US Patent 8004621 Switchable lens

A display apparatus has a switchable birefringent lens array. The display apparatus produces a substantially linearly polarised output. The lens array comprises birefringent material arranged between a planar surface of a first substrate and a relief substrate of a second substrate defining an array of cylindrical lenses. The lens array has electrodes for applying a control voltage across the birefringent material for electrically switching the birefringent material between a first mode and a second mode. In the first mode the lens array modifies the directional distribution of incident light polarised in a predetermined direction. In the second mode the lens array has substantially no effect on incident light polarised in said predetermined direction.