Cascaded FPI/LPFG interferometer for high-precision simultaneous measurement of strain and temperature

An all-fiber and low-cost strain and temperature sensor realized by the cascaded FPI/LPFG interferometer was developed. This device consists of an input single mode fiber (SMF), hollow core fibers (HCF), a long-period fiber grating (LPFG) inscribed by the CO2 laser pulses, and an output SMF. The Fabry-Perot interferometer (FPI) is insensitive to temperature and its reflective spectrum is utilized for strain measurement while the transmission spectrum of the LPFG is only utilized for temperature measurement. The actual measurement shows that the strain sensitivity of the proposed hybrid FPI/LPFG sensor can reach 4.16 pm/mu epsilon within the strain range of 0-1500 mu epsilon, meanwhile, the temperature sensitivity is 135.19 pm/degrees C when the temperature rises from room temperature to 82.11 degrees C. In addition, the proposed hybrid FPI/LPFG sensor has excellent linear response characteristics, and the R-Square values of the linear fitting curve of strain and temperature are 0.9995 and 0.9936, respectively. Therefore, the proposed hybrid FPI/LPFG sensor can simultaneously measure strain and temperature in the same location in the application field.