Birefringence and optical waveguiding losses in preferentially c-axis oriented LiNbO3 thin films oil SiO2 produced by electron cyclotron resonance plasma sputtering

LiNbO3 (LN) films deposited on SiO2 substrate by electron cyclotron resonance plasma sputtering and thermal treatment were structurally and optically characterized. Birefringence between 60 and 70% for single crystal was confirmed for c-axis oriented films on both Si and SiO2, whereas non-annealed amorphous film was optically isotropic. Crystallization during sputtering produced less than a 10% volume fraction of c-axis oriented spherical domains associated with the interface roughness layer. This sample had a large propagation loss of 32 dB/cm at 632.8 nm due to light scattering at the grain boundaries. LN films subjected to solid phase crystallization in a vacuum produced highly c-axis oriented columnar texture domains, which yielded propagation losses between 5 and 19 dB/cm, depending on the thickness (0.64-1.35 mu m) and the mode order. The bulk and Surface origins for waveguiding losses are discussed based on the film structure.