Optical Fibres in Aeronautics, Robotics and Civil Engineering
Tutorial on optical fibres
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Transcript of Tutorial on optical fibres
Tutorial on optical fibresTutorial on optical fibres
F. ReynaudIRCOM LimogesÉquipe optique
F. ReynaudIRCOM LimogesÉquipe optique
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E cra n : v isu a lisa t io n d u fa iscea u d iffra c té
F ib re o p tiq u e
/a
a (d ia m è tre c o e u r )
0 (d iam ètre d ’u n gra in )
D im en sio n
D irec tio n
0= 2 O N
~
C a s d ’u n e f ib re o p tiq u e m u ltim o d e
n 1
n 2
t
I
E la rg issem en t d e l’ im p u lsio n
t
Is
12
2 > > 1
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optical fibre structure optical fibre structure
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S te p in d e x p ro file
n
R a d iu s .
G ra d e d in d e x p ro f i le
n
R a d iu s .
1) Generalities1) Generalities
M e c h a n ic a l c o a t in g
C la d d in g C o re
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Silica fibres typical refractive index : 1,45 – 1,50Refractive index difference
Core diameter : 5 à 50 µm Cladding diameter : 125 à 500 µm
%1gaine
gainemaxcoeur
n
nnn
%1
maxcore
claddingnnn
n cladding
Refractive index profil
optical fibre manufacturingoptical fibre manufacturing
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G a z (o x y g è n e + d o p a n t)
s il ic e tu b e
H e a te r (1 7 0 0 ° C )
In tern a l co a tin g C o lla p se step
H e a te r (1 9 0 0 ° C )
C o re C la d d in g
P reform m a n u fac tu r in g b y M C V D p ro cess
In te r n a l c o a tin g
1) preform manufacturing1) preform manufacturing
2) Drawing process2) Drawing process
P refo rm
O v en
C o a tin g
P o ly m er iza tio n u s in g U -V
C a b esta n M eca n ica lTests
F ib re ro ll
F ib re d ia m eter sen so r )
D ra w in g sp eed serv o co n tro l
D raw in g p ro cess
(Modified Chemical Vapour Deposition). PCVD (Plasma Chemical Vapour Deposition)OVPO (Outside Vapour Phase Oxydation
1) Generalities1) Generalities
2) Propagation in optical fibres2) Propagation in optical fibres
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m a x
C a se o f a n o p tica l f ib re
n 1
n 2C la d d in g
C o re
Geometrical optics
1)isin(n
nlim
2
1
Snell Decartes law :
n
To ta l re flex io n
i1 i1
n 1
n 2
i1 > ilim
)isin(n)isin(n 2211
1)cos(n
nmax
2
1
)n
narccos(
1
2
Possibility to trap light beams in an high refractive index area surrounded by a low refractive index area
i1
n 1
n 2
i2
n
R efra ct io n
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)sin(2i
Wave theory
P la n a r w a v eg u id e w ith m irro rs
a
In ten s ity
P o s itio n
2) Propagation in optical fibres2) Propagation in optical fibres
First example planar mirror guide
Propagation without losses:Intensity = 0 on mirrors
a = n i with n = integer
Two directions interference between two plane waves
n
a
)sin(2
)a2
nsin(Arc
For each n
one propagation mode
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a
n 2
n 2
n 1
In ten s ité
P o s itio n
2) Propagation in optical fibres2) Propagation in optical fibres
)sin(2i
Propagation without losses:Intensity =0 close to the core/cladding interface
a+ 2 = n i with n = integer
Two directions interference between two plane waves
Second example
Planar dielectric waveguide
Wave theory
One mode n ))2a(2
nsin(Arc
One angle n solution of the equation
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2) Propagation in optical fibres2) Propagation in optical fibres
a
n 2
n 2
n 1
In ten s ité
P o s itio n
Second example
Planar dielectric waveguide
Wave theory
))2a(2
nsin(Arcn
Limited number of modeIf only one>>>monomode
)n
narccos(
1
2n
)n
narccos(
1
2n
max
0
solutions
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E x a m p les o f m o d es L P F ib re
L P 0 1 L P 11 L P 2 1 L P 0 2
L a rg e v a r ie ty o f d irec t io n
a (c o re d ia m e tre r )
0 (O ne spot d iam etre))
N ea r fie ld
~O p tica l f ib re
2) Propagation in optical fibres2) Propagation in optical fibresWave theory
3 D interference
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2) Propagation in optical fibres2) Propagation in optical fibres
Properties of the modal structure
Decomposition of any optical field on the mode basis
a
n 2
n 2
n 1
In ten s ité
P o s itio n
Wave theory
Same transverse field distribution at the input and output
Propagation = phase shift z
n is the propagation constant
n
z.jnnout
ne.emod.aEPropagation = phase shiftn
nnin emod.aE
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m u lt im o d e o p tica l fib re
n 1
n 2
t
I
P u lse sp rea d in g
t
Is
12
2 > > 1
In p u t p u lse
2) Propagation in optical fibres2) Propagation in optical fibres
depends upon
Dispersion
Mode in a multimode fibre
Modal or intermodal dispersion
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2) Propagation in optical fibres2) Propagation in optical fibres
Dispersion
