Curs 4

2013/2014

Curs◦ marti, 17-20, P4

◦ 2C 3C

14*2/3≈9.33

9÷10 C

Capitolul 4

3770

00

smc 8

00

0 1099790,21

f

c00

2

fT

12

n

cc 0

rn n

0

nfn

c 00

fT

12

1n

ITU G.692"the allowed channel frequencies are based on a 50 GHz grid with the reference frequency at 193.10 THz"SI"a source that emits monochromatic radiation of frequency 540·1012 Hz"

λ=f(n) !!

Examen!

Capitolul 5

un ghid de undadielectric ◦ miez

◦ teaca

Optical fibers

Tube

Strain relief(e.g., Kevlar)

Innerjacket

Sheath

Outerjacket

Unghi de acceptanta

Aperturanumerica

cACC nn sinsin 20

2

1

2

22

2

2

1

2

22 nn

n

nnnNA

ACCnNA sin0

n2 – miezn1 – teacan2 > n1 !!

Monomod

Multimod◦ cu salt de indice

◦ cu indice gradat

Frecventa normalizata

Numar de moduri

NAakNAa

V

2

22

2

g

gVN

L

mL

a - raza miezului

2k

Fibre monomod

NAa

NAV

a

C

C405.2

22

Exemplu:2a = 8.5μm

NA = 0.11

nm121011.0405.2

5.8C

405.2 CVV

exista un singur mod (solutiifc. Bessel)

b – coeficient de propagaremodal relativ

Propagarea luminiipoate fi explicatadoar prin teoriaelectromagnetica

Energia campului se extinde in teaca (diametrul efectiv al spotuluiluminos – MFD, Mode Field Diameter)

MFD > 2a Adancimea de patrundere in teaca

depinde de lungimea de unda, generand dispersia de ghid

Macrocurburi

Microcurburi

Imprastiere

Absorbtie

Multimod

Monomod v cresten scade

v scaden creste

2,1 nnRR extC

Absorbtie◦ 950nm

◦ 1244nm

◦ 1383nm

Apa!

in

out

P

PPierderi

in

out

P

P10log10dBPierderi

]lungime[km

B]Pierderi[ddB/kmAtenuare

dBmdBmdBPierderi inout PP

√

Stimulated Brillouin Scattering, SBC◦ difractia luminii inspre emitator datorita undelor

mecano-acustice generate in fibra◦ 6-10 dBm

Stimulated Raman Scattering, SRS◦ interactiunea luminii cu vibratiile moleculare◦ 27 dBm (~1W)

Self Phase Modulation, SPM◦ Frontiera impulsului implica indice de refractie variabil in

timp moduland faza impulsului◦ 5 dBm◦ Cross Phase Modulation, CPM

Four-Wave Mixing, FWM◦ 0 dBm

23

2

1NNNL

N = 2, NL = 4

N = 3, NL = 9

N = 16, NL = 1920

Propagarea cu viteze diferite a radiatiilor cu lungimi de unda diferite◦ intermodala (modala – depinde de prezenta

modurilor)

◦ intramodala (cromatica – depinde de lungimea de unda)

de material

de ghid

v

Lt 0

C

Cv

Lt

cos

2n

cv NAC cos

2

1220

n

nn

c

nLttt CSI

c

nLttt CSI

20

11

12

n

nn 2

2

02

NAnc

Lttt CSI

salt de indice

indice gradat

2

2

2

12

1

2

2

2 nc

NAL

n

nn

nc

nLdt

intarzierea intre

moduri cand1

1

12

n

nn

2

2

mod23

1

dt

2

2

2mod

3432 nc

NAL

c

nL

3

2

42

2

82 nc

NAL

c

nLdt

c

nL

34

2

2mod

12.01.0 NAn2 – miezn1 – teacan2 > n1 !!

d

dnnngr

2

2

d

nd

c

Lmat

SiO2

Neglijabila in fibrele multimod fata de dispersia modala

2

2

dV

VbdV

c

Lngh

b – constanta de propagarenormalizata

405.2 CVV

D(λ) ≈ 100 + 0.4 (850 - λ) [ps/nm/km] pentru 800 < λ < 900 nm

D(λ) ≤ 3,5 ps/nm/km pentru 1285 < λ < 1330 nm

D(λ) ≤ 17 ps/nm/km pentru 1525 < λ < 1575 nm

LDcr

3

400 -

4

S=)D(

3

400 -

4

S=)D(

S0 panta dispersiei –ps/nm2/km

0=)D( 0

nm002.0

Dispersia totala

Banda

Banda optica la 3 dB corespunde unei benzielectrice la 6 dB◦

Viteza legaturii

2

mod

2 crtot

GHz

nsB

tot

opt

44.0

elopt BB 2

GHzBsGbV el 2/

2~;~ IPIP elopt

Atenuarea e mai mica la 1550 nm

EDFAŸ (Erbium doped fibre amplifiers) opereaza in bandaaceasta

Sistemele WDM (Wavelength division Multiplexing) necestiabanda larga amplificata

Dispersie -100 ps/nm/km

Atenuare 0.5 dB/km

transmisii cu viteze diferite

LDcr

1550nm Efectul sursei

◦ fibra monomod cu dispersia 16ps/nm/km@1550◦ latimea spectrala a sursei Δλ=1nm◦ 50km

LDcr

pspscr 80050116

100<400<800<1600

1550nm Efectul sursei

◦ fibra monomod cu dispersia 16ps/nm/km@1550◦ latimea spectrala a sursei Δλ=0.1nm◦ 50km

LDcr

pspscr 80501.016

100≈80<400<1600

Efectul fibrei◦ fibra cu dipersie deplasata: 4ps/nm/km@1550◦ latimea spectrala a sursei Δλ=0.1nm◦ 50km

LDcr

pspscr 20501.04

20<100<400<1600

Efectul fibrei◦ fibra cu dipersie deplasata: 4ps/nm/km@1550◦ latimea spectrala a sursei Δλ=0.1nm◦ 150km

LDcr

pspscr 601501.04

60<100<400<1600

Diametru teaca = 125 μm

MFD = 9÷10 μm la 1300 nm

λC = 1100÷1280 nm Pierderi de curbura (la 1550 nm) mai mici de 1 dB

pentru 100 spire de fibra rulata pe un mosor cu 7.5 cm diametru

Dispersia in banda 1300 nm (1285-1330 nm) mai mica de 3.5 ps/nm/km. La 1550 nm dispersia trebuie sa fie mai mica de 20 ps/nm/km

Viteza de variatie a dispersiei (panta dispersiei S0) mai mica de 0.095 ps/nm2/km

ITU (International Telecommunication Union) is the United Nations specialized agency for information and communication technologies – ICTs

Atenuare 180 dB/km NA = 0.3 Diametru 1 mm Banda 125MHz (100m)

Laboratorul de microunde si optoelectronica

http://rf-opto.etti.tuiasi.ro

rdamian@etti.tuiasi.ro