Fig. 1. Experimental setup. (a) Picture of real products; (b) schematic diagram

Fig. 2. Cross section and horizontal coordinate of optical fiber structure. (a) Cross section; (b) horizontal coordinate

Fig. 3. Transmission spectrum and corresponding FFT figure of sensing structure with and without pre-twist. (a) Without pre-twist process; (b) with pre-twist process

Fig. 4. Response diagram and fitting diagram of dip to the torsion without pre-twist process. (a) Spectra shift with the change of the torsion; (b) wavelength and power fitting diagram of the dip to torsion

Fig. 5. Response diagram and fitting diagram of dip to the clockwise torsion with pre-twist process. (a) Spectra shift with the clockwise twisting in the range of 0°‒30°;（b）wavelength and power fitting diagram of the dip to torsion

Fig. 6. Response diagram and fitting diagram of dip to the counter-clockwise torsion with pre-twist process. (a) Spectra shift with the counter-clockwise twisting in the range of 0°~-30°;（b）wavelength and power fitting diagram of the dip to torsion

Fig. 7. Response diagram and fitting diagram of dip to the temperature with pre-twist process. (a) Spectra shift with the temperature change in the range of 25 ℃ to 65 ℃;（b）wavelength and intensity of the resonant dip change with the temperature change