Sensor with high-sensitivity optical fiber having a holographic detector comprising a liquid crystal light valve

An optical fiber sensor for locating an excitation in proximity to an optical fiber assembly, said excitation inducing a modulation of the phase of an optical signal propagating in said optical fiber assembly, said sensor comprising:

• a laser assembly of at least one laser, said laser assembly being configured to emit N laser beams indexed i with N>1, of respective emission wavelength λi,
• an optical fiber assembly comprising N successive sections indexed i, each section comprising a selective reflection device for an associated emission wavelength λi, the indexes being fixed relative to an end of said fiber assembly,
• an optical system configured to:
• inject, through said end, said laser beams
• receive, through said end, N signal beams indexed i respectively of wavelengths λi, each signal beam being derived from the reflection, on the reflection device associated with the wavelength Δi, of the laser beam of wavelength λi injected then propagated in said fiber assembly,
• generate N reference beams indexed i respectively of wavelengths λi, from the laser beam of emission wavelength λi,
• produce N interference areas indexed i, each area corresponding to the interference between a reference beam and a signal beam of the same emission wavelength λi,
• a holographic detector comprising:
• a liquid crystal light valve comprising a liquid crystal layer arranged between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths, said valve being arranged such that it at least partially covers said interference areas, said valve being configured to produce N holograms indexed i respectively from said N interference areas,
• at least one optical detector configured to detect N output optical signals indexed i diffracted respectively by said N holograms,
• a processing unit adapted to identify the section of said fiber assembly situated in proximity to said excitation to be located, from the N output optical signals detected.