Optical properties of a dielectric-metallic superlattice: The complex photonic bands

We have studied theoretically the photonic bands in a periodic dielectric-metallic superlattice. In the calculations the absorption in the metallic layers was taken into account using the well-known Drude model for the dielectric function, ε(ω)=1-ω_p²/ ω(ω+iγ). Due to the absorption in the metallic films, the Bloch vector becomes complex for all frequencies, and the waves are evanescent. The photonic band structure is strongly modified as compared to the band structure of the nonabsorbent superlattice, mainly in the region of low frequencies ω<ω_p where bands of odd behavior appear. We also have studied the absorption, reflection and transmission spectra of light incident on a finite superlattice. The spectra show that the complex bands, with complex wave vector and real frequency, are an appropriate resource to describe the optical properties of periodic absorbent structures.