Fiber laser

The embodiment of the invention discloses a fiber laser, which comprises a seed light source, a single-stage amplifier structure and an output terminal, and is characterized in that the single-stage amplifier structure comprises an isolator, a gain optical fiber, a beam combiner and a pumping source. The doping concentration of the gain ions is gradually increased in the transmission direction ofthe pulse signal light, the fiber core diameter and the cladding diameter of the gain optical fiber are the same in size, and the matrix materials are the same, so that the gain optical fiber absorbsthe pump light to form population inversion, and then the number of inverted particles in the transmission direction of the pulse signal light tends to gradually increase, so that the requirement of the pulse signal light for gradually amplifying the number of inverted particles can be met, and after the number of inverted particles is consumed on the basis of requirement matching, in order to maintain the steady state of