TI TNG QUANG V H THNG THNG TIN QUANG COHERENT

A) Ni dung :Gii thiu chung :cu trc c bn ca ca h thng:Cc dng iu ch quang coherent:My thu coherent:T s li bit trong my thuCc yu t nh hng n nhy my thu Nhng u im ca h thng coherent

Gii thiu chung :IM-DD ng mt vai tr rt quan trng trong ngnh vin thng, em li hiu qu kinh t to ln v cn ang c s dng rng ri nh c u im l n gin v gi thnh r.Tuy nhin h thng ny c mt s nhc im c bn nh t s tn hiu trn nhiu nhn c ti u ra b tch sng thp, nhy ca my thu khng cao lm khong cch truyn dn b hn ch.

ng thi do c im thu tn hiu theo nguyn l tch sng trc tip (khng qua i tn) nn t my thu khng th la chn cc knh quang tu trong mi trng a knh m phi kt hp thm cc b lc quang. Vic ny hn ch kh nng s dng chng trong cc mng truyn dn v phn phi a knh quang n trc tip cc thu bao trong tng lai.

Trong bi cnh vic s dng my thu mi c nguyn l hot ng khc - my thu Coherence - nhm nng cao nhy v c th chn knh trong mi trng phn phi a knh l mt yu cu cp thit v mang tnh hp dn cao.

H thng thng tin coherence ra i v khc phc c cc nhc im ca h thng IM-DD v l h thng thng tin ca tng lai. Hin nay, bc u n ang c p dng cc nc tin tin nhanh chng a vo s dng, khai thc rng ri trong mt tng lai gn, y l mt bc tin quan trng trong lnh vc vin thng.

cu trc c bn ca ca h thng:

Cc dng iu chA) K thut iu ch trong thng tin quang Coherence:a) iu ch kho dch bin (ASK) :iu ch trc tip ca mt diode laser bn dn l khng thch hp trong h thng vi tc d liu cao bi v n to ra hiu ng Chirp, lm thay i tn s ca tn hiu nh sng, gy kh khn cho tch sng ng tn hoc tch sng i tn. Do , thng thng ngi ta s dng phng php iu ch ngoi.

b) iu ch kho dch tn FSK V rng bng tn tng cng rt rng cho nn khng thch hp vi cc h thng c tc cao, nhng c th dng cho cc h thng n gin v r tin. C th gii iu tn hiu IF bng phng php tch sng i tn ng b hoc ng bao.

c) iu ch kho dch pha PSK iu ch PSK s dng b iu ch ngoi nh b iu ch pha LiNbO3. Ti my thu, tn hiu PSK c gii iu ch bng h thng tch sng ng tn hoc i tn, tn hiu trung tn IF c gii iu ch ng b hoc khng ng b

d) iu ch kho dch pha vi phn DPSK Dng ph DPSK ging PSK, ch khc quy lut m v trong DPSK, thng tin c m ho theo hiu pha gia hai tn hiu k tip nhau.Phng php ny thng c s dng trong thc t v khng cn cc b gii iu phc tp m vn cho c tnh tt, c dng trong h thng i tn v gii iu ch phn bit tn s bng ng dy tr.

e) iu ch phn cc PoLSK My pht c mt b iu ch phn cc v my thu c mt b chia phn cc tch v gii iu c hai trng thi phn cc trc giao. Ti my thu, sng ca tn hiu kt hp vi sng ca dao ng ni trong b trn quang, tn hiu u ra ca n a n b chia phn cc, trng tn hiu c chia thnh hai thnh phn trc giao. s dng phng php iu ch phn cc v my thu thc hin tch phn cc, gii iu ng bao gm hai nhnh i xng nhau. Thnh phn phn cc dc c a n b tch sng pha trn v thnh phn phn cc ngang c a n b tch sng di.

f) K thut iu ch ngoi laser + iu ch trong: l bm trc tip dng tn hiu vo laser. Phng php ny ph hp vi cc h thng thng tin tc thp, v laser diode bc l nhng hn ch nh suy gim ph v dch chuyn tn s khi iu ch tc cao.+ iu ch ngoi: l phng php iu ch nh sng bn ngoi laser. Phng php ny c nhiu u im v c ng dng nhiu trong k thut gii iu ch

B) Cc k thut gii iu ch:a) Gii iu ch tn hiu ASK: Gii iu ch ASK i tn ng b Gii iu ch ng bao ASK (ASK i tn khng ng b)b) Gii iu ch FSK :Gii iu ch FSK i tn ng b Gii iu ch FSK lc kpGii iu ch FSK lc nGii iu ch CPFSK vi phn

c) Phng php gii iu ch PSK +Gii iu ch PSK i tn ng b+ Gii iu ch DPSK

My thu coherent:

c im khi tch quang ca my thu Coherence :

S my thu i tn

T s li bit trong my thu

a)Nhiu trong my thu quang:khi cng sut tn hiu dao ng ni ln hn cng sut tn hiu ti b thu th ngun nhiu ch yu trong tch sng coherent l nhiu lng t ca b dao ng ni ,trong gii hn ny nhiu lng t c th c biu din di dng nhiu bn.

b)Tch sng heterodyne askc)Tch sng heterodyne FSKd)Tch sng heterodyne PSKe)Tch sng homodyne ask v pskf)hm xc sut lig)so snh nhy ca h thng coherent :tng kt xc sut li c ch tch sng ca cc dng iu ch tn hiu

Cc yu t nh hng n nhy ca my thua)Nhiu pha:lm gim nhy thu trong h thng ,nhiu pha c lin quan n b pht quang v b dao ng ni s thng ging v pha gia tn hiu ri v tn hiu dao ng n s dn n s thay i v dng ng ra ca b tch sng .T lm gim t s SNR ca tn hiu.

b)Nhiu cng

Tt c cng sut ca tn hiu ti v ca b dao ng ni c s dng mt cch c hiu qu tt c cc b thu cn bng u s dng ton b cng sut ca tn hiu v trnh c s mt mt ny .ng thi b thu cn bng cng s dng ht cng sut ca b dao ng ni nn d dng cho h thng hot ng trong gii hn ca nhiu lng t

c)Khng tng xng v phn cc d)Tn sc trong si quang:nh hng n c tnh ca h thng .L do l h thng coherent cn phi s dng cc laser bn dn hot ng ch n mode c vi rng ph hp

d)Cc yu t hn ch khc +Hi tip phn x +Cc hiu ng phi tuyn trong si quang +Tn x raman+Tn x brillouin

Nhng u im ca h thng Nng cao nhy thu+Tng khong cch trm lp cho h thng trn t lin v di bin+Tng tc truyn dn m khng cn gim khong cch trm lp +Tng qu cng sut b cc suy hao +Ci thin nhy cho thit b o quang nh my OTDR.

Nng cao kh nng truyn dn Kh nng kt hp thu coherent vi k thut khuch i quang

B) Kt lunTrong h thng thng tin quan coherent c th p dng cc k thut iu ch s quen thuc nh ASK FSK ,PSK ,trong thng tin quang coherent s dng cc tn hiu nh phn trn cc k thut iu ch kho dch tn s v dch pha BFSK v BPSK

Ti liu tham khoK thut thng tin quang 2 i hc T XaH thng thng tin si quang Coherence