The working medium used in the fiber laser has the form of fiber, and the fiber laser characteristics are affected by the fiber conducting properties.

The pump light entering the fiber has multiple modes. Signal optoelectronics may have multiple modes. Different pump modes have different effects on different signal modes, which makes the analysis of fiber lasers and amplifiers more complicated.

In many cases it is difficult to get an analysis and has to be calculated by means of numerical values. The doping profile in the fiber also has a large effect on the fiber laser. In order to make the medium have gain characteristics, working ions (ie, impurities) are doped into the fiber.

In general, working ions are evenly distributed in the core, but the distribution of different modes of pump light in the fiber is non-uniform. Therefore, in order to improve the pumping efficiency, we should try to make the distribution of ion distribution and pump energy coincide. In the analysis of fiber lasers, in addition to the general principle of the laser, it is necessary to consider the characteristics of the laser itself, introduce different models and adopt special analysis methods to achieve the best analysis results.

The fiber laser consists of three basic elements: pump source, gain medium, and resonant cavity, just like traditional solid-state and gas lasers. The pump source uses a high power semiconductor laser to gain a rare earth doped fiber or a common nonlinear fiber.

The resonant cavity may be composed of optical feedback elements such as fiber gratings to form various linear resonant cavities, or a coupler may be used to form various annular resonant cavities. The pump light is coupled into the gain fiber via a suitable optical system that, after absorbing the pump light, forms a population inversion, or a nonlinear gain and produces a spontaneous emission. The generated spontaneous emission light, after undergoing laser amplification and mode selection of the resonant cavity, finally forms a stable laser output.