E. Palacios-Lidón

Optical study of the full photonic band gap in silicon inverse opals

An optical study of the band structure of both silicon–silica composite and silicon inverse opals is presented. The study is aimed at demonstrating the development of a full photonic band gap for a system already revealed as paradigmatic. The characterization is based on the comparison between the band structure calculations and optical reflectance spectroscopy experiments. This study is carried out for various symmetry points in the Brillouin zone, some never explored before as K, (110) and W, (210). The results show that, in accordance with the band structure, there is a certain frequency range that produces a reflectance peak regardless of orientation and can be assigned to the band gap. Similarly all other reflectance peaks can be accounted for by other band structure features.

Optical and morphological study of disorder in opals

An optical and morphological study has been carried out to understand the role of intrinsic defects in the optical properties of opal-based photonic crystals. By doping poly(methylmethacrylate) (PMMA) thin-film opals with larger polystyrene (PS) spheres, structural disorder has being generated perturbing the PMMA matrix periodicity. It is shown that this disorder dramatically affects the optical response of the system worsening its photonic properties. It has been found that the effect of doping is highly dependent not only on the concentration but also on the relative size of the dopant with reference to the matrix. Through a detailed scanning electron microscopy inspection, the sort of structural defects involved, derived from the different particle size used, has been characterized. A direct relationship between the observed optical response with the different perturbations generated in the lattice has been found. In addition, from this study it can be concluded that it is possible to grow high quality...

Photonic slab heterostructures based on opals

In this paper the fabrication of photonic slab heterostructures based on artificial opals is presented. The innovated method combines high-quality thin-films growing of opals and silica infiltration by Chemical Vapor Deposition through a multi-step process. By varying structure parameters, such as lattice constant, sample thickness or refractive index, different heterostructures have been obtained. The optical study of these systems, carried out by reflectance and transmittance measurements, shows that the prepared samples are of high quality further confirmed by Scanning Electron Microscopy micrographs. The proposed novel method for sample preparation allows a high control of the involved structure parameters, giving the possibility of tunning their photonic behavior. Special attention in the optical response of these materials has been addressed to the study of planar defects embedded in opals, due to their importance in different photonic fields and future technological applications. Reflectance and transmission measurements show a sharp resonance due to localized states associated with the presence of planar defects. A detailed study of the defect mode position and its dependance on defect thickness and on the surrounding photonic crystal is presented as well as evidence showing the scalability of the problem. Finally, it is also concluded that the proposed method is cheap and versatile allowing the preparation of opal-based complex structures.

Materials aspects of opals as photonic crystals

Opals have only a relatively recent history as photonic materials. The tortuous route from materials to devices might perhaps find compensation in the case and low cost of fabrication. Issues relating to the optical properties (such as crystalline quality, finite size effects and infiltration with other materials) are examined and developments leading to possible devices shown. We perform a study of the influence of finite size effects on the optical properties of the samples prior to comparison of experimental results and calculated energy bands, which may be determined along desired directions in reciprocal space. The role of intrinsic defects in the optical properties of the samples has been investigated. The optimization of the procedure to grow accurate amounts of amorphous silicon and germanium by CVD free of contamination in opals has been tackled. Multilayer systems of both semiconductors have been fabricated. Finally we present a method to fabricate opal based photonic crystals containing 2D cavities.

Optical and morphological study of compound polymer opals

An optical and morphological study has been carried out to understand the role of intrinsic defects in opal-based photonic crystals. The inherent polydispersity in sphere size distribution yields imperfect crystallizations and worsens the photonic properties of these systems. By doping poly-(mehtymethacrylate) thin films opals with polystyrene spheres of larger size it is possible to study the disorder caused by the dopants and the negative influence in the optical response. In addition, it is feasible to grow mixed structures (alloys) with intermediate photonic properties by mixing spheres of different nature and the same size.