Directional torsion and strain discrimination based on Mach-Zehnder interferometer with off-axis twisted deformations

An all-fiber sensor based on a Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated to measure directional torsion and strain simultaneously. The MZI employing a pair of off-axis twisted deformations (OATDs) on single mode fiber (SMF) is fabricated by continuous arc discharge method. It performs OATDs causing permanent twisted distortion to form light beam splitter and combiner of the MZI. The transmission spectrum of the OATDs-MZI has multiple resonance wavelength dips, which correspond to different cladding modes. The torsion and strain measurement can be simultaneously achieved by monitoring changes in the dips of wavelength. Due to the OATDs, the proposed sensor has the ability to distinguish torsional direction, and a strain sensitivity as high as - 0.0285 nm/mu epsilon was obtained. The proposed sensor exhibits excellent torsion and strain resolution of +/- 0.0611 rad/m and +/- 0.8232 mu epsilon. The device has the advantages of low cost, small size, simple preparation steps, short preparation cycle, etc. Due to its excellent performance, it has the potential to become an excellent universal directional torsion and strain sensor.