nghiÊn cỨu chẾ tẠo cẢm biẾn quang sỢi sỬ dỤng cÁch tỬ bragg

7/31/2019 NGHIN CU CH TO CM BIN QUANG SI S DNG CCH T BRAGG

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I HC QUC GIA H NI

TRNG I HC CNG NGH

Nguyn Mnh Tng

NGHIN CU CH TO CM BIN QUANG

SI S DNG CCH T BRAGG

KHO LUN TT NGHIP I HC H CHNH QUY

Ngnh:Vt l k thut

H NI - 2011


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I HC QUC GIA H NI

TRNG I HC CNG NGH

Nguyn Mnh Tng

NGHIN CU CH TO CM BIN QUANGSI S DNG CCH T BRAGG

KHO LUN TT NGHIP I HC H CHNH QUY

Ngnh:Vt l k thut

Cn b hng dn: PGS.TS Phm Vn Hi

Cn b ng hng dn: TS Bi Huy

H NI - 2011


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LI CM N

Em xin chn thnh cm n thy PGS.TS Phm Vn Hi v TS Bi Huy tntnh hng dn, ch bo trong qu trnh em thc hin kha lun tt nghip.

Em xin chn thnh cm n cc anh ch ang cng tc ti Phng Vt liu v ng

dng Quang si, Vin Khoa hc Vt liu, Vin Khoa hc v Cng ngh Vit Nam

to iu kin tt nht gip em thc hin cc thc nghim trong qu trnh lm kha lun

ny.

Em xin chn thnh cm n cc Thy, C ging dy trong nhng nm hc tp,

v tp th lp K52V ng vin, gip trong thi gian qua.Cui cng em xin by t lng bit n su sc nht i vi gia nh,ngi

thn,bn b-nhng ngi lun ng vin v to nhng iu kin thun li nht em

yn tm hc tp.

Em xin chn thnh cm n!

H Ni, thng 06 nm 2011

Sinh vin thc hin

Nguyn Mnh Tng


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TM TT NI DUNG

Cch t Bragg trong si quang l linh kin quang t c lm bng si nhyquang, trong phn li si quang c chit sut thay i theo mt chu k nht nh dc

theo chiu di ca si quang, s thay i chit sut ny tha mn iu kin Bragg:

Bragg = 2neff.Bragg

Cch t Bragg c nhiu ng dng trong mng thng tin quang v trong nghin cu

cm bin quang si nh l ng dng ch to cc b tch bc sng quang, b tn sc

trn tuyn thng tinquang, lm phng ph khuch i quang cho thit b EDFA v c

bit c kh nng ng dng trong cc laser si vi n sc cao s dng trong mngvin thng quang v nghin cu ch to cm bin nhit , p sut,gia tc

Trong khun kh kha lun ca mnh,chng ti tm hiu mt s cu hnh ca

mt s cm bin s dng cch t Bragg trong si nh:cm bin o gia tc,cm bin o

d chn v xy dng mt cm bin o dch chuyn .Vi cc kt qu thu c c

th gip chng ta s dng FBG lm cc sensor ng dng trong thc t khi chng ta tch

hp, tinh gin cc thit b quang trong h thng.


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LI CAM OAN

Ti xin cam oan ni dung trong bn n tt nghip ny l kt qu trong cng

trnh nghin cu ca ring ti di s hng dn ca TS Bi Huy v PGS.TS PhmVn Hi.Tt c cc s liu c cng b l hon ton trung thc v cha tng c

cng b ti cc ti liu hay n phm no khc .Cc ti liu tham kho khc u c ch

dn r rng v ngun gc xut x v c nu trong phn ph lc cui kho lun.

H Ni ngy 20 thng 5 nm 2011

Nguyn Mnh Tng


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THUT NG VIT TT

ADM Add/Drop Multiplexing B tch ghp knh

CFBGChirped Fiber Bragg

Grating

Cch t Bragg si quang

chu k bin i

DWDMDense Wavelength

Division Multiplex

Ghp knh mt cao

phn chia theo bc sng

EDFA

Erbium Doped Fiber

Amplifier

B khuch i quang si

pha tp Erbium

FBG Fiber Bragg Grating Cch t Bragg si quang

LCFBGLinear Chirped Fiber Bragg

Grating


chu k bin i tuyn tnh

MUX Multiplexing B ghp knh

OADM Optical Add/DropMultiplexing

B ghp tch knh quang

OFA Optical Fiber Amplifier B khuch i quang si

UFBGUniform Chirped Fiber

Bragg Grating


chu k u

UV Ultra Violet Tia cc tm

WDMWavelength Division

Multiplex

Ghp knh phn chia theo

bc sng


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M U

M hnh cch t Bragg quang c a ra v chng minh cc tnh cht ca n lnu tin vo nm 1978 bi Hilletal. n nm 1989, n c m t mt cch r rng hn

bi Meltzetal, cch t Bragg quang c to ra bng cch s dng php chiu giao thoa

hai lung tia cc tm UV-exposure. Vi s pht trin ca mnh, FBG c lin quan trc

tip v cht ch vi s pht trin ca si quang, n c kh nng s dng trong vic xy

dng cc b lc dng tch ghp knh trong h thng truyn ti d liu a knh. Ni

bt nht trong nhng ng dng ny l FBG c dng cho h thng DWDM. FBG l c

s cho cc thit b la chn th ng cho cc bc sng n, ghp bc sng v chn

bc sng bng hp. N lm vic tt trong iu kin cc yu t v nhit v sc cngc m bo bi v cc iu kin ny c th nh hng n tin cy ca FBG.

S pht trin nhanh chng ca FBG v cc ng dng trong mng vin thng

quang v cc h thng cm bin thc y l nng cao tc t ph trong nghin

cu, nhng kt qu ny lm ci thin v pht trin cht lng cng nh cc tnh nng

ca cc thit b quang. Trong tng lai, cc tnh nng ca cc thit b ny c th vt

qua cc gii hn hin ti bng vic s dng k thut photonic.

Tnh nng nhy cm vi mi trng l mt im khng tt ca FBG, tuy nhinhin nay n li c s dng rt nhiu trong cc h thng cm bin. Mt trong cc ng

dng l cu ch sillica, n lin quan n tnh cht khng b nh hng bi in t trng

ca FBG.

FBG ang tr nn rt ph bin vi t cch l mt thit b quang n gin, linh

hot v c v s cc ng dng trong cc thit b v h thng quang.

Nh kh nng cm bin tt i vi s thay i ca mi trng nn ta da vo

FBG c th xc nh c cc thng s vt l c bn ca mi trng nh p sut, nhit,sc cng

Hin ti, cc FBG c rt nhiu ng dng trong cc h thng cm bin nh:

- Cm bin nhit .

- Cm bin sc cng .

- Cm bin p sut.

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- Cm bin gia tc.

- Cm bin dch chuyn..

Nh cc tnh cht m FBG c th mang li nn chng ti chn ti

Nghin cu ch to cm bin quang si s dng cch t Bragg lm ni dung nghincu trong kha lun ca mnh.

Mc ch ca kha lun: Nghin cu,ch to cm bin quang si s dng cch t

FBG v kho st chng khi thay i cc iu kin bn ngoi.Chng ti hy vng rng cc

kt qu thu c ban u c th l c s chng ta c th hon thin chng v ng

dng trong thc t.

Ni dung kha lun gm c 3 chng:

Chng 1. Nghin cu cch t Bragg trong si.

