Beat torsion sensor without temperature compensation based on long-period fiber grating written by CO₂ laser

The resonance peak of long period fiber grating fabricated in twisted optical fiber by using high-frequency CO₂ laser pulses could split into two peaks, after the twist applied to the fiber is removed. The splitting and the torsion characteristic of the special gratings are analyzed and explained by beat-frequency theory. As the temperature sensitivity of the two splitting peaks of the grating is almost the same, it is proposed that torsion can be measured by detecting the interval change between the two splitting peaks when torsion is applied. Besides, the torsion sensor can distinguish torsion direction as the distance of the two splitting peaks increases or decreases when different torsion is applied, therefore, this kind of torsion sensors has a great potential application in high sensibility torsion sensing.