Twisted Nematic (TN) liquid crystals are the most common type of LC’s used in the display industry. TN cells are basically 90° liquid crystal polarization rotators. As linear polarized light enters the cell it rotates along the LC helical structure formed from the front glass substrate to back substrate. TN cells can be made in either a normally black mode or normally white mode. Normally black mode is a dark state with zero voltage applied with polarizers mounted to the outside of the substrates in parallel to each other. As voltage is applied light transmission increases as a function of voltage. Normally white mode has maximum transmission with zero voltage applied with the polarizers orthogonally mounted on the glass substrates. The light is attenuated as voltage increases. This mode achieves higher contrast as the dark state takes advantage of the crossed polarizer configuration.

TN’s advantages are low voltage requirements and they operate over a large wavelength range. TN cells can be manufactured uniformly in mass volumes with thin glass. If low transmitted wavefront distortion is required, precision cells can be manufactured with polished glass substrates.