Chng 2. Cm bin quang si s dng cch t Bragg.

Chng 3. Thc nghim v kt qu.

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CHNG 1.

NGHIN CU CCH T BRAGG TRONG SI

1.1. Tng quan v cch t Bragg trong si (FBG)

1.1.1. Gii thiu

Khong cch =B/neff

Bphnx

B ti B truyn

Chitsu

t

z

Hnh 1.1: Cu to v chit sut ca FBG

Cch t Bragg quang thc cht l s xo trn cu trc ch s chit sut theo dng

chu k dc theo hng truyn sng ca si quang v c m t trong hnh trn.

Ch s chit sut ca FBG c tnh theo phng trnh sau :

2( , , ) ( , , ) ( , , ) cos(

n x y z n x y z n x y z = + (1. 1)

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Trong ( , , )n x y z l ch s chit sut trung bnh ca li si quang v ( , ,n x y z

l ch s iu ch v l chu k ca FBG.

Mt lng nh nh sng c phn x ti mi im ni ch s chit sut ca

FBG thay i. S phn x hon ton trong FBG xy ra ti cc bc sng ring khi xut hin mode ghp mnh nht. y gi l iu kin Bragg c m t trong phng

trnh (1. 2), bc sng m ti c s phn x hon ton c gi l bc sng Bragg

B. Ch c nhng bc sng tho mn iu kin Bragg l chu nh hng ca cch t v

phn x mt cch mnh m. FBG trong sut i vi cc bc sng nm ngoi vng bc

sng Bragg.

Bc sng Bragg c tnh nh sau:

B = 2 neff (1. 2)

Trong neff l ch s khc x nh hng v l chu k ca FBG. y chnh l

iu kin xy ra phn x Bragg. T phng trnh (1. 2) chng ta c th thy rng bc

sng Bragg hon ton ph thuc vo ch s khc x v chu k ca cch t.

Cc cch t di vi ch s khc x thay i khng ng k c nh phn x rt

nhn v bng tn phn x rt nh.

H s suy hao:

Gi Pin l cng sut ca tn hiu ti cch t, Prefl l cng sut tn hiu khi qua cch

t

Ta c h s suy hao l: 1010log ( )in

refl

PdB

p =

Khi qua FBG th ch mt bc sng b phn x cn cc bc sng khc truyn qua

do ph tn hiu truyn qua FB ti bc sng Bragg b gim.

1.1.2. Nguyn l hot ng

Xt hai sng truyn theo hai hng ngc chiu nhau vi hng s truyn dn 0

v 1 . Nng lng c ghp t sng ny sang sng khc nu chng tho mn iu

kin cn bng pha Bragg:

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0 1

2 =

(1.3)

Trong l chu k ca cch t. Xt mt sng nh sng vi hng s lan truyn

0 truyn t tri qua phi. Nng lng t sng ny c ghp vo sng tn x chuyn

dch theo hng ngc li ti cng bc sng nu tho mn iu kin pha Bragg.

0 0 0

22( )

=

= (1.4)

Ta c 00

2 effn

= , 0 l bc sng ca sng n, neff l ch s khc x hiu dng

ca si quang (vt lm cch t Bragg), sng c phn x vi iu kin l:

0 2 effn = (1.5)

Bc sng 0 ny c gi l bc sng Bragg. Trong thc t, hiu sut phn x

gim khi bc sng ca sng n khng n khp vi bc sng Bragg. Do nu c

mt vi bc sng c truyn vo cch t Bragg th bc sng Bragg c phn x

trong khi cc bc sng khc c truyn qua m khng b tn hao hoc tn hao rt t.

S hot ng ca cch t c th c hiu bng cch tham kho hnh 1.2, hnh vcho thy s thay i tun hon ch s khc x. Sng n c phn x t mi chu k

cch t. Cc s phn x ny c cng pha khi chiu di ng i ca sng 0 mi

chu k bng mt na bc sng n 0. iu ny tng ng vi 0 2effn = (iu

kin Bragg).

Hnh 1.2: Nguyn l hot ng ca cch t Bragg

1.1.3. Ph phn x v ph truyn qua ca FBG

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Hnh 1.3: Dng ph ca tn hiu khi qua cch t. a) Ph tn hiu vo, b) Ph tn

hiu c truyn qua, c) Ph tn hiu b phn x

Khi cho tn hiu di rng qua cch t th ch c bc sng ph hp vi bc sng

cch t c phn x tr li v cc bc sng cn li cho qua. Cng ca tn hiu

c phn x khi qua cch t ph thuc vo chiu di cch t, chnh xc ca cch t.

1.2. Cc phng php ch to FBG

ch to FBG ta da theo nguyn l: chiu chm t ngoi c nng lng ln

lm thay i cu trc v chit sut ca li si dc theo chiu di ca si. S thay i

chit sut trong li si quang theo quy lut tun hon l do c s giao thoa ca hai chm

tia UV.

Xt trng hp chiu chm UV c bc sng 248nm vo si quang c li l SiO 2

pha tp GeO2 l vt liu nhy quang (14% n 20%) nu pha tp thp s khng to c

FBG.

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Hnh 1.4: cu trc GeO2 trong li si quang

Khi chiu chm UV vo si ti mt v tr no cu trc ca GeO2 b b gy, khi nguyn t Oxi s khng cn v tr c na m lch i so vi hng ban u. Ti v

tr chit sut ca si thay i do c th to c chit sut khc nhau tng on

trong li si, ni c cng UV ln th chit sut tng, ni c cng UV thp th

gi nguyn chit sut nn to c cu trc ca FBG.

Khi ng sng ti b mt c s thay i chit sut s b phn x tr li, khi tho

mn iu kin Bragg th s thu c bc sng phn x Bragg.

Hnh 1.5 m t nguyn l ch to FBG da vo hin tng giao thoa ca hai chm

tia UV.

Hnh 1.5: S giao thoa ca hai chm tia UV to FBG

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Ch : khi s dng cht khc pha tp vo li th cn phi s dng bc sng khc

248nm b gy mch lin kt ca cht pha tp trong cu trc.

C rt nhiu phng php ch to cch t. Sau y chng ta tm hiu mt s

phng php ch to FBG.

1.2.1. Phng php ch to FBG s dng b chia chm tia

Phng php c m t nh trong hnh 1.6. Chm UV c chia lm 2 ti b

chia chm tia (beam splitter) v sau c hi t ti gc nh s phn x t hai

gng UV. Phng php ny cho php bc sng Bragg c chn ph thuc vo bc

sng UV theo cng thc sau:

sin2

eff uvB

uv

n

n

=

(1.6)

B bc sng phn x Bragg, neff l ch s mode hiu dng trong si, nuv l ch s

chit sut ca si trong UV, uv l bc sng ca bc x UV.

T cng thc trn ta thy B ph thuc vo bc sng ca chm tia UV v gc hp

bi hai chm tia ti gy giao thoa ti si v vy khi thay i uv v th B cng thay i

tc l chu k cch t thay i.Si c gi on giao thoa ca hai chm tia. y l phng php c s

dng thnh cng u tin ch to cch t ti bc sng nhn thy.

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Hnh 1.6: Ch to FBG dng Beam splitter.

y chm laser phi ln khi tch ra thnh hai phn th tnh cht ca chm

tia khng thay i. Trong cng nghip cch ny rt kh sn xut hng lot.

