Brillouin Gain Spectra of Few Mode Fibres Gain Spectra FMF.pdf · 2017-11-29 · DOFI DOFI...
Transcript of Brillouin Gain Spectra of Few Mode Fibres Gain Spectra FMF.pdf · 2017-11-29 · DOFI DOFI...
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Brillouin Gain Spectra of Few Mode FibresLars Grüner-Nielsen (1), and Søren Herstrøm (2)
(1) Danish Optical Fiber Innovation, (2) OFS Fitel Denmark ApS
Slide no. 1
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Introduction• Known model* for single mode fibres has been expanded to include few mode fibres
• Brillouin gain is found from the overlap between guided optical mode and guided acoustic modes
• Model is tested on a two LP mode fibre
• Simulations are compared to measurements
* A. Kobyakov et al, “Stimulated Brillouin scattering in optical fibers,” Advances in Optics and Photonics, Vol. 2, no. 1, p. 1 (2010)
Slide no. 2
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Modeling 1
Slide no. 3
Acoustic modes are found by solving the acoustic wave equation:
)r()r(vkdr
)r(d
r
v
dr
)r(dv 2
B
2
A
2
B
2
A
2
22
A
The acoustic velocity vA(r) is found from the index profile Dn(r):
DD
DD
0)r(nfor)r(n1v
0)r(nfor)r(n1v)r(v
F2SiO,A
2GeO2SiO,A
A
GeO2 is > 0 and F is < 0. I.e. both GeO2 doping and F doping will lead to acoustic guided regions
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Modeling 2
Slide no. 4
Only modes with velocity lower than in the cladding are guided: 2SiO,A
B
m,B
m vk
v
2m,Bbw
2
m,B
2
m,Bbw
m,0m2/
2/G)(G
D
D
2r
0
2
0
m
2
Bm,Bbw
3
2
12
8
effm,0
f
rdrdEc
pn4G
DDm
m )(G)(G
Calculation of Brillouin gain efficiency G:
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Measurement setup
Slide no. 5
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Results
Slide no. 6
Fibre under test: two LP mode graded index fibre: L. Grüner-Nielsen et al., “Few Mode Transmission Fiberwith low DGD, low Mode Coupling, and low Loss,” J. Lightwave Technol., Vol. 30, no. 23, p. 3693 (2012)
Mode no.(m)
nB, LP01 G0,m
LP01
nB, LP11 G0,m
LP11
GHz (Wm)-1 GHz (Wm)-1
1 10.768 0.144 10.747 0.010
2 10.776 - 10.756 -
3 10.801 - 10.780 -
4 10.824 0.031 10.804 0.037
5 10.842 - 10.822 -
6 10.882 0.007 10.861 0.025
7 10.899 - 10.878 -
Mode no.(m)
nB, LP01 G0,m
LP01
nB, LP11 G0,m
LP11
GHz (Wm)-1 GHz (Wm)-1
8 10.940 0.002 10.920 0.012
9 10.969 - 10.949 -
10 10.999 - 10.978 0.005
11 11.051 - 11.031 -
12 11.057 - 11.037 0.002
13 11.115 - 11.094 0.001
14 11.137 - 11.117 -
14 guided acoustic modes found
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Index profile and mode distribution optical and all guided acoustic modes
Slide no. 7
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Index profile and mode distribution optical and acoustic core modes
Slide no. 8
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Index profile and mode distribution optical and acoustic ring modes
Slide no. 9
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Index profile and mode distribution optical and acoustic core & ring modes
Slide no. 10
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Modelled and measured Brillouin spectra
Slide no. 11
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Conclusion• The Brillouin gain efficiency and its spectrum is determined from the overlap between the
optical mode and the guided acoustic modes
• The Brillouin gain spectra differ between different optical modes due to dissimilar overlap between optical and acoustic modes
Slide no. 12