Dielectric-Polymer Nanocomposite and Thin Film Photonic Crystals: Towards Three-Dimensional Photonic Crystals with a Bandgap in the Visible Spectrum

Abstract

The concepts of photonic crystals and photonic bandgap (PBG) were introduced in the in late 80s [1] and in first approximation they are the optical analogous to the semiconductor and the energy gap for electrons. They are based on periodic structures formed of two or more materials, which exhibit a periodicity in real space of the dielectric function. Moreover, the refractive index contrast has to be larger than certain value, depending on the relative fill factor of the respective materials. Thus, diffraction phenomena, such as Bragg difraction, take place. There are four main aspects currently motivating research in photonic crystals: (1) The realisation of a full PBG across the electromagnetic spectrum to act, for example, as highly efficient mirrors, optical limiters and optical switches. (2) The partial realisation of the PBG for waveguiding or for “moulding” the light, which is known as photonic crystal waveguides, as opposed as refractive index waveguiding. (3) The realisation of highly efficient light sources by making use of: (i) the strong coupling in a 3-dimensional (3D) optical cavity formed by the PBG crystal and, (ii) the enhanced spontaneous emission rate of a “defect”, the emission wavelength of which is highly defined spectroscopically and falls within the band-gap of the photonic crystal. (4) The use of the dispersion relations represented by the photonic band structure for ultra-refractive phenomena, super prism, spot focusing, super lens, among others, based on the changes of the group velocity in different parts of the Brillouin zone. This work attempts to address the third issue and to some degree the fourth.