Liquid-crystal cell with a wide viewing angle and a high cell contrast

Abstract

A liquid-crystal cell operating in the normally white mode is introduced that displays a wide viewing angle together with a high cell contrast. A wide viewing angle is achieved by reducing the twist angle in the cell to below 90 degrees and by reducing the Dnd parameter, while a high cell contrast is obtained by incorporating an in-plane, low-valued compensating retardation film with values lying in the range of 10-50 nm. The optimization of the cell parameters together with the polarizer arrangement permit cell transmittances approaching 100% to be obtained when the cell is in the inactivated phase and with Dnd values down toward the theoretical limit of 0.27 mum. Further improvements in the optical angular properties can be obtained by the placing together of two such cells so that the angular bisector of the surface alignment directors of the two cells lies antiparallel. Such optical shutters find applications in fast, automatically darkening welding filters where a fast response time from the light to the dark protective state is required, together with both a large viewing cone in the low transmittance state and a clear field of view in the light phase.