1.2.2. Phng php ch to FBG qua mt n pha( Phase Mask)

Phng php ny li dng mt phn t quang nhiu x iu chnh chm t

ngoi khc.

* Nguyn l nhiu x qua mt n pha(Phase Mask) : khi chiu chm tia UV

qua Phase Mask, chm tia ny s c nhiu x thnh mt vi bc m = 0, 1,iu

ny c cho thy trong hnh 1.7. Cc bc n v bc nhiu x tho mn phng trnh

nhiu x chung, vi pm l chu k ca Phase Mask:

sin sin2

pm

uv

mi

m

=

(1.7)

m/2 l gc ca bc c nhiu x, uv l bc sng UV v i l gc ca chm UV

ti.Trong cc trng hp khi chu k ca cch t nm gia uv v uv/2 th sng n ch

c nhiu x thnh mt bc (m = -1) vi phn cng sut cn li gi nguyn trong sng

c truyn qua m = 0.

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Hnh 1.7: Nhiu x ca chm tia ti Phase Mask.

* Nguyn l ch to vic khc cch t d dng v c hiu qu hn ngi ta s dng Phase Mask vi

cc tia UV ti vung gc vi Phase Mask v mt ct ca cch t tun hon trong Phase

Mask phi c chn sao cho khi chm tia UV n trn Phase Mask, chm tia nhiu x

bc khng c cng sut nh hn 5% cng sut truyn, bc 1 v -1 c cng sut ln nht

(ln hn 37 % cng sut truyn).

Hnh 1.8: Chm UV ti vung gc c nhiu x thnh hai bc 1

Khi bc x UV ti vung gc vi Phase Mask ( i = 0) th bc x ny c nhiu

x thnh cc bc m = 0 v m = 1 nh thy trong hnh 1.8. t si ngay sau Phase

Mask (nh thy trong hnh 1.9), mu giao thoa ti si ca hai chm nhiu x bc 1

c hi t c chu k g lin quan ti gc nhiu x m/2 theo phng trnh:

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( )2sin 2 2pmuv

g

m

= = (1.8)

g l chu k ca cc vn giao thoa. Chu k ca cch t c khc trong Phase

Mask c xc nh bi bc sng Bragg c yu cu B i vi cch t trong si v

s dng phng trnh (1.8) ta c:

2 2

Brag g pm

g

eff

N

n

= = (1.9)

Trong 1N l s nguyn ch ra bc ca chu k cch t.

lm ti thiu bc khng t chm tia UV n vung gc trn Phase Mask thchiu su c khc nh nht d ca cch t ca Phase Mask.

( )12uv

uvd n

= (1.10)

nuv l ch s ca vt liu Phase Mask ti bc sng uv .

Hnh 1.9: Ch to cch t FBG dng Phase Mask

u im:

- To ra bc sng phn x chnh xc, n gin.

Nhc im:

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- Mi loi Phase Mask ch ch to c mt loi FBG (chu k khng i = chu

k Phase Mask /2) m Phase Mask kh t.

- H s phn x thp di 80% do si kh t vo v tr giao thoa ca hai chm

tia v do si t gn Phase Mask chu nh hng ca rung ng c hc.

1.2.3. Phng php ch to FBG bng h giao thoa k

S nguyn l c m t trong hnh 1.10. Chiu chm UV vung gc vi

Phase Mask, sau khi qua Phase Mask chm tia b tn x thnh nhiu chm ng vi cc

bc 0, 1, 2,... Ta ch dng nhiu x bc 1 c cng ln nht v hng chng ti

h 2 gng giao thoa, sau khi phn x trn 2 gng giao thoa, hai chm tia s c

giao thoa trn si quang to cch t. Nu bc 0 chiu ti si s nh hng ti qutrnh ch to FBG, do ta phi chn chm bc 0 li. Chu k cch t g ch to c

c tnh theo cng thc:

( )2sin 2uv

g

B

= (1.11)

Hnh 1.10: S nguyn l ch to FBG bng h gng giao thoa

u im:

- C th ch to c FBG trong di bc sng rng (v d loi Phase Mask

1060 c th ch to c FBG c bc sng Bragg nm trong khong 1200nm ti

1600).

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- H s phn x cao ln ti trn 90%.

- Chiu di cch t c th thay i c bng cch iu chnh hai gng giao

thoa.

Nhc im

- S cn chnh h cn chnh xc cao.

Ngoi cc phng php k trn cn rt nhiu phng php ch to cch t.

1.3. ng dng ca FBG

1.3.1. Cc u im chnh ca FBG

- FBG thuc loi b lc phn x, FBG phn x bc sng cn dng thay cho struyn qua nh cc b lc truyn thng khc. N c kh nng tch bc sng vi

chnh xc cao ( 0,05nm l d dng t c).

- FBG c th c ch to vi s mt mt v cng thp (ti bc sng 1550nm c

suy hao thp nht 0,2dB).

- n nh trong qu trnh s dng v c hiu sut cao (phn x gn nh 100% nh

sng ti).

- C kch thc nh, d s dng v g b khi cn thit.

- Khng chu nh hng ca nhiu in t trng nn c th s dng FBG trong

mng thng tin nhng ni c in t trng mnh nh ti cc nh my in..

- D tch hp trong cc si quang s dng trong mng vin thng.

- D ch to, gi thnh khng cao.

1.3.2. ng dng ca FBG trong b tch ghp knh OADM

H thng ghp knh phn chia theo bc sng WDM l mt trong nhng gii php

quan trng nht ca cc h thng truyn dn quang tc cao. S pht trin ca cc

tuyn truyn dn quang im- im vi bc sng n ln thnh h thng truyn dn

quang ghp knh theo bc sng a ra nhu cu v cc b tch ghp knh theo bc

sng OADM dng tch ghp v nh tuyn cc knh bc sng khc nhau. Cc thit

b ny c th c s dng ti nhiu im khc nhau trn mng dc theo cc tuyn

truyn dn quang v c chc nng ghp/tch cc knh quang vi cc bc sng c

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la chn, vi chc nng ny mm do linh hot ca h thng c ci thin r

rt. N tr thnh mt phn rt quan trng ca cc ng dng WDM, chng hn nh cc

khu vc khc nhau c th cng kt ni trn mt tuyn quang bng vic tch / ghp knh

t mt ng truyn quang. Thm vo , s mm do trong tc d liu ca cc

knh WDM ring bit cho php cung cp tc tu theo nhu cu. M hnh ca b tch

ghp knh c m t trong hnh sau :

ADM1 In 2 out

3add

4drop

1 .. 16

1 3 5

1 .. 16

1 .. 16

M hnh c bn ca OADM

Hnh 1.11: M hnh c bn ca OADM

C hai dng OADM chnh c s dng trong cc mng quang WDM, l fixed

OADM c dng tch hoc ghp cc tn hiu d liu trn cc knh WDM ring bit

c nh v OADM c th iu chnh v vy n c kh nng la chn nh tuyn c

cc bc sng khc nhau trong mng quang. Chc nng chnh ca dng thit b OADM

th hai ny l cung cp nh tuyn li mt cch mm do cho cc lung quang, nh

tuyn vng cho cc kt ni hng, do vy n lm cho gim ti thiu vic phi ngt dch

v v cng nh kh nng thch ng hay nng cp mng quang vi cc k thut WDM

khc nhau.

