Birefringence devices, variable

In an electrooptic material the phase retardation angle is controlled by altering birefringence, which is in turn controlled by the potential of an apphed electric field. An electrooptic device thus acts as a variable phase optical retardation plate, and can be used to modulate the wavelength or intensity of an incident beam. 

Variable retardation can also be achieved using electric birefringence induced in liquid layers. Commercial devices are available that use this method. 

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