LiNbO_3:Fe晶体中光写入平面光波导的导光特性研究

Analyses of guiding properties of light-induced planar waveguides in LiNbO_3:Fe crystals

从光折变效应的单中心模型和载流子的光伏迁移机理出发给出了高斯片光在LiNbO3:Fe晶体中导致的折射率变化分布的解析表达式 .利用片光以“三明治”辐照方式在LiNbO3:Fe晶体中写入了平面光波导结构 .用切片干涉法测量了波导区的折射率分布 ,并对波导进行了简单的导光测试 .根据射线方程以及波导的折射率分布对光写入波导的导光特性进行了模拟计算分析 .研究结果表明 。

To our knowledge, we first deduced the analytic expression of the index-change-distribution in LiNbO_3:Fe crystal induced by a Gaussian sheet beam considering the photorefractive one-center model and the photovoltaic charge carriers transport mechanism. A planar waveguide structure was fabricated by sheet beam illumination employing the sandwich method in (LiNbO_3:Fe) crystal. The index distribution in the waveguide region was measured by using interferometric technique and the guiding test was also performed. The rationality of the deduced analytic expression was demonstrated by the fitting results of the measured data point. Based on the ray equation, the guiding properties of the light-induced waveguide were analyzed by using numerical simulation. The results show that the interferometric technique is valid for measuring the index distribution of waveguide with large width, and the guiding properties of the light-induced waveguide structures depend on the waveguide width strongly. Using sheet beam with small width, planar waveguide structure with high quality can be fabricated in LiNbO_3:Fe crystal. And the analytic expression of the index-change-distribution can be employed to predict the guiding properties of the light-induced waveguide.