Thermal treatment effect on the random lasing polarization of polymer optical fiber

•Based on the ferromagnetic nano-particles and the polymer optical fibers made by ourselves, random fiber lasers with high polarization degree was fabricated and experimentally demonstrated.•As far as we know, it’s the first time to verify the effect of thermal treatment on polarization degree of random polymer optical fiber lasers.•The polarization degree remains high and increases to 0.99 after annealing, which indicates that random lasers with stable and high polarization degree have been realized.