Birefringent optical element, lcd device with a birefringent optical element, and manufacturing process for a birefringent optical element

A birefringent optical element comprises a polymerized and/or cross-linked mixture (301) of a liquid crystalline compound and a photo-isomerizable compound. The birefringence of the element can be determined with high precision by manipulating the order parameter and polarization anisotropy of said mixture. For this purpose, the photo-isomerizable compound is converted from a trans-form to a cis-form during manufacturing by means of irradiation. Preferably the photo-isomerizable compound is a cinnamate compound. The irradiated mixture is polymerized and/or cross-linked after irradiation. The irradiation preferably takes place through a greyscale mask (305) so that within the mixture (301) portions (302R, 302G, 302B) are defined that obtain different birefringence values. The process is for example suitable for manufacturing a retarder layer or compensation foil inside the liquid crystalline cell of a Liquid Crystal Display (LCD) device, and in particular for manufacturing a patterned retarder layer having portions with different retardation, associated with the primary colors of a color LCD device.