  Optical depolarizers for monochromatic waves which work independent of input
polarization can be built from cascaded electrooptic rotating waveplates. If
the waveplate retardations deviate from their desired values then the
worst-case residual degree-of-polarization DOPmax is larger than its desired
value 0. In a depolarizer consisting of one rotating halfwave and one rotating
quarterwave plate, DOPmax roughly equals the retardation error, which is <<1.
However, with just one rotating quarterwave plate more, DOPmax roughly equals
the square of the retardation error which is a much smaller value. Thereby
depolarizer accuracy is substantially improved. Waveplate sequence and rotation
frequency combinations suitable for fast depolarization are discussed.
