质子交换LiNbO3波导表面裂纹的研究

为了研究x切铌酸锂波导表面裂纹的产生机理及对波导性能的影响,采用对比实验、波导表面观察、XRD晶相分析、红外吸收谱分析等方法,比较了退火后波导的微观结构、表面情况、波导中H+存在形式和浓度变化特征.结果表明,质子交换铌酸锂波导表面裂纹是波导层应力顺晶体主解理面释放而产生的,具有4个特点:裂纹是交换过程造成的,裂纹间相互平行,裂纹程度与交换时间成正比,退火工艺对裂纹程度有所改善;裂纹是波导层应力大小的宏观体现;退火工艺可以调整波导层中H+的存在形式及其浓度,调整波导层晶相和应力大小,从而改善波导性能.可见纯质子交换波导层中多相并存,各晶相晶格常数差异较大造成应力,导致裂纹产生.提出α相波导的晶格变形小,引起的应力也小,可以减少裂纹产生,有助于提高波导质量.

Investigation of the cracks on the surface of proton-exchanged LiNbO3 wave-guides

In order to investigate the generation mechanism of the cracks on the surface of proton-exchanged(PE)waveguides on the x-cut lithium niobate substrate and the influence on the characteristics of wave-guide. The crystal microstructure,the intensity of the cracks on the surface,the existing manner of hydrogen ion and the variation of density of the annealing protonexchanged(APE)wave-guide are studied by means of contrast experiments,observation on the surface of wave-guide,XRD(X-ray diffraction)analysis of the crystal phase in the wave-guide,infrared absorption spectra analysis of wave-guide,and so on. The results show that the cracks are made by the stress parallel with the principal cleavage plane of lithium niobate,which have four gharacteristics: made in the PE process,parallel with each others,deteriorated in proportion to the time of PE process and being ameliorated somewhat in the annealing process. It is also shown that the cracks are the macroscopical representation of the stress and that the annealing process could influence the existing manner of hydrogen ion and its density variation,alter the crystal phases and the stress in the wave-guide,and improve the performance of the wave-guide. It is concluded that multiple-phase coexistence and the difference of the crystal lattice coefficient resulted in the stress and then lead to the crackand that the smallest distortion in crystal lattice,the lowest stress and the αphase wave-guide may have the lowest possibility to bring out crack,and can improve the performance of the wave-guide.