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Optical fibers coated by magnetostrictive ceramic films were tested with a Mach-Zehnder interferometer in an open-loop mode. The sensors exhibited excellent linearity and good sensitivity. The response of ceramic-jacketed fibers was not affected by small dc fluctuations that are due to the linear behavior of tested ceramic coatings in low magnetic fields. Tested ceramic materials included magnetite, γ-Fe(2) O(3), nickel ferrite, and cobalt-doped nickel ferrite (NCF2) jackets. The latter showed the best performance. A minimum detectable field of 3.2 × 10(-3) A/m for optical fiber jacketed with 2-μm-thick and 1-m-long NCF2 material has been achieved. The capability of detecting magnetic fields as low as 2.6 × 10(-7) A/m with a 10-μm-thick cobalt-doped nickel ferrite jacket is proposed.

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The main characteristics, geometrical and stress-induced birefringence of polarization maintaining single mode fibers with layered periodically stepped core were studied. The propagation constants of TE and TM modes and resulting geometrical birefringence were computed for both planar and cylindrical layered structures.Maximal birefringence in limit case of infinite number of layers and infinite wavelength was evaluated analytically. The stress-induced birefringence for such structures was computed using the Boundary Element Method.