The rapid progress in fiber technology has led to the development of fiber laser systems that can compete with bulk solid-state lasers. Compact size, low cost and reliability of fiber systems make them attractive for both fundamental research and practical applications. The generation of optical pulses with extreme parameters (few-cycle duration and ultrabroad spectrum) was a striking achievement of nonlinear fiber optics, which led to the emergence of a new research trend — extreme fiber optics.

Schematic representation of an all-fiber laser system and experimental spectra of femtosecond radiation

The IAP RAS researchers have obtained funda-mental results on the nonlinear theory of wave solitons containing a small number of optical field oscillations, and the formation of few-cycle pulses in Kerr media (A. V. Kim, S. A. Skobelev). A number of technologies for creating all-fiber tunable femtosecond laser sources over a very wide wavelength range of 0.9—2.7 µm have been developed (E. A. Anashkina, A. V. Andrianov, A. V. Kim, S. V. Muravyev). At the core of these technologies is the conversion of femtosecond pulses from an erbium laser in nonlinear optical converters, which are mainly optical fiber waveguides with specially designed dispersion properties (dispersion-decreasing fibers DDF, dispersion-shifted fibers DSF, germanate and tellurite fibers). These technologies have yielded important results:
• laser pulses with 13 fs duration, which is 2 optical cycles at a wavelength of 1.7 µm, have been obtained in an all-fiber DSF based laser system;
• a scheme for generating microjoule level laser pulses at a wavelength of about 1 µm optically synchronized with few-cycle pulses in the range of 1.6—2 µm has been proposed and developed. Seed pulses of 1 µm are formed in DSF and amplified in large-mode-area ytterbium-doped active fibers;
• the possibility of advancing to the mid-infrared with the germanate and tellurite fibers has been de-monstrated.

	Few-cycle pulse at the output of the fiber system measured by the frequency-resolved optical-gating method (FROG)