In this study, we propose a widely tunable in the 1.6-2.65 μm range femtosecond fiber laser source, generating high-quality sech-shaped pulses with the duration of order 100 fs. Experimental setup contains hybrid all-fiber Er/Tm pump laser generating 150 fs pulses of 2 nJ in Erbium (1.56 μm) channel and 125 fs pulses of 4 nJ in Thulium (2 μm) channel respectively. This laser source was coupled to a 50 cm piece of suspended-core microstructured TeO<sub>2</sub>-WO<sub>3</sub>- La<sub>2</sub>O<sub>3</sub> glass fiber with launching efficiency of about 10%. We have observed Raman self-frequency shifting solitons in this fiber with maximum red shift of 2.25 μm for Erbium channel and 2.65 μm for Thulium channel. By varying energy of pump pulses, solitons can be tuned in broadband spectral region. We have made theoretical studies of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters. Numerical simulation is in a very good agreement with the experiment
Prospects of fabrication of solid-core photonic bandgap fibers with a large mode area (LMA) are discussed. Properties
of solid-core photonic bandgap fibers with a small ratio of the cladding element diameter d to the distance Λ between
neighboring cladding elements are studied. The range of fiber parameters at which the fiber is single-mode over the
fundamental band gap is found.
Initial and radiation-induced optical loss spectra of multimode pure-silica-core holey fibers drawn at different regimes are analyzed and compared with those of a conventional POD-fiber with the same KU-1 silica in the core. It is shown that by filling the holes with H<sub>2</sub> gas during fiber drawing, it is possible to fully suppress the drawing-induced 630 nm absorption band and to lower the amplitude of the radiation-induced 610 nm absorption band. The results of an experiment are discussed in which H<sub>2</sub> gas was conducted through the holes of a multimode pure-silica-core holey fiber immediately in the process of its γ-irradiation. The dose evolution of the 610 nm absorption band and of the short-wavelength (≤ 550 nm) absorption associated with hydrogen incorporation into the glass network is analyzed. It is concluded that H<sub>2</sub> gas is efficient at suppressing the 610 nm band in pure-silica-core holey fibers, but can cause a loss increase in the short-wavelength region, in case its pressure in the holes is not sufficiently high.
Optical losses induced in fibers at 300<sup>o</sup>C and in hydrogen atmosphere were studied. A non-linear dependence of hydrogen penetration through the carbon coating on hydrogen pressure was observed. It was demonstrated that carbon coating could not defend the fiber from hydrogen penetration for a long time period. At some time, the hydrogen presence in the fiber core resulted in high optical losses in all spectral range in the case of Ge-doped fibers. It was found that the short-wavelength loss edge (SWE) in a Ge-doped fiber co-doped with a small amount of phosphorus was significantly smaller than that in Ge-doped fibers without co-doping. Nevertheless, P-codoping effect did not decrease optical losses related with SWE completely.