Highly Sensitivity Fiber-Optic Vector Magnetometer Based on Two-Mode Fiber and Magnetic Fluid

A compact fiber-optic vector magnetic field sensor combining a tapered two-mode fiber (TMF) and magnetic fluid is proposed and experimentally demonstrated. The modal interference effect is mainly caused by LP₀₁ and LP₁₁ modes, and an additional refractive-index-modulation (RIM) on TMF taper lateral is introduced by femtosecond laser for enhancing the interference intensity. Moreover, the RIM provides the sensor a significant direction-dependence due to its asymmetric position relatively to fiber axis. The spectral response to magnetic field intensity and direction of the proposed sensors has been investigated. And, the results show that the wavelength-referenced magnetic field sensitivity reaches up to 71.98 pm/Oe in the range of 40-120 Oe and the intensity-referenced sensitivity reaches up to 0.11 dB/Oe. Meanwhile, the sensor presents great directional resolution with intensity-reference (0.11 dB/deg).