A special form of the solid-state laser is the fiber laser. The active medium is the doped core of an optical fiber. In other words, it is a glass laser with optical waveguide properties. Since the laser radiation is guided through a laser-active fiber, it undergoes enormous amplification due to its great length. The fields of application of fiber lasers are very broad and suitable for many laser applications. With low power, fiber lasers are used for data transmission in optical fibers. Systems with high power also in laser cutting and laser welding.