thiet ke tuyen cap quang theo quy cong suat va thoi gian len trong he thong thong tin soi quang...

7/31/2019 Thiet Ke Tuyen Cap Quang Theo Quy Cong Suat Va Thoi Gian Len Trong He Thong Thong Tin Soi Quang Chuong 5

1/18

CHNG 5: TNH TON THIT K TUYN CP

QUANG THEO QU CNG SUT V THI

GIAN LN5.1 Gii thiu chng

Cc h thng thng tin quang c ng dng c hiu qu nht trong

lnh vc truyn dn s. Do vy trong tnh ton, thit k ta xem xt h thng

truyn dn s IM-DD (Intensity Modulation-Direct Detection) th nhng

iu kin bt buc v k thut v tnh kinh t ng mt vai tr quan trong

trong tt c cc tuyn thng tin si quang. Ngi thit k phi chn cn thntng cng on m bo sao cho c h thng trong sut thi gian phc v

u hot ng tt.

5.2 Cc khi nim

Nh bit, h thng thng tin quang ph bin hin nay l h

thng IM-DD im-im. thit k tuyn ta cn quan tm n: Thit b

pht quang, thit b thu quang, si dn quang v cc yu t nh hng n

n chng hn nh mi hn v cc b connector nh hnh v di y:

Mc ch ca vic thit k tuyn l phi t c cc yu cu sau: C ly truyn dn theo yu cu.

Tc truyn dn.

T s li bit BER.


2/18

m bo cho vic thit k tuyn t c cc yu cu cn

phi chn cc thnh phn ca tuyn:

Si quang n mode hay a mode.

Kch thc li si. Ch s chit sut mt ct li.

Bng tn hoc tn sc.

Suy hao ca si.

Khu hay bn knh trng mode.

Ngun pht l LD hay LED

Bc sng pht.

rng ph.

Cng sut pht.

Vng pht x c hiu qu.

Thit b thu quang s dng PIN hay APD

H s chuyn i.

Bc sng lm vic.

Tc lm vic.

nhy thu.

la chn cc thnh phn sao cho m bao k thut ta phi xt

n qu cng sut ln v qu thi gian ln ca tn hiu trong h thng.

Qu cng sut c cng sut pht, nhy thu, cng sut d ph ng,

t ta thit lp t s BER. Cng sut d phng cho suy hao si, suy hao

mi ni...Khi la chn cc thnh phn ca tuyn m khng m bo khongcch ng truyn th c th thay i cc thnh phn hay ghp trm lp

vo tuyn tho mn yu cu v cng sut. Khi qu cng sut cn bng

ta kim tra qu thi gian ln ca tn hiu.

Cc bc thit k:


3/18

1. Chn bc sng lm vic ca tuyn

2. La chn thnh phn thit b hot ng bc sng ny

3. Chn thit b tho mn yu cu t ra

5.3 Qu cng sutTa xt phng trnh cn bng ca qu cng sut. l iu kin v

cng sut tuyn hot ng bnh thng.

Gi s bn pht v bn thu khng c s suy hao cng sut th:

0 rs PP

(5.1)

trong , sP : Cng sut pht. rP : Cng sut thu.

Suy hao trn tuyn bao gm suy hao trn si dn quang, trn cc b

ni v cc mi hn. Suy hao tng phn c xc nh theo cng thc:

A = -10login

out

p

p

(5.2)

Ngoi cc suy hao ni trn cn phi c mt lng cng sut d

phng cho tui th ca cc thnh phn, cho s thay i ca nhit . Gi tr

cng sut d phng ny c gi tr khong 6dB n 8dB.

