Patent ID: 7515273

Claim:
A method for measuring the Brillouin shift distribution in optical fiber, comprising the launch of an optical pump signal from one end of the measurement fiber and an optical probe signal from the other end of the fiber, including: A. launching a pump signal with an intensity that is sum of a continuous component and a sinusoidal component at frequency f 1 , I Pump (z=0,t)=I Pu0 (1+m 1 cos(2πf 1 t+φ 1 )), and an optical probe signal with an intensity which is sum of a continuous component and a sinusoidal component at frequency f 2 , I Probe (z=L,t)=I Pr0 (1+m 2 cos(2πf 2 t+φ 2 )), said two frequencies f 1 and f 2 differing of a predefinable quantity f m such that: f 1 −f 2 =f m and f m <<f 1 , f 2 L representing the total length of the measurement fiber, whilst φ 1 and φ 2 are two initial arbitrary phases, holding moreover the following relationship: m 1 , m 2 <<1; B. measuring of the component at frequency f m which is present in the intensity spectrum of the probe signal at the exit of the measurement fiber, C. repeating the phases A and B with varying f 1 and f 2 frequencies, with the above-mentioned constraints; D. repeating the phases from A to C, for a pre-determinable number of shifts at frequency ν i , i=1, . . . , N shift , between the optical carrier of the probe signal and the optical carrier of the pump signal, and obtaining the correspondent transfer functions H(f, ν i ) at frequency f≈f 1 ≈f 2 ; E. elaborating the transfer functions obtained at the end of step D, in order to reconstruct the Brillouin shift distribution along the measurement fiber.