Анализируются нелинейные волны в рамках базового уравнения третьего приближения теории дисперсии нелинейных волн. Данное уравнение, включающее в себя члены нелинейной дисперсии и линейной дисперсии третьего порядка, адекватно описывает короткие волновые пакеты протяжённостью до нескольких длин волн.
The basic equation of the third-order approximation of the nonlinear dispersion wave theory (third-order nonlinear Schroedinger equation) including both the nonlinear dispersion terms and third-order linear dispersion one and describing the propagation of intense short (of the order of few wavelengths) wave packets in dispersive media of different nature is analyzed. Both stationary waves and nonstationary wave packets are considered. The propagation of electromagnetic and Langmuir waves in isotropic plasma in the frame of the third-order approximation of the nonlinear dispersion wave theory are considered. Soliton solution of electromagnetic waves and plane Langmuir wave modulation instability are considered. In contradiction to the well-known parabolic approximation the velocity of the derived solitons depends on their intensity.