A high power optical fiber laser system comprising an initial amplifier stage comprising a first active optical fiber operatively coupled to one or more first pump sources, the first active optical fiber having an output, the initial amplifier stage being configured in a first enclosure; a first signal optical fiber having an input operatively coupled to the output of the first active optical fiber and an output; one or more final pump sources; one or more final pump optical fibers, each having an input coupled to one or more of the final pump sources and an output; and a power module comprising a final amplifier stage, the final amplifier stage comprising a final active optical fiber having an input operatively coupled to the output of the first signal optical fiber and an output, the final active optical fiber being operatively coupled to the outputs of the one or more final pump optical fibers, the power module being disposed in a power module enclosure separate from the first enclosure, wherein the first signal optical fiber extends from the initial amplifier stage to the power module, the optical path length between the first active optical fiber and the final active optical fiber is no more than about 100 m, the optical path length between each of the one or more final pump sources and the final active optical fiber is no more than about 100 m, the power module enclosure has no pump sources disposed therein, and the high power optical fiber laser system is configured to output at least about 20 W of optical power, and wherein the power module and the power module enclosure do not include any electrical or electronic devices, and no electrical wiring extends to or is included in the power module enclosure, such that the optical fiber system includes no electrical or electronic components in any connection to the power module enclosure, and the optical fiber system includes no metallic components in any connection to the power module enclosure, characterized in that the system is configured such that optical feedback from the power module, but no electrical or electronic feedback from the power module, is used in feedback control of the optical fiber system. an initial amplifier stage comprising a first active optical fiber operatively coupled to one or more first pump sources, the first active optical fiber having an output, the initial amplifier stage being configured in a first enclosure; a first signal optical fiber having an input operatively coupled to the output of the first active optical fiber and an output; one or more final pump sources; one or more final pump optical fibers, each having an input coupled to one or more of the final pump sources and an output; and a power module comprising a final amplifier stage, the final amplifier stage comprising a final active optical fiber having an input operatively coupled to the output of the first signal optical fiber and an output, the final active optical fiber being operatively coupled to the outputs of the one or more final pump optical fibers, the power module being disposed in a power module enclosure separate from the first enclosure, the first signal optical fiber extends from the initial amplifier stage to the power module, the optical path length between the first active optical fiber and the final active optical fiber is no more than about 100 m, the optical path length between each of the one or more final pump sources and the final active optical fiber is no more than about 100 m, the power module enclosure has no pump sources disposed therein, and the high power optical fiber laser system is configured to output at least about 20 W of optical power, and the power module and the power module enclosure do not include any electrical or electronic devices, and no electrical wiring extends to or is included in the power module enclosure, such that the optical fiber system includes no electrical or electronic components in any connection to the power module enclosure, and the optical fiber system includes no metallic components in any connection to the power module enclosure, characterized in that the system is configured such that optical feedback from the power module, but no electrical or electronic feedback from the power module, is used in feedback control of the optical fiber system.