Temperature sensitivity enhancement of platinum-nanoparticle-coated long period fiber gratings fabricated by femtosecond laser.

The temperature sensing performance of long period fiber gratings (LPFGs) written by femtosecond laser pulses coated with platinum nanoparticles (PtNPs) is proposed and demonstrated. It is found that the PtNPs increase the wavelength sensitivity of the LPFG significantly compared with the bare LPFG. The temperature sensitivities of the bare LPFG for three dips, corresponding to 1438, 1485, and 1585 nm, are 74.04, 77.23, and 86.26  pm/°C, respectively, when the temperature changes from 10°C to 500°C, whereas the corresponding sensitivities of PtNP coated LPFGs are up to 90.58, 93.51, and 103.43  pm/°C, respectively. Moreover, the PtNP coated LPFG has shown better wavelength repeatability. A small wavelength hysteresis of ∼0.5  nm is observed when the temperature is less than 300°C.