A Highly Sensitive Torsion Sensor With a New Fabrication Method

A novel long period fiber grating (LPFG) made by using CO ₂ laser is proposed as torsion sensor. The fiber sheets fabricated clockwise/anticlockwise in the optical fiber causes the dextrorotation/levorotation of the polarization state of the light during propagation in the sensor. The experimental results indicate that the sensors, with the fiber sheets in different rotation, will appear opposite torsion sensitivities. While twisting the proposed sensor, the resonant wavelength shows good linear relationship with the torsion rate. From −360° to 360°, the LPFG with the clockwise revolving fiber sheets (dextrorotation grating) has a torsion sensitivity of 0.175 nm/(rad/m), whereas the LPFG with anticlockwise revolving fiber sheets (levorotation grating) has a torsion sensitivity of −0.153 nm/(rad/m). In addition, the temperature sensitivities of the two LPFGs are approximately the same, 73 pm/°C and 67 pm/°C, respectively. In conclusion, it is strongly believed that this structure can be used to measure the torsion rate and distinguish the torsion direction, and it may have excellent significance for the development of optical fiber torsion sensors in the future.