Phng trnh cn bng qu cng sut (im-im) l:

devicedSccaps mnLMDPhsP ...log10

(5.3)

Trong : sP l cng sut pht [mW]

hs: Hiu sut ghp quang [%]

MDP: nhy my thu

MDP=-27,5dBm [7]


4/18

cap, : H s suy hao cp v d phng cho cp [dB/km]

L: Khong cch gia pha pht v thu [km]

sc , : Suy hao connector v suy hao mi hn [dB]

n, m: S connector v s mi hn

d : Suy hao ghp si quang-b thu[dB]

device : Suy hao dphng cho thit b [dB]

Cng sut quang ti dP [dB]:

devicedsccapsd mnLhsPP ....log10

(5.4)

Khi cng sut quang ti nm trong khong gia [MDP n

(MDP+Over)] vi Over l h s qu ti my thu. Lc ny t s li bit BER

s nh hn mong mun v khng b qu ti my thu.

5.4 Qu thi gian ln

Trong mt h thng thng tin quang, tn hiu c truyn t thit

b pht n thit b thu thng qua mi trng truyn dn l si quang. Trong

qu trnh , rng xung ca tn hiu b gin ra. Do , ta c th xem tn

hiu i qua h thng nh l i qua mt b lc thng thp. Khi , thi gian

ln ca h thng c nh ngha l khong thi gian t sao cho bin tn

hiu xung tng t 10% n 90% bin cc i ca n.

Ta c th tnh thi gian ln ca tn hiu xung vung khi i qua

mch lc thng thp RC:

Hnh 5.1: p ng xung ca b lc thng thp.


5/18

Tn hiu vo l xung vung nn c dng:

p

VpVtVV inin

00 1.

(5.5)

Hm truyn: p

pH

1

1vi RC

(5.6)

pp

VpVpHpV inout

1. 0

(5.7)

tVtVout exp1.0

(5.8)

ti 1t :

100 exp11,0

tVV

9,0exp 1

t

ti 2t :

2

00 exp19,0t

VV

(5.9)

1,0exp2

t

(5.10)

T (5.9) v (5.10) ta c:

RCRCttt

2,29ln

.9ln12

(5.11)


6/18

T (5.6) ta c: fRCj

fH21

1

(5.12)

Do bng thng ca mch: RCB 21

(5.13)

T (5.11) v (5.13) ta c:

BBt

35,0

2

2,2

(5.14)

Bng thng ti thiu ca b lc phi bng bng thng ca tn hiu

th ta mi c th thu c tn hiu, iu ny tng ng vi thi gian ln ti

a:

rxB

t35,0

max

(5.15)

Vi tn hiu loi NRZ: Rtrx7,0

max

(5.16)

Vi loi tn hiu RZ:R

t35,0

max

(5.17)

khi thi gian ln ca tuyn:

N

i

it tt1

2

(5.18)

-Thi gian ln ca thit b thu.

Gi B l bng tn in 3dB tnh bng MHz th thi gian ln ca thit b thu

c tnh


7/18

B

tn350

(5.19)

-Thi gian ln tn sc mode ca si quang

0

mod .440 BLt

q

e [ns]

(5.20)

Trong q: tham s c gi tr t 0,5 n 1

0B : Bng tn 1 Km cp si quang [MHz]

L: Chiu di ca cp

-Thi gian ln tn sc vt liu dng ng dn sng

..LDtVL

(5.21)

Trong D: H s tn sc

: rng ngun pht

(5.17) c th c vit li:

2

0

22 350440..

rx

q

txtBB

LLDtt

(5.22)

5.5 Nhiu trong h thng thng tin quang

Nhu l khi nim m t cc thnh phn tn hiu in khng mong

mun

C chiu hng gy ri qu trnh truyn dn v x l tn hiu trong h thng

m chng ta khng kim sot y . Trong h thng tch sng, nhy ca

h thng ph thuc rt nhiu vo cc loi nhiu v hai ngun nhiu chnh

y l nhiu lng t v nhiu nhit.

5.5.1 Nhiu lng t.


8/18

Nhiu lng t ca photodiode sinh ra do s lng cc ht ti in i

qua mt khe nng lng hay vt qua hng rao th nng c tnh ngu nhin

theo thi gian gy ra. Dng chy ca cc ht electron qua tip gip p-n l

ring r v ngu nhin. Cc ht n khng ng thi nn pht sinh ra nhiuny.