Wavelength dependent
t
M o n o m o d e fib re
n 1
n 2
t
IIs
12
P u lse sp rea d in gIn p u t p u lse
Chromatic or intramodal dispersion
-10
-5
0
5
10
15
20
25
1200 1300 1400 1500 1600
Wavelength (nm)C
hro
mat
ic d
isp
ersi
on
(p
s/n
m.k
m)
G.6
52 (0
.08
ps/n
m2 .k
m)
G.6
53
ED
FA
ban
dw
idth
G.6
55
G.6
55
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N ea r fie ld
0
F a r f ie ld
m a x 0 = /
D iffra c t io n =
Tra n sfo rm F o u r ier
D im e n s io n s D ire c tio n s (fa r f ie ld )
/a
F o u r ie rTr a n sfo r m
N ea r fie ld
3) Determination of the mode number3) Determination of the mode number
M
N
O
M N = a
x
d x
O ’
F e n te é lé m en ta ire d e la r ge u rd x s itu é e à la d is ta n ce x d e O
O O ' = x sin
Diffraction properties
Basic rules
General caseMultimode beam
Monomode beam
Cargèse sept 2002
L a rg e v a r ie ty o f d irec tio n
screen : fa r fie ldv isu a lisa tio n
/a
a (c o re d ia m e te r )
0 (O ne spot d iam eter))
N ea r fie ld
F a r f ie ld
0= 2 N A
~O p tica l f ib re
F o u r ie rTr a n sfo r m
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3) Determination of the mode number3) Determination of the mode number
Core diameter /a
Numerical apertureNA
Number of spots or speckles Number of modes
2221
nn)sin(NA Case of an optical fibre
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3) Determination of the mode number3) Determination of the mode number
NA20
2
220
)NA2(44s
4
aS
2
2
2
2
)NA2(4
4a
s
SN
2)NA2(
S4
a2
2
SN
a (c o re d ia m e tre r )
0 (O ne spot d iam etre))
N ea r fie ldOne specklediameter surface
Fibre core
Number of degrees of freedom
diameter surface
a
Warning: N is wavelength dependent
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3) Determination of the mode number3) Determination of the mode number
Two examples
n2=1.450
a=8µm
rad12.0nn)sin(NA 2221
Monomode fibre
1S
N2
n1=1.455
a=50µm
n2=1.450
n1=1.462
rad19.0nn)sin(NA 2221
esmod60S
N2
Multimode fibre
Warning: N is wavelength dependent
@ = 1.3µm @ = 1.3µm
4) Characterisation of optical fibres4) Characterisation of optical fibres
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F ib re h o ld er
F ib re
D étec to r
2221
nn)sin(NA
2
21
21
nn
nnR
Numerical aperture
Refractive index distribution
L ig h t so u rce
R e flec ted p o w er
O p tica l fib ren(radius)
radius
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4) Characterisation of optical fibres4) Characterisation of optical fibres
First step
Detector
Launching assembly
Fibre length L
10/010 LII
)I
I(Log
L
10
z
0
dB)P
P(Log10Loss
out
in
Fibre losses
1000 1200 1300 1400 1500 1600
1.0
Loss
(d
B/k
m)
0.1
0.5
0.2
Wavelength (nm)
Transmission fibre loss (silica)
I2
I1
Second step
Detector
Fibre length d
Launching assembly
=0
5) Optical fibre implementation5) Optical fibre implementationEquipe Optique
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x
0
L o sses d B
x / 0
0 .1 0 .2 0 .3 0 .4 0 .5
0 .5
1
2
3
0 .2
1 .7
Connectors
Plug with a ceramic ferule
FCPC
E2000
body
Loss as function of The transverse position error
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5) Optical fibre implementation5) Optical fibre implementation
A b r a s io n C o lla g e
1
2
3
F u s io n E tir a g e
F ib re o p t. 1
F ib re o p t. 2
1
2
3
4
1
2
3
4
couplers
Fusion splicing
polishing Glued
From 2 to 2
From 2 to 8
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principal use>> optical fibre telecommunications
6) Application of optical fibers6) Application of optical fibers
V (t)
L a ser P h o to d io d e
V ’(t)
Very high bit rate 1 Tbit/sec Very low losses
The solution for long distance signal propagation
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S o u rce
F ib reo p tiq u e
F ib reo p tiq u e
T (x )
M esu re d e la p u issa n ce
S o u rce
F ib reo p tiq u e
R (x )
M esu re d e lap u issa n ce
Optical fibre sensors
TemperaturePressureRotationChemical concentration
6) Application of optical fibers6) Application of optical fibers
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Possibility to built interferometers
Mach Zehnder configuration
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6) Application of optical fibers6) Application of optical fibers
See next lecture
D etec to r
L a ser d io d e
M o n o m o d e fib re
B S )
S
F O 1 (L )
F O 2 (L )
I= 2 I [1 + co s(2 )]0
L
L
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7) Material and new optical fibers7) Material and new optical fibers
UV0.3µm Visible
Near IR2µm
Far IR10µm
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DGD
Slow PSP
Fast PSP
7) Material and new optical fibers7) Material and new optical fibers
Polarisation preserving fibers
Highly birefringent fibres
core
cladding
Stress area
Propagation
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7) Material and new optical fibres7) Material and new optical fibres
structure
Photonic crystal fibres
Monomode over a very large spectral domain