phn 2. cng ngh sdh

Phn 1. Si quangChng I : Gii thiu tng qut

1.1. Lch s pht trin: thc t v cn qu nhiu ngun nhiu lm gim cht lng ca ng truyn. 1934 : NORMAN R. FRENCH, k s ngi M, nhn c bng sng ch v h thng thng tin quang. Phng tin truyn dn ca ng l cc thanh thu tinh. 1958 : ARTHUR SCHAWLOW v CHARLES H. TOWNES, xy dng v pht trin laser. 1960 : THEODOR H. MAIMAN a laser vo hot ng thnh cng. 1962 : Laser bn dn v photodiode bn dn c tha nhn. Vn cn li l phi tm mi trng truyn dn quang thch hp. 1966 : CHARLES H. KAO v GEORGE A. HOCKHAM, hai k s phng th nghim Standard Telecommunications ca Anh, xut vic dng thu tinh truyn dn nh sng. Nhng do cng ngh ch to si thu tinh thi y cn hn ch nn suy hao ca si qu ln ( ~ 1000 dB/km). 1970 : Hng Corning Glass Works ch to thnh cng si quang loi SI c suy hao nh hn 20 db/km bc sng 633 nm. 1972 : Loi si GI c ch to vi suy hao 4 dB/km. 1983 : Si n mode (SM) c xut xng M. Ngy nay si n mode c s dng rng ri. suy hao ca loi si ny ch cn khong 0,2 dB/km bc sng 1550 nm. ng truyn s liu, mng LAN Mng truyn hnh. Trong tng lai si quang c th c s dng trong mng thu bao.1.2. u im ca thng tin si quang:So vi dy kim loi si quang c nhiu u im ng ch l: Suy hao thp: cho php ko di khong cch tip vn do gim c s trm tip vn Di thng rt rng: c th thit lp h thng truyn dn s tc cao Trng lng nh, kch thc nh Hon ton cch in khng chu nh hng ca sm xt Khng b can nhiu bi trng in t Xuyn m gi cc si dy khng ng k Vt liu ch to c rt nhiu trong thin nhin Dng h thng thng tin si quang kinh t hn so vi si kim loi cng dung lng v c ly.

* * * n tt ngip - Thng tin quang

phn 1. si quang Chng I. Gii thiu tng qut

1

_____________________________________________________________________________________________________________________________________________________________________________________- 2- Chng II : L thuyt chung v si dn quang2.1. c s quang hc:nh sng dng trong thng tin quang nm vng cn hng ngoi vi bc sng t 800 nm n 1600 nm. c bit c 3 bc sng thng dng l 850 nm, 1300 nm, 1550 nm. Chit sut ca mi trng:Trong : n: chit sut ca mi trng. C: vn tc nh sng trong chn khng C = 3. 108m/s V: vn tc nh sng trong mi trngV V C nn n 1 S phn x ton phn: nh lut Snell : n1 sin = n2 sin Tia khc xTia phn xTia phn xMi trng 2: n2Mi trng 1: n11112233

T

S phn x v khc x nh sng

Nu n1 n2 th nu tng th cng tng theo v lun lun ln hn . Khi = 900 tc l song song vi mt tip gip, th c gi l gc ti hn T nu tip tc tng sao cho T th khng cn tia khc x m ch cn tia phn x hin tng ny gi l s phn x ton phn.

Da vo cng thc Snell c th tnh c gc ti hn T :

2.2. S truyn dn nh sng trong si quang:* Nguyn l truyn dn chung:ng dng hin tng phn x ton phn, si quang c ch to gm mt li (core) bng thu tinh c chit sut n1 v mt lp bc (cladding) bng thu tinh c chit sut n2 vi n1 n2 nh sng truyn trong li si quang s phn x nhiu ln (phn x ton phn) trn mt tip gip gia li v lp v bc. Do nh sng c th truyn c trong si c c ly di ngay c khi si b un cong vi mt cong c gii hn. n1n2nLp bc (cladding) n2Lp bc (cladding) n2Li (core) n1Nguyn l truyn dn nh sng trong si quang

2.3. cc dng phn b chit sut trong si quang:a) Si quang c chit sut nhy bc (si SI: Step- Index):y l loi si c cu to n gin nht vi chit sut ca li v lp v bc khc nhau mt cch r rt nh hnh bc thang. Cc tia sng t ngun quang phng vo u si vi gc ti khc nhau s truyn theo cc ng khc nhau n2n1nn2n2n1 > n2S truyn nh sng trong si quang c chit sut nhy bc (SI)

Cc tia sng truyn trong li vi cng vn tc : y n1 khng i m chiu di ng truyn khc nhau nn thi gian truyn s khc nhau trn cng mt chiu di si. iu ny dn ti mt hin tng khi a mt xung nh sng hp vo u si li nhn c mt xung nh sng rng hn cui si. y l hin tng tn sc,do tn sc ln nn si SI khng th truyn tn hiu s tc cao qua c ly di c. Nhc im ny c th khc phc c trong loi si c chit sut gim dnb) Si quang c chit sut gim dn (si GI: Graded- Index):Si GI c dng phn b chit sut li hnh parabol, v chit sut li thay i mt cch lin tc nn tia sng truyn trong li b un cong dn.n(r)n1n2n2n2S truyn nh sng trong si GI

ng truyn ca cc tia sng trong si GI cng khng bng nhau nhng vn tc truyn cng thay i theo. Cc tia truyn xa trc c ng truyn di hn nhng li c vn tc truyn ln hn v ngc li, cc tia truyn gn trc c ng truyn ngn hn nhng li c vn tc truyn nh hn. Tia truyn dc theo trc c ng truyn ngn nht v chit sut trc l ln nht . Nu ch to chnh xc s phn b chit sut theo ng parabol th ng i ca cc tia sng c dng hnh sin v thi gian truyn ca cc tia ny bng nhau. tn sc ca si GI nh hn nhiu so vi si SI.c) Cc dng chit sut khc:Hai dng chit sut SI v GI c dng ph bin , ngoi ra cn c mt s dng chit sut khc nhm p ng cc yu cu c bit: Dng gim chit sut lp bc: Trong k thut ch to si quang, mun thu tinh c chit sut ln phi tim nhiu tp cht vo, iu ny lm tng suy hao. Dng gim chit sut lp bc nhm m bo chnh lch chit sut nhng c chit sut li n1 khng cao.

Dng dch tn sc: tn sc tng cng ca si quang trit tiu bc sng gn 1300nm. Ngi ta c th dch im tn sc trit tiu n bc sng 1550nm bng cch dng si quang c dng chit sut nh hnh v:

Dng san bng tn sc:Vi mc ch gim tn sc ca si quang trong mt khong bc sng. Chng hn p ng cho k thut ghp knh theo bc sng ngi ta dng si quang c dng chit sut nh hnh v:

Dng chit sut ny qu phc tp nn mi ch c nghin cu trong phng th nghim ch cha a ra thc t.2.4. si a mode v n mode:a) Si a mode (MM: Multi Mode):Cc thng s ca si a mode thng dng (50/125m) l: ng knh li: d = 2a = 50m ng knh lp bc: D = 2b = 125m chnh lch chit sut: = 0,01 = 1% Chit sut ln nht ca li: n1 1,46Si a mode c th c chit sut nhy bc hoc chit sut gim dn. 50 m50 m125 m125 mn1n2n2n1 a) Si SI b) Si GI

b) Si n mode ( SM: SingleMode ):Khi gim kch thc li si ch c mt mode sng c bn truyn c trong si th si c gi l n mode. Trong si ch truyn mt mode sng nn tn sc do nhiu ng truyn bng khng v si n mode c dng phn b chit sut nhy bc.125 mn1n29 m

Cc thng s ca si n mode thng dng l:ng knh li: d = 2a =9m 10mng knh lp bc: D = 2b = 125m lch chit sut: = 0,003 = 0,3%Chit sut li: n1 = 1,46 tn sc ca si n mode rt nh, c bit bc sng = 1300 nm tn sc ca si n mode rt thp ( ~ 0). Do di thng ca si n mode rt rng. Song v kch thc li si n mode qu nh nn i hi kch thc ca cc linh kin quang cng phi tng ng v cc thit b hn ni si n mode phi c chnh xc rt cao. Cc yu cu ny ngy nay u c th p ng c do si n mode ang c s dng rt ph bin.

phn 1. si quang Chng II.L thuyt chung v si dn quang

***_____________________________________________________________________________________________________________________________________________________________________________________- 28- Chng III : cc thng s ca si quang3.1. Suy hao ca si quang:Cng sut trn si quang gim dn theo hm s m tng t nh tn hiu in. Biu thc tng qut ca hm s truyn cng sut c dng:

Trong : P0 : cng sut u si (z = 0)P(z): cng sut c ly z tnh t u si: h s suy hao Lz

suy hao c tnh bi:

Trong : P1 = P0 : cng sut a vo u siP2 = P(L) : cng sut cui siH s suy hao trung bnh:

