  We analyze the transition between different coupling regimes of two
dielectric rods, which occurs at a critical distance between them. The hallmark
of strong coupling regime is the peak splitting effect observed in spectra.
Here we comprehensively evaluate the critical distance as a function of the rod
permittivity using a number of different approaches. The scattering spectra of
the two rods in dependence on the distance demonstrate the weak to strong
coupling transition. We start the analysis by introducing a region of a tidal
energy flux around a single isolated rod (the region is related to the near
field) and demonstrate that its effective radius corresponds to the critical
distance obtained from the scattering spectra. Next, we study the
eigenfrequencies of the dimer as functions of distance by 'diagonalizing' the
coupled multipole matrix. In order to find an analytical formula for the
critical distance, we consider the problem under several approximations, which
yield similar results.

Optics