MetglasTM 2605 SC cast alloy was deposited directly onto single-mode optical fibers. Very thick amorphous films of 5 to 15 micrometers thickness were produced by triode-magnetron sputtering. The coated fibers were used as magnetic field sensing elements in one arm of a Mach-Zehnder interferometer. In the reference arm a section of fiber was wound around a piezoelectric (PZT) cylinder which was driven by a feedback correction signal to keep the sensor operating at quadrature. The sensing element was placed inside a chamber containing Helmholtz coils which produced both a dc field and an ac dither field. The magnetostructure response of the coating and the resulting phase shift in the optical fiber are dependent upon both of these fields. The phase shifts were measured as a function of the magnitudes of the dc and ac fields and the frequency of the ac field. The magnetostrictive responses had maximum values at discrete resonance frequencies. Experimental values of the magnetostriction parameter were obtained using experimental values of the phase shifts along with theoretical calculations of the magnetostrictive response. These calculations were based on a model of coherent rotation of magnetization and also an elastic model of the magnetostrictive strains for a cylindrical geometry. The maximum values of the magnetostriction parameter for the coated- fiber FOMS at resonance was estimated to be 10-5/Oe2 in comparison with non-resonant values of 5X10-5/Oe2 and 1X10-6/Oe2 for amorphous metal wire transducers and Metglas strip transducers, respectively, and 5X10-6/Oe2 for resonant Metglas cylindrical transducers.
Fiber optic Mach-Zehnder interferometric sensors for the measurement of various physical parameters such as pressure temperature and magnetic fields are well known and documented. This paper deals with the construction of a fiber optic sensor incorporating He-Ne and diode lasers. Preliminary experimental results for temperature sensing are reported.
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