Torsion, Refractive Index, and Temperature Sensors Based on An Improved Helical Long Period Fiber Grating

The sensors measuring torsion, refractive index, and temperature are demonstrated, based on an improved helical long-period fiber gratings (HLPFG), in which the refractive-index and torsion sensitivity were significantly enhanced by reducing the grating diameter. This was achieved using the velocity difference between two translational stages as the optical fiber was heated by a hydrogen-oxygen flame. As the grating diameter decreases from 109 to 85 μm, the sensor's refractive-index sensitivity at RI of 1.444 increases from -1210.20 to -3133.80 nm/RIU, and torsion sensitivity was enhanced from -245.80 to -942.77 nm/(rad/mm), respectively. Moreover, the sensor's temperature sensitivity was measured to be about 77.17 pm/°C. Hence, such a sensor based on improved HLPFG could have great potential in sensing applications.