Invariant imbedding in time-varying homogeneous nondispersive media

The invariant imbedding approach is applied to electromagnetic wave propagation in homogeneous temporally varying media. As a convenient example a plane wave is considered. The result is a coupled pair of complex first-order linear differential equations for the amplitude of the forward and backward propagating waves which arise when the index of refraction of the medium is changed in an arbitrary way from one steady-state value to another. This approach provides an alternative point of view in the analysis of time-varying medium devices such as electrooptic phase modulators.