  Investigation of light in the waveguide structures is a topical modern
problem that has long historical roots. A parallel-plate waveguide is a base
model in these studies and it is intensively used in numerous investigations of
nanooptics, integrated circuits and nanoplasmonics. In this letter we first
have found the analytical solution for the light modes in this waveguide. The
solution provides a clear physical picture for description of a light within
the broadband spectral range in the waveguide with various physical parameters.
Potential of the analytical solutions for studies of light fields in the
waveguides of nanooptics and nanoplasmonics has been also discussed.
