  A coherent definition of the reflection and transmission factors at a plane
interface separating two uniaxial crystals is proposed, from the photons
impulsion-energy 4-vectors conservation. This definition, different from the
classical electromagnetic one, is compatible with the completely resolved
extended Fermat's principle of the geometric optics for extraordinary luminous
rays inside uniaxial media, and allows the exact calculation of the
transmission factors at the plane interface for any practical configuration,
combining all possible optical axes and anisotropy factors variations.
Furthermore, this particular technique points out the existence of
quasi-particles strongly associated to the photons, whose behaviour is highly
correlated to the photons transmission/reflection possibilities.
