Fig. 1. Schematic diagram of the sensing system.

Fig. 2. Schematic of the sensing head based on an MF-coated U-bent fiber structure.

Fig. 3. Schematic diagrams for measuring (a) the gain characteristic of the EDFA module depending on wavelength and (b) the transmission spectrum of the sensing head in the MF under 0 Oe. OPM, optical powermeter; BBS, broadband source (Lightcomm Tecnologia Ltd.); OSA, optical spectrum analyzer (Advantest Q8384).

Fig. 4. Measured transmittance spectrum of the sensing head and the gain characteristic curve of the EDFA module.

Fig. 5. (a) Spectral response of the sensing head to the applied magnetic field. (b) The transmittance change at 1575 nm depending on H.

Fig. 6. Output decay trains and the corresponding exponent fittings of the peaks under H of (a) 0 and (b) 250 Oe.

Fig. 7. Measured ring-down time depending on H. Inset: the statistics and fitting results.

Table 1. Values of $G_{\text{nor}}$, $V$, $N$, and $Q$ at Different Wavelengths