An optical fiber high-temperature strain sensor is proposed and fabricated which is formed by combining an in-line photonic crystal fiber Fabry-Perot interferometer(FPI) with an air bubble cavity and a long-period fiber grating(LPFG) written in a standard single mode fiber using high-frequency CO2 laser.The in-line FPI was constructed by directly splicing a mutimode photonic crystal fiber(MPCF) to a conventional single mode fiber with a commercial splicer.The air microbubble inserted between the...