Influence of factors on the growth of the Er³⁺/Tm ³⁺-codoped LiNbO₃ crystal by Er³⁺/Tm ³⁺ codiffusion

The influence of factors on the growth of the Er³⁺/Tm ³⁺-codoped LiNbO₃ (LN) crystal by codiffusion of stacked Er and Tm metal thin films was studied. These factors include the thicknesses and the coating sequence of the Er and Tm metal films, and the growth is characterized by the diffusivity and solubility. To achieve the goal, Er ³⁺/Tm³⁺-codoped LN crystals were grown by codiffusion in air at 1130 C of stacked Er and Tm metal thin films coated onto the surface of Z-cut congruent LN plates. The metal films have different thicknesses and coating sequences. After the growth, the Er³⁺ and Tm³⁺ profiles were analyzed by secondary ion mass spectrometry. The Er ³⁺/Tm³⁺ diffusivity and surface concentration were obtained from the measured profiles. The diffusivity is influenced by neither the thickness nor the coating sequence of metal films. The solubility consists of Er³⁺ and Tm³⁺ components, and the two components equal the respective concentrations in the diffusion reservoir and change with the initial metal film thickness. Nevertheless, their sum, i.e., the solubility, remains a constant at a given temperature and shows a weaker effect of either the crystal cut or the coating sequence of Er and Tm films, together with the two components. In addition, the emission characteristics of the Er ³⁺/Tm³⁺ diffusion-codoped LN were investigated. The results show that the codoping allows the combination of the wavelength emissions of both ions, and the resultant emission band in the telecommunication window around 1.5 μm is as wide as 150 nm, providing the possibility of S+C+L broadband amplification by employing the commercial 980 and 795 nm laser diodes as the pump sources.