Dual-parameter measurements of torsion and temperature based on the tilted Bragg grating in few-mode fiber

In this study, a fiber Bragg grating (FBG) with different tilt angles was written at the same position on a few-mode fiber (FMF) from two directions utilizing the phase-mask technique. The torsion direction and magnitude were measured utilizing the cross-coupled peak formed by the core fundamental mode LP01 and the second-order mode LP11 at the grating position. Experimental results indicate that when the tilt angles of the two opposite gratings are 0.5 degrees and 1 degrees, the torsion sensitivity is 0.272 dB/(rad/m) and 0.301 dB/(rad/m) respectively, within the range of -30 degrees to -150 degrees counterclockwise torsion and 40 degrees to 140 degrees clockwise torsion. The variations in reflection peak intensity due to clockwise and counterclockwise torsions exhibit distinct trends. Simultaneously, by monitoring the changes in grating wavelength, temperature can be measured, with the sensitivity of reflection peak drift for both gratings maintained at 11.8 pm/degrees C within the range of 0 degrees C to 90 degrees C.