Extraordinary phase-index angular dependence
= Extraordinary phase-index angular dependence
For a lossless uniaxial <dielectric>, $n_{\rm ex}^{-2}=\cos^2\vartheta/n_o^2+\sin^2\vartheta/n_e^2$, where $\vartheta$ is the angle between the <wave vector> and <optic axis>. Along the axis $n_{\rm ex}=n_o$, while perpendicular propagation gives $n_{\rm ex}=n_e$.