lý thuyết quang- full

7/30/2019 L thuyt Quang- full

1/19

Phn 1.

Cu 1: nu cc tham s ca h thng WDM.

- Slng knh bc sng N- Khong cch gia cc knh bc sng DI- Bng thng s dng ca h thng N x DI- Tc truyn tin trn mi knh bc sng B- Dung lng ca h thng N x B- Dung lng truyn dn ca h thng N x B x L- Hiu sut s dng knh bc sng B/DI

-Cu 2: cc di bng tn hot ng ca h thng WDM.

- Bng O: 1260nm 1360nm- Bng E: 1360nm 1460nm- Bng S: 1460nm 1530nm- Bng C: 1530nm 1565nm- Bng L: 1565nm 1625nm- Bng U: 1625nm 1675nm

Cu 3: Vs khi v trnh by nguyn l hot ng ca h thng thng tin ghp knhtheo bc sng WDM n hng/ song hng.

Phn 2

Cu 1: Nguyn l c bn ca K quang? Cc u im ca bK quang so vi cc trmlp quang-in

Bc sng

#1 #2 # k # N-1 #N

Cng

sutqu

ang

Hnh 1.3. M t trc quan cc tham s ca h thng WDM

Bng thng s dng ca h thng

~ B


2/19

Nguyn l

- BK quang K nh sng ti thng qua pht x kch thch nh laser, nhng bK quang ko c hi tip quang

- BK quang s dng NL bm quang hoc in thc hin o mt . Hintng o mt l:+ Khi cha c dng bm, BK mc gi bn, ko c ht

+ khi c dng bm, bK trng thi kch thch, nu c AS tc ng vo th ns pht ra photon AS+ H sK quang ph thuc vo tn s ca tn hiu quang ti v cng AS

bm trong bK. ph thuc nhiu hay t cn ty thuc vo mi trng K

So snh

- K trc tip tn hiu quang- Ko ph thuc vo Rb = 1/Tbv phng thc iu ch tn hiu vo nn vic nng

cp h thng ddng hn

- K ng thi dc nhiu knh bc sng khc nhau trong h thng quang.Cu 2: Cho bit cc tham sc bn ca bK quang

- H skhuch iG = Pout / Pin

G (dB) = 10 log (Pout / Pin)

Pin v Pout l cng sut u vo v u ra ca b khuch i quang [mW].

- rng bng tn K+ l p ng tn s quang ca bK quang G(f) khi o h s khuch i G cacc tn hiu quang cc tn s khc nhau+ B0c xc nh bi im -3dB so vi h s khuch i nh ca b khuch i

- Cng sut ra bo ha+ h sK G gim khi CS tn hiu tng (bo ha G)


3/19

+ CS u ra ti im G gim 3dB c gi l CS ra bo ha

Hnh 2 biu din sthay i ca h sK G theo chit sut quang u ra Pout. CSu ra ti im G gim 3dB c gi l CS bo ha Psat,out, cho bit CS u raln nht m bK quang c th hot ng c. Nu 1 bK quang c th ch sK cao s c Psat,out cao v s nghch o nng cao c th dc duy tr trong1 di CS vo, ra rng

- H s nhiu+ Ngun nhiu trong bK quang do s pht x t pht l cc s kin ngunhin, pha ca cc photon pht x tpht cng ngu nhin. Nu pha ny c hnggn vi hng truyn ca cc photon t/h gy nn sdao ng vpha v bin + Kh , NL do s pht x t pht to ra cng sc K khi chng truyn quan bK vpha u ra. Ti , Pout bao gm ct/h c K v CS nhiu pht x t

pht c K (ASE)Pout = GPin + PASE

+ H s nhiu (NF)NF = SNRin/SNRout

NF(dB) = 10log(SNRin/SNRout)

NFmin = 3dB

Cu 3: Vs cu trc ca bK EDFA theo 3 chbm, nu chc nng cckhi v nguyn tc hot ngHnh 1: BK EDFA chbm thun


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Hnh 2: chbm 2 chiu

Chc nng cc khi:- Si quang pha ion t him Eribium(EDF): l ni xy ra qu trnh K(vng tch

cc) ca EDFA. Trong vng li trung tm ca EDF c pha trn ion Er3+ lni c cng sng bm v tn hiu cao nht. Vic pha cc ion Er3+ trong vngny nhm to ra s chng ln ca nng lng bm v tn hiu vi cc ion erbiumln nht dn n khnng khuch i tt hn. Lp bc c chit sut thp hn baoquanh vng li. Lp v bo v bao quanh si quang to bn knh si quang tng l