Cc cu hnh gii thiu trc y dng thc hin tch hay ghp knh quang

s dng c hai cng ngh Planar v cng ngh si. Cc thit b Planar cung cp cc thp gii php vi kh nng tch v ghp nhiu knh s dng duy nht ch mt mch

quang tch hp s dng k thut dy cch t dn sng AWG (arrayed waveguide

gratings) hoc k thut nh tuyn cch t dn sng WGR (waveguide grating router).

Mt hn ch chnh ca thit b Planar l suy hao xen cao, c th ln ti 7 dB v tnh ph

thuc phn cc. Mt khc cc thit b ton quang l cng l cc gii php rt hp dn

bi v tnh suy hao xen thp, tnh nhy phn cc (ph thuc vo si v cu hnh) v d

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dng s dng cho vic ghp gia cc thit b u vo v u ra ca mng quang bng

vic s dng cc ghp ni n gin.

Mt dng ring ca cc OADM ton quang l da trn cch t Bragg t gia

cc coupler quang. Cu hnh ny c chng minh l ph hp cho vic thc hintch ghp knh, bao gm cc cch t Bragg v cc dng coupler nh l coupler na

vng (half cycle), coupler kn (full cycle).

Cc cu hnh OADM

OADM da trn FBG v coupler 3 dB

Cu hnh m bo tnh n nh v thc hin tt chc nng tch ghp knh c

a ra da trn thit b 4 cng PW (planar waveguide) c m t trong hnh N bao

gm cc thit b : b chia 3 dB v cch t mt trong cc cng ra output ca couplerlm nhim v chn bc sng.

1 .. 16

isolator

1 isolator

3

1 .. 16

G

Drop

3 dB

coupler

3 dB

coupler

In

out

grating

4

2

G

add

Hnh 1.12: M hnh OADM da trn FBG v coupler 3 dB

Nguyn l hot ng ca m hnh thit b ny nh sau: nh sng a vo cng 1

v c chia lm 2, ti cng ra FBG s phn x cc nh sng c bc sng G v quay

tr li cng Dropped 4 v c ly ra ngoi. Cng ra cn li ca Coupler c ngmchm vo trong vo trong cht lu c ch s chit sut ph hp lm cho nh sng

khng phn x tr li. Tn hiu c chn s xut hin ti c cng 1 v 4 (cng In

v Drop). Mt thit b Isolator t ti cng 1 ca Coupler bo v tn hiu vo ca h

thng khng b nh hng bi cc tn hiu phn x. Tn hiu tch yu hn 6 dB so vi

tn hiu gc a vo. Trong truyn dn, mt Coupler 3 dB th hai s chia tn hiu khng

c cch t phn x. Chc nng thm vo ny c thc hin bng cch a mt tn

hiu vo cng 3, bc sng ca tn hiu la chn sao cho n b phn x bi cch t ( G)

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v v vy n c ghp vo tn hiu quang cng 2 theo nguyn l hot ng ca

Coupler. Mt thit b Isolator cng c s dng v t ti cng 3 cch ly tn hiu

a vo v tn hiu truyn dn t cng vo a ti. Khi s dng hai Isolator ti cng

vo v cng ghp thm , cu hnh khng giao thoa cho php thc hin kh nng tch

ghp rt tt. Trong cu hnh ny khng c gii hn hay iu kin no v di, v tr

hay apodisation ca cch t. Cch t lc bc sng c th c thit k s dng

phng php inverse scattering. Nhc im ca cu hnh ny l vic h tr mt dung

lng cho tt c cc knh thp nht 6 dB. Tuy nhin khi so snh n vi cc thit b da

trn c s PW (planar waveguide) c mt tn hiu tng t nhng li c s linh hot

hn trong vic ch to v iu chnh bc sng la chn ca cch t.

OADM da trn FBG v cu hnh giao thoa March-Zehnder

Mt phng php khc phc vic mt tn hiu ca cu hnh trn yu cu thm

mt cch t ging ht nh cch t u tin v tt c cc cng ca Coupler u s dng,

v vy cu hnh ny cn gi l cu hnh giao thoa Mach Zehnder. C hai dng thit b

ch to theo cng ngh planar hay cng ngh ton quang s dng cho cu hnh ny u

c m t v thc nghim.

V mt l thuyt thit b ny l i xng v c th mang li nhng kt qu kh

quan trong chng mt tn hiu, s phn x ngc v chng xuyn m.

Identicalgrating

1 8

1 8

3 dB coupler 3 dB coupler

G

G

G

1 In

4 drop

3 add

2 out

Hnh 1.13: OADM da trn cu hnh giao thoa Mach-Zehnder

Nguyn l ca cu hnh ny c miu t trong hnh v trn: Mt Coupler 3 dB

chia nh sng a vo t cng 1 v nh sng c bc sng G c phn x bi hai

cch t FBG ging nhau. Cc tn hiu phn x ny c a tr li vo Coupler v

c ly ra ti cng Drop. Tn hiu phn hi ngc tr li cng 1 c trit tiu hon

ton nh s dng Coupler ph hp (b chia 50%). Cc bc sng pht c lm nhiu

trong Coupler 3 dB th hai v th chng n cng ra m khng c phn d no phn x

tr li cng Add, tnh nng ny cng do Coupler quyt nh. Cu hnh ny da trn c

s chia v nhiu ca nh sng v v th kh nhy trong vic thay i di truyn tn

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hiu, c im ca cc cch t ging nhau, tnh cht ca b Coupler 3 dB. V vy n

nh ca mi trng, ca cc Coupler ging nhau, ca cc FBG quyt nh vic thit b

thc hin cc tnh nng ca n c m bo hay khng. S n nh v kh nng chu nh

hng ca thit b ny trong h thng WDM thc t c phn tch bi Erdogan: cu

hnh ny nu s dng cc thit b theo cng ngh Planar c di truyn dn ngn hn

v vy d n nh hn. Nhng mt khc cc thit b da trn si li kp trnh c yu

cu v lung UV s dng trong cu hnh giao thoa Mach Zehnder.

Cu hnh OADM s dng FBG v Circulator

Cu hnh ny tng t nh cc cu hnh 4 cng ni trn, nhng trong cc

Coupler c thay th bng cc Circulator quang. V l thuyt, cu hnh ny s dng

cc thit b khng giao thoa l l tng. Cc tnh cht ph theo nguyn l ph thuc vo

hot ng v tnh cht ca FBG v c th c thit k nh mt b lc trc giao l

tng s dng k thut scattering ngc, s mt tn hiu v xuyn m ch yu ph thuc

vo hot ng ca cc Circulator quang.

G

grating

circulator

1 .8

1

drop add

out

2

34

1 .8

G G

circulator

Hnh 1.14: OADM da trn FBG v Circulator

Nguyn l hot ng ca OADM dng ny nh sau : nh sng c a

vo cng In 1 v c nh hng ti FBG c bc sng phn x l G, nh sng c

bc sng ny c cch t phn x tr li Circulator v c tch ra cng Drop 4,

cc phn nh sng cn li s chuyn qua cch t v a ti Circulator 2. Circulator 2,

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mt tn hiu khc c bc sng G c a vo cng Add 3, tn hiu ny c cch t

phn x tr li v i ra cng Out 2.

Nhc im chnh ca cu hnh OADM dng ny l Circulator tng

i t v cng knh. Tuy nhin, cng vi s pht trin ca cc cng ngh Circulatorgi r v mt mt tn hiu khng ln, cu hnh ny l mt gii php rt tt cho thit b

OADM bi v tnh n nh ca n.

