In uniaxial birefringence crystals are observed two refractive index of refraction (no and ne) with its dispersion curves, that can intersect for a given wavelength. Phenomenon of intersect the dispersion curves no and ne observed in the crystals due to the fact that as the light energy from the minimum band gap, change the nature of the electronic transition. The spatial dispersion, depending optical function on the orientation wave vector K in the crystal, is an important role in gyrotropic crystals. The amplitude of the contour of the reflection spectra were calculated using the dispersion relations. Using of the filters based on isotropic wavelength give a definite advantage when measuring Raman spectroscopy.