Waveguiding Er3+/Yb3+:LiNbO3 films prepared by a sol–gel method using polyvinylpyrrolidone

Abstract

LiNbO3 waveguiding structures are mainly prepared by the chemical or structural modification of LiNbO3 single crystals. An alternative method is the preparation of epitaxially grown LiNbO3 films with waveguiding ability using sol–gel procedures. Our aim was to test the use of 2-methoxyethanol solutions containing polyvinylpyrrolidone (PVP) in the preparation of Er3+/Yb3+doped LiNbO3 thin films. The solutions were spin-coated on sapphire (0001) substrates and then heat-treated under different regimes on the basis of thermal analysis results. The microstructure of the films was compared using scanning electron microscopy and atomic force microscopy. Optical properties in the IR range were validated by the measurement of luminescence spectra and waveguiding properties (m-line spectroscopy). The influence of the thermal treatment and of PVP molar mass used (29,000 or 360,000g/mol) was established. Also the influence of additional crystallization on the films properties was tested. A suitable combination of PVP molecular mass and thermal treatment led to the successful preparation of LiNbO3 planar waveguides in the IR range. Thus, the sol–gel deposition from solutions containing PVP is a feasible non-hydrolytic method applicable for the preparation of planar waveguides.