Novel Way for Full Characterisation of Splayed Retarders using Wentzel–Kramers–Brillouin Method

The viewing angle dependency of transmissive liquid crystal (LC) displays can be reduced by use of compensation foils (retarders) exhibiting specific optical properties such as splays or tilt gradients. Thin films with tilt gradients can be characterised using the prism coupling method. This method comprises the excitation of waveguide modes in the investigated film using the evanescent field at the base of a prism in total reflection without the requirement of an immersion liquid. The resulting reflectivity curves are simulated with the help of the Berreman method. The simulations provide insights into simpler ways to evaluate the data for thin films exhibiting a tilt gradient along the layer normal. The Wentzel–Kramers–Brillouin (WKB) method for inhomogeneous films can be applied to the full characterisation of the tilt gradient without prior knowledge of thickness and refractive indices of the film. A polymerised liquid crystal sample example was investigated and a linear gradient was found for this example.