250 m. Lp v ny c chit sut ln hn so vi lp bc dng loi b bt knh sng khng mong mun no lan truyn trong si quang

- Laser bm: Cung cp nng lng nh sng to ra trngthi nghch o nng trong vng tch cc. Laser bm pht ra nh sng c bc sng 980nm hoc1480nm

- WDM Couupler: Ghp tn hiu quang cn khuch i v nh sng t laser bmvo trong si quang. Loi coupler c s dng l WDM coupler cho php ghp

cc tn hiu c bc sng 980/1550nm hoc 1480/1550nm.B cch ly quang:Ngn khng cho tn hiu quang phn xngc vpha u pht

hoc cc tn hiu quang trn ng truyn phn xngc v EDFA.Nguyn l hot ng:

- Da trn hin tng phn x kch thch- Khi s dng ngun bm laser 980nm, cc ion Er3+vng nn s hp thlng t

cc photon v chuyn ln trng thi cao hn vng bm- Ti vng bm, cc ion Er3+ phn r ko bc x rt nhanh (khong 1s) v chuyn

xung vng gi bn- Cc ion Er3+ trong vng gi bn lun c khuynh hng chuyn xung vng NL

thp- Sau khong thi gian sng (~10ms) nu ko c kch thch bi cc photon c NL

thch hp, cc ion Er3+ s chuyn sang trng thi NL thp hn vng nn v phtx ra photon

- Khi cho tn hiu AS i vo EDFA, s xy ra ng thi 2 hin tng


5/19

+ Cc photon tn hiu b hp th bi cc ion Er3+vng gi bn. T/h AS b suyhao

+ Cc photon tn hiu kch thch cc ion Er3+vng gi bn. hin tng pht xxy ra khi cc ion Er3+ b kch thch s chuyn sang trng thi NL t mc cao

vng gi bn xung mc thp vng pht x, pht x ra photon mi c cnghng truyn, phn cc, pha, bc sng. T/h AS c K

Cu 4: Trnh by cu to v gii thch nguyn l hot ng ca bK Raman/SOA

1. SOA

Cu trc bK quang bn dn SOA

- SOA c iu khin bi dng in- Vng tch cc: K AS u vo nhqu trnh pht x kch thch- t/h u ra bao gm c t/h truyn dn v nhiu pht x tpht c K (ASE) do

qu trnh K gy ra- BK SOA c cu trc tng t laser bn dn nn cn dc gi l bK laser bn

dn- Dng bm bn ngoi c cung cp bi dng in phn cc

Nguyn l hot ng

- Da trn c ch pht x kch thch ca lp tip gip p-n-

Khi c dng in k, cc in ttrng thi NL E1 c kch thch bi dng ink s nhy ln mc NL cao hn E2 v to nn so nng


6/19

-- Khi c AS ti kch thch cc in tang trng thi kch thch E2, cc in t

ny s hp th NL AS trv trng thi E1 n s gii phng ra 1 NL sng in tdi dng AS c NL ln hn E2-E1

- Qu trnh kch thch cc in tang trng thi kch thch E2 b tip tc din ra.Khi t/hAS c K. Tuy nhin cng c 1 sin ttrng thi E1 v pht x racc photon. Qu trnh pht x ny l qu trnh pht x t pht

- S khc nhau gia SOA v laser bn dn l SOA hot ng di mc ngng daong.

2. Raman(RA)Cu trc:

- Coupler: dng ghp t/h vo vi bc sng bm- Isolator: Ngn chn tn hiu phn x2 u bK. ng thi gip loi b nhiu

ASE theo hng ngc vpha u vo c th gy ra nh hng n t/h vo- Laser bm: c tn sPdng cung cp NL cho cc nguyn t ca si quang

chuyn ln trng thi kch thch, gip to ra s nghch o nng laser pht raAS c bc sng thch hp ty thuc vo vng bc sng cn K


