Fig. 1. Schematic diagram and polarization dependence spectra of ExTFG

Fig. 2. The simulation results of waveguide dispersion factorγ, effective refractive index of TE mode, axial strain sensitivity factorΓstrain, axial strain sensitivity dλ/dε of the first 40 order cladding modes for different cladding radius (40 μm, 50 μm and 62.5 μm)

Fig. 3. Spectral changes after etching in HF solution with volume fraction of 20%

Fig. 4. Low-frequency vibration sensing experimental system diagram based on cantilever beam

Fig. 5. Amplitude-frequency response characteristics in the vibration frequency range of 40~200 Hz (the inset is a partial enlargement of the vibration frequency close to 72 Hz) and time domain response at 72 Hz for the same order mode

Fig. 6. Amplitude-frequency response characteristics in the vibration frequency range of 40~200 Hz (the inset is a partial enlargement of the vibration frequency close to 72 Hz) and time domain response at 72 Hz for different order modes

Fig. 7. The output amplitude response of ExTFG vibration sensor for different cladding diameter at vibration frequency at 72 Hz