If the incoming light is linearly polarized (plane-polarized), the s and p components are initially in phase ; hence, after two reflections, "the p component is 90° ahead in phase", so that the polarization of the emerging light is elliptical with principal axes in the s and p directions (Fig. 1). Similarly, if the incoming light is elliptically polarized with axes in the s and p directions, the emerging light is linearly polarized.