This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 mu m producing 5-ns, 100-mu J pulses. These pulses are generated at a 100 kHz repetition rate, corresponding to 10 W of average power. The seed source is a low-power, current-modulated, single-frequency, distributed feedback semiconductor laser. System output is obtained from a standard single-mode fiber (Corning SMF-28). Consequently, the beam is truly diffraction limited, which was independently proven by M-2 measurements. Further increase of peak power is limited by onset of significant spectral broadening due to nonlinear effects, primarily four-wave mixing. Numerical simulations based on six-level rate equations with full position-and time-dependence were developed to model propagation of pulses through the amplifier chain. This capability allows minimization of the amplified spontaneous emission, which can be directly measured using a fast acousto-optic modulator to gate the pulses. (C) 2014 Optical Society of America