ABSTRACT
The progress made in the technology of fabricating silica-based glass optical fibres has ensured that the transmission losses are less than 1dB/km over a fairly wide range of the near-infrared wavelength region. Absorption from lattice vibrations occur in the infrared, decaying exponentially with decreasing wavelength. Different kinds of nonlinear phenomena can be observed depending on the sign and magnitude of the group velocity dispersion. The transition from bulk nonlinear media to fibre not only quantitatively reduces the threshold powers of nonlinear processes, but also has certain qualitative advantages. It is well-known that the self-focusing of radiation is frequently the main negative factor at high laser radiation powers—in particular, it prevents the utilization of a number of nonlinear effects. In fibre optics, there are methods for compensating the material dispersion in order to achieve phase matching in four-photon processes—both in multimode and single-mode fibres.
