Inter-mode reactive coupling induced by waveguide-resonator interaction

We report on a joint theoretical and experimental study of an integrated photonic device consisting of a single mode waveguide vertically coupled to a disk-shaped microresonator. Starting from the general theory of open systems, we show how the presence of a neighboring waveguide induces reactive inter-mode coupling in the resonator, analogous to an off-diagonal Lamb shift from atomic physics. Observable consequences of this coupling manifest as peculiar Fano lineshapes in the waveguide transmission spectra. The theoretical predictions are validated by full vectorial 3D finite element numerical simulations and are confirmed by the experiments

Silicon oxynitride waveguides as evanescent-field-based fluorescent biosensors

Channel waveguide-based evanescent-field optical sensors are developed to make a fully integrated chip biosensor. The optical system senses fluorescent analytes immobilized within a micrometric sized bioreactor well realized within an optical waveguide. The main novelty of this work is related to the fact that, within the bioreactor well, the excitation of the fluorescent signal is achieved by means of the evanescent field propagating through a silicon oxynitride waveguide. The immobilization of the emitting molecules is realized by functionalization of the waveguide surface by a wet chemical method. These photonic biosensors are successfully applied to detect low surface concentration (10−11 mol cm−2) of a green emitting organic dye. This approach could permit the selective detection of a wide range of chemical and biological species in complex matrices and can be exploited to set-up array-based screening devices. In this regard, the preferential excitation of the dye molecules in the close vicinity of the exposed waveguide core is also analysed

Optical losses and gain in silicon-rich silica waveguides containing Er ions

Rib-loaded waveguides containing Er(3+) coupled to Si-nc have been produced by magnetron sputtering and Successive thermal annealing to investigate optical gain at 1535 nm. It has been shown that all Er ions are optically active, whereas the fraction that can be excited at high pump rates under non-resonant excitation is strongly limited by confined carrier absorption (CA), up-conversion processes, and mainly by the lack of coupling to the Si-nc. Er(3+) absorption cross-section is found comparable to that of Er(3+) in SiO(2), but a dependence with the effective refractive index has been found. Although the presence of Si-nc strongly improves the efficiency of Er(3+) excitation, it introduces additional optical loss mechanisms, such as CA. These Si-nc losses affect the possibility of obtaining net optical gain. In the present study, they have been minimized by lowering the annealing time of the Er-doped Si-rich oxide. In pump-probe measurements it is shown that signal enhancement of the transmitted signal can be achieved at low pumping rate when the detrimental role of confined CA is attenuated by reducing the annealing time. A maximum signal enhancement of about 1.30 at 1535 nm was observed

Engineering silicon nanocomposites for efficient light emitting diodes

We will discuss few perspective directions in engineering and optimization of Er-doped and undoped Si nanocomposites to develop efficient light-emitting diodes for infrared and visible light applications, respectively