Variable-Index Prism

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The refractive index of nematic liquid crystals can be continuously varied between a maximum value and a minimum value for correctly polarized incident light. This variable index, the extraordinary index, is controllable with an applied voltage. Light having the other polarization experiences a constant refractive index called the ordinary index and is not actively steered.

The animation at left shows how the extraordinary refractive index of the prism can be adjusted so that the light emerges from the prism in a fixed direction even as the source moves.