Strain-Insensitive Simultaneous Measurements of Torsion and Temperature Using Long-Period Fiber Grating Inscribed on Twisted Double-Clad Fiber

Jonatan Martino Windi Saputro,Jihoon Kim,Minchan Bae,Yong Wook Lee

doi:10.1109/jsen.2023.3246079

Jonatan Martino Windi Saputro, Jihoon Kim + Show 2 more

https://doi.org/10.1109/jsen.2023.3246079

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Abstract

Here, we report an optical fiber sensor capable of performing strain-insensitive simultaneous measurements of torsion and temperature using a long-period fiber grating (LPFG) inscribed on twisted double-clad fiber (DCF) with a CO 2 laser. The LPFG written on twisted DCF, referred to as TDC-LPFG, exhibited multiple resonance dips with different cladding-mode orders, and two of them were selected as sensor indicators for the simultaneous measurement of torsion and temperature. The measured torsion sensitivities of the sensor indicators were approximately –2.167×10 2 and –4.667×10 2 pm/(rad/m) in a twist angle range of –180° to 180°, and their temperature sensitivities were measured as ~6.580×10 1 and ~7.189×10 1 pm/°C in a temperature range of 25–100 °C. Their linear and independent responses to torsion and temperature made possible the discrimination of the two measurands. Moreover, the strain sensitivity of the TDC-LPFG was measured and found to be less than 2.750×10 1 pm/με in magnitude, over four times less than that of a standard LPFG. This strain insensitiveness contributes strongly to diminishing strain-induced measurement uncertainties associated with torsion and temperature. Finally, we validated the simultaneous measurement capability of twenty-five applied points of torsion and temperature variations. The average torsion and temperature standard deviations were ~3.44×10 -2 rad/m and ~3.01×10 -1 °C, respectively.

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