In recent years, with the potential advantages of compact size, high resolution, low cost and light weight, fiber optic devices such as fiber optical gratings have attracted increasing attention for twist sensing applications. In principle, fiber-based torsion sensors are divisibleinto twoclasses: the sensors based onlong-period gratings (LPGs), and the sensors based onfiber Bragg gratings (FBGs). However, the former are fragile andsuffer from large cross sensitivity of the axial strain and temperature, the latter are expensive and have relatively low torsion sensitivity.
To solve the above problems,PhD student, Bo Huang andProf Xuewen Shu from Wuhan National Laboratoryfor Optoelectronics developeda novel temperature- and strain-independent optical fiber torsion sensor based ona phase-shiftedFBGfabricated with the femtosecond-laserline-by-lineinscription technique.By simplymonitoring the variation of the amplitude difference between the two polarization-peaks, thefiber torsion angle and the fiber torsion direction can be simultaneously deduced withouttemperature and strain confusion. The torsion sensor exhibits a high torsion sensitivity of upto -1032.71 dB/(rad/mm), with the distinct advantages of low manufacture cost, smalldimension (just ~1.72mm), and extremely robust and simple structure, which make it veryattractive for practical applications. To the best of our knowledge, this is the smallest torsionsensor ever reported.
Fig. 1. (a) Transmission spectra evolution ofπ-PSFBG under torsion in clockwise directionfrom 0° to 80° in an elevation step of 20°. (b)Measured P1-P2under torsion in clockwise andanticlockwise directions from 0° to 360°.
Fig. 2. For 0°, 30° and 60° twisted PSFBG, the measured P1-P2under different (a) temperatureand (b) strain levels.
On August 8, 2016，this work “Ultra-compact strain- and temperature-insensitive torsion sensor based on a line-by-line inscribed phase-shifted FBG” was published on Optics Express(vol. 24, no. 12, pp. 17670-17679, 2016).
Prof. Shu’s group recently also developed a novel passively mode-locked fiber laser based on a chiral fiber grating. The work“All-fiber passively mode-locked laser based on a chiral fiber grating”was published onOpticsLetters(Vol.41, No.2, pp.360-363, 2016).
Theseworkaresupported by the Director Fund of Wuhan National Laboratory for Optoelectronics and National 1000 Young Talents Program, China.
