Development Of Twist Sensor Based On Few-mode Fiber

Fiber optic torsion sensors have been widely used in the fields of engineering,construction,and artificial intelligence due to the merits of small size,light weight,anti-electromagnetic interference,and high sensitivity.So far,linear response expansion,small pre-twisting angle and low-cost intensity demodulation are hot topics in the research of torsion sensors.In this paper,an in-line Mach-Zehnder interferometer(MZI)based on few mode fiber(FMF)is proposed by core-offset splicing technique,and the twist sensitive characteristics of interferometer are investigated comprehensively.The main contents are as follows:(1)The principle of mode interference is theoretically studied in core-offset based FMF-MZI.Through beam propagation method,the guided mode and mode allocation of FMF-MZI are simulated and analyzed,which provides the theoretical basis for structure optimization.In addition,the sensing principles in terms of temperature and torsion are analyzed.(2)The parameter effects on the output interference spectra are quantitatively studied,such as the length of FMF,core-offset value,and offset angle.The torsion tests are then conducted.The experimental results show that the remarkable intensity modulation is demonstrated in the range of 360? to-360?.Moreover,during the twisting,the interference have the clear turning points from dip to peak of fringes.That means the torsion direction can be easily recognized through pre-twisting.Consequently,the proposed FMF-MZI has a sensitivity of ?110 d B/(rad/cm)in the range from 0 to ?13.08 rad/m.In addition,the measurements of temperature and curvature are performed.(3)Based on angle-offset splicing,the characteristics of torsion in a novel FMF-MZI is performed,and the relationships are verified between the offset angle and linear response range.Furthermore,the experiment of partial torsion is carried out and the inverse-proportional relationship is revealed between the wavelength shift and shear strain.Under partial torsion,for the first time,the near zero visibility and direction recognition with the zero rotating state are obtained by fine offset-modulation.The experimental results show that,in the range of-40?40 rad/m,a competitive sensitivity of 21.485 d B/(rad/cm)is gained with high linearity and low-temperature crosstalk.