Diffusion Properties of Tm3+ in Congruent LiNbO3 Crystal

Authors

  • De-Long Zhang,

    Corresponding author
    1. Key Laboratory of Optoelectronic Information Technology, Tianjin University, Ministry of Education, Tianjin, China
    2. Department of Electronic Engineering, City University of Hong Kong, Hong Kong, China
    • Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin, China
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  • Wen-Zhu Zhang,

    1. Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin, China
    2. Key Laboratory of Optoelectronic Information Technology, Tianjin University, Ministry of Education, Tianjin, China
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  • Ping-Rang Hua,

    1. Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin, China
    2. Key Laboratory of Optoelectronic Information Technology, Tianjin University, Ministry of Education, Tianjin, China
    3. Department of Electronic Engineering, City University of Hong Kong, Hong Kong, China
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  • Dao-Yin Yu,

    1. Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin, China
    2. Key Laboratory of Optoelectronic Information Technology, Tianjin University, Ministry of Education, Tianjin, China
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  • Edwin Yue-Bun Pun

    1. Department of Electronic Engineering, City University of Hong Kong, Hong Kong, China
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Author to whom correspondence should be addressed. e-mail: dlzhang@tju.edu.cn

Abstract

Diffusion properties of Tm3+ in congruent LiNbO3 crystal have been investigated, together with other two related issues, i.e., Tm3+-doping contribution to refractive index of LiNbO3 substrate and Li out-diffusion. Four X-cut and four Z-cut congruent LiNbO3 substrates locally coated with 15–31 nm-thick Tm-metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm3+-doped and Tm3+-free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li2O contents were evaluated from measured refractive index. The results show that Tm3+ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti4+- or Zn2+ doping. The Li2O content at the Tm3+-doped surface equals that at the Tm3+-free surface. The Li out-diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out-diffusion is not measurable. At 1130°C, a 30-h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li2O content. Secondary ion mass spectrometry was used to study the Tm3+ diffusion properties. The results show that the diffused Tm3+ ions in all samples follow a complementary error function profile. From measured Tm3+ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er3+ diffusion. In comparison with Er3+ diffusion, the Tm3+ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm3+ has a lower diffusivity than the Er3+, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.

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