Trong :A: suy hao ca siL: chiu di si3.2. Cc nguyn nhn gy suy hao trn si quang:Cng sut truyn trong si b tht thot do s hp th ca vt liu, s tn x nh sng v s khc x qua ch si b un cong.a) Suy hao do hp th: S hp th ca cc cht kim loi:Cc tp cht trong thu tinh l mt trong nhng ngun hp th nh sng. Cc tp cht thng gp l St (Fe), ng (Cu), Mangan (Mn), Chromium (Cr), Cobal (Co), Nikel (ni).v.v.. Mc hp th ca tp cht ph thuc vo nng tp cht v bc sng nh sng truyn qua n. c si quang c suy hao di 1dB/Km cn phi c thu tinh tht tinh khit vi nng tp cht khng qu mt phn t (10-9) S hp th ca OH:S c mt ca cc ion OH trong si quang cng to ra mt suy hao hp th ng k. c bit hp th tng vt cc bc sng gn 950nm, 1240nm, 1400nm. Nh vy m cng l mt trong nhng nguyn nhn gy suy hao ca si quang. Trong qu trnh ch to nng ca cc ion OH trong li si c gi mc di mt phn t (10-9) gim hp th ca n. S hp th bng cc tm v hng ngoi:Ngay c khi si quang c t thu tinh c tinh khit cao s hp th vn sy ra. Bn thn ca thu tinh tinh khit cng hp th nh sng trong vng cc tm v vng hng ngoi. hp th thay i theo bc sngb) Suy hao do tn x: Tn x Raylegh:Ni chung khi sng in t truyn trong mi trng in mi gp nhng ch khng ng nht s xy ra hin tng tn x. Cc tia sng truyn qua ch khng ng nht ny s to i nhiu hng, ch mt phn nng lng nh sng tip tc truyn theo hng c phn cn li truyn theo cc hng khc thm ch truyn ngc v pha ngun quang. Tn x do mt phn cch gia li v lp v bc khng hon ho:Khi tia sng truyn n nhng ch khng hon ho gia li v lp bc tia sng s b tn x. Lc mt tia ti s c nhiu tia phn x vi cc gc phn x khc nhau, nhng tia c gc phn x nh hn gc ti hn s khc x ra lp v bc v b suy hao dn.c) c tuyn suy hao: (dB/km)543210,40,2500,811,21,41,31,55 (m)

Trn c tuyn suy hao ca si quang c 3 vng bc sng c suy hao thp, cn gi l 3 ca s suy hao: Ca s th nht bc sng 850nm: c xem l bc sng c suy hao thp nht i vi nhng si quang c ch to giai on u. Suy hao trung bnh bc sng ny t 2 3 dB/km. Ngy nay bc sng ny t c dng v suy hao cha phi l thp nht. Ca s th hai bc sng 1300nm: suy hao bc sng ny tng i thp, khong t 0,4 0,5 dB/Km. c bit bc sng ny tn sc rt thp nn c s dng rng ri hin nay. Ca s th ba bc sng 1550nm: cho n nay suy hao bc sng ny l thp nht, c th di 0,2dB/Km. 3.3. Tn sc:Tng t nh tn hiu in tn hiu quang truyn qua si quang cng b bin dng hin tng ny gi l s tn sc. S tn sc lm mo dng tn hiu analog v lm xung b chng lp trong tn hiu digital. S tn sc lm hn ch di thng ca ng truyn dn quang. Cc nguyn nhn gy ra tn sc: Tn sc mode ( modal dispersion):Do nng lng nh sng phn tn thnh nhiu mode. Mi mode li truyn vi vn tc nhm khc nhau nn thi gian truyn khc nhau.S ph thuc ca dmodvo s m g: dmod t cc tiu khi g ~ 2 v dmod tng kh nhanh khi g c gi tr khc 2 v hai pha. y l mt yu cu nghim ngt trong qu trnh ch to si GI. Tn sc th mode (dmod) thay i theo dng chit sut

2,42,62,82,22,01,81,60,010,11gdmod(ns/km)Tn sc Mode (dmod) thay i theo chit sut

Tn sc th (chromatic dispersion): Do tn hiu quang truyn trn si khng phi l n sc m gm mt khong bc sng nht nh. Mi bc sng li c vn tc truyn khc nhau nn thi gian truyn cng khc nhau Tn sc cht liu: Chit sut ca thu tinh thay i theo bc sng nn vn tc truyn ca nh sng c bc sng khc nhau cng khc nhau. l nguyn nhn gy nn tn sc cht liu. V mt vt l, tn sc cht liu cho bit mc ni rng xung ca mi nm b rng ph ngun quang qua mi km si quang, n v ca tn sc do cht liu M l ps/nm.Km. bc sng 850 nm tn sc do cht liu khong 90 120 ps/nm.Km. Nu s dng ngun quang l LED c b rng ph = 50 nm th ni rng xung khi truyn qua mi Km l:Dmat = M Dmat = 100ps/nm.Km 50nm = 5ns/KmCn nu ngun quang l Laser Diode c = 3 nm th ni rng xung ch khong 0,3 ns/Km. bc sng 1300nm tn sc do cht liu bng tn sc ng dn sng nhng ngc du nn tn sc th bng khng. Do bc sng 1300nm thng c chn cho cc ng truyn tc cao. bc sng 1550nm tn sc do cht liu khong20ps/nm.Km04-48-812-1216-16d(ps/nm.km) (nm)1600140013001200Tn sc dn sngTn sc sc thTn sc cht liuTn sc cht liu, tn sc dn sng v tn sc sc th thay i theo bc sng

Tn sc do tc dng ca ng dn sng:S phn b nng lng nh sng trong si quang ph thuc vo bc sng, s phn b ny gy nn hin tng tn sc ng dn sng. Tn sc ng dn sng rt nh ch ng ch vi si n mode. Tn sc th ca cc loi si:21313001200140015001600 (nm)12840-4-8-12dchr(ps/nm.km)Tn sc th ca cc loi si

1: Si bnh thng (G652) 2: Si dch tn sc (G653) 3: Si san bng tn sc.

***

phn 1. si quang Chng III.Cc thng s ca si quang

chng IV : Cu trc si quangThnh phn chnh ca si quang gm li (core) v lp bc (cladding). Trong vin thng dng loi si c c hai lp trn bng thu tinh. Li dn nh sng v lp bc gi nh sng tp trung trong li nh s phn x ton phn gia li v lp bc. bo v si quang, trnh nhiu tc dng do iu kin bn ngoi si quang cn c bc thm mt vi lp na: Lp ph hay lp v th nht (primary coating) Lp v th hai (Secondary coating)4.1. Lp ph:Lp ph c tc dng bo v si quang: Chng li s xm nhp ca hi nc. Trnh s try st gy nn nhng vt nt Gim nh hng v un cong Lp ph c bc ngay trong qu trnh ko si. Chit sut ca lp ph ln hn chit sut ca lp bc loi b cc tia sng truyn trong lp bc v khi s phn x ton phn khng th xy ra phn cch gia lp bc v lp ph. Lp ph c th c nhum mu hoc c thm vng nh du, khi hn ni si hoc ghp nh sng vo si nht thit phi ty sch lp ph. ng nht, b dy v ng tm ca lp ph c nh hng n cht lng ca si quang.4.2. Lp v:Lp v c tc dng tng cng sc chu ng ca si quang trc cc tc dng c hc v s thay nhit , cho n nay lp v c cc dng chnh sau: Dng ng m lng (Loose buffer) Dng m kht (tight buffer) Dng bng dt (Ribbon)Mi dng c nhng u nhc dim khc nhau do c s dng trong tng iu kin khc nhau.Lp vliLp bcLp ph250m125mCu trc si quang

a) Dng ng m lng: Si quang ( bc lp ph) c t trong mt ng m c ng knh ln hn ng kch thc si quang. si quanglp phngmcht nhi1,2 2mmCu trc ng m lng (Loose buffer)

ng m lng thng gm hai lp, lp trong c h s ma st nh si quang di chuyn t do khi cp b ko cng hoc co li, lp ngoi bo v si quang trc nh hng ca lc c hc. i vi cp trong nh th bn trong ng m lng khng cn cht nhi nhng vi cp ngoi tri th phi bm thm cht nhi c cc tnh cht sau: C tc dng ngn m C tnh nht khng tc dng ho hc vi cc thnh phn khc ca cp D ty sch khi cn hn ni Kh chy. Cu trc ng m lng c nhiu u im nn c dng trong cc ng truyn dn cn cht lng cao, trong iu kin mi trng thay i nhiu.b) Dng m kht: Mt cch n gin bo v si quang di tc dng ca nhiu iu kin bn ngoi l bc mt lp v m st lp ph. Phng php ny lm gim ng knh ca lp v do gim kch thc v trng lng ca cp, song si quang li chu nh hng trc tip khi cp b ko cng gim nh hng ny ngi ta chn thm mt lp m mm gia lp ph v lp v. Hnh thc ny c gi l cu trc m tng hp. Si quang c v m kht v m tng hp thng c dng lm cp t trong nh, lm dy nhy u ni cc trm u cui...Si quanglp phlp m mmlp v0,9mmCu trc si quang c v m tng hp

