Patent ID: 6885784

Claim:
A fiber laser sensor, in particular suitable for pressure measurement in oil boreholes, comprising a DFB fiber laser, which has a laser-amplifying fiber with a fiber Bragg grating resonator written in distributed fashion therein, a measurement quantity making it possible to induce a birefringence and beat frequency (Δν 1 , Δν 2 , Δν 3 ; Δν a , Δν b , Δν c , Δν d ) between modes (X, Y, LP 01 , LP 11 even , LP 11 odd , LP 21 even ) of the laser-amplifying fiber and measurement means for determining the beat frequency (Δν 1 , Δν 2 , Δν 3 ; Δν a , Δν b , Δν c , Δν d ) being present, wherein a) the laser-amplifying fiber has a nonrotationally symmetrical structure, b) an emission wavelength range and parameters (a, b, ΔN) of the laser-amplifying fiber are chosen in such a way that the emission wavelength range and a wavelength range in which at least two different spatial modes (LP 01 , LP 11 even , LP 11 odd , LP 21 even ) are propagatable overlap in a spectral region, and c) at least one grating period Λ of the fiber Bragg grating resonator is chosen in such a way that Bragg wavelengths (λ LP01 , λLP 11 even , λ LP11 odd , λLP 21 even ) assigned to the different spatial modes (LP 01 , LP 11 even , LP 11 odd , LP 21 even ) lie in the spectral region.