单晶铌酸锂薄膜光波导的制备研究

Fabrication of Ridge-Waveguide with LiNbO Thin Films: A Methodological Study

为了优化单晶铌酸锂薄膜光波导的性能,研究了基于单晶铌酸锂薄膜材料的光波导刻蚀工艺。虽然Ar^(+)物理刻蚀能够达到最高95 nm/min的刻蚀速率,但难以获得光滑的波导侧壁,且以Cr作为掩膜的刻蚀选择比为1∶1,这意味着较差的选择性使其难以实现铌酸锂的深刻蚀。而采用反应离子刻蚀(RIE)得到的刻蚀速率较低,但是以Cr作为掩膜的刻蚀选择比能够达到6∶1以上,同时能够获得光滑、陡直的侧壁形貌。最终在450 nm厚度的单晶铌酸锂薄膜上,采用RIE制备了宽度为4μm、高度为370 nm的脊型光波导,并以端面耦合的方法进行测试,得到该波导的传输损耗约为5.2 dB/cm。

The high quality ridge-waveguide,an optical modulator,was fabricated,with 450 nm thick LiNbO3 coatings on Si-substrate,by Ar+-ion etching and reactive ion etching(RIE),respectively.The influence of the RIE conditions,including the pressure,CHF3/Ar flow-rate ratio and ICP/RIE power,on the etching rate,etching selectivity ratio,roughness/steepness//straightness of sidewalls,was investigated with scanning electron microscopy and atomic force microscopy.The results show that the reactive ion-etching outperforms Ar^(+) ion-etching,because of much higher etching-selectivity ratio,fairly smoother/steeper/straighter side-walls,in spite of its lower etching-rate.Specifically,etched under the optimized conditions and measured in the end-coupling method,the transmission loss of the ridge waveguide(10 mm-long,4 μm-wide,370 nm-high and dipping at 72°) was found to be ~5.2 dB/cm.