mu s pulsed, low repetition rate, 30 W fiber laser at 1550 nm.

High-power Er and Er/Yb co-doped fiber laser systems, operating at 1550 nm are attractive for many practical applications. At present, the most efforts of the laser developers are focused on the production of such lasers either with ultrashort (fs) or ns pulse duration. For the ns operation, master oscillator power amplifier (MOPA) design is commonly used, where the master oscillator is semiconductor DFB or DBR laser. It allows on the fly electronically configurable design of the laser, with adjustable repetition rate and pulse duration. Such concept cannot be applied if μs pulse-width is required, especially at low repetition rate due to several reasons, where the main are: pulse steepening during the amplification, and significand amplified spontaneous emission (ASE) growth. Pulsed pumping, is a common solution to avoid ASE at low repetition rate for the ns or fs laser sources. However, for the μs laser it does not solve the problem of pulse steepening, which decreases the pulse duration from μs range to almost ns, and, due to specific Er-Yb band configuration, at reasonable pump level the inversion population increases slowly, reaching the maximum nearly 150-300 μs after the pump starts. It makes impossible to create homogeneous rectangular-shape μs pulses. In our work, all these features were analyzed by performing numerical simulation, based on the model described in [1].