Abstract
Investigation of light in waveguide structures is a topical modern problem that has long-standing historical roots. A parallel-plate waveguide is a basic model in these studies and is intensively used in numerous investigations of nano-optics, integrated circuits and nanoplasmonics. In this letter we have first found an approximate analytical solution which describes the light modes with high accuracy in the subwavelength waveguides. The solution provides a way of obtaining a clear understanding of the light properties within the broadband spectral range in the waveguide with various physical parameters. The potential of the analytical solution for studies of light fields in the waveguides of nano-optics and nanoplasmonics has also been discussed.