We report generation of femtosecond optical pulses tunable in the 1.6-2.5 μm range using GeO2-doped core silica-cladding fibers. Optical solitons with a duration of 80-160 fs have been measured by the FROG technique in the 2-2.3 μm range. To the best of our knowledge, these are the longest wavelength temporally characterized solitons generated in silica-based fibers. We have also demonstrated more than octave-spanning femtosecond supercontinuum generation in the 1.0-2.6 μm range.

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The coherent propagation and amplification of high-power laser radiation in a multicore fiber consisting of a square array of weakly bound cores are studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams in such fibers. The analytical results are confirmed by direct numerical simulation of the wave equation. The stability conditions of the out-of-phase mode in the active medium are found.

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