Multi-longitudinal mode fiber laser sensing system based on resonant cavity dispersion-frequency mapping

In this paper, a multi-longitudinal mode fiber laser (MMFL) sensing system is proposed and experimentally demonstrated. The longitudinal mode beat frequency (LMBF) of the MMFL is related to the effective optical path length of the laser's resonant cavity, which is determined not only by the physical length of the resonant cavity but also by its dispersion characteristic. Thus, when the total dispersion of the resonant cavity varies with the disturbance caused by external physical factors, the LMBF of the laser would shift and can be used for sensing applications. A chirped FBG was induced in the MMFL to enable such dispersion-frequency mapping. The model of such MMFL system is proposed and verified theoretically and experimentally. Experimental result shows that the proposed sensing system has a more compact size and higher resolution compared to conventional configure.