Direction-Discriminating torsion sensor based on optical fiber Mach-Zehnder interferometer

Optical fiber torsion sensors play a pivotal role in artificial intelligence, construction engineering, structural health monitoring and other fields. Research on low cost, simple structures and measurement methods has become a priority for researchers. Here, we propose an intensity-modulated and direction-recognizing torsion sensor based on two mode fiber with a sandwich structure, that serves as a mode interferometer formed by fundamental modes LP01 and second order core modes LP11 excited by means of offset fusion splicing. The ca-pacity of intensity modulation and torsional direction recognition comes from the antisymmetric phase of fiber mode, which makes the sensor work like Marius' law. The antisymmetric phase of the LP11 mode leads to an asymmetric transmission spectrum, whose direction enables the sensor to distinguish the torsion direction. Peaks and troughs in the measured spectrum interchange when the torsion direction is reversed. The initial angle between two offset directions enables control of the zero-crossing point within in the twisting range. The torsion sensitivity reaches 364%/(rad/cm) with a measurement accuracy of & PLUSMN; 0.22 rad/m.

Automated summary

In this research, an intensity-modulated and direction-recognizing torsion sensor based on a sandwich structure of two mode fiber is proposed. By utilizing the antisymmetric phase of the fiber mode, the sensor operates like Marius' law. The torsion direction can be distinguished by the asymmetric transmission spectrum, where peaks and troughs interchange. The sensor achieves a torsion sensitivity of 364%/(rad/cm) with a measurement accuracy of ±0.22 rad/m.