RÉALISATION D'UN FILTRE SPECTRAL ACCORDABLE ÉTROIT À 1.55 μm EN OPTIQUE INTÉGRÉE SUR NIOBATE DE LITHIUM. ÉTUDE DES LIMITATIONS IMPOSÉES PAR LA TECHNOLOGIE.

摘要

The exponential growth of the data rate in future telecommunication networks, requires the use of new transmission ways. Optical based networks show great promise for replacing 'slow' electronics technology. Through the use of wavelength division multiplexing technique (WDM), it becomes possible not only to increase the data rate on the line (here, an optical fibre) but also to use new alloptical based network. One of the key devices in these architectures is the tunable spectral filter. The work presented in this thesis deals with the theoretical study, practical realisation and future development of a narrow-band tunable filter integrated on lithium niobate and working around 1.55 μm. Firstly we compare different principles of integrated tunable filter and choose a fully electrooptic device that allows a high switching speed between channels. Its principle of operation is described using similarity with the birefringent Šolc filter that can be considered as a wavelength selective polarisation converter placed between crossed polarisers. The complete theoretical study shows that the irregularities observed in the experimental transfer function can be explained by unavoidable variations of birefringence along the diffused waveguide. These variations can be related to defects in the technological process. We proceed with the modelisation of the filter by a systematic investigation of typical classes of defects, that result in the irregularities observed in the transmittance of the filter. These simulations yield improvements at different steps of the integration process on lithium niobate, allowing the bandwidth limit predicted by theory to be obtained experimentally. Finally we present applications of the filter (wavelength tuning and intensity modulation of a fibre laser) and discuss perspectives of development (polarisation insensivity).