激光直写法制备条形光波导中的功率密度阈值

Thresholds of Laser Power Density in Fabricating Strip Optical Waveguides by Laser Direct Writing Method

采用溶胶-凝胶法(sol-gel)在Si基SiO2衬底上制备了SiO2-TiO2芯层薄膜,构成了以SiO2为下包层,空气为上包层的平面光波导。利用光纤激光器对平面波导的芯层进行直写,结合后续的化学腐蚀工艺得到了SiO2-TiO2条形光波导,并着重研究了激光直写波导过程中存在的功率密度阈值以及阈值随薄膜预热处理温度的变化关系。研究结果表明,激光直写SiO2-TiO2波导存在起始收缩阈值和烧蚀损伤阈值;随着薄膜热处理温度的提高,两个阈值同时增大,其中损伤阈值的增大趋势要大于收缩阈值;因而薄膜可承受的直写光斑直径变小,所得波导宽度显著减小。最后对直写制得条形光波导的导光性能作了测试分析,验证了波导的三维导光性。

SiO2-TiO2 planar waveguides on Si/SiO2 substrate were prepared by sol-gel method. A fiber laser was used to fabricate strip optical waveguides in the core layer of the planar waveguides by laser direct writing of the solgel coatings. The thresholds of laser power density for laser direct writing optical waveguides on the SiO2-TiO2 planar waveguides were studied systematically. Moreover, the relationships between the thresholds of laser power density and anneal temperature on sol gel films were also discussed. The experimental results show that there are initial shrinkage threshold and damage threshold when laser direct writing strip optical waveguides on the SiO2-TiO2 coatings are fabricated by sol-gel technique. Both the two thresholds mentioned above increase with the anneal temperature on films respectively, but the increasing trend of the damage threshold is more prominent than that of the shrinkage threshold, which indicates a much smaller laser spot allowed in laser direct writing. Therefore, narrower strip optical waveguides in width can be fabricated in this situation. At last, the light propagation character of the strip waveguides was measured, the three-dimensional light propagation mode of the strip waveguides was confirmed.