Temperature-insensitive torsion sensor with sensitivity-enhanced by processing a polarization-maintaining photonic crystal fiber

We propose an optical fiber twist sensor by employing a Sagnac interferometer based on polarization-maintaining photonic crystal fiber (PM-PCF). To enhance the torsion sensitivity, a short length of PM-PCF is processed by heating-torsion using carbon dioxide laser. It is demonstrated experimentally that the birefringence of PM-PCF is decreased after processed, and the torsion sensitivity is improved in varying degrees for different lengths of heating-torsion. The maximum sensitivity can achieve 7.09 nm/(rad/m) after post-processing, which is two times higher than that of unprocessed one (3.75 nm/(rad/m)). In addition, the temperature sensitivity of twist sensor drops significantly after post-processing. The result shows that heating-torsion is a novel method to improve the torsion sensitivity of PM-PCF.