;In this thesis we discuss the anisotropic propagation properties of light waves in multilayer films. The effective optical parameters of the multilayer dielectric films are obtained by using crystal optics and photonic crystal theories, and their physical meanings are explained. We analyze and compare the applicability and limitation of each effective medium theory in the literature, and try to combine their advantages in our newly developed theory. Based on a lot number of numerical simulations, we propose the "applicability condition" of our effective crystal theory as: the optical thickness of a single period must not exceed 0.4 wavelength of the incident light (Nd<0.4λ). Under this condition, our effective crystal theory has good predictability. In this thesis, the traditional EMA (effective medium approximation) is used as the reference, and compared in the simulations with our effective crystal theory based on the iso-frequency curve. The essential difference between these two kinds of theory is the calculation method of the effective dielectric constants. We analyze the physical causes for the difference in the simulation results, and list the advantages and disadvantages of both. The first three chapters focus on the introduction of existing theories and the related derivation details which will be used later. In the fourth chapter we construct the effective crystal theory in detail, and analyze the simulation results according to this theory. In the last chapter we propose some future works and possible applications.
