Blue-shift ultrasensitivity using rhombus-shaped plasmonic crystal on Si3N4 membrane

Harnessing ultrasensitivity from optical structures to detect tiny changes in the targeted samples is the main goal of scientists in the field of sensor design. In this study, an uncommon rhombus-shape plasmonic structure is proposed for providing blue-shift ultrasensitivity. The physical origin of this optical response relies on multi-faces of gold rhombus and their electromagnetic coupling with their induced images in a high-refractive-index substrate (Si3N4). A characteristic of blue-shift emerges as the Fano resonance in the reflection spectrum. We have experimentally shown that this novel structure has the surface sensitivity to the refractive index difference in the order of 10(-5). These characteristics have been applied for non- and conditioned- cell culture medium with refractive differences in this order.This level of sensitivity is interesting for enhanced fingerprinting of minute quantities of targeted molecules and interfacial ion redistribution. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Accordabilité de la réponse optique des cristaux photoniques par infiltration de matériaux organiques

Pascale El-Kallassi

Photonic crystals are stuctures in which the refractive index varies periodically on the wavelength scale in one, two or three dimensions. Due to interference effects, these structures can forbid light propagation over a large spectral range called "the photonic bandgap". Integrated optics is one of the potential applications of photonic crystals in which the information can be treated as a light signal that propagates through photonic crystal-based devices, such as filters, lasers, waveguides, bends and multiplexers. The photonic crystals structures studied for integrated optics applications consist of periodic arrays of holes etched through classical semiconducteur-based planar waveguides. For any practical application, the optical properties of the fabricated components have to be tuned by external means. In this thesis, we explore a possible approach to photonic crystal tuning : the infiltration of photoactive organic materials in the holes of these photonic structures. First we considered liquid crystals, which exhibit anisotropic optical properties like birefringence due to their long-range orientational order. This latter molecular organization can be modified by external factors, i.e. temperature and electric field. Nematic liquid crystals were infiltrated in the holes of the photonic crystals to tune their properties by changing the temperature and applying an electric field. Moreover, the organization of liquid crystals in the nanometric holes were studied by optical techniques. The demand for all-optical tunable devices in integrated optical circuits led us to consider the possibility of optically tuning the response of photonic crystal structures. For this purpose, we used photo-induced phase transitions of a liquid crystal blend doped with azobenzene photochromic molecules. Since the phase transitions in these mixtures depend on the concentration of the photochromic compound and on the temperature, we studied in detail the phase diagram of the blend. The last part of this thesis focused on one of the most innovative aspects in the domain of photonic crystal tuning : selective infiltration to locally modify the optical properties of the photonic structures. We used the photopolymerization of acrylate monomers by ultraviolet laser irradiation. Finally, with three clear examples, this thesis shows that organic photoactive materials are well-adapted to be combined with photonic crystals. We demonstrated that the obtained hybrid structures are very promising for integrated optics applications.

EPFL2009

Blue surface plasmon propagation along thin gold film-gas interface and its use for sensitive nitrogen dioxide detection

Giovanni Dietler

We demonstrate effective surface plasmon propagation along thin gold film in a blue spectral range: the measured 0.6 degrees angular width of the plasmon excitation peak corresponds to the propagation length around 7 mu m. For this end, we prepared a specially designed photonic crystal (PC; 18-layer 1D structure of altering transparent dielectric layers with relatively large and low refraction indices deposited onto a silica support) coated by a 8 nm thick gold layer. For given blue light wavelength (405 nm) and certain light incidence angle this 1D PC structure supports ultralong surface plasmon propagation along the gold nanofilm. This structure has been tested as a surface plasmon resonance sensor to detect small concentrations of nitrogen dioxide in air. This sensor exhibited the sensitivity similar to earlier works where surface plasmon resonance in red spectral range has been used for this purpose. (C) 2013 Elsevier B.V. All rights reserved.

Elsevier2013

Accordabilité de la réponse optique des cristaux photoniques par infiltration de matériaux organiques

Pascale El-Kallassi

EPFL2009