Switchable Wavelength-/Intensity-Modulated Directional Torsion Sensor Via Bias-Twisted PMF-Sagnac-Loop Interferometer

In this article, a quasi-second-order Lyot-Sagnac filter is theoretically and experimentally developed by applying the partial-bias-twisting in a polarization maintaining fiber based Sagnac-loop interferometer. It is the first time that a switchable intensity-/wavelength-modulated fiber directional torsion sensor is accurately demonstrated under the quantitative polarization states. In intensity modulation, high-discriminative simultaneous measurement of torsion and temperature can be achieved with the resolutions of 0.015 ° and 0.035 °C. In wavelength modulation, without any pre-twisting, the ultra-wide linear measurement range from −520 ° to 520 ° is gained, and the maximum sensitivity reaches ∼0.32 nm/° by simply reducing the twisting length. With the merit of ease of operation, our sensor is very practical and promising in the fields of the torsion-related high-precision engineering measurement and sensing.