Abstract
The fundamental modes of nonlinear optical weakly guiding fiber with
circular cross section are studied analytically. The dielectric constant of the fiber core is
assumed to be differing from the dielectric constant of the fiber cladding. The change
between them occurs abruptly when the light intensity reaches a certain level. The core
radius formed at a certain intensity level in dependence of the optical characteristics of
the waveguide mode and fiber is specified. It is shown that the core radius can be
reduced by increasing the frequency of the wave or the magnitude of the jump in the
dielectric constant, and also by decreasing the propagation constant. The self-confinement
core radius decreases with increasing frequency, but this increases the diameter of the
light beam localization in the fiber cross section. Increasing the propagation constant has
the opposite effect.