A novel fiber torsion sensor using a high-birefringence fiber Bragg grating for demodulation

A novel high-birefringence (Hi-Bi) fiber torsion sensor demodulated by a Hi-Bi fiber Bragg grating (FBG) is proposed in this study. The characteristics of a twisted Hi-Bi fiber sensor are analyzed by using the Jones matrix. As a result, the ratio of intensities from two reflecting Bragg wavelengths is varied with the twist angle in the measured Hi-Bi fiber. The advantages of the novel torsion sensor are: (1) insensitivity to intensity variations from the light source, (2) insensitivity to the torsion gauge length, (3) insensitivity to the thermal variation and external axial strain, (4) absolute measurement in the twist angle, and (5) multiplexing. Therefore, it could be applicable for smart structure applications, especially in bridges or other civil structures. However, freedom from transverse loading in order to prevent birefringence change in the twisted Hi-Bi fiber is necessary.