An optical fibre sensor for locating an excitation in the vicinity of an optical fibre assembly, said excitation inducing a modulation of the phase of an optical signal propagating in said optical fibre assembly, said sensor comprising: - a laser assembly of at least one laser, said laser assembly being configured to emit N laser beams (Fi) indexed i, with N > 1, with a respective emission wavelength λi; - an optical fibre assembly comprising N successive sections (Ti) indexed i, each section comprising a selective reflection device (Mi) of an associated emission wavelength λi, the indices being referenced relative to an end of said fibre assembly; an optical system configured to: inject said laser beams (Fi) via said end; receive N signal beams (Fsi) indexed i, respectively with wavelengths λi, via said end, each signal beam (Fsi) coming from the reflection, on the reflection device (Mi) associated with the wavelength λi, of the injected laser beam (Fi) of wavelength λi, then propagating in said fibre assembly; generate N reference beams (Fri) indexed i, respectively with wavelengths λi, from the laser beam (Fi) of emission wavelength Ai; produce N interference zones (Zi) indexed i, each zone corresponding to the interference between a reference beam (Fri) and a signal beam (Fsi) of the same emission wavelength λi, the sensor being characterised in that it comprises a holographic detector comprising: - a liquid crystal optical valve (LCLV) comprising a liquid crystal layer disposed between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths (λi), said valve (LCLV) being disposed so that it at least partially covers said interference zones (Zi), said valve being configured to produce N holograms (Hi) indexed i, respectively from said N interference zones (Zi); - at least one optical detector configured to detect N output optical signals (Fouti) indexed i, respectively diffracted by said N holograms; - a processing unit adapted to identify the section of said fibre assembly that is located in the vicinity of said excitation to be located from the N detected output optical signals (Fouti). - a laser assembly of at least one laser, said laser assembly being configured to emit N laser beams (Fi) indexed i, with N > 1, with a respective emission wavelength λi; - an optical fibre assembly comprising N successive sections (Ti) indexed i, each section comprising a selective reflection device (Mi) of an associated emission wavelength λi, the indices being referenced relative to an end of said fibre assembly; inject said laser beams (Fi) via said end; receive N signal beams (Fsi) indexed i, respectively with wavelengths λi, via said end, each signal beam (Fsi) coming from the reflection, on the reflection device (Mi) associated with the wavelength λi, of the injected laser beam (Fi) of wavelength λi, then propagating in said fibre assembly; generate N reference beams (Fri) indexed i, respectively with wavelengths λi, from the laser beam (Fi) of emission wavelength Ai; produce N interference zones (Zi) indexed i, each zone corresponding to the interference between a reference beam (Fri) and a signal beam (Fsi) of the same emission wavelength λi, the sensor being characterised in that it comprises a holographic detector comprising: - a liquid crystal optical valve (LCLV) comprising a liquid crystal layer disposed between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths (λi), said valve (LCLV) being disposed so that it at least partially covers said interference zones (Zi), said valve being configured to produce N holograms (Hi) indexed i, respectively from said N interference zones (Zi); - at least one optical detector configured to detect N output optical signals (Fouti) indexed i, respectively diffracted by said N holograms; - a processing unit adapted to identify the section of said fibre assembly that is located in the vicinity of said excitation to be located from the N detected output optical signals (Fouti). - a liquid crystal optical valve (LCLV) comprising a liquid crystal layer disposed between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths (λi), said valve (LCLV) being disposed so that it at least partially covers said interference zones (Zi), said valve being configured to produce N holograms (Hi) indexed i, respectively from said N interference zones (Zi); - at least one optical detector configured to detect N output optical signals (Fouti) indexed i, respectively diffracted by said N holograms; - a processing unit adapted to identify the section of said fibre assembly that is located in the vicinity of said excitation to be located from the N detected output optical signals (Fouti).