Gi tr ca nhiu lng t ph thuc vo cc tham s:

Bieishot ...22

(5.23)

Trong : B l rng bng ca b thu

I l dng trung bnh n b tch sngGi tr ca dng nhiu lng t l Bieishot ...2 , t biu thc ny ta

thy dng nhiu lng t tng theo B .

5.5.2 Nhiu nhit

Nhiu nhit xut pht t in tr ti b tch sng v cc linh kin in

t trong b khuych i, c xu hng chi phi trong qu trnh khuych i

khi s dng photodiode PIN vi t s tn hiu trn nhiu thp, c th t

c h s khuych i ti u bng thit k cn bng gia nhiu nhit v

nhiu lng t khng ph thuc vo h s khuych i.

Cng thc tnh ton nhiu nhit: LRKTBi 42

(5.24)

Tong : K l hng s Bozman, K=1,38.1023

T l nhit n v kenvin, T = t(0c) + 273

R l in tr ti

5.6 T l tn hiu trn nhiu

5.6.1 i vi photodiode PIN


9/18

Trong h thng tch sng trc tip, s dng diode tch sng PIN th gi

tr dng v cng sut ti quan h nh sau:

ss p

hv

ei

(5.25)

Vi: l hiu sut lng t

h l hng s plank, h =6,626.10-34 Js

Mt khc ta c cng sut trn ti:

S = i2.RL

S= ( hv

e

.ps )

2

.RL

5.26

-Cng sut nhiu lng t vi dng bao gm c dng ti:

. LdsLLshotshot RBiPhv

eeBReIRiN .).(2..2.2

5.27

-Dng v th ca nhiu nhit:

L

nhR

KTBi

42 : 2nhu 4KTB.RL

Cng sut nhiu nhit:

KTBRR

KTBN L

L

nh 44

5.28

T ta c t s tn hiu trn nhiu my thu s dng photodiodePIN:


10/18

TBKRBip

hv

ee

Rphv

e

N

S

Lds

Ls

..4.).(2

)(2

5.29

5.6.2 i vi photodiode APD

Nh bit APD bao gm lp chuyn i quang in v lp nhn

in, do vy nhiu xut hin lp chuyn i quang in i2shot = 2.e.I.B

cng nhn c ln lp nhn vi h s nhn M.

BMiphv

ei xdshot

.22 ).(

5.30

L

x

dsLLshotshot RBMiPhv

eeBReIRiN ..).(2..2. 22

5.31

Trong biu thc trn tr s Mx gi l nhiu qu mc. y l gi tr c

sinh ra trong hiu ng thc.

Vi x l h s tp m qu mc. Gi tr ca x ph thuc vo vt liu chto photodiode APD. i vi photodiode si = 0.3

photodiode InGAs x = 0.7

photodiode Ge x = 1

Do t s tn hiu trn nhiu my thu s dng photodiode APD l:

TBKRBMip

hvee

RpMhv

e

N

S

Lx

ds

Ls

..4.).(2

).(

2

2

(5.32)


11/18

T l li bit:.2

)2

exp(2

q

q

BER

(5.33)

Vi q=SN/2

T s BER cng nh th cht lng ca h thng cng cao v iu ny cn

ty thuc vo tng h thng. Thng BER = 910 hay < 1210 .

5.7 Cc gi tr ca cc thnh phn

Thit b pht quang: [7]

Tham s Gi tr

Bc sng lm vic 1300nm hay 1550nmDi sng lm vic nm50

Cng sut ra LED: -32 n 15dBm

LD: -12 n 7dBm

Thi gian ln LED: 3ns(max)

LD:


12/18

SM ti 1550nm


13/18

4. LD-DMTT-PIN

5. LD-DMDC-APD

6. LDDM-DMTT-APD

7. LDDM-DMDC-APD

5.8 Bi ton tnh ton v thit k theo qu cng sut v thi gian ln

Trong bi ton, h thng s dng ln lt 2 thit bi thu quang l

photodiode PIN v photodiode APD, tnh ton cng sut pht ti u.

