PURPOSE:To obtain a fiber laser system whose threshold value is low and whose output is high by using a quartz-related optical fiber whose core is doped with P together with Nd. CONSTITUTION:An optical fiber 4 is a quartz-related optical fiber which is doped with, e.g., Ge so that a refractive index is distributed; its core is doped with at least Nd and P. In addition, a reflector is installed at the output side. That is to say, because P together with Nd is doped, the extinction by density due to the increase in the Nd can be suppressed, it is possible to increase laser- active ions Nd3+. Accordingly, even when the high-concentration Nd is doped, the extinction by density due to the simultaneous doping of the P is not caused. By this setup, it is possible to obtain a high-output fiber laser system.
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