We demonstrate an all-fiber-integrated, high-power chirped-pulse-amplification system operating at 1550 nm. The seed source is a soliton fiber laser with 156 MHz repetition rate. Two-stage single mode amplifier provides an amplification of more than 40 dB without significant spontaneous amplified emission. The power amplifier is based on cladding-pumped 10 µm-core Er-Yb co-doped fiber, the output of which was spliced into standard singlemode fiber. We obtain 10 W average power in a strictly singlemode operation. After dechirping with a grating compressor, near transform-limited, 450 fs-long pulses are obtained. The laser source exhibits excellent short and long-term intensity stability, with relative intensity noise measurements characterizing the short-term stability.

This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 μm producing 5-ns, 100-μJ 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 M2 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.

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There is rapid progress in the development of high-power fiber lasers due to their robust operation, low cost, high beam quality at high powers. There are various applications, such as laser sensing, LIDAR applications, processing of specific materials, which require robust and high-power pulsed laser sources at 1550 nm with high beam quality. Achievement of high peak power with low repetition rate is challenging due to well-known problems of strong nonlinear effects and amplified spontaneous emission (ASE) build-up between pulses. In order to reach highest efficiency, the design of each stage of amplification should be carefully optimized. Numerical modeling can be a great tool due to the large number of parameters involved [1]. To date, most modeling efforts of fiber amplification have assumed either a lumped gain model for pulse propagation or a distributed, position-dependent gain model for CW signal for computational simplicity. Here, we investigate both time-and position-dependent gain dynamics numerically, which are used to optimize experimental results. We solve rate equations for Er-doped fiber (three-level system) and Er-Yb-co-doped fiber (six-level system) using finite differences method. The fiber is divided into small segments and for each segment, the rate equations are solved for both forward and backward propagating signals for a fixed time interval. Next, the time step is increased, and the process is iterated. This scheme allows us to analyze pulse propagation with population levels dependent both on time and position along the fiber. This treatment is evidently necessary to correctly model processes such as dynamic gain saturation and ASE creation, since the physical length of a few-ns pulse is comparable to the length of a typical gain fiber. Simulation results were confirmed by experiments, based on which the experimental setup was iteratively optimized. The experimental setup is shown in Fig. 1(a). It consists of a seed source, which is a current-modulated diode laser, a core-pumped Er-fiber preamplifier, an acousto-optic modulator to reduce repetition rate to 50 kHz or 100 kHz and a three-stage amplifier system. The first stage comprises of a single-clad Er-doped fiber and the last two stages are based on cladding-pumped Er-Yb co-doped fiber with 10-μm and 12-μm core diameter. Following the final amplifier, pulses traverse standard singlemode fiber (SMF-28) to clean up any residual high-order modes before being extracted from fiber. In simulations, the seed source is modeled with Gaussian pulses with peak and average power of 50 mW and 0.3 mW, respectively, corresponding to our experimental values. Simulation results confirm that sufficient seed power is needed from each stage to the next for its saturation and prevention of ASE creation. However, even at high pulse energy and average power after the middle stage (1.2 W in simulation and experiment), at 50 kHz repetition rate we observe significant amount of ASE creation between pulses (see Fig. 1 (d)). By comparison, at 100 kHz, the ASE g...

We demonstrate all-fiber-integrated nonlinear CPA system operating at 1550 nm, seeded by a solitonsimilariton laser. Chirped 2-µJ pulses are compressed to 700-fs, 0.5-µJ pulses at 1 MHz. Amplifier output is through a strictly singlemode fiber.