It is known that a stack of anisotropic films lying on a plane substrate and illuminated with a linearly polarized plane wave generally gives rise to an elliptically polarized reflected field. With a view of application in optical data storage (the anisotropy being for example created by a static magnetic field), we may wonder whether this change in polarization can be enhanced by modulating the interface between the substrate and the layers. The following theoretical and numerical considerations have been developed in our laboratory while some measurements were performed in PA Cambridge Laboratory in the framework of a contract.