7/19

- Si quang: l ni xy ra qu trnh K. Trong K raman thng s dng si SMF,DSF

Nguyn l hot ng

- Lung AS bm c tn sP v AS t/h tn sScng c a vo si quangthng qua 1 coupler quang

- NL sc truyn tAS bm sang AS t/h thng qua hiu ng SRS trong siquang. C th l+ AS bm t 1 laser bm c bc sng thp hn bc sng ca t/h cung cp Nlcho cc nguyn t ca si quang. Khi cc nguyn t ca si quang s hp th

NL AS bm v chuyn ln mc NL cao hn(mc kch thch) to so nng + Khi c t/h AS ti, n s kch thch cc nguyn tang mc NL cao chuynsang trng thi NL thp hn v gii phng ra 1 NL di dng photon AS c cng

bc sng v cng pha vi t/h n. Do t/h c K

Phn 3: Truyn ti Ip/quang

Cu 1: Nu cc phng thc tch hp IP/quang

- Kin trc IP/ATM/SDH/WDM- IP/ATM/WDM- IP/SDH/WDM- IP/WDMMc tiu ca phng thc tch hp IP/WDM

- Gim tnh nng d tha- Gim kch thch mo u- n gin ha cng vic qun lPhng thc truyn ti IP/WDM vn phi m bo khnng cung cp dch v vinhiu cp dch v, kh dng v bo mt cao

Cu 2: Trnh by cu to v gii thch nguyn l hot ng ca chuyn mch burstquang/ gi quang

1. Burst quang


8/19

- c im c/m burst quang: dng sn 1 ng gi yu cu thit lp, nhiu giquang cng n ch xc nh, mo u iu khin burst c pht trc burst 1

khong thi gian.- Nguyn tc hot ng:

+ Trong chuyn mch burst quang, mo u iu khin burst c truyn dctuyn iu khin v pht trc burst mt khong thi gian.+ mo u iu khin sn cc nt chuyn mch trung gian trc, cho php mint chuyn mch thc hin cc tnh ton chuyn mch v tin hnh ci t kt nicho chuyn mch ng thi im trc khi burst d liu n.+ Theo cch ny, burst d liu quang c thc gn vo ng i ca n quamng tu vo n u ra+ Tr gia mo u iu khin v burst tng khi slng cc chng v tr x lyti cc nt chuyn mch trung gian tng.

+ Chuyn mch burst quang dnh sn mt ng gi yu cu thit lp v sau

gi burst m khng cn i xc nhn thit lp. S d nh vy l v thi giantruyn burst l tng i nh.


9/19

2. Gi quang

- c im: tng gi quangh c truyn n tch xc nh, mo u iu khin gic gi cng vi gi d liu dc theo cng tuyn

- Nguyn tc hot ng:+ Cc gi thng tin c gi trn tuyn thch hp c la chn bi b nhtuyn ti nt khi gi n+ trong c/m gi, mi gi c 1 mo u tng ng mang thng tin vgi cng nha ch ca gi v nt c/m trong mng s nhn. Thng tin ny s gi i trn tuyn

thch hp

+ Mo u k gi cng c thc xl nh nhn v c gi cng vi gi dliu dc theo cng tuyn. Xt n thi gian cn thit tnh ton thit b c/m gid liu thng c nh tuyn qua ng dy trquang lc n c//m trung gian+ Gi tr trc la chn sao cho khi gi d liu c pht hin tng dy tr

th ci t kt ni cho quang c thc hin. gi tr tr ny l cc bv khng iti mi nt c/m trung gian


10/19

Cu 3: Trnh by cu trc mng IP/WDM phn loi theo mt bng d li

1. IP/WDM im-im

B nhtuyn IP

B nhtuyn IP

B nhtuyn IP

B nhtuyn IP

Cc tmng dy

Cc bcsng

Mux/Demux

Lin kt cpvt l

Hnh: IP/WDM im-im

Chc nng cc khi:

- Bnh tuyn IP: kt ni nh hng n cc bnh tuyn IP khc qua cc tuynsi quang trn cc bc sng khc nhau

- Bnh tuyn ln cn: dnh ra cc giao din cnh chuyn giao- BMUX: ghp cc bc sng thnh cc tn hiu- BDEMUX: tch bc sng

Nguyn tc hot ng

- Vi cu trc ny, cc tuyn quang WDM im-im dc s dng cung cp ccdch v truyn ti cho lu lng IP

