In an example, a tandem pumped fiber amplifier may include a seed laser, one or more diode pumps, and a single or plural active core fiber. The single or plural active core fiber may include a first section to operate as an oscillator and a second different section to operate as a power amplifier. The one or more diode pumps may be optically coupled to the first section of the single or plural active core fiber, and the seed laser may be optically coupled to the single active core or an innermost core of the plural active core fiber.