c) Dng bng dt:Cu trc bng dt cung l mt dng v m kht nhng bc nhiu si quang thay v mt si. S si trong bng c th ln n 12, b rng ca mi bng tu thuc vo s si trong bng. Nhc im ca cu trc ny ging nh cu trc m kht, tc l si quang chu nh hng trc tip khi cp b ko cng.bng 4 sibng 8 si

phn 1. si quang Chng IV.Cu trc si quang

chng V : Linh kin bin i quang in5.1. Tng qut: Linh kin bin i quang in c t hai u si quang. C hai linh kin quang in: Linh kin bin i t tn hiu in sang tn hiu quang, c gi l ngun quang. Linh kin ny c nhim v pht ra nh sng c cng sut t l vi dng in chy qua n. Linh kin bin i tn hiu quang sang tn hiu in, cn gi l linh kin tch sng quang (hay linh kin thu quang). Linh kin ny c nhim v ngc li so vi ngun quang , tc l to ra dng in t l vi cng sut quang chiu vo n.Cht lng ca linh kin bin i quang in v cht lng si quang quyt nh c ly, dung lng v cht lng ca tuyn truyn dn quang. Yu cu k thut ca linh kin quang in:a) i vi ngun quang: Bc sng ca nh sng pht ra:Mc suy hao ca nh sng truyn trn si quang ph thuc vo bc sngca nh sng. C ba bc sng thng dng l 850nm, 1300nm, 1550nm. Do nh sng do ngun quang pht ra cng phi c bc sng ph hp. Thi gian chuyn: c th truyn c tn hiu s c tc bit cng cao th thi gian chuyn trng thi ca ngun quang phi cng nhanh. Cng sut pht: C ly thng tin ph thuc vo nhiu yu t trong cng sut pht ca ngun quang l mt trong nhng yu t chnh. Cng sut pht cng ln th c ly thng tin cng xa. rng ph:nh sng m ngun quang thc t pht ra khng phi l ch c mt bc sng duy nht m gm mt khong bc sng. Khong sng ny cng rng th tn sc cht liu cng ln do lm hn ch di thng ca tuyn truyn dn quang. Nh vy rng ph ca ngun quang cng hp cng tt. Gc phng nh sng:Nh ta bit ng knh li ca si quang rt nh nu kch thc ca ngun quang ln v gc phong nh sng rng v cng sut pht quang vo c li s rt thp. Do ngun quang c vng pht sng v gc pht sng cng hp cng tt. n nh:Cng sut quang m cc ngun quang thc t pht ra t nhiu ph thuc vo nhit mi trng, thi gian s dng v i khi cn ph thuc vo cng sng xung quanh. V vy cng sut do ngun quang pht ra cng n nh cng tt. Thi gian s dng lu, gi thnh h.b) i vi linh kin tch sng quang: Bc sng:Nhy i vi bc sng hot ng ca h thng nhy:C nhy cng cao cng tt. Tc l kh nng tch c cc tn hiu quang tht nh vi s li (BER) trong phm vi cho php. Linh kin tch sng quang cng nhy th cng c kh nng ni rng c ly thng tin. p ng nhanh: c th lm vic trong h thng c tc bit cao. Dng ti nh:Khi cha c nh sng chiu vo nhng linh kin tch sng quang vn c dng in tch sng nhiu chy qua. Dng in ny cng nh cng tt. Tp m:C tp m cng thp cng tt m bo t s tn hiu trn tp m (S/N). tin cy cao , gi thnh h.5.2. Ngun quang:5.2.1. Nguyn l chung:C hai loi linh kin c dng lm ngun quang hin nay l: Diode pht quang hay LED (Light Emitting Diode) Diode Laser hay LD (Laser Diode)C hai linh kin trn u pht trin t diode bn dn, Tc l t tip gip ca bn dn loi P v loi N. Cc c tnh k thut ca ngun quang phn ln ph thuc vo cu to ca chng, ring bc sng do ngun quang pht ra ph thuc vo vt liu ch to ngun quang. Mi cht bn dn c b rng khe nng lng Eg khc nhau. M Eg quyt nh tn s v do quyt nh bc sng ca nng lng nh sng pht ra theo cng thc sau:

hay:

Trong :h = 6,625 . 10-34 j.s : Hng s PlanckC = 300.000 Km/s : Vn tc nh sng trong chn khngEg : b rng khe nng lng, n v (eV)v : tn s nh sng pht ra, n v HzT cng thc trn ta thy bc sng cua nh sng pht ra t l nghch vi b rng khe nng lng ca cht bn dn ch to ngun quang. Do mun ngun quang pht ra nh sng c bc sng di th phi dng cht bn dn c b rng khe nng lng hp.GaPGaAsPAlGaAsGaAs/InPInGaAsP0,850,70,60,511,31,551,8 (nm)Ga : GalliumP : PhosphorusAs : ArsenicAl : AluminiumIn : IndiumBc sng pht x ca cc cht bn dn dng trong thng tin quang

5.2.2. LED:a) Cu to v phn loi:Mc d nguyn l pht quang trong mi ni P N kh n gin song cu trc ca cc n LED phc tp hn mt diode bn dn bnh thng v phi p ng ng thi cc yu cu k thut ca mt ngun quang. LED tip xc mt GaAs:y l loi c cu trc n gin nht, dng bn dn GaAs vi nng khc nhau lm lp nn loi N v lp pht quang loi P. Lp P dy khong 200m, mt ngoi ca lp P c ph mt lp chng phn x ghp nh sng vo si quang. Bc sng pht ca LED GaAs trong khong t 880 n 950nm.Lp chng phn xTip xc PLp cch inLp P-GaAs (khuch tn)Lp N-GaAs (nn)Tip xc NCu trc LED tip xc mt GaAs

LED Burrus:LED Burrus c ch to theo cu trc nhiu lp (Heterostructure) bao gm cc lp bn dn loi N v P vi b dy v nng khc nhau. Vi cu trc nhiu lp v vch tip xc P c kch thc nh, Vng pht sng ca LED Burrus tng i hp. Ngoi ra trn b mt ca LED c khot mt l a si quang vo gn vng pht sng. Bc sng ca LED Burrus dng bn dn AlGaAs / gaAs trong khong t 800 n 850nm. Nu dng bn dn InGaAsP / InP th bc sng pht ra di hnTip xc NLp N - GaAs ( lp nn )vng pht sngLp N - AlGaAsLp P - AlGaAS ( lp tch cc )Lp P+ - AlGaAsLp cch in Al2O3Tip xc P ( ng knh nh )Cu trc LED Burrus

LED pht bc sng di:Mt loi LED pht bc sng di (1300nm v 1550nm) dng bn dn InGaAsP / InP . Tng t nh LED Burrus, loi ny cng c cu trc nhiu lp v c ng knh vch tip xc P nh (25 n 30m) nn c vng pht sng hp. im khc bit so vi LED Burrus l thay v khot l ghp nh sng vo si quang, y dng lp nn InP c dng mt thu knh ghp nh sng vo si quang.

Lp chng phn xTip xc NLp N - InP ( lp nn )Vng pht sngLp P - InGaAsPLp P+ - InPLp P+ - InGaAsPLp cch in Al2O3Lp to nhitTip xc P ( 25 30m )LED pht bc sng di

LED pht x ra: (ELED: Edge Light Emitting Diode)LED pht x ra c cu to khc vi LED thng thng, cc in cc tip xc (bng kim loi) ph kn mt trn v y ca ELED. Do nh sng khng th pht ra pha hai mt c m b gi trong vng tch cc c dng vch hp. Lp tch cc rt mng, bng vt liu c chit sut ln kp gia hai lp P v N c cit sut nh hn. Cu trc nh vy tng t cu trc si quang. Hay ni cch khc, tng ng vi mt ng dn sng. nh sng pht ra c hai u ng dn sng ny, mt trong hai c ni vi si quang. Cu trc ny c u im l vng pht sng hp v gc pht sng nh nn hiu sut ghp nh sng vo si quang cao. Tuy nhin n cng c mt hn ch l khi hot ng nhit ca ELED tng kh cao nn i hi phi c gii nhit.Tip xc PCch in SIO2Tip xc NVng pht sng( lp tch cc )Lp P - AlGaAs Lp P - AlGaAs Lp P - AlGaAs Lp N - AlGaAs LED pht x ra (ELED)

