title: Nonparaxial equation for linear and nonlinear optical propagation.
abstract: The formalism of coupled-mode theory, specialized to the continuum of radiation modes, allows us to extend the standard parabolic wave equation to include nonparaxial terms and vectorial effects, and, in particular, to generalize the nonlinear Schrödinger equation that describes propagation in the presence of an intensity-dependent refractive index.
authors.forename: B
authors.initials: B
authors.lastname: Crosignani
authors.forename: P
authors.initials: P
authors.lastname: Di Porto
authors.forename: A
authors.initials: A
authors.lastname: Yariv