Vic tnh ton da trn nhng thng s c th ca cc thit b c trong

tuyn , cc thng s ny c cho bi nh sn xut.

Yu cu c th ca tuyn nh sau:

- Tuyn A-B vi c ly truyn dn: L = 100 km

- Tc bit : Bt =2,5 Gb/s

- M s dng l m RZ

- S conector(mi ni) : 2

- S Slice(mi hn) : 20

- BER cho php 10-10 v khng s dng b khuych i quang

5.8.1 Chn bc sng lm vic ca tuyn.

Chn bc sng lm vic ca tuyn c lin quan n rt nhiu tham

s khc ca tuyn. C ba vng ca s c th la chn khi tht k l

850nm, 1300nm, 1550nm.

Nghin cu v cp quang cho thy rng, cp quang c c tnh tt

hn vng bc sng di. Khi tn hao truyn dn v tn sc l cc nhn t

quyt nh xc nh c chiu di ca tuyn.Bc sng ngn thng dng s dng nhng h thng thng tin

hat ng vi tc thp. Trong vng bc sng di, cc h thng hat

ng bc sng 1550nm cho mc suy hao thp nhng li c mc tn x


14/18

ln hn 1300nm, tuyn trn, do chiu di ca tuyn l 100km nn ta cho

bc sng lm vic ca tuyn l 1550nm c mc suy hao thp.

5.8.2 Chn loi si quang

Theo s trnh by phn l thuyt si quang c phn thnh 3 loi:n mode, a mode ch s bc, a mode ch s lp. Loi si n mode c

c tnh tn hao v tn s rt tt cho nn loi ny c s dng ph bin cho

ng di, dung lng truyn dn cao i hi bng thng rng v tn hao

thp.

Loi si quang ca tuyn c chn l: si quang n mode vi ch

s suy hao l 0,25dB/km v h s tn sc D=17ps/nm.km.

5.8.3 Thit b thu quang

Chn thit b thu quang tha mn cc yu cu sau:

- nhy cao vi bc sng lm vic ca tuyn.

- Hiu sut lng t ln

- c tnh nhiu phi thp

- Hot ng n nh vi s thay i ca mi trng

Vic chn thit b thu ng vi mt t l li bit BER cho trc lmt cng

on quang trng, bi l nhy tnh c ta s c cng sut pht ti u v

nh vy s lm cho tuyn hot ng n nh.

Vi BER cho trc th ta s c t l tn hiu trn nhiu t bng di

y: S/N (dB)

10 10-2 10-3 10-710-610-5 10-8 10-9 10-10 10-11 10-1210-4

BER = 1/2 erfc(Q)

1

2

3

4

5

6

7

5

10

15

20

23

Q =N

S

2

1


15/18

Vi BER=10-11 th t hnh v ta s c S/N = 22,6dB hay S/N = 182 ln

5.9 Tnh ton tn hao trn ng truyn

Loi tn hao n v S lng Tng

Tn hao si 0,25dB/km 100km 25dBTn hao mi

hn

0,1dB 20 2dB

Tn hao mi

ni

1dB 2 2dB

D phng 5dB 5dB

PA =34dB

5.10 nhy ca my thu trong trng hp s dng PIN

Ta s c cng thc S/N i vi thit b thu PIN nh sau:

TBKRBiphv

ee

Rphv

e

N

S

Lds

Ls

..4.).(2

)( 2

L

ds

s

R

TBKBip

hv

ee

phv

e

N

S

..4).(2

)( 2

Vi B t= B = 2,5Gb/s (do m s dng l RZ)


16/18

Ch thit b thu l photodiode PIN G6742-003 ca Hamamatsu

Photonic (c thng s km theo)

Cc thng s ca PIN:

R =hve =0,95A/W

RL = 50

Id = 0,3.10-9 A

Cc hng s :

