title: Description of nonlinear couplers by power conservation.
abstract: Poynting's vector theorem describes power flow on twin-core couplers with arbitrary axial perturbations, both linear and nonlinear. This bypasses the coupled amplitude formulation and unifies nonlinear two-mode interactions in general.
authors.forename: A W
authors.initials: AW
authors.lastname: Snyder
authors.forename: D J
authors.initials: DJ
authors.lastname: Mitchell