do s pht x t pht ASE(amplifier Spontaneous emission)

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3. Cc thng s c bn

10/2012Hnh 10: Tn hiu ca ngun bm v tn hiu ng ra ca b khuch i


Nhiu trong b khuch i:Mt ph cng sut nhiu ASE c tnh nh sau:

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3. Cc thng s c bn

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2

2 1sp

nn

n n=

AS ( ) [ ( ) 1] /E sp ASE optS f hvn G f P v= =

Trong :PASE l cng sut nhiuvopt l bng thng khuch i quangnsp l h s pht x t phtn1 , n2 l h s chit xut ca b khuch i trng thi 1 v 2

(17)

(18)


Nhiu trong b khuch i:Nhiu ca b khuch i khng nhng ph thuc vo

cng sut ngun bm m cn ph thuc vo chiu di siquang

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3. Cc thng s c bn

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Hnh 11. S thay i nhiu ASE theo chiu di v cng sut bm

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H s nhiu:Sau khi i qua b khuch i, tn hiu quang b nhiu

ASE tc ng lm gim t s tn hiu trn nhiu. H snhiu NF(noise figure) th hin s nh hng ca nhiu lntn hiu.

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3. Cc thng s c bn

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1 2 ( 1)spinout

n GSNRNFSNR G

+ = =

Trong l hiu sut b photodetector, nsp l h spht x t pht, G l li khuch i.

(19)


Bng thng li:Tn s khc nhau li b khuch i quang khc

nhau. p ng tn s quang ca b khuch i G(f) lchnh l ph li ca b khuch i quang.

Bng thng li b khuch i quang c gi lBo c xc nh bi im -3dB so vi nh ca bkhuch i.

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3. Cc thng s c bn

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Bng thng li:

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3. Cc thng s c bn

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Gain Bandwidth ca b khuch i SOA ti cc bc sng 1310 nm v 1550nm.

Hnh 12: Bo = 55nm Hnh 13: Bo ~ 45nm


Cng sut ra bo ha:Khi cng sut ng vo b khuch i nh, cng sut

quang ng ra s tng tuyn tnh vi cng sut quang ngvo, theo h s li G. Tuy nhin cng sut ng ra khngth tng mi c. Bng thc nghim, ngi ta thy rngkhi cng sut ng vo Pin tng n mt mc no , liG bt u gim. Kt qu l cng sut ng ra s khng cntng tuyn tnh theo cng sut ng vo.

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3. Cc thng s c bn

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Cng sut ra bo ha:

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3. Cc thng s c bn

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Hnh 14: Cng sut ng ratheo cng sut ng vo

Hnh 15: Cng sutng ra theo li


Mt s ng dng ca b khuch i quang nh sau:- Khuch i cng sut.- Khuch i trn ng truyn.- Tin khuch i.- Khuch i trong h thng a bc sng.- ng dng trong b chuyn i bc sng.

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4. ng dng ca b khuch i

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Bi tp:Bi 11.1Bi 11.7Bi 11.8Bi 11.9Bi 11.10,

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