An electro-optic waveplate for changing the state of polarization of light passing therethrough is disclosed. The waveplate provides a substantially constant birefringence when the principle birefringent axes of the electro-optic waveplate are rotated. The waveplate is an electro-optical material having two principle orthogonal birefringent axes that are rotable when suitable voltages are applied. Two related different voltages are applied along sequential or contiguous regions along the length L of the electro-optical waveplate for providing a controllable and varying electric field along the length L, such that retardance of the waveplate of the length L remains substantially constant while the birefringent axes of the electro-optic waveplate are rotated by varying the voltages. The two different voltages have a phase relationship or a phase and magnitude relationship therebetween.