Preparation Of Polarization Maintaining Fiber Interference Structure And Research On Its Torsional Sensing Characteristics

Torsion,as one of the most important mechanical parameters of object structure monitoring,has important reference significance for many practical engineering applications.In recent years,various types of torsion sensors have been widely used in areas ranging from health monitoring of large buildings such as bridges,tunnels,and dams,to tracking of joint structures of intelligent robots,and minimally invasive detection of biomedicine.Compared with the traditional electromagnetic and electronic torsion sensors,fiber optic devices have attracted increasing attention for twist sensing applications due to its small size,easy integration,resistance to electromagnetic interference and high sensitivity.In this paper,a high-sensitivity twist sensing structure based on polarization-maintaining fiber is proposed and fabricated,and its twist sensing performance is theoretically and experimentally studied.The relationship between the transmission spectrum of the torsion sensor structure and the torsion angle of single-mode fiber and polarization maintaining fiber was theoretically analyzed and simulated.For the interference structures of different lengths of polarization maintaining fiber,the single-mode fiber and the polarization maintaining fiber in the sensing structure were twisted respectively,and the torsional sensing sensitivity of different fiber positions was measured.The main work content is as follows:Based on the theory of matrix optics,the transmission characteristics of polarized light in the polarization-maintaining fiber interference structure were analyzed,and the Jones matrix expression of the transmitted light intensity when the twisted single-mode fiber and the polarization-maintaining fiber are twisted.The transmission spectrum and the change of transmission spectrum with the twist angle of single-mode fiber and polarization-maintaining fiber were simulated.By changing the length parameter of the polarization-maintaining fiber,numerical simulation showed that the torsional sensing sensitivity of the interference structure based polarization-maintaining fiber with different length was independent of the length of the polarization-maintaining fiber.An optical fiber torsion sensing platform was built,and an interference torsion sensing structure based on polarization maintaining fiber was fabricated.The sensing structure was composed of two fiber polarizers and a section of polarization maintaining fiber.When twisting the single-mode fiber in the sensing structure,the twist sensitivity was measured to be 5.73 d B/rad from 0° to ±100°.When the polarization-maintaining fiber was twisted,the intensity of the transmission resonance peak changes periodically liked a quadratic curve with the twist angle,thereby enabling high-sensitivity sensing in a small twist angle range.The torsion sensitivity is 89.4 d B/rad and 30.36 d B/rad in the range of 0° to ±10° and ±10° to ±20°,respectively.The torsional sensing sensitivity of polarization-maintaining fiber was improved by nearly an order of magnitude compared to single-mode fiber.The experimental results showed that changing the length of the polarization-maintaining fiber had no effect on the torsional sensitivity of the sensor structure,which was consistent with the theoretical simulation results.