OADM da trn cch t t gia Coupler

Tnh n nh ca OADM da trn cu hnh ca giao thoa Mach-Zehnder cng c

th c ci thin nh s dng nhiu gia cc mode ca Coupler quang. Vic to ra mt

cch t gia mt coupler na vng (100%) c chng minh trong c hai dng cu

hnh thit b Planar v thit b ton quang.

G

grating

100%

coupler

2

3

41 .8

1 In

drop

G

add

G

out1 .8

Hnh1.15: Cu hnh OADM dng cch t nm gia Coupler

Thit b ny rt nh gn, tuy vy v nguyn l ch c s i xng hon ton khi

ch to cch t c dng nh mt b phn x im. iu ny ch c kh nng thc hin

khi s dng cc cch t rt ngn hoc cc coupler rt di. Hnh trn cho thy cu hnh

dng ny : nh sng c a vo cng 1 v c truyn ti trung tm ca coupler. Mtcch t c t ti trung tm ca coupler ni s khc pha gia cc mode eigen l /4,

ni nh sng c chia mt cch u nhau gia hai cc phn dn sng ca coupler.

Knh c bc sng G dc phn x tr li do cch t v phn tn hiu cn li truyn

qua coupler n cng ra 2. Trong qu trnh phn x, cc eigenmode phn x trong

coupler t n khc pha tng cng l /2 v v th knh c bc sng G c tch

ra ti cng 4. V nguyn l, n nh ca thit b giao thoa c ci thin vi cu hnh

Mach-Zehnder bi v s phn x im v nhiu t c thng qua vic truyn cc

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eigenmode ca coupler. Tuy nhin cc gii hn ca i vi di cch t v di cc

coupler ch to i hi phi c cc tnh ton ph hp.

1.3.3. FBG dng b tn sc

Tn sc trong si quang n mode nh hng rt ln n cht lng ca mng

thng tin quang tc cao dng nh sng trong ca s 1550nm, n lm tng t l li bit,

gii hn tc hoc khong cch truyn ca mng. c mng kch thc ln, tc

cao phi gim ti thiu tn sc trong si quang.

Mt s gii php khc phc hin tng tn sc ang c p dng hin nay trn

th gii l s dng cc si cp quang thng tin c tn sc ti thiu hoc cp quang c

kh nng b tn sc. Tuy nhin cc phng php ny c nhc im l chi ph ln dogi thnh cc loi cp ny rt t so vi cp quang thng thng.

Hin nay ngi ta ang nghin cu s dng FBG c chu k thay i b tn sc.

u im ca phng php ny l thit b c kch thc nh gn, d ch to v hot

ng c hiu qu.

FBG chu k bin i tuyn tnh l mt si quang n mode c mt on li c

ghi nhng cch t c chu k thay i tuyn tnh dc theo chiu di ca si quang.

( ) ( )0 lz z = + (1.12)

0 l chu k im bt u ca on cch t, l l s thay i tuyn tnh dc

theo chiu di ca on cch t.

Ti v tr z trn on cch t Bragg, mt sng nh sng s b phn x ngc tr li

nu bc sng ca n tho mn cng thc:

( ) ( ) ( )2B effz n z z = (1.13)

( )B z l bc sng ti v tr z tng ng vi chu l cch t ( )z .

c tnh ca FBG chu k bin i tuyn tnh l ti nhng v tr tng ng vi chu

k di hn s phn x nhng nh sng c bc sng di hn.

Gi s xung tn hiu i vo u c chu k di hn ca on cch t.Khi , nhng

bc sng di hn s b phn x gn phn u ca on cch t hn. Ni cch khc,

nhng bc sng ngn hn s phi i mt qung ng xa hn trong on cch t trc

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khi chng c phn x ngc tr li. Kt qu l mt khong thi gian tr d s c to

ra gia thnh phn bc sng ngn so vi thnh phn bc sng di.

e2 1ff

c

n Ld

c =

(1.14)

Trong d l khong thi gian tr, neff l chit sut hiu dng, L l di on

cch t Bragg, c l vn tc nh sng trong chn khng, c l hiu s gia bc sng b

phn x u on cch t (thnh phn bc sng di nht) so vi bc sng b phn

x cui on cch t (thnh phn ngn nht).

ngn di

FBG

Hnh 1.16: Nguyn l b tn sc ca FBG chu k bin i tuyn tnh

y l hin tng ngc vi hin tng tn sc v l nguyn l ca thit b b tn

sc trong mng thng tin quang dng cch t Bragg chu k thay i tuyn tnh.

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Tx

EDFA

Rx

Circulator

inputBroadened

pulseRecompressed

pulse

Hnh 1.17: M hnh c bn ca thit b b tn sc

dng cch t Bragg chu k thay i tuyn tnh

Trn hnh v circulator l thit b ghp ni quang ch cho nh sng i ln lt cc

cng 1, 2, 3 theo chiu kim ng h. Mt xung b gin rng sau khi c khuch i s

i qua mt circulator ti on cch t Bragg c chu k bin i nh hnh v. Ti

on cch t, thnh phn bc sng ngn ti trc do tn sc s phi i thm qung

ng na trc khi c phn x ngc li ti thit b u 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 i qua thit b b c co li.

1.3.4. ng dng trong cm bin

Bng nhng u im ca mnh, hin nay FBG v ang c ng dng rt nhiu

trong ch to cm bin quang.Cc ng dng ny s c nghin cu chi tit hn trong

chng 2.

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CHNG 2. CM BIN QUANG SI S DNG CCH

T BRAGG

Vi rt nhiu u im ca mnh nh n nh trong qu trnh s dng, hiu sut cao

,c kch thc nh, d s dng v g b khi cn thit,c bit l khng chu nh

hng ca nhiu in t trng,FBG hin ang c nghin cu v ng dng rt nhiu

trong vic ch to cm bin quang si.

Trong chng 2 ny chng ta s i tm hiu mt s loi cm bin ang c ng

dng rng ri trong thc t hin nay:

Cm bin nhit . Cm bin sc cng.

Cm bin gia tc FBG.

Cm bin o mi trng lng.

Cm bin o a chn.

2.1. FBG lm cm bin nhit

Nguyn l: ta c

( )[ ]1B eB

p T

= + (2.1)

l h s dn n nhit (khong 610 ), ep l h s quang n hi ca thu tinh (

0,22e

p cho Silica), l h s quang nhit ca thu tinh (chit sut thay i theo T,

khong

5

10

).

T cng thc (2.1) ta thy T thay i khi B thay i, do da vo s dch

bc sng Bragg ta c th bit c s thay i ca nhit . Cm bin nhit s

dng FBG thng s dng k thut nhng FBG vo mi trng c h s dn n nhit

ln lm tng nhy theo T ca FBG. Cm bin dng ny kt hp c dn n v sc

cng tc ng ln si quang .

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2.2. FBG lm cm bin sc cng

Nguyn l: S cm bin do lc cng dc theo trc ca FBG cho bi phng trnh

1 12

eff eff BB eff

B eff

n nn L LL L n L L

= + = +

teff

e

eff

nLP

n L

=

v kt hp vi 1 1 1

LN

L L L

= =

ta c:

( )1B eB

LP

L

= (2.2)

Trong :

B l dch bc sng,

N l s chu k ca cch t trong FBG,

eP l hng s n hi quang hiu dng (gi tr trung bnh ca eP l 0,22)

T phng trnh (2.2) ta thy L thay i khi B , do da vo s dch bc

sng Bragg ta c th bit c s thay i sc cng.

