Rayleigh backscattering induces mode hopping of distributed feedback (DFB) fiber lasers in the sensor array, and the critical length related to Rayleigh backscattering limits the size of DFB fiber laser sensor networking. Based on a three-mirror cavity model, the critical length for a DFB fiber laser is derived. It increases nearly exponentially with the coupling coefficient for the ideal pi-shifted DFB fiber lasers. The reflectivity of the sub-fiber Bragg grating at the lasing wavelength is the main factor to resist Rayleigh backscattering for a nonideal DFB fiber laser. The corresponding experiments have been carried out, and the critical length of larger than 150 m was achieved for 42-mm-long DFB fiber lasers.

distributed feedback fiber laser; optical fiber sensor; mode hopping; Rayleigh backscattering

Institute of Semiconductors, Chinese Academy of Sciences