n - Fachhochschule Jena
n - Fachhochschule Jena
n - Fachhochschule Jena
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Distributed Fiber-Optic Sensor Systems<br />
• Principle: Optical Time Domain Reflectometry (OTDR)<br />
• Useable optical scattering processes:<br />
– RAMAN scattering R(T)=I a /I s =(λ s /λ a ) 4 exp(-hν/kT) → temperature<br />
– BRILLOUIN scattering ν B =2 n v A /λ → temperature, strain<br />
Local resolution: ∆L=c ∆t/2n ∆L=1m →∆t=10ns<br />
c – vacuum light velocity, n=1.5 (silica refractive index)<br />
Scattering spectrum of Ge-doped silica<br />
fiber (schematically)<br />
Raman scattering<br />
(Antistokes)<br />
≈<br />
∆λ R ≈40nm<br />
(≈13THz)<br />
≈<br />
Rayleigh scattering<br />
Brillouin scattering<br />
≈<br />
ν B ≈12GHz<br />
Raman scattering<br />
(Stokes)<br />
λ<br />
FOS - 55
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