The paper is devoted to the study of the connection between
the numerical dispersion arising in FDTD modeling of electromagnetic
signal propagation in nondispersive homogeneous
media optically different from vacuum and the Courant number
in the 2D case. The main results are formulated in the
form of four statements, as well as a number of corollaries
and remarks that determine the nature of the numerical dispersion,
the optimal value of the Courant number and the limitations
of the method. It is proved that the optimal choice of
the Courant number eliminates the numerical dispersion and
extends the capabilities of the developed numerical algorithm
to media, which refractive index is lesser than refractive index
of vacuum, as well as media with negative refraction.