 A quarter-wave plate can be used to produce elliptical polarization as well.Waveplates are constructed out of a birefringent material (such as quartz or mica, or even plastic), for which the index of refraction is different for light linearly polarized along one or the other of two certain perpendicular crystal axes.The behavior of a waveplate (that is, whether it is a half-wave plate, a quarter-wave plate, etc.)