2.3. Cm bin gia tc da trn FBG cho cng trnh kin trc xy dng dn

dng

2.3.1. Gii thiu

Cm bin gia tc l mt phn quan trng cu thnh mt h thng gim st cht

lng cng trnh kin trc xy dng dn dng c bit l pht hin nhng thit hi do

ng t v gi bo.Cm bin gia tc quang c rt nhiu u im so vi cm bin gia tc in thng

thng v d nh s min dch ca n vi nhiu in trng v kh nng truyn tn

hiu qua khong cch xa m khng cn c thm cc b khuch i.Mi y,chng ta

pht trin mt loi cm bin gia tc quang mi s dng yu t cch t Bragg trong si.

Cm bin gia tc ny c ch to c nhy cao c 1 pm/Gal trong phm

vi tn s thp. nhy qua trc c gim ti mc ti thiu bng cch s dng mt l

xo l.C ch lm vic ca sensor ny bo m s phn b sc cng ng u trn yu t

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cch t Bragg do phn x Bragg ti a s khng b gim.Mt khc,mi trng cch

t Bragg cn c gn mt ci gi ko cng to ra bin dng mt cch thch

hp.Bin dng ny khng c ln hn gii hn lm vic ca si quang trong cng

nghip truyn thng.Nhng mc bin dng s gy nguy hi v kt qu l s hng trong

mt thi gian ngn s dng. vt qua khuyt im ny th vic phn loi bin dng

c ch n.Vi vic phn loi ny, thi gian tn ti ca cch t Bragg c

ko di ti khong 50 nm bng vi 8000 bin dng nh t vo cch t Bragg.Nhng

im c li ca kh nng phi hp c chng minh bi cm bin o gia tc s

dng cch t FBG v cm bin o p lc s dng FBG.

2.3.2. Thit k ca sensor gia tc FBG

S ca mt sensor gia tc FBG c th hin trn hnh 2.1.Sensor gia tc ny

gm mt n cn bng cng hnh ch L,mt khi c v mt l xo. pht hin bin

dng tc ng vo sensor th cch t Bragg trong si quang phi t v tr gia 2 im

A v B. N c lin kt vi cm bin gia tc 2 im ny.Cch t Bragg cn c

ko cng . s dng c cu hnh ny th mi trng cch t Bragg phi c phn

b bin dng mt cch ng u v vic o di ca n phi c c im l kt qu

phn hi nhanh m khng b m rng ra.im c bit l gi c phn gii ca

sensor trong phm vi bin rng.

Hnh chiu mt v hnh chiu cnh ca nguyn mu mt sensor gia tc c thhin trong hnh 2.2.Phn bn trong c th hin trong hnh 2.3.Mt l xo l c s

dng trong sensor cc tiu nhy qua trc. t c nhy cao trong vng tn

s thp,tn s t nhin c chnh thnh 45Hz.Trong phn tch di y,sensor gia tc

c lm mu ca mt h thng t do khng c s chng rung, vng chc ca cch

t Bragg c xt n yu t l xo K .

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Hnh 2.1: S khi ca sensor gia tc FBG

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Hnh 2.2: Hnh chiu mt v cnh ca sensor gia tc FBG

Hnh 2.3: Hnh dng bn trong ca sensor gia tc FBG

Phng trnh chuyn ng m t h thng trong hnh 1 :

(2.3)

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Khi

(2.4)

Chia c 2 v cho M ta c:

(2.5)

Trong

0

K

M = (2.6)

Tng ng vi tn s t nhin ca sensor gia tc.Khi m gia tc trng trng l

hm iu ha ca tn s

(2.7)

Cho php chng miu t chuyn ng ca vt M dng sau:

(2.8)

Bin thu c khi thay th phng trnh (2.7) v (2.8 ) vo phng trnh

(2.3):

2 20 0

1 1

1 ( / ) gY A

=

(2.9)

Ta c th hiu rng gia tc trng trng t l vi dch chuyn ca vt khi Y

trong mt vng tn s thp v bin t l nghch vi bnh phng tn s t nhin.Tr

s bin dng gy ra trong cch t Bragg c biu din xp x di dng:

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2

0

/ 1g

d lA

L

(2.10)

Tn s t nhin ca nguyn mu l 45 Hz.Chiu di hiu dng ca cch t Bragg

l 30 mm.H s /d l l 0.2.Vi iu kin 1.0 Gal( 2/c m s ) gy ra 0,83 n v bin

dng trong cch t Bragg.Khi mt cch t Bragg bc sng 1550nm c s dng,

nhy ca s thay i bc sng l 1,2 pm/n v bin dng.V th, bin gia tc ca

1.0 Gal tng ng vi 1pm bc sng thay i ca bc sng cch t Bragg.Mi quan

h gia dch bc sng Bragg (pm) v bin gia tc gA (Gal ) c th c

biu din n gin di dng sau:

1.0 gA = (2.11)2.4. S dng FBG trong cm bin o mi trng lng

S dng kh nng ghp chung ca cc cm bin ri rc da trn FBG, mt cm

bin gia tc c th FBG c tch hp chung cm bin p lc o mi trng lng.

Mt cm bin gia tc FBG c th c s dng pht hin cc phn ng gy ra gia tc

ca lp t, trong khi cc b cm bin FBG p lc s o p lc nc trong lng t. Kt

hp cc d liu p lc nc vi d liu gia tc trong cc mi trng lng di mt t

c th nh gi kh nng xy ra trn ng t. Nh nu trong v d ny, mt s loighp cc b cm bin s l mt tnh nng hp dn ca h thng da trn cm bin FBG.

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Hnh 2.4: FBG cm bin p lc

Hnh 2.5: Cm bin o mi trng lng bao gm cc b cm bin gia tc FBG

v cm bin p lc FBG

2.5. Cm bin FBG o a chn

Cm bin si quang s dng cch t Bragg c mt s li th nh khng b

nhiu trng in t, gn nh, v tiu th nng lng thp. Quan trng nht, cm bin

FBG c nhy cao trong vic thu cc bin dng c hc (c th pht hin c s bin

dng c micro). Nguyn tc c bn ca h thng cm bin a chn FBG l n bin rungng ca mt t vo cc tn hiu cm bin ca FBG thng qua thit k c kh, v sau

khi qua iu ch quang hc to ra in p u ra tng t t l thun vi nhng thay

i ca chng.

Mu th nghim cm bin FBG o a chn bao gm vic thit k in-quang,

thit k c kh v phn cng v giao din phn mm ca h thng cm bin. Vic th

nghim th nghim ca h thng c thc hin c h thng trn nhiu tn rung ng.

Cc nghin cu v cc tnh cht cm bin cho thy cm bin c nhy cao (2500 mV /

g 90 Hz) cho tn hiu gia tc trong phm vi 80 dB, tuyn tnh tt v n nh sau khi

tch hp thnh thit b.

2.5.1. Cu trc c kh ca cc u cm bin

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Hnh 2.6:

S thit

k

Vic thit

k c kh

cm bingia tc s

dng FBG c th hin trong hnh 2.6. Hai u ca cm bin si cch t Bragg c

gn trc tip trn thanh l xo l ca mt cu hnh L. Cch t Bragg c ko cng

t c s phn b bin dng ng u dc theo cch t Bragg. Bng cch s dng

cu hnh ny, cch t Bragg lun lun b cng phn phi ng u dc theo chiu di

o ca n m bo c tnh phn x sc nt m khng m rng trong ph phn x.

