Bias twisting in side-tapered PMF Sagnac loop interferometer for simultaneous measurement of directional torsion and temperature

The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from − 30 to 30 rad/m. Moreover, the temperature sensitivity was found to be − 1.579 n m / ∘ C , with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.