会聚激光扫描铌酸锂晶体写入光波导时的最佳曝光间距

Optimum exposure intervals for light-induced optical waveguides in lithium niobate crystals by laser micromachining

对利用激光精细加工技术在铌酸锂(LiNbO3)晶体中写入光波导时的最佳曝光间距进行了详细地理论分析和实验研究.通过数值求解简化后的光折变动力学方程组,对会聚激光束沿不同方向扫描晶体时的最佳曝光间距进行了详细的数值模拟.结果表明:最佳曝光间距的选取与写入光束的扫描方向无关;当聚焦激光束平行于光轴扫描晶体时,得不到波导结构,但可以采用“三明治”辐照方式得到对称的折射率分布.采用会聚的绿激光束扫描掺铁铌酸锂(LiNbO3:Fe)晶体进行了实验研究,晶体中的光致折射率变化通过数字全息术进行测量,实验结果与数值模拟相吻合.最后,采用最佳曝光间距,成功地在LiNbO3∶Fe晶体中写入了Y型波导,并进行了导光测试.

The optimal exposure intervals for optical waveguides induced by laser micromachining in LiNbO3 crystals are theoretically and experimentally investigated. When the focused laser beams scan along different directions, the optimal intervals for waveguide fabrications are numerically specified by solving the photorefractive dynamic equations. The simulations show that the index distributions of the fabricated waveguides are strongly dependent on the optimal exposure interval, and the optimal exposure interval is not dependent on the scanning directions of the writing beam. When the writing beam scans the crystal along the c axis for sandwich illumination, optical waveguides cannot be fabricated efficiently. However, in this case, symmetric refractive index changes can be obtained. Experimental demonstrations are performed by scanning LiNbO3 ： Fe crystal with a focused green laser beam. The light-induced index changes are measured by digital holography. The experimental results conform to the theoretical analyses. Additionally, a Y-branche waveguide is experimentally formed and the results of the guiding tests are showed in this paper