L xo l c s dng y gim thiu s nhy rung ng qua trc.Vt

khi (vt liu: ng thau, trng lng: 10,6 gram) c gn vo mt u ca l xo l

(vt liu: thp khng r, chiu di: 4 cm, chiu rng: 1,2 cm, dy: 0,2 cm). u cn

li ca l l c gn bi mt ct (chiu cao: 1,27 cm). Ct ny l c nh trn v

cu hp cha cm bin.

Tt c cc yu t ca cm bin c ng gi ch c si quang ko di ra. N

bo v cc thnh phn di tc ng c hc bn ngoi khng b va p hoc h hng.

Trong th nghim ton b cm bin c trn di mt t. Cc cm bin tip tc

c ng hp c c cc giao din kt ni (FCPC) gia cp quang v im ni lnkhi mt t.

Sng a chn t tt c cc hng va chm mt t dc theo b mt trn u

cm bin,nhng sng a chn ny to ra nhng rung ng thay trn v cm bin cng

vi cc cc h tr ti mt u ca l xo l. Trong khi vt khi u kia ca l xo l

vn cn tnh, n gy ra s rung ng trn cm bin FBG.

S thay i bin dng ca si cch t Bragg c th c pht hin bi s dch

chuyn bc sng Bragg theo hiu ng Bragg . Trong thit k, cch t Bragg hot ng

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ti bc sng 1550 nm. bin dng bc sng 1550 nm l ~ 1pm/. Nh vy, ng

vi bin dng 1000 s dn n mt s thay i bc sng 1 nm ca mt b cm

bin FBG. S thay i bc sng ca b cm bin FBG c pht hin thng qua h

thng bin i quang in.

Vic thit k gim xc cng l mt yu t quan trng trong h thng l xo khi

lng. Mt gim xc tt s sinh cc phn ng tn s thp, trong khi mt gim sc cht

lng thp s cho kt qu dao ng khng ng vi dao ng ca l xo l. Gim xc

bng cch gn keo silicon di ca khi lng v u cm bin c bn cho kt qu

kh tt o dao ng a chn.

Hnh 2.7: S h thng thit b cm bin FBG o a chn

S thit b cm bin FBG o a chn c trnh by trong hnh 2.7.Thnh

phn thit b gm cc ngun pht quang ph rng, FBG kt hp vi cu hnh l xo khi

lng v b gim xc, FBG so snh, b phn x quang vng, b chia 3dB quang si, b

thu tn hiu quang v phn cng x l tn hiu.

nh sng t mt ngun pht ph rng (bc sng trung tm ti 1550nm v chiurng mt quang ph ca 40 nm) c a vo mt si n mt, v sau c a vo

mt cng ca b phn x vng. nh sng i vo b phn cm bin v c phn x t

cc cm bin FBG quay tr li vo mt cng ca b ghp 3dB, sau i vo vo b

cch t Chirp so snh.

nh sng phn x t cch t Chirp i ra b ghp 3dB, v sau i vo b tch

sng quang (photodiode) tn hiu quang hc c chuyn thnh tn hiu in. Tn

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hiu in t photodiode s c khuch i v lc in t , sau c x l bng

chng trnh LabVIEW.

C hai cch t FBG cm bin v so snh c cng mt bc sng trung tm

trong iu kin tnh (bc sng 1550nm). Cm bin FBG o mi trng c thay ibc sng do tc ng c hc trong khi cc cch t so snh khng c tc ng lc c

hc trn . Cm bin cn c thit k c iu chnh tn s trong vng 10-200 Hz.

th nghim v chun ha thit b cm bin, u FBG o c gn trn mt

my rung vi cc gi tr gia tc c bit trc .

Hnh 2.8: S th hin s tuyn tnh v lp li gi tr o ca FBG

Hnh 2.8 trnh by kt qu th nghim v chun ha FBG o gia tc, ta c th

thy tn hiu c c trng tuyn tnh gia lc tc ng v gi tr chuyn dch bc sng

ca FBG. Th nghim c tin hnh bng tc ng sng hnh sin v quan st u ra cacc cm bin FBG. lp li ca cc gi tr o ca cm bin FBG cng c kim

nghim. n nh ca FBG o gia tc theo thi gian hot ng c trnh by trn

hnh 2.9.

2.5.2. Tn s p ng ca cm bin FBG gia tc

Cc th nghim tn s p ng c thc hin bng cc my rung vi sng

hnh sin c cc tn s khc nhau t 10 n 120 Hz so snh vi cc ga tr cc i ca tn

hiu li ra ca cm bin FBG. Ti tn s dao ng 110 Hz tn hiu li ra ca FBG t

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cc i, ngha l FBG c nhy ln nht ti tn s ny. Tuy nhin cm bin FBG c

th o c cc dao ng a chn trong di tn s 10-110 Hz vi nhy c th x l

c.

Hnh2.9: Tn hiu o dao ng ca FBG thay i theo thi gian hot ng

Hnh 2.10: nhy ca tn hiu FBG ph thuc tn s dao ng

Ta c th tng nhy cm bin FBG o rung ng a chn bng cch tng

cng sut pht x ca ngun pht quang ph rng hoc s dng photodiode c nhy

cao. Tng cng sut quang trong FBG s nng cao t s tn hiu trn nhiu (Signal-

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Noise-Ratio:SNR) do lm tng nhy ca thit b. Cc ngun nhiu (tp m) cng

nh hng n bng tn hot ng v nhy pht hin ti thiu ca h thng. Ngoi

ra, nhy pht hin ti thiu ca thit b c th tng ln bng phng php nng cp

cc b khuch i in bng rng v b lc tn.

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CHNG 3. THC NGHIM V KT QU THU C

Trong chng 2 chng ta i nghin cu v tm hiu v mt s loi cm bin

c s dng trong thc t hin nay.

Trong chng 3 ny (phn thc nghim), chng ta s tin hnh xy dng v kho

st mt loi cm bin khc l cm bin o dch chuyn FBG.

3.1. Kho st FBG sensor o dch chuyn

- Mu lm th nghim

Hnh 3.1: S mu th nghim

Trong th nghim ny,chng ta dng mt thanh nhm c chiu di L=20cm c

t trn cao v mt u c gi c nh trn .Trn thanh ta gn mt FBG co bc

sng phn x l 1552nm.Ngun ASE v si quang pha tp Er c s dng nh l

ngun sng vo thng qua b ghp ni quang 3dB.nh sng phn x s c o bng

my ph OSA.

cong ca thanh ti v tr x s c tnh bi:

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3

( ) 12 ( )( )

( )

M x F L xx

EI x Eh b

= = (3.1)

Trong ( )M x v ( )I x ln lt l moment un cong v moment qun tnh ca tit

din ca thanh ti v tr x.E l h s Youngs. L v h ln lt l di v dy cathanh.F l lc tc dng vo u t do ca thanh. b l rng ca thanh ti im c

nh.Trn hnh 3.1 chng ta s dng thanh hnh ch nht,trong trng hp tng qut th

cong s l hm ca dch chuyn ti v tr x :

322 2

2( ) | | [1+( ) ]d s ds

xdx dx

= (3.2)

Trong s l dich chuyn ca thanh ti v tr x.

