Thong Tin Quang

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HC VIN CNG NGH BU CHNH VIN THNG ******BO CO CHUYN THNG TIN QUANG

TI: Ghp Knh Quang Phn Chia Theo Thi Gian OTDMGV hng dn: TS Hong Vn V SV thc hin : inh Huy Mi L Trng Nam Trn Vn Binh Nhm 27 - Lp: H10.VT1 H Ni 03,2012

MC LC CHNG I. KHI QUT V H THNG THNG TIN QUANG CHNG II. CP SI QUANG CHNG III. NGUN PHT QUANG CHNG IV. NGUN THU QUANG CHNG V. GHP KNH QUANG PHN CHIA THEO THI GIAN KT LUN

CHNG I. KHI QUT V H THNG THNG TIN QUANG

1.1. Tng quan v h thng thng tin quangCng vi s pht trin ca x hi th nhu cu ca con ngi i vi thng tin ngy cng cao. p ng c nhu cu i hi mng vin thng phi c dung lng ln, tc cao,bng thng rng Mt khc my nm gn y do dch v thng tin pht trin nhanh chng, thch ng khng ngng vi s pht trin ca dung lng truyn dn thng tin, th h thngthng tin quang ra i khng nh c chnh mnh. Vi vic pht minh ra laser lm ngun pht quang m ra mt thi k mi c ngha rt to ln vo nm 1960. Bng khuyn ngh ca Kao v Jockham 1966 v vic ch to ra si quang c tn tht thp. Bn nm sau, Kapron ch to ra c si quang trong sut c suy hao ng dn khong 20dB/km

CHNG I. KHI QUT V H THNG THNG TIN QUANG

1.2. S khi ca h thng thng tin quang

Thit b u cui pht quang Tn hiu vo

Trm lp Si quang

Thit b u cui thu quang Tn hiu ra

Hnh 1.1. S khi ca h thng thng tin quang

CHNG I. KHI QUT V H THNG THNG TIN QUANG 1.2.1. Chc nng cc khi1. Khi dn knh /tch knh (MUX/DEMUX) nhm ghp cc lung tn hiu c tc thp (2Mbit/s, 4Mbit/s, 140Mbit/s, 158Mbit/s.) thnh lung tn hiu c tc cao hn v ngc li. 2. Khi pht c mch iu khin, ngun quang thc hin vic iu bin cc tn hiu in thnh cc tn hiu quang truyn thng qua cp si quang. 3. Cp si quang c nhim v truyn dn tn hiu nh sng. 4. Trm lp (Reqeater) hoc b khuch i quang i vi tuyn c c ly di. 5. Khi thu quang gm c photodiode chuyn tn hiu quang thnh tn hiu in, khi khuych i v khi phc tn hiu.

1.2.2. Cc tham s c bn ca h thng thng tin quangC ly tuyn truyn dn L (km), tc bit B (Mbit/s) T s tn trn tap in S/N (SRN) hay quang OSNR T s li bit BER rng bng tn in BW (MHz) hay quang BWo (MHz) i vi si quang: h s suy gim ring (dB/km), m s NA, tch c ly v tc bit BxL (Mbit/skm) i vi my pht quang: cng sut pht ghp vo si Pt (mW hay dBm), bc sng lm vic, rng ph (nm), thi gian tng trng pht (ns) i vi my thu quang: nhy thu Pr min (mW hay dBm)

CHNG II. CP SI QUANG2.1. Cu to v phn loi cp si quang2.1.1. Cu to cp si quang Si quang c cu to hnh tr, gm hai lp chnh t cht in mi ng tm nhau. Lp trong gi l lp li (core), lp ngoi l lp v (clading). Ngoi ra cn c lp bo v v v bc bn ngoi 2.1.2. Phn loi si quang: C nhiu cch phn loi si quang nh phn loi theo vt liu ch to, phn loi theo phn b chit sut, phn loi theo mode lan truyn. Phn loi theo vt liu ch to gm c si quang thch anh, si quang lm bng thy tinh hn hp v si quang lm bng cht do. Phn loi theo phn b chit sut c si quang chit sut nhy bc SI (Step Index), si quang chit sut bin i Gradien GI (Gradex Index).

CHNG II. CP SI QUANG2.2 C s l thuyt truyn dn nh sng s 2.2.1 C s l thuytVic truyn dn sng nh sng trong si quang da trn hin tng khc x trong li si v phn x ton phn nh sng trn b mt phn chia gia lp li v lp v ca si quang. gii thch hin tng trn ta xt s phn x v khc x sng nh sng trn b mt phn chia hai mi trng in mi c chit sut khc nhau l n1>n2 khi sng nh sng truyn t mi trng mt sang mi trng hai. cho n gin ta coi mt phn chia hai mi trng l phng rng v hn.

