Cu to ca Laser thng thng: -Cu trc nhiu lp bn dn p,n -nh sng pht ra v c gi trong lp tch cc (active layer) -Lp tch cc rt mng,lm bng vt liu c chic sut ln kp gia 2 lp P v N c chit sut nh hn.Cu trc ny to thnh ng dn sng. - 2 u lp tch cc l 2 lp phn x vi h s phn x R y l iu kin phn x Bragg. Da vo nguyn l Bragg ta c th to ra cc loi laser c th cho mode dc n duy nht l laser hi tip phn b DFB 2.Cu trc DFB laser: Cu trc ca laser DFB c biu din nh hnh 2:

Lp kim loi

Mng AR

Cch t u ra quang Lp kim loi tip xc v to nhit Lp hot Tnh

3.Nguyn l hot ng: Cc photon nh sng do hin tng pht x kch thch to ra trong vng tch cc phn x nhiu ln ti cch t (khc vi laser FP ch phn x ti hai mt phn x ca hc cng hng). Ti mi on dc ca cch t, mt phn nng lng nh sng b phn x. Tng hp nng lng nh sng phn x ti mi cch t ny trong laser lm cho phn ln nh sng trong laser c phn x c bc sng tha mn iu kin Bragg. Kt qu l, laser DBF ch pht x ra nh sng c bc sng B tha iu kin Bragg ( khc vi laser FB c nhiu bc sng nh sng tha iu kin phn x trong hc cng hng).

Cu trc ca laser DBF Cu trc ca laser DBF c biu din trn hnh 1.1. Qu trnh cng hng v chn lc tn s xy ra trong laser DBF c thc hin nh cu trc cch t Bragg t bn cnh, dc theo vng tch cc ca laser DFB. Sng nh sng pht x trong laser lan truyn dc theo vng tch cc v phn x ti mi on dc ca cch t. iu kin s pht x v cng hng c th xy ra l bc sng nh sng phi tha mn iu kin Bragg: B = 2..neff Trong : + l chu k ca cch t Bragg + neff = n.sin vi n l chit sut ca cch t Vi: + n l chit sut ca cch t, + l gc phn x ca nh sng ( hnh 1.2)

Phn x ti cch t Bragg

rng ph ca laser DFB Nu iu kin (1) khng tha mn th nh sng tn x t cch t s giao thoa trit tiu ln nhau,kt qu l sng khng th truyn i c.Khi m=1 th bc sng B c gi l bc sng Bragg bc mt v B 2 neff 3.ng dng ca DFB laser - DFB laser ch pht x ra mt mode sng c rng ph rt hp khong (0,1 0,2nm) so vi laser c cu trc c in (khong 2nm). Ngoi ra bc x ny cng khng nhy cm vi s

thay i ca nhit ca dng iu khn. Vi c im nh vy, laser DFB v ang c s dng trong cc h thng thng tin quang c c ly truyn dn di v tc bt truyn cao. -Cc laser DFB thng hot ng ti bc sng B = 1. m. Do tnh cht chn lc mode, DFB

laser c kh nng pht ra tn hiu quang n mode. DFB laser c hiu sut cao vi di nhit rt rng nn thit b ny c s dng rng ri trong kin trc mng PON c bit l pha OLT. DFB laser (khng c b phn lm mt) thng c dng ngng thp, di nhit hot ng rt rng, t s nn mode cnh cao (thng thng l 40 dB) v p ng nhanh ( 0.12 ns thi gian ln v xung ly trong khong bin t 20-80%). - Tnh n nh ca bc sng tt hn.