Temperature and transverse load sensing characteristics of twisted long period fiber gratings fabricated by femtosecond laser

Temperature and transverse load sensing characteristics of twisted long period fiber gratings (T-LPFGs) written by femtosecond laser have been experimentally investigated. The temperature sensitivity of the proposed T-LPFGs reaches 65.31 pm/°C with a linearity of 0.992 within the temperature range from 20 °C to 300 °C, and the coincidence of temperature increase and decrease is good enough. The transverse load characteristic of the T-LPFGs is quite different to the traditional LPFG, within the circular position 0° to ±15°, the T-LPFGs is load-sensitive, corresponding to the resonant wavelength “blue” shift and within other orientation the T-LPFGs is load-insensitive. Specifically, there is 1 dB separation between the two resonance peaks with 400 g loading applied or not to the T-LPFGs fiber, giving a transverse load sensitivity of 4.03 dB/mg. In addition, the proposed T-LPFGs are very suitable for the applications in the temperature and transverse load sensor.