28 Avril – Thesis defense - Régis Roblès
15 h Amphi Jean-Paul Dom - Laboratory IMS / building A31 (Talence campus)
Design and fabrication of SiON-based guiding devices using integrated optics operating in the visible range.
Aperture synthesis is an interferometric imaging technique that consists in correlating the light signal from two or more apertures and allowing the image of an observed object to be reconstructed from the resulting interferences profile. Such a technique gives the opportunity to overcome the Rayleigh criterion, that limits the lateral resolution obtained with a single aperture, by creating a synthetic aperture diameter to achieve a resolution largely higher than that of the one produced by conventional imaging techniques.
For example, this imaging technique is widely used in astronomy making the observation and the measurement of distant stars possible with a resolution in the order of a millisecond of arc ; remaining very difficult with traditional imaging techniques used with standard telescopes. However, such devices suffer from a lack of miniaturization and portability, presenting an obvious complexity of implementation particularly linked to the diameter of the mirrors, the alignment of the delay lines and the infrastructural space required for their deployment into embedded and miniaturized systems. The implementation of basic building blocks as required for aperture synthesis using integrated optics technologies appears as a real opportunity to bypass this complexity and develop future high-resolution imaging systems both compact and portable.
These PhD works aim at the development of guiding and power division devices using integrated optics technologies derived from microelectronic processes. The originality of this study is to design and fabricate such structures for the visible range using a "full-SiON" technology, forcing to overcome many scientific and technological challenges particularly in terms of waveguides dimensions in order to guarantee a single-mode operation, low power losses and the widest operating spectral range.
A first axis is dedicated to the optimization of fabrication processes of targeted structures in order to adopt the best choices and compromises in terms of design and geometry. The other axis is devoted to their characterization and assessment of their performances on a dedicated optical bench. This technological development has enabled the fabrication of SiON-based waveguides with propagation losses as low as 2.6 dB/cm over a 532 nm - 760 nm spectral range as well as 1x2 multimode interference couplers with high manufacturing tolerances.