# Directional Torsion Sensor Based on a Paired Helical-Type Multimode Fiber

## TL;DR

A new fiber-based sensor can detect the direction of twisting with high sensitivity and minimal temperature interference.

## Contribution

A novel STMS fiber structure enables directional torsion sensing with low temperature crosstalk.

## Key findings

- Clockwise twisting shifts resonance wavelength to shorter wavelengths, while counterclockwise does the opposite.
- The sensor has wavelength and transmission sensitivities of −1.38 nm/rad·m−1 and 3.12 dB/rad·m−1.
- Temperature crosstalk is minimal at 0.0072 (rad/m)/°C.

## Abstract

A torsion sensor with directional discrimination based on a single-mode–twisted multimode–single-mode (STMS) fiber structure is demonstrated. The STMS fiber structure is fabricated by fusion-splicing a segment of multimode fiber (MMF) between two single-mode fibers (SMFs), where the MMF is simultaneously heated and twisted to form paired helical-type structures. The experimental results indicate that the resonance wavelength shifts towards shorter wavelengths as the twist rate increases in the clockwise direction, while an opposite shift occurs in the counterclockwise direction. Within a twist rate range of −5.2 rad/m~5.2 rad/m, the wavelength and transmission sensitivities are determined to be −1.38 nm/rad·m−1 and 3.12 dB/rad·m−1, respectively. Furthermore, the proposed twist sensor exhibits minimal temperature crosstalk of 0.0072 (rad/m)/°C, making it highly desirable for mitigating temperature-induced cross-sensitivity in torsion measurement applications.