A Compact Sensor Capable of Temperature, Strain, Torsion and Curvature Measuring

We experimentally proposed a helical long-period fiber grating (HLPG), which was produced by twisting a tri-hole fiber (THF) with arc discharge technology. The optical field distribution in THF-HLPG was analyzed and its transmission spectrum was studied. The simulation results prove that the light wave propagating along the fiber core can be strongly coupled into cladding modes within a short transmission distance, thus making the THF-HLPG more compact. In the experiment, a sensor with a length of 4.2 mm was manufactured by using an arc heating system. With this processing device, the air holes of the THF-HLPG can effectively avoid shrinkage during heating. Temperature, strain, torsion and curvature properties were investigated experimentally. Owing to the peculiarity of THF-HLPG, this sensor shows a high mechanical response and is suitable for identifying curvature changes with a large bending radius. The demonstrated THF-HLPG offers a promising application for precisely detecting mechanical deformation of micro-structure.