Hnh 2.1. Hin tng phn x v khc x nh sng

Hnh 2.2 Truyn nh sng trong si quang

CHNG II. CP SI QUANG

2.2 C s l thuyt truyn dn nh sng2.2.2. Khu iu ch s

Hnh 2.3. Khu iu ch s Trn hnh v ta thy, tia ti 1 khi t khng kh vo li si lp vi trc si mt gc l , ng vi gc ti nh hn gc ti hn khi n mt phn chia s khc x ra vng v v b tiu hao, khng truyn dc theo si. Tia ti 2 khi i vo li si lp vi trc si mt gc ng vi gc ti hn nn n mt gii hn s truyn dc theo mt ny

CHNG II. CP SI QUANG2.2 C s l thuyt truyn dn nh sng 2.2.3. L thuyt mode sng L thuyt mode sng da trn vic tm nghim phng trnh Mac-xoen hay phng trnh sng thun nht trong v iu kin b trn mt phn chia ca cc lp si quang. Cc phng trnh c dng nh sau:

CHNG II. CP SI QUANG 2.3. Cc c trng suy hao ca si quang2.3.1 Cc c trng suy hao ca si quang Sng nh sng khi truyn dc theo si quang b suy gim cng theo chiu di si. l c tnh vt l vn c ca si quang gi l s suy hao. Nu xt trn 1km chiu di si quang, Pv l cng sut ti cui si quang th lng suy hao ca nh sng trn on si tnh theo n v dB c dng l:

CHNG II. CP SI QUANG2.3.2. Ph suy hao V cc suy hao ca si quang ph thuc vo bc sng lm vic nn suy hao tng hp ca si c biu th l hm ca bc sng gi l ph suy hao.

Hnh 2.4. Ph suy hao ca si quang

CHNG II. CP SI QUANG2.3.3. c tnh tn sc ca si quangS tn sc ca si quang: khi nh sng truyn trong si quang ngoi b suy hao cn b m rng rng xung quanh, hin tng trn gi l s tn sc nh sng trong si quang. Hnh 2.6 di m t s tn sc ca si quang

Hnh 2.5. th biu din c tnh tn sc ca si quang

CHNG III. NGUN PHT QUANG

3.1. Nguyn l bc x nh sng ca cht bn dn 3.1.1. Nguyn l bc x nh sng Ngun pht quang dng trong thng tin si quang thch hp l cc linh kin quang bn dn gm diode bc x nh sng LED v diode laser LD. Cc ngun pht quang bn dn dng trong thng tin quang nh LED v diode laser LD da trn nguyn l bc x nh sng do s ti hp gia in t v l trng xy ra trong vng chuyn tip P-N ca cht bn dn c t di in p thun 3.1.2. Cc cht bn dn dng ch to ngun pht quang Khng phi mi cht bn dn u c th bc x ra nh sng, m ch c mt s cht bn dn c cc tnh cht nht nh mi bc x ra nh sng. Qu trnh ti hp gia in t v l trng tun theo nh lut bo ton nng lng v bo ton xung lng.

Hnh 3.1.Di cm nng lng trc tip

Hnh 3.2. Di cm nng lng gin tip

CHNG III. NGUN PHT QUANG3.2 Phn loi ngun pht quangNgun pht quang l linh kin bin i tn hiu in thnh tn hiu nh sng c cng sut t l vi dng in chy qua n.C hai loi ngun quang c s dng trong thng tin quang.

3.3. Diode pht quang (LED)Hin nay, ngi ta s dng ch yu hai loi LED trong cc h thng thng tin cp si quang l SLED pht x mt (surface light emitting diode) v ELED pht x cnh (Edge Light Emitting Diode). C hai loi ny u dng cu trc d th kp giam ht a s v nh sng vo mt lp hot tnh.

Bng 3.1. So snh ELED v SLED

CHNG III. NGUN PHT QUANG3.3.1. LED pht x mtDiode d th kp c hnh thnh trn nn ca mt cht bn dn loi N, pha trn ca diode c khot thm mt l trn.

Hnh 3.3. Cu to ca LED pht x mt

CHNG III. NGUN PHT QUANG3.3.2. LED pht x cnh gim mt mt do hp th trong lp hot tnh v lm cho chm tia nh hng hn, ta c th ly nh sng ra t cnh ca led. Loi led ny c gi l led pht x cnh (ELED). Cu trc nh hnh v.

