Fabry-Perot interferometric fibre optic temperature sensor with polyvinylidene fluoride (PVDF) coating

A novel polyvinylidene fluoride (PVDF) coated fiber-optic Fabry–Perot interferometric (FFPI) sensor for temperature measurement is proposed and experimentally validated. The sensor head consists of a PVDF thin film formed by the phase inversion process via immersion precipitation at the freshly cleaved endface of a single mode telecommunications optical fibre. The resin polyvinyl butryl (butvar) was used as a cross-linker to promote good adhesion between the optical fibre glass and PVDF in order to reduce operational coupling loss. Sensor operation is demonstrated by shifts of the FFPI reflection spectra and its performance was analysed through measurement of optical thickness or path difference with temperature variation. Experimental data shows that the thermal expansion effect of the PVDF coating is more dominant than its thermo-optic effect. The proposed sensor exhibits an exponential response over 21 to 160 °C inside a tube furnace with a sensitivity that spans between 1.6 nm/°C and 7.5 nm/°C.