- Kin trc IP/WDM im-im cn c bnh tuyn IP kt ni nh hng ticc bnh tuyn ti cc bnh tuyn IP khc qua cc si quang trn cc bc

sng khc nhau

- Tp mng l cnh v cc cu trc mng hon ton tnh


11/19

- Cc h thng qun l i vi mng u dc tp trung ha, c tng tc vi nhaugia cc lp TCP v WDM

2. IP/WDM cu hnh lai

Chc nng cc khi

- OADM: b xem r quang thc hin chc nng xen r1 vi bc sng v chuyntip cc bc sng cn li

- OXC: phn t ni cho thc hin chc nng ging nh phn t xen r v n cnthc hin thm chc nng kt ni cho cc ng quang

- Bnh tuyn IP: Kt ni gia giao din bnh tuyn vi giao din khch hngqua mng WDM. Kt ni gia giao din bnh tuyn nh vi giao din b

nh tuyn khc- Cc bnh tuyn ln cn: dnh cho giao din bnh tuyn nh cu hnh pha

di cu trc ny

Nguyn tc hot ng


12/19

- Di cu trc IP/WDM cu hnh lai, cc giao din bnh tuyn kt ni ti giaodin khch hng ca mng WDM

- Cc giao din kt ni cho WDM v xen r t kt ni trong mng WDM c cctuyn si nhiu bc sng

- Mng WDM t c cc tp vt l v topo tuyn quang. Topo vt l gm cc NE ktni vi nhau qua si quang topo tuyn quang c thc hin nh kt ni knh

bc sng- Trong WDM cu hnh lai, qu trnh thit lp v hy bknh bc sng dc iu

khin trong cc giai on rieenhg bit- Chuyn mch lu lng IP v chuyn mch sng ko bao gihot ng trong cng

lp ca mng IP cu hnh lai.3. IP/WDM ti chuyn mch

Chc nng cc khi

- Bnh tuyn gi quang OPR: i din cho thc hin quang ca nh tuyn IP nnn h try cc chc nng IP


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- Bnh tuyn IP: kt ni nh hng n cc bnh tuyn IP khc. Kt ni giagiao din bnh tuyn vi giao din khch hng ca mng WDM

- Bnh tuyn chuyn mch quang OLSR: OLSR bin cung cp in t nn ccgi IP i n c th xp hng chi ti bn trong trng hp thit lp LSP ng

Nguyn tc hot ng

- Trong kin trc IP/WDM chuyn mch, c sh tng WDM c khnng h trtrc tip c/m gi

- Trong mng WDM c 3 phng php c/m gi c bn: chuyn mch burstquang(OBS), c/m nhn quang(OLS), c/m nh tuyn gi quang(OPR)

- OBS v OLS s dng m hinhg c/m gi quang kch thc ln. chng ko th hincc mo u gi IP

- Cc h thng WDM c/m chnh l ko nhm. cc ng dy tr dc s dng m phng b m quang, t phc tp hn nhiu so vi b nh truy nhp ngunhin

- Cc h thng WDM c/m da vo x l in t ca mo u gi k cc hotng c/m.

- OPR c thc trin khai nh cc bnh tuyn IP in t v n c nhiu giaodin hn. Thc t, giao din dnh sn l 1 trong cc biu khin chnh pha sauOPR trn bnh tuyn in

- OBS v OLS c m t nh OLSR: OBS s dng c/m gi nhanh, OLS c/mlung, s dng bc sng phtrong bng truyn thng tin k

- OLSR c kt ni nhcc si qaung khi h trcc knh bc sng. OLSR thngc trin khai trong 1 cm. trong , ch c OLSR bin yu cu bsung y

ngn xp giao thc IP

Phn 4

Cu 1: Nu cc phng php b tn sc trong h thng thng tin quang

- m bo cht lng truyn dn, cn phi c cc bin php b tn sc cho knhtn hiu trn ng truyn hoc gi tr pha thu thm ch to nn 1 hin tngngc tn sc ngay ti pha pht. C 1 s loi phng php b tn sc+ Gii php b trc: s dng k thut in, lm thay i cc c tnh ca xungvo ti my pht trc khi truyn vo si quang


14/19

+ Gii php b sau: s dng cc k thut in b tn sc GVD trong my thu.D tn hiu quang b suy gim do GVD th c th lm phng cc hiu ng tn sc

bng in t nu si thc hin vai tr nh 1 h thng tuyn tnh+ Gii php b quang: Cc k thut c s dng s dng si quang b tn sc

(DCF), s dng cc b lc quang, s dng cch t si quang, s dng k tht kthp pha quang

Cu 2: trnh by nguyn l b tn sc s dng cch t Brrag si quang.

