Wave vectors of light beams in anisotropic crystals

Starting with the introduction of wave vectors of light beams in anisotropic crystals, we examine the relationship between wave vector and electric displacement vector. Based on the fact that the two wave vectors with different magnitudes and directions in a crystal can be solved by the determinantal equations of the wave differential equations an ambiguity in representation of birefringence phenomena is pointed out and a way to free of the ambiguity is set forth.