Abstract
A new setup is presented that solves the isolation problem, optimizes the recovery of the light signal, and prevents any unwanted reflex in a Michelson scheme on an interferometric fiber sensor. Phase modulation (PM) and frequency modulation (FM) are both treated as the result of the fiber-optic-induced phase shift. The demodulation aspect involved in the FM detection is investigated especially in order to establish a direct link between the modulation index and the integral phase shift. A novel approach that permits the direct FM–index recovery is also reported. PM– and FM–demodulating processes are tested experimentally to detect the phase shift induced by a 20-Hz dynamical deformation on the fiber. The FM results are compared for small values of phase shift with the ones given by the PM scheme, whereas for large values of phase shifts, they are compared with others obtained directly from the spectral display. The measurements confirm the linear behavior of the fiber-strain sensor in the four decades of values, show the correctness of the analysis, and point out the possibility of using the fiber-strain sensor with engineering values of deformation.
© 1985 Optical Society of America
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