Patent ID: 8575540

Claim:
A filter for an optical fibre ( 13 ) temperature sensor comprising at least one first ( 14 , 30 ) and one second optical filter for filtering an optical pulse reflected by said optical fibre ( 13 ), wherein said optical pulse lying within the range from 1570 nm and 1580 nm; said at least one first filter ( 14 , 30 ) and one second filter filtering two adjacent spectral windows ( 21 , 22 ) of the Raman anti-Stokes optical signals or Raman Stokes optical signals; said two adjacent spectral windows ( 21 , 22 ) of the Raman anti-Stokes optical signals or Raman Stokes optical signals are converted into a first electrical signal and a second electrical signal; said first filter ( 14 , 30 ) is a stopband filter centered on the Rayleigh optical signal; said second filter comprises a third and a fourth filter ( 31 ), said third filter being a passband filter centered on a first spectral window ( 21 ) of the Raman anti-Stokes signals, said fourth filter being a stopband filter for blocking said first spectral window ( 21 ) of the Raman anti-Stokes optical signals; said second filter comprises a fifth filter ( 32 ), coupled to said fourth filter, said fifth filter ( 32 ) being a passband filter which supplies a second spectral window ( 22 ), adjacent to said first spectral window ( 21 ), of the optical Raman anti-Stokes signals; said two adjacent optical spectral windows ( 21 , 22 ) lie within the range respectively of about 1450-1510 nm and about 1525-1565 nm.