Cui cng phi ghi nhn rng cu trc ca LED cng phc tp th cng sut pht cng cao, gc pht sng cng hp, thi gian chuyn cng nhanh. Tt nhin, cng nh mi linh kin khc, cu trc cng phc tp th gia thnh s cng cao. b) c tnh k thut:Cc c tnh k thut ca LED ph thuc rt nhiu vo cu to ca chng. Ngoi ra theo pht trin ca cng ngh bn dn, cht lng ca LED ngy cng nng cao hn. Thng s in: Dng in hot ng tiu bi: t 50mA n 300mA in p st trn LED: t 1,5V 2,5V Cng sut pht:L cng sut tng cng do ngun quang pht ra. Cng sut pht ca LED t 1 3mW. i vi loi pht sng cao (High - Radinnce) cng sut pht c th ln n 10mW. Cc LED pht x mt cng sut pht cao hn LED pht x ra vi cng dng in kch thch. Nhng iu khng c ngha l si quang nhn c cng sut quang t LED pht x mt cao hn LED pht x ra. LED (pht x mt) ELED (pht x ra)1005003004002000510P(mW)I(mA)Cng sut pht ca LED v ELED

Gc pht quang:Cng sut nh sng do ngun quang pht ra cc i trc pht quang v gim dn theo gc hp vi trc. Gc pht quang c xc nh mc cng sut pht quang gim mt na (3dB) so vi mc cc i. LED pht x mt c gc pht quang ln hn so vi LED pht x ra.

pht x mtpht x ra0 (gc pht)Cng sut tng i1

0,5

0900900004504503001200Gc pht quang ca LED v ELED

Hiu sut ghp quang:Hiu sut ghp quang c tnh bi t s cng sut quang ghp vo si quang vi cng sut pht quang tng cng ca ngun quang. Hiu sut ghp quang ph thuc vo kch thc vng pht quang, gc pht quang ca ngun, gc thu nhn (NA) ca si quang v v tr t ngun quang v si quang. Hiu sut ghp ca LED pht x mt khong 1 5% v LED pht x ra trong khong 5 15%. T , tuy cng sut pht ca LED pht x mt ln hn nhng cng sut a vo si quang ca LED pht x ra li ln hn ( thng ln hn khong hai ln ). rng ph:Ngun quang pht ra cng sut cc i bc sng trung tm v gim dn v hai pha. rng ph l khong bc sng m trong cng sut quang khng nh hn phn na mc cng sut nh. Thng thng LED c rng ph trong khong 35 100 nm

800 850 900 Bc sng (nm)

1

0,5

0Cng sut tng i

40nm rng ph ca LED

Thi gian chuyn ln (Rise time):L khong thi gian cng sut ra tng t 10% n 90% mc cng sut n nh khi c xung dng in kch thch ngun quang. Thi gian chuyn ca ngun quang c nh hng n tc bit ca tn hiu iu ch, mun iu ch tc cng cao th ngun quang phi c thi gian chuyn cng nhanh. Gii thng ti a ca tn hiu iu ch ph thuc vo thi gian chuyn. nh hng ca nhit :Khi nhit mi trng tng th cng sut pht gim, tuy nhin mc nh hng bi nhit ca LED khng cao: bc sng 850nm: nh hng l -1% / 0C bc sng 1300nm v 1550nm: nh hng t -2% n -4% / 0C5.2.3. LASER:a) Cu to v nguyn tc hot ng:Laser bn dn hot ng theo nguyn l pht x kch thch. Cu to ca n gn gi vi cu to ca LED pht x ra (ELED). im khc bit c bn l trong Laser c hai mtphn x hai u lp tch cc to nn mt hc cng hng quang. Phn nh sng pht ra theo chiu dc ca hc cng hng s b phn x qua li gia hai mt phn x. Trong qu trnh di chuyn theo chiu dc ca hc nh sng kch thch cc in t kt hp vi cc l trng phng ra cc photon mi. Phn nh sng thot ra theo cc phng khc b tht thot dn. nh vy ch c phn nh sng pht ra theo chiu dc mi c khuch i.Mt sau ca Laser c ph mt lp phn x cn mt trc c ct nhn mt phn nh sng phn x cn mt phn chiu ra ngoi. Bn dn loi PLp tch ccBn dn loi N+

-Mt phn xnh sngNguyn l cu to LASER bn dn

Nhm tng hiu qu pht x, cc Laser thc t c cu trc phc tp hn chng hn loi Laser c cu trc nhiu lp chn cn gi l Laser BH (Buried Heterostructure) c vng pht sng rt hp (2m 0,2m) nn hiu sut ghp nh sng vo li si quang rt cao.Tip xc PCch in ( SiO2 )Lp N ( InP )Lp N ( InP ) Lp P ( InP )Lp N ( InP ) Tip xc NLp P + ( InGaAsP )Lp P ( InP )Lp tch cc( InGaAsP )

b) c tnh k thut: Thng s in: Dng in ngng: Khi dng in kch thch cho Laser c tr s nh, Laser hot ng ch pht x t pht nn cng sut pht rt thp. Khi c kch thch vi dng in ln, Laser hot ng ch kch thch cng sut quang tng nhanh theo dng kch thch. 0510P (mW)100200I(mA)Dng ngngLASERLEDT1T1T2 >T1T2 >T1

Dng ngng ca Laser thay i theo nhit . i vi nhnh Laser i c, dng ngng c gi tr t 50mA 100mA. Nhng Laser i mi dng ngng ch trong khong 10mA 20mA. Dng in kch thch: t vi chc n vi trm mA tu theo loi. in p st trn Laser: t 1,5V 2,5V Cng sut pht:Cng sut pht ca Laser t 1 10mW, i vi nhng Laser i mi c th ln n 50mW hay hn na.

Gc pht sng:Gc pht sng ca Laser theo phng ngang ca lp tch cc ch trong khong 5 100 , cn theo phng vung gc vi lp tch cc gc pht c th ln n 400 . Nh vy mt bao ca gc pht khng phi l mt nn trn xoay m l mt nn hnh elip Hiu sut ghp:Laser c vng pht sng nh, gc pht sng hp nn c hiu sut ghp nh sng vo si quang cao. Trung bnh hiu sut ghp ca Laser trong khong:30% 50%: i vi si n mode (SM)60% 90%: i vi si a mode (MM) tng hiu sut ghp, ngi ta c th to thm cc chi tit ph gia ngun quang v si quang nh t thm thu knh gia ngun quang v si quang, to u si quang c dng mt cu,... rng ph:Dng ph pht x ca Laser l tng hp c tuyn khuch i (do b rng khe nng lng thay i) v c tuyn chn lc ca hc cng hng quang ( ph thuc vo chiu di hc). So vi LED th ph pht x ca Laser rt hp, trong khong t 1 n 4nm. Dng ph gm nhiu vch ri rc nn c gi l ph ca Laser a mode. Ngi ta c khuynh hng ch to Laser c ph ngy cng hp gim tn sc cht liu khi s dng bc sng 1550nm. V trong tng lai c th s dng rng ri k thut ghp knh theo bc sng.

P-30 = 1 - 4 nm 0 Ph pht x ca LASER dng thc t

Laser hi tip phn b DFB: thay th cho cc mt phn x hai u l mt chui gn sng trn lp bn dn lm nn ch phn x nhng bc sng nht nh do gn nh ch c mt bc sng c cng hng v khuch i. Ph ca Laser DFB rt hp ch vo khong 0,1nm n 0,2nm. Ph ca Laser DFB c dng:P0-3-20-25 0,1nm1nm0

Laser hc ghp C_cubed: hai chp Laser ri c ghp quang vi nhau nhng cch ly v in t c s gii hn bc sng pht Laser hc ngoi (external Cavity): l loi Laser c mt phn x bn ngoi thay v trng mt phn x trong Laser thng thng. Thi gian chuyn ln:Thi gian cng sut quang tng t 10% 90% mc cng sut xc lp ca Laser rt nhanh, thng thng khng qu 1ns. nh hng nhit :Khi nhit thay i dng ngng ca Laser thay i do cng sut pht ra cng thay i nu gi nguyn dng in kch thch. Khi nhit tng th dng ngng cng tng theo dng hm m ca s gia tng nhit . Trung bnh, gia tng dng ngng vo khong +1%/0C. Ngoi ra khi nhit thay i th cng sut pht ra cng thay i, nhng mc nh hng rt thp.5.3. Tch sng quang: 5.3.1. Nguyn l chung:Cc linh kin tch sng quang hin nay cng l loi linh kin bn dn. Cu to ca chng cng pht trin t tip gip PN. C hai loi linh kin tch sng quang c s dng hin nay l: PIN: loi diode thu quang gm ba lp bn dn P,I v N. Trong P v N l hai lp bn dn c pha tp cht cn I (Intrinsic) khng pha tp cht hoc pha vi nng rt thp. APD (Avalanche Photo Diode): Diode thu quang c nhy v tc cao. Ngoi ra cn c transistor quang (Phototransistor) c kh nng bin i tn hiu quang sang tn hiu in nhng c thi gian p ng chm nn t c s dng. Nu c cng ch xut hin trong cc h thng c c ly ngn v tc chm.Cc linh kin tch sng quang hot ng theo nguyn tc ca mt tip gip PN phn cc ngc.

