Fig. 1. (a) Schematic diagram of the micro-SI magnetic field probe based on an SI sensor. (b) The guiding mode of D-shaped waveguide with the diameter of 1.2 μm and the analyte RI of 1.3, 1.36, and 1.4, respectively. (c) The simulation results about the effective OPD variation of the TM mode and TE mode of the D-shaped waveguide versus the fluid RI in the waveguide cavity with different waveguide diameters. SLED, superluminescent emitting diode; FC, fiber coupler; PC, polarization controller; CW, clockwise light; CCW, counterclockwise light.

Fig. 2. (a) The SI structure fabrication with direct laser writing on a substrate. (b) The microscope image and the SEM image of the SI device printed on a substrate.

Fig. 3. (a) MF under a magnet, UV adhesive, and syringe. (b) Schematic diagram for connecting and sealing the hollow fiber and syringe, and for filling the MF and adhesive into the syringe. (b') Schematic diagram for sealing one side of the gap between single-mode fiber and the glass tube. (c) Schematic diagram for sealing the two ponds of the SI structure with stages and microscope. (d) Schematic diagram for fixing the 3D-printed SI structure on a bigger substrate, focusing SMF to port 1 of Y-branch, and fixing the SMF on the bigger substrate. (e) Schematic diagram for taking the SI device into a glass tube and fixing it with UV adhesive. (f) Schematic diagram for filling MF into the glass tube with stages and microscope. (g) Schematic diagram for sealing the other side of magnetic field probe with UV adhesive and UV lamp. (h) The fabricated magnetic field probe.

Fig. 4. (a) Schematic diagram of the magnetic field probe measurement. SLED, superluminescent light emitting diode; OSA, optical spectrum analyzer; SMF, single-mode fiber; OC, optical fiber circulator. (b) The reflection spectra of the device in air and MF.

Fig. 5. (a), (b) Transmission spectral evolutions with an increasing applied magnetic field in the linear response region from 10 to 100 Oe and in the sluggish one from 0 to 10 Oe, respectively. (c) Variation of the fringe dip wavelength and peak-to-valley intensity with respect to an applied magnetic field. (d) Variation of the fringe dip wavelength with respect to an applied magnetic field in the sluggish area and low-sensitivity area.

Fig. 6. (a) Repeated tests of the dip wavelength under different magnetic fields. (b) The dip wavelength at different magnetic field with temperature of 20°C, 30°C and 40°C, respectively, and the maximum dip wavelength errors for three repeated tests under different magnetic fields under 20°C, 30°C and 40°C, respectively. (c) The dip wavelength fluctuations within 72 h at a temperature of 20°C and under a magnetic field of 0, 50, and 100 Oe, respectively.

Fig. 7. (a) Demonstration for measuring the response of SI to different magnetic fields. (b) The experimental results of response under different magnetic fields.