Highly sensitive magnetic field sensor using tapered Mach–Zehnder interferometer

A fiber-optic Mach–Zehnder interferometer is proposed and experimentally demonstrated for magnetic field measurement. The device comprises an in-line sandwiched structure, i.e., a multi-single-multi mode structure that is sealed in a tube with a magnetic fluid (MF). The diameter of the single mode fiber is tapered down to 4.2 µm, which effectively improves the coupling and recoupling of the cladding-to-radiation modes and increases the interferometer's sensitivity to the refractive index change in the MF. As a result, the interference spectrum is highly sensitive to a magnetic field ranging from 0.24 to 2.0 mT with a wavelength-referenced magnetic sensitivity of −2.886 nm/mT and an intensity-referenced sensitivity of −8.0 dB/mT.