Optical fibre magnetic field sensors using ceramic magnetostrictive jackets

Abstract Optical fibres coated by magnetostrictive ceramic films were tested using a Mach–Zehnder interferometer in open-loop mode. The sensors exhibited excellent linearity and good sensitivity. The response of ceramic-jacketed fibres was not affected by small DC fluctuations due to the linear behaviour 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 Ni 0.97 Co 0.03 Fe 2 O 3 jackets. The latter one showed the best performance. A minimum detectable field of 3.2×10 −3 A/m for optical fibre jacketed with 2-μm-thick and 1-m-long Ni 0.97 Co 0.03 Fe 2 O 3 material has been achieved. A capability of detecting magnetic fields as low as 2.6×10 −7 A/m using a 10-μm-thick and 1-m-long Ni 0.97 Co 0.03 Fe 2 O 3 fibre jacket is proposed.