用MgF_2作为镁离子扩散源实现铌酸锂单晶光纤包层

ACHIEVING OF LITHIUM NIOBATE SINGLE CRYSTAL FIBER CLADDING BY MgF_2 AS A DIFFUSION SOURCE FOR Mg-ION INDIFFUSION

首次利用ＭｇＦ_２作为镁离子内扩散源以实现铌酸锂单晶光纤的芯－包层波导结构，此包层晶纤比未包层晶纤的损耗降低约１０倍。对镁离子内扩散机理进行了分析。对扩散表面进行Ｘ射线衍射分析和扫描电镜观察，发现当镁离子内扩散超过一定程度时，在镁的扩散层出现ＬｉＮｂ_３Ｏ_８物相结构，该物相结构的出现与铌酸锂体内锂离子的外扩散及扩散表面的氟离子存在有关，即氟离子与锂离子结合生成ＬｉＦ。随着扩散时间的增长或扩散温度的升高，ＬｉＦ逐渐挥发并脱离开扩散层表面。

A core-cladding waveguide structure of lithium niobate single crystal fiber is achieved by using MgF_2 firstly as a diffusion source for Mg-ion indiffusion. The propagation loss of the cladded fiber is measured, and a reduction of loss about 10 times has been achieved. The mechanism of Mg-ion indiffusion is analyzed. By means of X-ray diffraction analysis and scanning electron microscopy, it is found that LiNb_3O_8 compound appears in the magnesium diffused layer with Mg-ion indiffusion beyond a certain extent. The existence of LiNb_3O_8 compound is related to the Li-ion outdiffusion from the bulk of lithium niobate and the existence of F-ion of the diffused surface layer, i. e. the F-ion appears in the form of LiF. The LiF will depart gradually away from the surface of the diffused layer with the lengthening of diffusion time or the increase of diffusion temperature.