Do dng c th nghim cn thiu nn y,chng ta ch kho st FBG sensor ny

iu kin nhit khng thay i ( 029 C).

- Cc thit b chnh dng trong th nghim

* My phn tch ph

Cc thng s chnh ca my phn tch ph Advantest Q8384:

- Hng sn xut Advantest Japan

- Nm sn xut 2005

- Vng bc sng 600nm1700nm

- chnh xc = 20pm

- phn gii 0,01nm

- Vng ng lc 60dB 0,05dB

- Vng hot ng -87dBm23dBm

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Hnh 3.2: My phn tch ph (OSA)

*My hn si quang: Model Fiter S199 Japan

Si quang c hn bng ngun h quang (nhit ln hn 20000K). Cc mi

hn c suy hao thp (khong 0,01 0,08dBm).

* Ngun

Ngun pht sng ph rng c dng trong thc nghim l ngun pht x ngunhin c khuych i (ASE) ca b khuych i quang si pha tp Erbium (EDFA)

cho vng bc sng 1550nm, rng ph ASE l 50nm (1520nm 1570nm) hon

ton nm trong vng ca s th 3 ca mng thng tin quang hin nay.

* B ghp ni quang: 3dB coupler

* Cc FBG

Cc FBG s dng trong cc thc nghim c chiu di 1cm c phn x t t70% n 90% c ch to t si quang SiO2pha 1820% GeO2 c ch to ti

phng th nghim trng im Quang hc thuc Vin Khoa hc Vt liu-Vin Khoa hc

v Cng ngh Vit Nam.

- Tin hnh th nghim:

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Tc dng ln lt cc lc khc nhau vo u kia ca thanh bng cch t cc qu

nng c khi lng khc nhau ln u thanh .Sau o ph phn x v cng sut bng

my ph (OSA) tng ng vi dch chuyn ca thanh.

3.2. Kt qu v nhn xt

Trong th nghim ny, ta s dng FBG c nhy cao 100%.Bc sng nh ca

FBG l 1552nm. Bng cch thay i lc tc dng vo u ca thanh ti nhit xc

nh ( 029 c ) ta thu c mt s kt qu nh sau:

Hnh 3.4: S thay i bc sng phn x theo dch chuyn

Ta thy dch chuyn ca u thanh to ra mt ng bin thin tuyn tnh trong

rng di tn phn x ca cch t, v c hin th bng cch tn hiu phn x t cch

t s dng OSA.

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Trong th nghim ny, dch chuyn ca thanh trong khong 030 mm, tng

ng vi l dch bc sng trong khong 1552.136 1552.405 nm.

dch bc sng khng ln l do mt s nguyn nhn nh khi ta tc dng lc

vo u thanh lm cho thanh dao ng dn ti ph b thay i theo, thanh lm bng chtliu nhm (Al) c tn s dao ng khc vi (Fe).

Bng tng kt s thay i bc sng theo dch chuyn

dch chuyn (mm) Bc sng(nm)

0 1552.1365 1552.244

9 1552.302

13 1552.351

17 1552.376

23 1552.396

27 1552.405

Cc kt qu thc nghim kho st s dch nh ph phn x khi ta thay i dch

chuyn ca thanh bng cch tc dng cc lc khc nhau vo u ca thanh c th

hin trn hnh 3.5 di y:

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Hnh 3.5: dch ph phn x khi thay i dch chuynVi kt qu thu c ta c th thy s thay i ca ph phn x khi thanh dch

chuyn tuy nhin dch ph o c l khng ln ( ch nm trong khong

15521552,5 nm )

-Mt s hng pht trin ca sensor o dch chuyn FBG:

Ta c th ci tin phn c kh ca mu thay i dng lc tc dng vo thanh.

Lc F y c th sinh ra t cc dng khc nhau nh : lc do tc ng ca d chn, lc

do tc ng ca phng tin ln cu ng,.T ta c th thay i c dch

chuyn ca thanh v nh th sensor o dch chuyn FBG ny s c tc dng nh

sensor o gia tc hay sensor o d chn,.

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KT LUN

Qua mt thi gian tm hiu nghin cu v tng hp v cch t Bragg si quang,

em thu c mt s kt qu nh sau:

Nm bt c tng quan v cc tnh cht quang ca cch t Bragg trong si(FBG).

Tm hiu v tham gia ch to FBG bng phng php giao thoa k s dngchm Laser UV 248nm.

Tm hiu mt s cu hnh ca mt s cm bin s dng cch t Bragg trong sinh:cm bin o gia tc,cm bin o d chn, cm bin o dch chuyn.

Xy dng mt cm bin o dch chuyn s dng cch t Bragg trong si,vthu c kt qu l dch trong khong 0-30mm,v bc sng thay itrong khong 1552-1552.5 nm.

Vi cc kt qu thu c trong kha lun,em hy vng rng c th dng FBG

lm cc sensor vi nhy cao v chnh xc.

Trong tng lai, cch t Bragg si quang s cn c nhiu ng dng quan trng cn

c nghin cu s dng ht tim nng. iu i hi phi c nhng nghin cu

su v ton din hn na v kh nng ca dng thit b ny.Trong kha lun ny chc chn em khng th trnh khi nhiu thiu st. Em mong

c s ch bo v gp ca cc thy c v cc bn.

xut hng nghin cu tip theo:

Kho st qu trnh dch nh ph ca FBG vi cc iu kin vt l khc nhau,cc

thit k c kh khc nhau ca sensor.

Ch to cc h thng cm bin s dng FBG v ng dng chng trong thc t

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TI LIU THAM KHO

Ting Vit

[1] Thanh Hu-Lun Vn Thc s Khoa hc Vt l, i hc S phm H Ni 2006.

[2] V Don Min-Bi ging thng tin quang cho ngnh Vt l k thutKhoa Vt l

k thut v cng ngh nano, i hc Cng ngh, i hc Quc gia H Ni ,2007.

Ting Anh

[3] H.Y.Au, S.K.Khijwania, H.Y.Tam-Fiber Bragg Grating Based Accelerometer-

Department of Electronic Engineering, The Hong Kong Polytechnic University,

Hong Kong, China Department of Physics, Indian Institute of TechnologyGuwahati, Assam, India.

[4] A.Mita- Fiber Bragg Grating-Based Acceleration Sensors for Civil and Building

Structures Graduate School of Science and Technology, Keio University 3-14-1

Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

[5] Y.-J.Rao,In-Fiber Bragg Grating Sensors, Meas.Sci.Technol, 8, 1997, 355-375.

[6] Changyu Shen, Chuan Zhong- Novel Temperature-insensitive fiber Bragg grating

sensor for displacement measurement Institute of Optoelectronic Technology,China Jiliang University, Hangzhou, China, 310018.

[7] Yan Zhang,Sanguo Li,Jing Ning,Zhifan Yin,Hong-liang Cui- Sesmic wave detection

system based on fiber optic sensor- Department of Physics and Engineering Physic

Stevens Institute of Technology, Castle Point on Hudson, Hoboken , NJ, USA,

07030.

[8] Zhi Zhou, Thomas W.Graver,Luke Hsu,Jin-Ping Ou-Techniques of Advanced FBG

sensors: fabrication, demodulation,encapsulation and their application in thestructural health monitoring of bridges-Pacific Science Review,vol .5, 2003, pp .

116-121.

nghiÊn cỨu chẾ tẠo cẢm biẾn quang sỢi sỬ dỤng cÁch tỬ bragg

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