High-pulse-contrast-ratio nanosecond fiber laser

The invention discloses a high-pulse-contrast-ratio nanosecond fiber laser which comprises a pump laser, a pump combiner, a gain fiber, a fiber loop mirror and a fiber bragg grating. Lasers which are propagated along a fiber ring, in the clockwise direction and the counter clockwise direction, in the fiber loop mirror, are mutually intervened at the output port, the splitting ratio of the coupler is changed, power size of transmission light and reflected light can be changed, and the fiber loop mirror and the fiber bragg grating collectively form a resonant cavity. The high-pulse-contrast-ratio nanosecond fiber laser has the advantages of being compact in structure, good in stability, high in switching speed, and high in pulse contrast ratio. In addition, light leakage cannot occur when the high-pulse-contrast-ratio nanosecond fiber laser is used for marking and engraving and the like of sensitive materials, machining edges are clear, and effects are better.