Simultaneous measurement of transverse load and temperature using a single long-period fibre grating element

A single long-period fibre grating (LPFG) element written by focused high-frequency CO2 laser pulses is demonstrated for simultaneous measurement of transverse load and temperature. Temperature and transverse load can be directly measured by detecting the resonant wavelength shift and the resonant peak amplitude change of the LPFG, respectively, as there are two special circular orientations along the fibre axis where the resonant peak amplitude change of the LPFG has a linear relationship with the load applied and is insensitive to the resonant wavelength shift. Such a sensor could solve the cross-sensitivity problem between transverse load and temperature due to the unique feature of this type of LPFG, i.e. the wavelength-load-sensitivity of the LPFG strongly depends on loading orientations due to the non-uniform distribution of the refractive index on the cross-section of the LPFG caused by the thermal shock effect and other effects of the high-frequency CO2 laser pulses exposure method used.