Absorption effects in liquid crystal waveguides.
An analytical and numerical study of the propagation of optical fields through a nematic hybrid slab is developed. We take into account explicitly the absorption of radiation by the liquid crystal by introducing a complex dielectric tensor. For a low intensity beam we first derive the eikonal equation and from it we calculate the ray trajectories in the optical limit. We show that in the presence of absorption, there are no caustics within the slab. Then we consider the WKB limit and calculate the field transverse magnetic modes, their number and their cutoff frequencies. We show that for both limits the agreement between our analytical and numerical results for the propagation constants is excellent, while there are larger differences in the analytically and numerically calculated field amplitudes. These differences show that absorption effects are important for this quantity and have their origin in the fact that the chosen parameter values in our exact numerical calculations, strictly speaking, do not lie within the limits of validity of the WKB approximation. Although a more precise comparison between these approaches requires the use of different sets of values of the relevant parameters, our analysis shows the effects and complications arising from the inclusion of absorption. Finally, we discuss the scope and limitations of our approach.