Point-coated long-period fiber grating for temperature measurement.

In this paper, a temperature sensor based on a point-coated long-period fiber grating (PC-LPFG) is proposed and investigated. This structure is fabricated using a thermal filling method. The point-coating approach effectively increases the coupling efficiency between the sensing unit and the surrounding medium. The polymethyl methacrylate (PMMA), with high thermal optical coefficient (TOC) and thermal expansion coefficient (TEC), improves the temperature sensitivity of the PC-LPFG. Experimental results show that the temperature sensitivities of this sensor are 2.948 nm/°C and 6.717 nm/°C in the temperature ranges of 80.4-91°C and 91-97°C, respectively. The hot point-coating method of the PC-LPFG provides a new, to the best of our knowledge, approach to combining optic fiber sensors with high polymer materials.