Structural and Optical Properties of Rare-Earth Doped Lithium Niobate Waveguides Formed by Mev Helium Implantation
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ABSTRACT Results of investigations of optical waveguides formed by high energy helium implantation into lithium niobate codoped with 5 mol% MgO and 1 mol% Tm3+ or 1 mol% Er3+ are reported. A comparative study of structural and luminescence properties between implanted and untreated samples has been performed by means of Rutherford backscattering (RBS) combined with channeling and photoluminescence methods, respectively in order to investigate residual lattice damage and the incorporation of the optical active rare earths. For the case of Tm a full substitutional incorporation on the lithium site and a high crystal quality in both bulk and implanted waveguide material has been found. For Er doped lithium niobate the channeling results show a fraction of Er randomly incorporated or forming precipitates and a deterioration of the waveguide's lattice. The optical investigations show in both cases only a slight broadening of the emission lines of the rare earths in the waveguides compared
to the bulk material. INTRODUCTION For the development of future communication and information processing waveguiding devices fabricated in materials with nonlinear optical properties like lithium niobate are of high interest. Doping of such waveguides with optically active ions enables the fabrication of lasers with favorable properties [1], e.g., low threshold power. Therefore, intense research efforts are made in order to optimize the properties of optical waveguides formed by different processes such as Ti-indiffusion, proton-exchange and ion implantation. During the last years the MeV ion implantation of helium ions into various optical materials has been demonstrated to be a versatile tool for the formation of surface waveguides [2]. The waveguide is embedded between a buried layer with increased refractive index, due to end-of-range nuclear damage induced by the implanted ions and the crystal surface. Studies on the residual damage in the waveguiding layer and its influence on the spectroscopic and structural properties of the optically active dopant are of high importance, in order to optimize the performance of these waveguide structures. In this paper we report the results of a comparative investigation of optical and structural properties of MeV He+ implanted waveguides in LiNbO 3 :Er,Mg and LiNbO 3 :Tm,Mg performed by means of photoluminescence and Rutherford backscattering spectroscopy. 355 Mat. Res. Soc. Symp. Proc. Vol. 396 @1996 Materials Research Society
EXPERIMENTAL Lithium niobate single crystals were grown from a congruent melt containing 5 mol% MgO and 1 mol% of Tm '+ (Tm 2O3 ) or Er3 + (Er 2O 3 ), respectively, at the Universidad Aut6noma in Madrid using the Czochralski method. Samples were cut from these samples with faces both, perpendicular and parallel to the c-axis and carefully polished. Waveguide formation was achieved by implantation of He+ with an energy of 2.0 MeV for the LiNbO 3 :Er,Mg and 2.6 MeV for the LiNbO 3 :Tm,Mg sample, at a fluence of 2 x1016 cm- 2 at the University of Sussex in Brighton. Du
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