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Structural and optical characterisation of planar waveguides obtained via Sol-Gel

F. Rey-García, C. Gómez-Reino, M. T. Flores-Arias, G. F. De La Fuente, W. Assenmacher, W. Mader, Manuel F. Costa
2011 International Conference on Applications of Optics and Photonics  
Planar waveguides of SiO2:TiO2 (multilayer structure) and SiO2:CeO2 (thick layer) were prepared onto commercial glass substrates using a sol-gel technique combined with dip-coating. These glassy coatings were structural characterised by Transmission Electron Microscopy (TEM) Energy Dispersive X-ray analysis and by Confocal Microscopy. Thicknesses of 1230 nm and 4,15 μm and refractive indices of 1.59 and 1.48 for SiO2:TiO2 (70:30) and SiO2:CeO2 (95:5) waveguides were obtained, respectively, by
more » ... respectively, by Spectroscopic Ellypsometry. Losses of 0.8 dB/cm were measured by double prism method in the SiO2:CeO2 system. INTRODUCTION The preparation of planar waveguides has attracted considerable attention because of their possible use and applications in photonics devices in the field of communications and data transmission. Ion-exchange and chemical or physical vapor deposition methods have been extensively used to develop this kind of materials. Recently, laser deposition and direct writing techniques have been also employed to obtain planar waveguides on glass substrates of different compositions. These techniques have high economical cost and the compostions used raise the process complexity. Recently researchers have focused their attention on glasses based on oxides of heavy metals (TeO2, GeO2, Bi2O3, PbO, etc.) as promising materials for photonic devices. But the obtention of these materials suppose the obtaining of bulk materials, special reactives (heavy metals are restricted in use by European union) or the use, in the most of cases, of special atmospheres or high melting temperatures. An alternative method to obtain planar waveguides is based on sol-gel technology. This technology is widely used in different fields of life, from materials science to biological applications; there are developed bisosensors, bulk materials, superconductors, fuel cells, ceramic composites etc; performing a wide range of compositions. In particular, this technology permits us to obtain coatings with controlled thickness and refractive index. The sol-gel process is suitable to produce both thin and thick films by single and multideposition techniques. A several number of papers dealing with planar waveguides fabricated with this method have been reported in literature. The microstructure of sol-gel derived coatings, thus their optical properties, is affected by different parameters involved in their synthesis. These include starting materials, and thermal processing conditions, among others. The optimization and control of all these parameters should allow us the production of efficient sol-gel derived planar waveguides. Following this concept, one important advantage provided for the sol-gel technology is the lower surface roughness obtained for the coatings. This fact allows us to drastically reduce guiding losses for geometry. The roughness is investigated by confocal microscopy. Only few papers have employed the transmission electron microscopy to study the structural characteristics between solgel films and substrates and the process involved in the union between them; the most of the literature reports the study of thin films, their interfaces and the crystalline structures presents.
doi:10.1117/12.891941 fatcat:hmw4rqzpwvdhjaia66w4irczia