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Novel microbend loss fiber optic hydrophones for direction sensing
Dual purpose fiber optic microbend loss sensors have been developed for
measurement of underwater acoustic wave amplitudes and for detection of the
direction of wave propagation. Cylindrical sensing elements with external threads
have fibers wound around them. Axial slots, cut along the length of the cylinder
and deeper than the threads, provide the microbends. Three different
construction schemes for cylindrical sensing elements are built. The dual purpose
hydrophones are characterized for frequencies ranging from 15 kHz to 75 kHz.
Based on the results, an improved design that uses the wavelength dependence
of microbend loss in a single mode fiber is proposed.