Study on the mechanism of fiber-optic hot-wire sensing based on DFB-FL thermally induced chirp effect

In this paper, we propose an intensity demodulated fiber-optic hot -wire sensing method based on the thermally induced chirp effect of distributed feedback fiber lasers. The cobalt-doped fiber is fused at the rear end of the erbium-doped distributed feedback fiber laser to constitute a hot fiber wire with a gradient temperature distribution. The cobalt-doped fiber is heated up under the excitation of the residual pump light. Then the thermally chirp of the erbium-doped phase-shifted fiber grating brings out the change of the lasing threshold condition of the distributed feedback cavity and a significant reduction of the output power. When this structure is further altered by thermal induced chirp under external thermal field, the lasing output power will be further changed. The experimental results of the dynamic fluid thermal field and the static thermal field shows that, the fiber-optic hot -wire structure can sensitively detect the weak airflow and the thermal field of the environment by monitoring the laser power.