Electro-optic sensors: a precise in-situ alignment of quarter-wave plate

For a highly accurate electro-optic sensor, the tolerance of the quarter-wave plate phase retardation should be at least (lambda) /250, and the azimuthal alignment error should be within +/- 0.5 degrees. Also the phase retardation depends on the angle of incidence, which makes the alignment more difficult. The method we present uses the extinction ratio as a measure of the quality of alignment. It enables in-situ alignment of the quarter-wave plate to the phase retardation accuracy of +/- 0.5 degrees using only the components of the electro- optic sensor. The method can easily be generalized for any application and for an automated and direct measurement of the phase retardation of a wave plate with high accuracy.