5.3.2. Nhng thng s c bn:a) Hiu sut lng t:

Hiu sut lng t c tnh bi t s lng in t tch ra v s photon c hp th. Trong : : Hiuut lng tnph : s lng photon hp thne : s lng in t tch raGi tr ln nht ca l 1, tc l mt photon c hp th s lm bc x nhiu nht mt cp in t v l trng. Thng thng nh hn 1 v c tnh theo phn trm (%). Trong nhng trng hp c bit (c hiu ng nhn) mt photon c hp th c th lm pht sinh nhiu in t.b) p ng:

p ng ca linh kin tch sng quang l t s ca dng in sinh ra v cng sut quang a vo. Trong :R: p ngIe: Dng quang inPopt: cng sut quangc) nhy: nhy ca linh kin thu quang l mc cng sut quang thp nht m linh kin c th thu c v mt t s li (BER) nht nh. Theo tiu chun G956 ca CCITT, BER = 10-10 . nhy ca linh kin thu quang ph thuc loi linh kin tch sng quang v mc nhiu ca b khuch i in. Ngoi ra tc bit truyn dn cng cao th nhy ca thit b thu cng km.d) Di ng:Di ng ca linh kin thu quang l khong chnh lch gia mc cng sut cao nht v mc cng sut thp nht (tc nhy) m linh kin c th thu c trong mt gii hn t s li (BER) nht nh.e) Tp m:Tp m trong cc linh kin thu quang c th hin di dng dng in tp m. Cc ngun tp m ng k ca linh kin thu quang l: Tp m nhit:

L tp m gy ra do in tr ti ca diode thu quang cng nh tr khng vo ca b khuch i u. Tp m nhit It ph thuc nhit , bng tp m, in tr ti theo cng thc:Trong : K: hng s Boltzman; 1,38 10-38 J/0KT: nhit tuyt i, KB: b rng bng, n v HzR: in tr ti, n v OhmTp m nhit ca my thu quang cn ph thuc h s tp m ca b khuch i. Tp m lng t:

Do bin ng ngu nhin nng lng ca cc photon p vo diode thu quang. Dng tp m lng t Iq c tnh bi: Tp m dng ti:

Dng in nhiu do cc diode thu quang pht ra khi khng c nh sng chiu vo cng gy nn tp m thng ging. Tp m do dng ti c tnh bi cng thc:Trong : iD l dng ti ca diode pht quang.5.3.3. Diode thu quang PIN:Cu to ca diode thu quang PIN gm ba lp bn dn P-I-N, trong lp I (Intrinsic) l lp bn dn khng pha tp cht hoc pha vi nng rt thp. Qu trnh hp th photon tch ra cc in t v l trng xy ra trong lp I . Do lp I cng dy th hiu sut lng t cng cao nhng ng thi thi gian tri ca in t s cng chm. iu ny lm gim kh nng hot ng vi tc cao ca PIN. B dy lp P ph thuc kh nng thm nhp ca nh sng vo bn dn. nh sng c bc sng cng di th kh nng thm nhp vo bn dn cng ln. P I NLp chng phn xCch in ( SiO2 )

Vng tip xc( kim loi )Tip xc ( kim loi )nh sngCu to ca diode thu quang PIN

5.3.4. Diode thu quang APD:ng dng hiu ng nhn in t trong bn dn, ngi ta ch to APD, trong P+ v N - l hai lp bn dn c nng tp cht cao cn P - l lp c nng tp cht rt thp (thay th v tr lp I trong PIN)Di tc dng ca ngun phn cc ngc, s phn b cng in trng trong cc lp bn dn khng u nhau, in trng trong vng tip gip PN- cao nht , qu trnh nhn in t xy ra trong vng ny. Vng ny cn c gi l vng thc l.Khi c nh sng chiu vo, cc photon b hp th trong lp P - v to ra cc cp in t - l trng. L trng di chuyn v pha lp P+ ni vi cc m ca ngun; cn in t di chuyn v pha tip gip PN- , in trng cao trong vng ny s tng tc cho in t. in t va chm vo cc nguyn t ca tinh th bn dn to ra cc cp in t - l trng mi (gi l s ion ho do va chm). Cc in t th cp mi c to ra li c kh nng gy ra s ion ho do va chm. Qu trnh tip din v s lng cc ht ti in tng ln rt ln. nh sngTip xc NTip xc PN- ( InGaAs )N ( InGaAs )N ( InP )P ( InP )P ( InP )Cu to APD

Nh vy trong APD dng quang in c nhn ln M ln vi M l s in t th cp pht sinh ng vi mt in t s cp.Dng quang in do APD to ra s l: Iph = R.M.Popt Trong :R : p ng (A/W)M : h s nhnPopt : cng sut quang(W)H s nhn M thay i theo in p phn cc ngc v cng ph thuc nhit nn vic gi cho h s nhn M n nh rt kh khn.Ngoi ra, nu vng thc l cng rng th h s M cng cng ln. Nhng lc thi gian tri ca in t cng chm nn tc hot ng ca APD gim.Gi tr ca h s nhn M t 10 1000 ln. trn thc t ch chn im phn cc cho APD sao cho M = 50 200 ln v M cng ln th dng nhiu ca APD cng cng cao. c tnh k thut ca PIN v APD: nhy:APD nhy hn PIN. nhy ca APD ln hn PIN t 5 n 15 dB-30-40-50-60-70Nhy (dBm)1101001000Mb/sPINAPD

Tuy nhin nu dng PIN kt hp vi FET th nhy ca PIN - FET gn bng nhy ca APD. Di ng:Di ng ca APD rng hn PIN v c th iu chnh c bng cc thay i in p phn cc thay i h s nhn M. Dng ti:Dng ti ca APD ln hn so vi PIN. n nh: n nh ca PIN tt hn so vi APD v h s nhn M ca APD va ph thuc in p phn cc va thay i theo nhit . in p phn cc:APD cn in p phn cc ngc cao hn PIN. in p phn cc ca APD c th ln n hng trm volt trong khi in p phn cc cho PIN thng di 20 volt.u nhc im ca hai loi tch sng quang PIN v APD tri ngc nhau khng ging nh hai loi ngun quang LED v LASER. c tnh k thut ca LASER tt hn LED v nhiu mt trong khi APD ch hn PIN v nhy v tc lm vic. Cc mt hn ch ca APD l: Ch lm vic km n nh nn cn mch in phc tp. Dng nhiu ln in p phn cc cao v yu cu n nh cao Gi thnh caoDo nhng dc tnh k thut trn m c APD v PIN u tn ti song song.C th gi c cc u im ca PIN v khc phc cc nhc im ca n bng cch dng kt hp PIN vi mt Transistor trng (FET) trong mch tin khuch i. Hai linh kin kt hp ny c gi l PIN - FET, chng c s dng kh ph bin trong cc h thng thng tin quang hin nay, nhy ca PIN - FET c th so snh c vi APD.

***

phn 1. si quang Chng V.Linh kin bin i quang in

Phn 2. Cng ngh SDHGii thiu v k thut SDH :1) Cc yu cu v mng truyn dn :Song song bn cnh cc dch v v thoi, ngy nay ngi ta pht trin thm nhiu loi hnh dch v mi quan trng nh l telefax, truyn dn data, truyn dn video... trong cht lng v kh nng p ng cc yu cu v bng tn hoc cc giao tip tng thch... Lun lun ng mt vai tr quan trng hng u. tho mn cc yu cu trn, ngnh vin thng phi c cc thay i cn thit p ng kp thi. Thi gian thit lp lung truyn dn ngn dung lng tho mn theo mi yu cu. Tng cng kh nng sn sng phc v cc mng vin thng. Gi thnh thit lp mng thp, chi ph dnh cho cc khon khai thc, bo tr, bo dng... Phi gim. C kh nng quc t ho dch v.2) Khi nim v SDH ( Synchronous Digital Hierachy ): Cc h thng PDH pht trin khng p ng c cc nhu cu trn do phi c mt th h truyn dn mi trn th gii. K thut SDH ra i to ra mt cuc cch mng trong nghnh vin thng, th hin mt k thut tin tin c th p ng rng ri cc yu cu ca cc thu bao, ngi khai thc cng nh cc nh sn xut...Tho mn cc yu cu i hi t ra cho ngnh vin thng, khc phc cc nhc im ca th h PDH m chng ta ang s dng hin nay.Trong tng lai h thng ng b SDH s ngy cng pht trin mnh nh cc u im vt tri hn so vi PDH v mt im quan trng l SDH c kh nng kt hp vi PDH trong mng li hin ti, n cho php thc hin vic hin i ho dn dn theo tng giai on pht trin. S lngNm2000SDHPDH