K = 1,38.10-23 J/K, h = 6,626.10-34 Js, c= 3.108 m/s

Thay cc gi tr vo ta c phng trnh:

182 =

50

10.5,230010.38,1410.5,2)10.3,095,0(10.2,3

95,0923

9919

2

S

S

P

P

Ta c phng trnh theo PS :

0,9025.PS -138,3.10-9PS -15,1.10

-11 = 0

Gii phng trnh bc hai ta c: PS = 13.10-6 W

PS = -12,8.10-6W (loi)

Vy nhy ca my thu l: PS = 13.10-6 W hay PS =-18.7dBm

T ta c cng sut pht ti u cho laser trong trng hp s

dng PIN: PT =PA +PS = 34 + (-18,7) = 15,34dbm

Nh vy chn thit b pht vi cng sut danh nh l: PT = 15,12mW

5.11 nhy my thu trong trng hp s dng APD

Ta c cng thc S/N i vi thit b thu APD nh sau:

TBKRBMip

hv

ee

RpMhv

e

N

S

L

x

ds

Ls

..4.).(2

).(

2

2


17/18

hay

L

x

ds

s

R

TBKBMip

hv

ee

pMhv

e

N

S

..4.).(2

).(

2

2

Chn thit b thu l photodiode APD loi Suo020 ca sensor Ulimited

Inc (c thng s km theo)

Cc thng s ca APD:

R =hv

e=0,8A/W

RL = 50

X = 0,7

M = 10

Id = 30 nA

Cc hng s:

K = 1,38.10-23 J/K, h = 6,626.10-34 Js, c= 3.108 m/s

Thay cc gi tr vo ta c phng trnh:

182 =

50

10.5,230010.38,1410.5,2.10.)10.3,08,0(10.2,3

8923

97,02919

2

S

S

P

P

Ta c phng trnh theo PS:

64. 2SP - 29,189.10-6PS - 7,717.10

-11 = 0

Gii phng trnh bc hai ta c: PS = 1,35.10-6 W

PS = - 8,93.10-6W (loi)

Vy nhy ca my thu l: PS = 1,35.10-6 W hay PS = - 28,7dBm

T ta c cng sut pht ti u cho laser trong trng hp s

dng PIN: PT =PA + PS = 34 + (-28,7) = 5,3dBm

Nh vy chn thit b pht vi cng sut danh nh l: PT = 5,34mW


18/18

5.12 Tnh ton thi gian ln

-Thi gian ln ti a ca h thng

tt = 0,7/Bt = 0,7/2,5.109 = 2.8.10-10 s

-Thi gian ln ca thit b thu:tn = 350/B = 350/2,5.10

9 = 14.10-10 s

-Thi gian ln tn sc mode ca si quang:

tt = 440.Lq/B0 = 440.100

0,5/2,5.107 = 176.10-6 s

Trong : q l tham s c gi tr t 0,5 n 1

Bo : bng tn mt km cp si quang (MHz)

L : chiu di ca cp

- Thi gian ln tn sc vt liu ng dn sng:

tvl = D.L. = 17.0.04.100 = 68ps = 68.10-12

- Khi thi gian ln ca tuyn :

tt =

2

22 350440)..(

rxo

q

txBB

LLDt

tt = 2,65.10-10 s

Nh vy thi gian ln ca tuyn l: tt = 2,65.10-10 s

5.13 Kt lun chng

Kt qu vic tnh ton da vo cc thng s cho trc ca tuyn

cho thy rng, APD c h s nhn M nn t l tn hiu trn nhiu S/N c

gi tr ln hn nn nhy my thu c nng cao hn so vi PIN.

Do , vic la chn APD lm thit b thu quang s ko theo thun li

l ch cn s dng diode Laser vi cng sut pht nh hn rt nhiu so vi

khi dng PIN lm thit b thu quang.

thiet ke tuyen cap quang theo quy cong suat va thoi gian len trong he thong thong tin soi quang...

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