Twist sensor based on fiber Bragg grating fiber laser frequency splitting effect

A twist sensor based on the frequency splitting effect of fiber Bragg grating laser is proposed and experimentally demonstrated. Laser longitudinal mode was split into two frequencies under the action of birefringence induced by fiber twist and by monitoring the periodical beat frequency response, the twist angle could be deduced. The experimental results show that the relationship between the fiber twist angle and the beat frequency is linear (linearity is more than 99%) when the twist angle is in the range of 10 degrees-55 degrees. Moreover, the wavelength drift caused by the temperature does not affect this linearity. Since the sensor is based on frequency rather than on the wavelength, its sensitivity is not limited to the resolution of the spectrometer, and has been improved to 31.59 MHz/rad (0.55 M/degree).