Cc tiu chun ca SDH c bt u t nm 1985 ti M. Bt u l cc n lc to ra mt mng giao tip quang c th hot ng vi tt c cc h thng truyn dn khc nhau ca cc sn phm khc nhau (theo tiu chun chu u v chu M). Sau cc tiu chun m rng dn ln c th s l cho mng hin ti v c cho cc loi tn hiu trong tng lai cng nh cho c phng tin vn hnh v bo dng.Nm 1985 cng ty Bellcore l cng ty con ca cng ty Bell ti M xut mt k thut truyn dn mi nhm khc phc nhng nhc im ca h thng cn ng b PDH v c t tn l SONET (Synchronous Optical Network) mng quang ng b da trn nguyn l ghp ng b v tt c cc tn hiu ng b c ng b vi nhau, trong cp quang c s dng lm mi trng truyn dn. Sau cc tiu chun v giao tip thit b cng c nghin cu c th kt ni cc thit b vi nhau vi nhng tiu chun khc nhau m khng gy tr ngi. Khi ng dng k thut mi ny vo mng li vin thng hin hu, p ng cc tiu chun ngi ta phi lu n s tiu chun ho cc tn hiu bo dng, gim st, chuyn mch bo v v c vn qun l mng li ca cc loi thit b khc nhau .Nm 1988 mt tiu chun quc gia ca M c thng qua ng thi vi SONET cng gy c s ch v cng c pht trin ti Chu u bi cc nh sn xut da trn mt tiu chun ring ph hp vi cc mng PDH theo tiu chun Chu u ang hin hnh. CCITT xut cc tiu chun ca h thng SDH.SDH c xy dng to ra mt mng tiu chun quc t, n cho php tip nhn c tt c cc tn hiu PDH trc y.US1,5 45Mbit/s6CEPT2 140Mbit/s34Containerbyte-by-bytemultiplexingbyte-by-bytemultiplexingSTM-1155,520 Mbit/sSTM-NN155,520 Mbit/sPOHThng tin gim stSOHThng tin qun lPtrPointerKhi nim v SDH

Tiu chun phn cp ng b SDH xy dng theo tiu chun do ITU-T xut trn c s mt h thng cc khuyn ngh :G.707 Cc mc phn cp s ng b.G.708 Giao din ti nt mng cho phn cp s ng b.G.709 Cu trc ghp knh SDH.G.780 Cc nh ngha v thut ng trong SDH.G.781 Cu trc ca cc khuyn ngh i vi thit b ghp knh SDH.G.782 Cc loi v c tnh chung ca cc thit b ghp knh SDH.G.783 Cc dc tnh ca khi chc nng thit b ghp knh SDH.G.784 Qun l SDH.G.957 Giao din quang cho cc thit b v cc h thng lin quan n SDHG.958 Cc h thng truyn dn SDH s dng cp si quang.3) Cc c tnh ca PDH v SDH : Nhc im ca h thng PDH : Mng PDH ch yu p ng cc dch v in thoi, i vi cc dch v mi nh: mng ISDN, truyn data, dch v in thoi truyn hnh... th mng PDH kh c th p ng c. Mng PDH khng linh hot trong vic kt ni cc lung lin tc. Khi c nhu cu rt lung t mt lung c dung lng ln th phi qua cc cp trung gian h tc t cao xung thp tng ng, cng nh vic ghp lung phi tri qua y cc cp t tc thp ln tc cao. iu ny r rng l khng mm do, khng thun tin cho vic kt ni, cn phi c cc cp thit b gii php lung do khng tit kim v kh thc hin ng thi i hi nhiu thit b phc tp. Cc thng tin v bo tr khng c lin kt trn ton tuyn thng tin m ch i vi tng on truyn dn ring l. Th tc bo tr cho ton tuyn phc tp. cha c tiu chun chung cho thit b ng dy, cc nh sn xut mi ch c tiu chun c trng ring cho thit b ring ca h. C nhiu thit b ghp lung. Mt lung 2Mbit/s c th s i qua nhiu hng trc khi i n ch do vn qun l lung ti mi trm phi ng b v cht ch. Trong thc t nhiu khi sinh ra li lm trong thc t hoc u ni khng ch nh hng n lung ang kt ni m c th s gy ra mt lin lc cho nhng lung khc ang khai thc. H thng PDH thiu cc phng tin gim st, o th t xa m ch tin hnh ngay ti ch. c im ca SDH :u im :Trong PDH vic ghp knh c tin hnh ti mi cp, qu trnh ghp phi ln lt qua cc mc trung gian t 2 n 140 Mb/s. Vic truy cp trc tip n mt lung 2Mbit/s trong mt lung 140 Mb/s l khng th thc hin c. Chng hn nh khi cn ni cho cc lung 2 Mb/s th phi thc hin h knh t lung 140 Mb/s qua nhiu cp xung n 2 Mb/s ri mi dng cp nhy thc hin ni cho. Mng li ny rt cng knh v phc tp v khng linh hot ng thi chi ph vn hnh rt ln do i hi nhiu sc lao ng trong cc khu lp t chuyn cp...i vi SDH th u im ni bt hn l n gin ho mng li, linh hot trong s dng khai thc. Khc vi PDH, trong mng SDH qu trnh ghp knh ch thc hin qua mt giai on, do vic tch mt knh 2Mbit/s trong mt lung tc cao l n gin. Hn na, vic s dng phn mm trong qun l bo dng lung 2 Mbit/s lm cho vic u cho cc lung 2 Mbit/s tr nn thc s n gin v nhanh chng. Chnh v th vic vn hnh v qun l mng li n gin hn nhiu so vi cng cng vic ny mng PDH. Trong SDH tc bit ln hn 140 Mbit/s ln u tin c tiu chun ho trn phm vi ton th gii. M truyn dn ca tn hiu quang c tiu chun ho tng thch cc thit b ca cc nh sn xut. C cu trc khi : Tc bit v cu trc khung ca cp cao hn c to thnh t tc bit v cu trc khung ca lung c bn cp thp hn do vic tch ghp lung thng tin d dng. C cc knh ring cho gim st, qun l, o th hoc iu khin trong phn mng qun l. Tt c cc tn hiu PDH c tc thp hn 140 Mbit/s u c th ghp c vo cp SDH thp nht l STM - 1 c tc 155 Mbit/s.Nhc im ca h thng SDH : K thut phc tp hn do phi ghi li s tng quan v phase gia cc tn hiu lung v overhead Vic nhi byte - byte tng Jitter hn kiu bit - bit ca PDH. ng h phi cung cp t ngoi Truyn d tha v thiu mc 8 Mb/s.Ta c th tm tt s tng quan khc nhau gia k thut PDH v SDH nh sau :PDH B dao ng ni dao ng t do Ghp knh khng ng b Cu trc khung c trng Ghp lung theo nguyn l xen bit Truy nhp lung ring l sau khi gii ghp n cp tng ng.SDH B dao ng ni c ng b vi ng h ngoi Ghp knh ng b Cu trc khung ng nht Ghp lung theo nguyn l xen byte Truy nhp lung trc tp t lung c tc cao hn.

4) Phn cp h thng SDH :Ngy nay c 3 cp ca tn hiu SDH c nh ngha. Cp v mc bit c ch ra trong bng sau :

Mc SDHTc bit

STM - 1STM - 4 STM - 16155,52 Mbit/s622,08 Mbit/s 2488,32 Mbit/s

Cn ng b ( SDH ) : OLTUOLTUOLTUOLTUOLTUOLTU34 -14034 -14034 -14034 -14034 -14034 -140 8 - 34 8 - 34 8 - 34 8 - 34 8 - 34 8 - 34 2 - 8 2 - 8 2 - 8 2 - 8 2 - 8 2 - 82Mbit/s2Mbit/s2Mbit/s2Mbit/s6464Thit b u cui ng dyThit b u cui ng dyTrm xen/rTrm xen/r140 Mbit/s140 Mbit/s140 Mbit/s

ng b SDH :

II. Cu trc ghp knh :1) Cu trc ghp knh c bn :STM ( Synchronous Transport Module ) Module truyn ng bCc cp STM - n c ghp t STM - 1Cc tn hiu PDH c th c ghp vo SDH v c truyn dn thng qua h thng ny, iu ny gii thch ti sao CCITT xut ra STM - 1 v tt c cc tn hiu PDH 1,5 Mb/s n 140 Mb/s c th ghp vo tr thnh tn hiu SDH theo kin ngh G. 709.Trong :Cn : Container ( cp n ) n v cha thng tinVCn : Vitualy Container ( cp n ) Container o cp nTUn : Tributtari Unit n v lung cp nTUGn : Tributtari Unit Group Nhm n v lungAU : Administrative Unit n v qun lAUG : Administrative Unit Group Nhm n v qun lPOH : Path Overhead Thng tin gim stSOH : Section Overhead Thng tin qun l Ghp knh SDH:STM - nAUGAU4VC4C4AU3VC3TUG3TU3VC3TUG2TU2VC2C3C2TU12VC12C12TU11VC11C11139,264 Kbit/s44,73634,386 Kbit/s6,312 Kbit/s2,048 Kbit/s1,544 Kbit/sS lcon trGn / tchPOHS lcon trGn / tchPOHGn / tchSOH134331177

