Abstract: In order to precisely monitor and forecast noxious and harmful gases in the air， an optical fiber gas sensor was proposed including a section of tapered and dislocated optical fiber， and the tapered region was coated with graphene. The tapered fiber sensing area which was wrapped with graphene and intermodal interference caused by the dislocation of fiber would substantially increase evanescent field， which transmitted along the surface of fiber， and would have a significant sensitizing effect on the gas sensing of the optical waveguide. At the same time， the gas molecules adsorbed on the surface of graphene would lead to change of the effective refractive index of the composite waveguide， resulting in the corresponding wavelength drift and attenuation. By detecting the change of the output optical signal， the concentration of gas molecules could be detected. Based on this principle， the sensor realized a gas sensitivity of 1.2×10⁴nm. The research shows that the sensing structure has the advantages of small volume， good mechanical strength， good spectral quality and high sensitivity etc.

Key words: graphene, optical fiber sensor, gas sensor, intermodal interference, high sensitivity