- c im ca cch t Bragg si quang: chit sut dc si thay i tun t. cngthc xc nh bc sng phn xB(z) = 2.neff(z).(z)

(z): chu k cch t ti v tr z(z) = 0+ 1(z)

0: chu kim bt u ca on cch t1(z): sthay i tuyn tnh dc theo chiu di ca on cch tB(z): bc sng Bragg ti v tr z

Neff(z): chit sut hiu dng ti v tr z- S phn x ca cc thnh phn tn s khc nhau

+ ti on cch t thnh phn bc sng ngn ti trc do tn sc s phi i thmqung ng na trc khi c phn xngc li ti thit bu thu

+ Trong khi , thnh phn bc sng di hn, n chm hn do b tn sc, s

c phn x ngay khi ti cch t bragg. Kt qu l xung tn hiu sau khi qua thitbb c co li

- Hnh v m t b tn sc s dng cch t Bragg si quang. Gi s tn hiu i vou c chu kdi hn ca on cch t


15/19

-- Nguyn l b tn sc ca quang si cch t Bragg chu k bin i xung tn hiu c

bc sng di hn i vo u c chu k di ca on cch t s b phn xgnphn u ca on cch t. ng thi, nhng bc sng ngn hn s phi i 1qung ng xa hn trong on cch ttrc khi chng c phn xngc li.

Khong thi gian trc to ra gia thnh phn bc sng ngn so vi thnhphn bc sng di

L: di on cch t

C: vn tc AS = 3.10^8 m/s

C = maxmin

Cu 3: hiu ng phi tuyn l g? Cho bit cc hiu ng phi tuyn trong h thng quang.

- K/n:+ hiu ng phi tuyn trong si quang l hiu ng m cc tham s ca si quang(suyhao v chit sut) ph thuc CS tn hiu quang tron si. tnh phi tuyn trong si quangl do cc hiu ng phi tuyn trong si quang gy nn

+ khi CS trn si quang vt qu gii hn no , tnh phi tuyn ca si quang snh

hng ti qu trnh truyn dn tn hiu trong si quang. Tnh phi tuyn ca si quang


16/19

s gy ra hin tng nh xuyn m gia cc knh, suy gim mc tn hiu ca tngknh dn n suy gim t s S/N

- Cc hiu ng phi tuyn trong si quang+ hiu ng tn x gm:

+ hiu ng tn xRaman(SRS): lin quan n qu trnh tng tc ca sng AS v mitrng truyn dn

+ hiu ng tn xBrillouin(SBS): lin quan n qu trnh tng tc gy suy gim CS

tn hiu AS ti.

+ Hiu ng iu ch pha phi tuyn gm:

+ hiu ng tiu ch pha (SPM): pha ca tn hiu sthay i 1 cch phi tuyn tnhkhi bin ng bao xung tn hiu thay i to ra cc tn s mi ti sn ln vxung ca cc xung tn hiu khin ph ca tn hiu b gin ra, nh hng ca tn scln

+ hiu ng iu ch pha cho (XPM): pha ca tn hiu trn 1 knh khng ch chu nhhng t bn thn sthay i CS trong knh m cn chu nh hng t cc knh

khc. nh hng ca XPM tng tnh SPM nhng mc nh hng th ln hnnhiu

+ Hiu ng trn 4 bc sng (FWM): gi s trn 3 bc sng: 123 to ra 123 =m1+ n2+ l3

Cu 5: Nu cc u nhc im ca h thng thng tin quang coherent so vi h thngthng tin quang IM-DD

- u im:+ Nhiu nhhn do khng s dng b thu tch sng trc tip

+ nhy ca bthu quang cao hn nn bthu coherent cho php: Tng khong

cch trm lp cho h thng trn t lin v di bin, tng tc truyn dn mko cn gim k/cch trm lp, tng qu cng sut b cc suy hao ti coupler vthit b ghp tch bc sng, ci thin nhy cho thit b o quang nh myOTDR.