S ghp knh t C - 12 qua AU - 4C - 12

VC - 12POH

TU - 12PtrTU - 12PtrTU - 12PtrTUG - 3TUG - 3TUG - 3TUG - 3VC - 4 POHAU - 4 PtrAU - 4 Ptr CSOHAUGAUGVC - 12TU - 12TUG - 2VC - 4TUG - 3AU - 4AUGSTM - n

S ghp knh t C - 4 qua U - 4 :VC - 4 POHAU - 4 PtrAU - 4 PtrSOHAUGAUGVC - 4AU - 4AUGSTM - nC - 4C - 4

2) Cu trc cc khi :a) Container C:L n v nh nht trong khung truyn dn, l ni ta b tr vo cc lung tn hiu truyn dn cp thp nht nh l cc lung PDH, lung hnh, lung s hiu.C cc loi container c s dng tng thch vi cc tc truyn dn khc nhau cho hai h SONET v SDH.Cc loi container :K hiuTn hiu ng truyn Mbit/s

C - 11C - 12C - 2C - 3C - 41,5442,0486,31244,736 & 34,368139,264

D liu c ghp vo container theo nguyn l theo bit hoc byte. i vi tn hiu cn ng b cc container gm c : Cc lung d liu ( nh l tn hiu PDH ) Cc bit hoc byte nhi c nh trong khung khng mang ni dung thng tin m ch s dng tng thch tc bit ca tn hiu PDH c ghp vi tc bit container cp cao hn. Ngoi ra cn c cc byte nhi khng c nh t c s ng chnh mt cch chng xc. Khi cn thit cc byte ny c th c s dng cho cc byte d liu ( databyte ). Trong trng hp ny trong khung cn c cc bt iu khin nhi thng bo cho u thu bit cc byte ny c th l byte d liu hoc cc byte nhi thun tu.Tu theo kch thc ca lung data u vo m ta gn container C tng ng ph hp.b) container o VC ( Virtual container ) :Mt VC l s kt hp ca container C vi POH ( VC = C + POH ) to thnh mt khung hon chnh truyn n u thu. Chc nng ca POH l mang thng tin b tr, gim st v bo tr ng truyn ng thi thng bo v tr m container s truyn n. Trong VC th POH c gn vo u khung v ti u thu s c dch ra trc khi m container c gii m.VC cng c tu loi tng ng vi kch thc ca container C. Mt VC c th truyn ring r trong mt khung STM - 1 hoc l truyn xen k nhau trong mt VC ln hn ri mi c truyn n STM - 1 . Ta c th phn bit hai cp VC tu theo container C nh sau : Tt c container khi c ghp vo container ln hn th c gi l container cp thp LOC ( Low Order Container ), tng ng vi container o cp thp LOVC ( Low Order Virtual Container ), l VC - 11, VC - 12, VC - 2 v VC - 3. Tt c cc container c truyn trc tip trong khung STM - 1 th c gi l container cp cao HOC ( Hight Order Container ) tng ng ta c container o cp cao HOVC (Hight Order Virtual Containe) l VC - 4 v trong trng hp VC - 3 c truyn trc tip vo khung STM - 1 th VC - 3 cng c coi l mt HOVC. Cu trc cc VC : VC - 11 : gm 25 byte d liu cng vi mt byte POH c sp xp trn 3 hng dc 9 byte. c s dng truyn dn tn hiu 1,5 Mb/s theo tiu chun chu M. VC - 12 : gm 34 byte d liu cng vi mt byte POH c s dng tng thch vi lung 2 Mb/s theo tiu chun chu u v c sp xp theo 4 hng dc 9 byte. C 3 loi tn hiu 2 Mb/s c th b tr trong VC - 12: Tn hiu 2 Mb/s khng ng b : cho php mang tn hiu 2 Mb/s nhng khng c kh nng gim st trn tng bit. Tn hiu 2 Mb/s ng b bit ( bit synchronous ) : Cho php gim st trn tng bit nhng khng nhn dng c khung. Tn hiu 2 Mb/s ng b byte : cho php gim st v nhn dng tt c cc bit d liu.9394: POHCu trc VC - 12Cu trc VC - 11

VC - 2 : gm 160 byte d liu vi mt byte POH dng tng thch vi lung 6,312 Mb/s theo tiu chun ca M. Cu trc gm 12 hng dc 9 byte.

C - 2129 : POH

VC - 1x/VC - 12 : C th c truyn i theo phng thc xen byte vo trong VC - 3 hoc VC - 4. VC - 1x/VC - 2 : c truyn i theo tng a khung 500 ms gm 4 khung 125 ms v c gn vo trong mt TU, cc con tr gn vo cc VC - 1x/VC - 2 theo tng 125 ms mt. VC - 3 : Gm 750 byte d liu cng vi 9 byte POH sp xp trn mt hng dc trong mi byte POH thc hin mt chc nng ring ca mnh. Cu trc gm 85 hng dc 9 byte. C - 3859VC - 3 POH

c) n v lung TU ( Tribuari Unit ) :Gm VC cng vi pointer : TU = VC + PtrTrc khi chuyn n STM - 1 c pht i cc cp VC cp thp s c ghp vo mt VC cp cao hn. to ra cc phase ca cc VC ngi ta dngPtr (Pointer) ghp theo vo VC ti mt v tr c nh trong VC v thng bo s bt u ca VC . Tng ng vi VC, TU cng c nhiu bc t 1 n 3.Vic truyn dn cc byte pointer s sy ra ln lt. C mt khung 125 ms s c mt byte pointer. Byte pointer ghp theo vo VC ti mt v tr c nh trong khung cp cao hn ( VC - 3 hoc VC - 4 ). Nh vy tng cng s c 3 byte pointer cho khung 125 ms cn byte th 4 ca a khung 500 ms cng mang mt byte pointer nhng byte ny cha c quy nh r chc nng hin nay ang c dng d phng. Cu trc ca cc TU : Cc TU - 11, TU - 12, TU - 2 u c cu to bi cc VC tng ng cng thm mt byte pointer :TU - 11 = VC - 11 + PtrTU - 12 = VC - 12 + PtrTU - 2 = VC - 2 +Ptr S hnh thnh cu trc TU - 11 v TU - 12 :

+ pointer + pointer93VC - 1194VC - 1294TU - 1293TU - 11

S hnh thnh cu trc TU - 2 t VC - 2 :

C - 2129TU - 2VC - 2C - 2129 : POH + pointer

TU - 3 :TU - 3 = VC - 3 + Ptr3xVC - 3 c th ghp vo VC - 4 theo nguyn tc xen tng byte sau c pht i trong khung AU - 4. trong qu trnh truyn dn c hai cp container c ghp vo. Pointer AU - 4 trong SOH ch th VC - 4 trong khung STM - 1.3 pointer TU - 3 (mi pointer 1 byte) c gn vo trong VC - 4 thng bo v tr ca VC - 3 trong khung VC - 4.S hnh thnh ca VC - 3 c ch ra di hnh v sau :

C - 3VC - 3 POHVC - 3859TU - 3 PTRTU - 3859+ 3 byte pointer

d) Nhm n v lung TUG (Tributary Unit Group) :TUG l nhm cc TU ghp li theo phng thc xen byte. c hai loi TUG l TUG - 2 v TUG - 3. Cu trc cc TUG : TUG - 2:Mt TUG - 2 c th hnh thnh bi :TUG - 2 = 3 x TU - 12TUG - 2 = 4 x TU - 11TUG - 2 = 1 x TU - 2Do vy TUG - 2 c kch thc l 108 byte vi tc bt l 6912 Kb/s. TUG - 2 hnh thnh t TU - 11 :

91293TU - 11TUG - 2

TUG - 2 hnh thnh t TU -12 :99412TU - 12TUG - 2

TUG - 2 hnh thnh t cc TU - 2 :

912TU - 2TUG - 29 : Pointer

Nhn xt : Cc byte u tin ca hng u tin tng ng vi kiu cu trcl cc byte pointer cc byte sau l cc byte data. TU - 2 c kch thc tng ng vi mt TUG - 2. C hai cch b tr VC - 2 vo trong TUG - 2 : Cht ( locked mode ) Ni ( Floating mode )Kiu Floating cho php cc VC c gn vo khung TUG tai mt v tr no v s dng Pointer lin kt vi mi VC ch th im bt u ca VC trong TUG. V tr con tr s c gn c nh trong TUG tng ng bt k v tr ca VC.Kiu Locked th ngc li, VC c gn vo trong TUG ti mt v tr c nh do khng cn s dng pointer nh kiu Floating. TUG - 3 :Mt TUG - 3 c th hnh thnh bi :TUG - 3 = 1 x TU - 3TUG - 3 = 7 x TUG - 2 Kch thc TUG - 3 gm 774 byte vi tc bit l 49536 Kb/s. Nu TUG -3 cha mt TU- 3 th ct u tin cha 3 byte pointer TU-3 v 6 byte cn li l byte nhi c nh ( Justification ).TU - 3 PTRTUG - 39TU - 3 PTRTU - 398586: byte nhi c nh

Nu TUG - 3 c cu thnh t 7 x TUG - 2 th nguyn tc ghp cng l ghp tng byte, ct u tin cng cha 3 byte pointer v 6 byte nhi c nh. Tuy nhin trong trng hp ny pointer trong TUG - 3 khng c chc nng nh v a ch trm n ca cc lung tn hiu m lc ny cc byte pointer ring l nh v a ch ca cc VC - x1 hoc VC - 2 s l cc pointer nm trong TUG - 2. Cc byte ny c sp xp trong hng u tin ca ct TUG tng ng. Cc TUG - 2 c b tr theo kiu c nh vo trong cc TUG - 3, 3 byte trong ct u tin ca TUG - 3 ny s khng mang ngha no m n ch mang nhng mu bit c nh gi l cc ch th pointer khng c gi tr NPI ( Null Pointer Indication ).Ngi ta s dng cc byte ny phn bit trng hp TUG - 3 c cu thnh t TU - 3 hay t cc TUG - 2.