Hnh 3.4. Cu trc LED pht x cnh

CHNG III. NGUN PHT QUANG3.3.3. Cc c trng k thut ca LEDc tnh ph: s pht x nh sng do dch chuyn ngu nhin ca cc in t qua di cm gi l pht x t pht

3.4. LASER (Light Amplification by the Stimulated Emission of Radiation)Thng thng diode laser c s dng trong cc tuyn c li di tc cao (cc tuyn ny dng si quang n mode SM). Ni chung yu cu t ra i vi diode laser trong thng tin quang l gim thiu rng vch ph v hot ng ch n mode v yu cu quan trng l tng hiu sut th cn phi gim dng in ngng.

3.4.1. Cu trc v nguyn tc lm vicKhng ging nh LED (nh sng pht ra l do bc x t pht), nh sng LASER c to ra bng bc x kch thch. Bc x kch thch xy ra khi mt photon s cp (hv)1 va p vo mt nguyn t c kch thch v thay v hp thu photon ny li kch thch cho mt in t dch chuyn xung qua di cm v sinh ra mt photon mi gi l photon th cp (hv)2

VC

photon

VC

VB

( hv) 1VB

O

( a)

( hv) 1 ( hv) 2

Hnh 3.5 thch

O

( b)b) bc x kch

a) Bc x t pht

CHNG III. NGUN PHT QUANG3.4.2. Mt s loi laser c s dng 3.4.2.1. Laser a mode Fabry_Pero (F_P) 3.4.2.2. LASER n mode a. Laser DFB (Distribued Feed Back) laser ny c s phn hi quang c thc hin khng phi 2 gng m tin hnh trn c chiu di vng hot tnh ca hp cng hng, gi l s phn hi phn b. to ra s phn hi phn b, ngi ta to ra cc b phn x cch t c tnh chn b. Laser n mode cng hng lin kt Mt phng php n gin ch to laser c th iu chnh c bc sng nh sng ra l s dng b chn lc bc sng ngoi s chn lc mt mode sng Fabry- perot duy nht trong s cc mode Fabry- Perot cng tn ti ca laser bng cch iu chnh cc tham s ca b lc

Hnh 3.6. Cu trc ca b lc ngoi

CHNG III. NGUN PHT QUANG3.4.3. Cc c trng ca laser a) c tnh ph ca diode laser Trong trong diode laser ch mt s sng nh sng c bc sng nht nh mi c th lan truyn c trong bung cng hng. iu kin truyn lan nh sng l sng phn x v sng ti phi ng pha vi nhauP nh sng ra

1

0.5

0(a) rng vch ph (b) Hnh 3.7. th ph bc x ca LASER

1

0.5 rng vch ph

nh sng ra

(c)

(d)

CHNG IV. NGUN THU QUANG4.1. Khi qut v ngun thu quangNgun quang s dng trong thng tin si quang l diode bn dn quang gi l photo diode. C hai loi photo diode c s dng ph bin l photo diode PIN v v photo diode thc APD. Photo diode c nhim v thu v bin i tn hiu quang t my pht truyn dc si quang v dng tn hiu in.

4.2. Photo diode P-N 4.2.1. Cu to v nguyn tc tch sng quang ca photo diode P-NPhoto diode P-N c cu to t mt chuyn tip P-N t bn dn nh Si v c cp mt thin p ngc (hnh 4.1) Do s khuch tn ca in t v l trng nn gia hai lp P-N ca bn dn hnh thnh mt lp chuyn tip P- N c rt t in tch t do c gi l lp ngho vi rng l l v c mt in trng tip xc Etx. trng thi cn bng, in trng ny ngn cn s khuch tn tip theo ca cc in t v l trng qua lp ngho

CHNG IV. NGUN THU QUANG4.2.3. Cc c tnh k thut ca photo diode P- N a. nhy R nhy ca photo diode c biu din qua hiu sut lng t ca n theo biu thc: R=

e = hv 1,24

y: e=1,6.10-19C l in tch ca in t b. Hiu sut lng t Hnh 4.1 biu din cc ng cong nhy R v hiu sut lng t phu thuc vo bc sng ca cc cht bn dn dung ch to photo diode nh Si, Ge v InGaAs. T th ta thy mi photo diode ch lm vic trong vng. Bc snggi l bc sng ct. Ti vng nhy ca photo diode.Hnh 4.1. ng cong nhy R v hiu sut lng t

CHNG IV. NGUN THU QUANG4.2.3. Cc c tnh k thut ca photo diode P- N4.3. Photo diode PIN 4.3.1. Cu to v nguyn l lm vicPhoto