+ Cho php thc hin tch knh hoc la chn knh thu trong h thng WDM mko cn dng cc b lc quang


17/19

- Nhc im:+ Thit b thu pht phc tp hn+ yu cu laser pht v laser dao ng ni c ph hp+ S dng phng php iu ch phc tp hn (ASK,FSK,PSK)

Cu 4: Cho bit cc cng ngh ca mng quang thng PON

- Khi nim+ mng quang thng PON l kin trc mng im-a im s dng cc b chiaquang thng chia CS quang t 1 si quang ti cc si quang cung cp cho

nhiu khch hng+ Mt mng PON bao gm: OLT t ti tng i ca nh cung cp dch v v cc

ONU t ti pha khch hng- u im PON

+ ko cn ngun cung cp nn ko bnh hng bi nhiu ngun+ tin cy cao+ ko cn phi bo dng nh i vi cc phn t tch cc

- Cc cng ngh v cc chun PON+ APON: c ban hnh thnh tiu chun trong G983.1 ca ITU

+ Trn c s APON xy dng PON bng rng (BPON) theo chun ITU-TG983

+ Mt mng APON/BPON in hnh cung cp 622Mb/s. Bng thng ng xung

v 155Mb/s ng ln+ GPON (chun ITU-T G984) M t sgia tng trong cbng thng v hiu suts dng bng thng nh s dng gi ln, c di thay i. Chun G984 cho

php la chn tc bit, thng s dng tc 2,488 Mb/s cho lung xuongs vtc 1,244Mb/s cho ng ln

+ GPON cho php ng gi lu lng d liu ngi dng rt hiu qu, vi sphn on khung m bo cht lng dch vQoS cao hn phc v cho truyn

hnh v video

+ Chun IEEE 802.3 Ethernet PON (EPON hay GEPON): s dng khung Ethernet

i xng 1,24Gb/s tc lung ln v lung xung, c s dng cho cc mngtrung tm d liu, mng cung cp dch v thoi, d liu, video

+ tnm 2006, tip tc thc hin chun EPON tc cao 10Gb/s (chun XEPONhay 10-GEPON)

+ WDM-PON: l mng quang th ng kt hp vi ghp knh phn chia theobc sng.


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Cu 6: Trnh by cu trc c bn ca h thng thng tin quang coherent

- Khi nim+ tng nhy ca b thu quang ta s dng k thut tch quang coherent

+ Tch sng coherent: trc tin b thu quang s cng tn hiu quang ti vi tn hiu

quang c to ra ti ch, sau tch tn hiu quang tng ny thnh tn hiu in. uim ln nht trong h thng l tc cao hot ng tng vng bc sng di

+ b thu coherent hot ng trong vng bc sng 1,3m -1,6m, NL tn hiu t 10-

20photon/bit

- B thu quang cho php+ khong cch trm lp cho h thng trn t lin v di bin

+ Tng tc truyn dn m ko cn gim k/cch trm lp

+ Tng quCS b cc suy hao ti coupler v cc thit bghp tch bc sng

- Ci thin nhy cho thit b o quang nh my CTDR: cc dng iu ch:ASK,FSK, PSK

--

Chc nng cc khi

- DE(Drive Electronic): khuch i tn hiu ng vo nhm to tn hiu c mc phhp vi cc khi pha sau.

- CWL(Continuous Wave Laser): y l b dao ng quang s dng laser bn dnc rng ph hp pht ra nh sng lin tc c bc sng 1.


19/19

- LC (laser control): khi ny nhm n nh bc sng pht ra ca b dao ngquang.

- MOD(Modulator): y l khi iu chquang, s dng k thut iu chngoi to ra tn hiu iu chdng ASK, FSK, PS, hay PolSK.

- LLO(Laser Local Oscillator): y l b dao ng ni ti b thu s dng laser bndn to ra tn hiu quang c bc sng 2.

- DEC(Detector): u tin s dng coupler FBT cng tn hiu thu c (1) v tnhiu ti ch (2). Sau a tn hiu tng ti photodiode thc hin tch sng

trc trip theo qui lut bnh phng.

- LOC(Local Oscillator control): khi ny nhm iu khin pha v tn s ca tnhiu dao ng ni n nh.

- AMP(Amplifier): khi ny khuch i tn hiu in sau khi tch sng quang.- DEMOD (Demodulator): khi ny ch cn thit khi b thu hot ng ch

heterodyne.

lý thuyết quang- full

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