Structure of light waves in a waveguide tapered to subwavelength transverse size

The penetration of an H wave through a waveguide whose radius varies continuously from about the wavelength size to subwavelength dimensions (of the order of 1/10 wavelength) is calculated. The method for the field analysis is developed and the range of its applicability is studied by considering some numerical examples. The dependence of the transmission coefficient of a tapered waveguide on the radiation wavelength and on the profile steepness of the waveguide is studied. It is shown that a sharper decrease in the waveguide radius provides higher values of the field transmission coefficients.