Symmetry of beamsplitting angle for uniaxial crystal prism

Usually,the beam splitting angle of a Wollaston prism has no symmetry to the direction of incident light. According to the theoritical calculation,if a double Wollaston prism has the feature of high symmetry of beam splitting angle,it is necessary that the sum of the structure angle β1 and β2 of two Wollaston prisms is equal to 90 degree, and β1 and β2 are not identical.The theoretical analysis andthe experimetal results proved that the selections of β1 and β2bear no relation to light wave length and the refractive index of the crystal,so this method can be wide used in many optical systems.