A novel highly sensitive refractive index sensor based on Fabry-Perot interferometer which is formed by hollow core photonic crystal fiber is realized.This sensor can realize refractive index measurement through the optical path difference of the interference spectrum,which changes with the refractive index of the measured liquid in the PCF-FP cavity.The experimental results show that the optical path difference changes 9.508 μm when the refractive index of alcohol liquid varies in the range of ...