Method for measuring the Brillouin shift distribution along optical fiber based on the optical demodulation of the signals, and relevant apparatus

摘要

The invention concerns 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, characterised in that it comprises the following steps:A. launching a pump signal with an intensity that is sum of a continuous component and a sinusoidal component at frequency f₁, I_Pompa(z=0,t)=I_Pu0(1+m₁ cos(2πf₁t+φ₁)), and an optical probe signal with an intensity which is sum of a continuous component and a sinusoidal component at frequency f₂, I_probe (z = L,t) = I_pr0(1+m₂ cos(2πf₂t + φ₂)), said two frequencies f₁, and f₂ differing of a predefinable quantity f_m such that:$\mathop{\mathrm{image}}$L representing the total length of the measurement fiber, whilst φ₁ and φ₂are two initial arbitrary phases, holding moreover the following relationship : m₁,m₂1;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 f₁, and f₂ frequencies, with the above-mentioned constraints;D. repeating the phases from A to C, for a pre-determinable number of shifts at frequency v_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,v_i) at frequency f≈f₁ ≈f₂;E. elaborating the transfer functions obtained at the end of step D, in order to reconstruct the Brillouin shift distribution along the measurement fiber.;The invention further concerns an optoelectronic measurement apparatus (200) for distributed measurements of the Brillouin shift in optical fiber (40), characterised in that it implements the method according to the invention.