M.S. Vasconcelos

Octonacci photonic quasicrystals

Abstract We study theoretically the transmission spectra in one-dimensional photonic quasicrystals, made up of SiO2(A) and TiO2(B) materials, organized following the Octonacci sequence, where the nth-stage of the multilayer S n is given by the rule S n = S n - 1 S n - 2 S n - 1 , for n ⩾ 3 and with S 1 = A and S 2 = B . The expression for transmittance was obtained by employing a theoretical calculation based on the transfer-matrix method. For normally incident waves, we observe that, for a same generation, the transmission spectra for transverse electric (TE) and transverse magnetic (TM) waves are equal, at least qualitatively, and they present a scaling property where a self-similar behavior is obtained, as an evidence that these spectra are fractals. The spectra show regions where the omnidirectional band gaps emerges for specific generations of Octonacci photonic structure, except to TM waves. For TE waves, we note that all of them have almost the same width, for different generations. We also report the localization of modes as a consequence of the quasiperiodicity of the heterostructure.

Theory of exciton–polariton in GaN thin films

Abstract In this work we study exciton–polariton modes confined in wurtzite GaN thin films on sapphire substrates. Using standard electromagnetic boundary conditions, together with the exciton additional boundary condition, the exciton–polariton dispersion relation is then obtained, in both s and p-polarization, by solving a secular determinant. Our results show that the exciton quantized energies lie outside the bulk modes, with mixed surface and guided modes.