High sensitivity directional torsion sensor based on double-helix long-period grating in tapered polarization-maintaining fiber.

We propose a fiber torsion sensor based on double-helix long-period grating (DH-LPG) written in a tapered polarization-maintaining fiber (PMF). A series of DH-LPGs were fabricated in the tapered PMFs with waist diameters of 85 to 67 μ m by a CO 2 -laser heating and twisting system. The torsion, temperature and surrounding refractive index sensing characteristics were investigated experimentally. Thanks to the special structures combined DH-LPGs with tapered PMFs, the proposed sensor can realize directional torsion measurement. The maximum torsion sensitivity of the proposed grating could be up to -2.28 nm/(rad/m) when the tapered waist diameter was 67 μ m. The DH-LPGs have potential application in field of all-fiber high sensitivity directional torsion sensing. • Novel and repeatable fabrication methods for double-helix long-period gratings. • Detailed analysis in the sensing characteristics with various waist diameters. • Available for vector torsion measurements. • High torsion sensitivities and wide measurable twist rate ranges. [ABSTRACT FROM AUTHOR]