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Thèse : Une étape vers la réalisation par échange protonique de fils quantiques et de circuits intégrés à fort confinement sur niobate de lithium

Oleksandr Stepanenko

Mercredi 18 décembre 2013

à 10h en salle C. Brot

Up to now a tight optical confinement in waveguides realized on LiNbO3 was always achieved to the detriment of the nonlinear properties of the substrate. The present work aimed to develop and to study a new method of waveguide fabrication, High Index Soft Proton Exchange (HISoPE), which allows realizing highly confining waveguides in LiNbO3 (δne=0.1). Characterizations by localized SHG experiments showed that the nonlinear properties of the HISoPE waveguides are not destroyed, but modes with high propagation loss were observed for planar HISoPE waveguides on Z-cut wafers. These losses can be eliminated by performing the exchange in more acidic bath, but this results in more important deformations in channel waveguides and in the hybrid nature of the propagating modes. In the frame of the project PhoXcry, we tried to realize a highly efficient electro-optical modulator by combining photonic crystals and HISoPE waveguides on X-cut wafers of LiNbO3. The losses of the waveguides fabricated on X-cut, attributed to the hybrid nature of the propagating modes, were estimated to be around 1.75dB/cm. The nanostructured waveguides exhibited high losses and it was not possible to identify clear optical band gap. HISoPE in combination with reverse proton exchange (RPE) showed a great potential for buried waveguide fabrication. We used them in a SHG experiment and despite elevated losses of 2dB/cm, the conversion efficiency was estimated as high as 160%W-1cm-2. A directional coupler behavior was observed in the buried waveguides due to different RPE kinetics in different parts of the waveguide. A further development of the HISoPE+RPE process will improve the quality of the buried waveguides.

Keywords : Proton exchange, Nonlinear optics, Integrated optics, Lithium niobate