All-fiber interferometers employing magnetostrictive elements have successfully measured magnetic fields down to the 10−5-10−6-G level at various frequencies in the dc 10-Hz range.1,2 Typically, the transducing element in fiber magnetometers consists of single-mode fiber bonded to a metallic glass ribbon in either a planar or cylindrical configuration.3 A dither magnetic field hω cosω t is applied to the transducer. Due to the nonlinear magnetostrictive response of the metallic glass, the dither field mixes with the external low-frequency field to be measured, HΩ cosΩt (ω » Ω). Consequently, information on the HΩ field is contained in the phase signal sidebands ϕω±Ω and can be conveniently detected using lock-in amplification. We demonstrate a minimum detectable field level (HΩ)min of 0.2 × 10−6 G, rms/√Hz at 10 Hz.
© 1987 Optical Society of AmericaPDF Article