Abstract: In order to enhance the gas measurement sensitivity， a reflective optical fiber gas sensing technology was proposed using photonic crystal fiber (PCF). Firstly， the harmonic detection technology of broadband source was used in combination with the practical application demands. Then， aimed at the problems of coupling between hollow core PCF and single mode fiber， and the long infiltrating time of measured gas， a new measured gas chamber was designed， which integrated seal， fixation and connection. Finally， taking acetylene gas as an example， the sensing properties of the proposed sensor were measured. Experiment results demonstrated that the minimum detectable concentration could be as accurate as 0.02%， and the maximum relative error was 1.39%. The proposed technology can further promote the applications of PCF in gas sensing， and lay the theoretical and experimental foundations for its practical applications.

Key words: gas sensing, hollow core photonic crystal fiber, gas chamber, acetylene gas, reflective sensor