The excitation of soliton states in optical layers exhibiting Kerr nonlinearities is theoretically investigated. The optical transmission coefficient is obtained as a function of the nonlinearity power of an incident monochromatic electromagnetic wave polarized in the transverse electric configuration. In materials exhibiting a defocusing nonlinearity, soliton excitations are not observed if the nonlinearity power associated with the incident electromagnetic wave is below a well-defined value. At such a limiting value of the nonlinearity power, a soliton excitation with an electric-field amplitude independent of the position is found within the nonlinear layer, regardless of the incident-wave frequency value.