 If the axis of polarization of the incident wave is chosen so that it makes a 45° with the fast and slow axes of the waveplate, then "Ef" = "Es" ≡ "E", and the resulting wave upon exiting the waveplate is
and the wave is circularly polarized.If the axis of polarization of the incident wave is chosen so that it makes a 0° with the fast or slow axes of the waveplate, then the polarization will not change, so remains linear.If the angle is in between 0° and 45° the resulting wave has an elliptical polarization.