The relation between the propagation of extraordinary ray and the optical axis in the uniaxial crystal

With the development and application of uniaxial crystal optics, crystal device is widely applied in various fields. The light propagation in the uniaxial crystal has attracted the attention of researcher. Natural light is divided into ordinary ray (o-ray) and extraordinary ray (e-ray) after entering into uniaxial crystal. The propagation of o-ray in the uniaxial crystal obeys Snell's law but the e-ray in the uniaxial crystal does not obey Snell's law. The e-ray obeys the extension Snell's law because the refractive index of e-ray is changed with the angle of wave vector and optical axis. The propagation of e-ray in the uniaxial crystal is relevant to not only the refractive index of isotropic media, the refractive index of uniaxial crystal but also optical axis. The relation between e-ray and optical axis are given by calculation and numerical simulation when incident plane and the principle section are perpendicular.