8692112994NPITUG - 3TUG - 2TU - 12#1#7#2#1#2#3 : byte nhi c nh : Pointer

3 x TUG - 3 c ghp vo VC - 4 theo trnh t ct th nht ca VC - 4 cha VC - 4 POH. Ct th hai v ct th ba cha cc byte nhi c nh.e) Cc n v qun l AU (Adminis trative Unit) :Cc AU bao gm cc container ca cp cao cng vi pointer.AU = HOVC + pointerTrong trng hp ny cc gi tr ca pointer AU - Ptr c gn trong khung STM - 1 ghi nhn mi tng quan Phase gia khung truyn dn v cc VC tng ng.Cc byte AU - Ptr c gn khng c nh vo trong 9 byte u tin ca hng th t trong khung STM - 1 c chc nng nh du cc AU. Tuy nhin cn phi lu rng cc AU - Ptr ca AU - 3 v AU - 4 l khc nhau.Cc AU c th cu thnh t :AU - 3 = 1 x VC - 3AU - 4 = 1 x VC - 4 AU - 3 :c to thnh t 1 x VC - 3: mt VC - 3 c thit k truyn dn tn hiu 45 Mb/s hoc 34 Mb/s PDH.Cu trc AU - 3 gm 9 x 87 + 3 byte. Ngoi ra v dung lng truyn dn ca AU - 3 (87 ct) ln hn dung lng truyn dn ca VC - 3 (85 ct) nn ngi ta b tr cc byte nhi c nh vo trong ct tha. POHC - 3VC - 385POHC - 3AU - 3AU - 3Pointer873

3 x AU - 3 c ghp xen byte trong khung STM - 1. Mi AU - 3 gm 3 byte pointer c chc nng nh v tr cho VC - 3 bng cch ch th byte u tin ca POH trong VC -3 tng ng. AU - 4 :c to thnh t 1 x VC - 4: c cu trc gm 9 x 261 + 9 byte pointer tng ng vi khung STM - 1 c cu thnh t container C - 4 gm 9 x 260 byte + 1ct VC - 4 POH ( 9 byte ).Cu trc AU - 4 t VC - 4 :

POH2609VC - 4

POH2619AU - 49AU - 4Pointer

f) Nhm n v qun l AUG (Administrative Unit Group) :Nhiu AU c ghp vi nhau theo phng thc xen byte to thnh mt AUG. Cu trc AUG gm 9 x 261 + 9 byte, ging nh cu trc khung STM - 1 khi cha c SOH.g) Cu trc khung STM -1 :STM - 1 = AUG + SOH Khung STM - 1 gm 9 x 270 byte v c truyn theo nguyn tc t tri sang phi, t trn xung di. Trong SOH l thng tin qun l c dng cho h thng SDH. Thng tin qun l ny c b tr trong v tr 9 ct u tin tnh t tri qua phi bao gm : Thng tin qun l trm lp RSOH ( Repeat Section Over Head ) gm:3 hng x 9 byte ( 3 hng pha trn ) Cc byte hng th 4 dng cho pointer gm 1 hng x 9 byte. Thng tin qun l ghp knh MSOH ( multiplex Section Over Head ) gm :5 hng x 9 byte ( 5 hng di ) Cn li 9 x 261 byte dng ti tin.Cu trc STM - 1:SOHSOHAU - 4PointerPlayload26199Thng tin qun l trm lpThng tin qun l ghp knh

Khung STM - 1 c truyn dn 8000 ln/s l tc bit s dng cho tn hiu PCM. Mi khung STM - 1 chim 125 ms do c tc bit l :8000khung x 9hng/khung x 270byte/hng x 8bit/byte = 155 Mb/s.Vic b tr VC - 4 vo STM - 1 cng tng t nh b tr VC - 12 vo khung TUG - 2. VC - 4 cho php b tr khng c nh vo khung STM - 1, v tr ca n c xc nh bi AU - 4 pointer gm cc byte H1, H2, H3. Bnh thng VC - 4 ch cn 2 byte xc nh v tr l byte th nht ca H1 v byte th nht ca H2. Cn byte H3 l byte nhi ch dng trong trng hp cn thit.S b tr 3 x AU - 3 trong STM - 1 phn pointer :C - 3J1B3C2G1F2H4Z3Z4Z5SOHAU - 3Pointer

SOH2702619315VC - 3 POHVC - 3STM -185

S b tr 3 x AU - 3 vo STM - 1 phn d liu:2702619SOHAU - 3Pointer

SOH315VC - 3STM -1J1B3C2G1F2H4Z3Z4Z5FIXED

STUFFFIXED

STUFF22930575885

h) C trc khung STM - N (N = 4; 16): Cu trc STM - N ging nh cu trc khung STM - 1 ch khc l tc truyn c trong khong 125 ms l N x 9 x 270 byte. STM - N (vi N = 4 hoc N = 16) l mc truyn dn cp cao ca SDH, t c bng cch ghp STM -1 theo phng thc ghp tng byte to thnh cc mc sau : STM - 4 c tc truyn dn 155,52 x 4 = 622,08 Mb/s STM - 16 c tc truyn dn l 16 x 155,52 = 2,488 Gb/sTo khung STM - 16 t STM - 1 :A1B1C1D1P1A2B216..........STM - 16P2P1A2A1STM - 1 #1STM - 1 #16MUX16 : 1

Ngoi ra c c STM - 16 ta cng c th ghp 4 x STM - 4 vi nhau theo phng thc ghp tng 4 byte mt.To khung STM - 16 t STM - 4 :MUX

4 : 1MUX4:1MUX4:1MUX4:1MUX4:1A1A2D1....4E1E2H1....4I1I2L1....4M1M2P1....4A2A1STM - 1 # 1D2D1E2E1H2H1I2I1L2L1M2M1P2P1STM - 1 # 4STM - 1 # 1STM - 1 # 1STM - 1 # 1STM - 1 # 4STM - 1 # 4STM - 1 # 4A1........D1E1H1A2P1....1644STM - 16

ln v tc bit ca cc loi container :Container ln (byte)Tc (Kbit/s)C - 11251600C - 12 342176 C - 21066784C - 375648384C - 42340149760

Virtual container ln (byte)Tc (Kbit/s)VC - 11161664VC - 12352240VC - 21076848VC - 376548960VC - 42349150336

Tributary unit ln (byte)Tc (Kbit/s)TU - 11 271728 TU -12362304 TU - 21086912TU - 376849152

Tributary unit group ln (byte)Tc (Kbit/s)TUG - 21086912TUG - 3774495236

Aministrative unit ln (byte)Tc (Kbit/s)AU - 378650304AU - 42358150912

Aministrative unit group ln (byte)tc (Kbit/s)AUG2358150912

S tng kt qu trnh to khung STM - 1

DS 6TUG-2eTU-2 PTRTUG-12aTU-12 PTRTUG-12bTU-12 PTRTUG-12cTU-12 PTRC - 12V5TUG - 2

TUG-12a

TUG-12b

TUG-12c3 x TU-12 PTRTU-2C - 2V6TUG-2gTUG-2aTUG-2cTUG-2bTUG-2dTUG-2fZ3H4Z4Z5J1B3C2G1F2H1H2H3TU - 3C - 37 x 3 TU-12 PTRTUG - 37 x TUG-2

FIXED

STUFFTUG-3aTUG-3bTUG-3cTUG-3dTUG-3eTUG-3fTUG-3gNPIJ1B3C2G1F2Z3H4Z4Z5

FIXED

STUFF

FIXED

STUFFTUG-3aTUG-3bTUG-3cC - 4AU-4 PTRSOHSOHSTM - 1J1DS 2DS 1,5DS 45DS 34DS 14012128686261270VC - 4