Impact of the crystal orientation of Fe-doped lithium niobate on photo-assisted proton exchange and chemical etching

Shaobei Li,Feifei Li,Xuju Jiang,Hongjian Chen,Bolin Fan,Guohong Liang,Chao Liang,Xuliang Wang,Lipin Chen,Wenbo Yan,Zhitao Zan,Lihong Shi

doi:10.1038/s41598-017-16454-7

Abstract

Photo-assisted proton-exchange (PAPE) is carried out on the +c- and y-surfaces of Fe-doped LiNbO3 crystals and the impact of the crystal orientation on the PAPE and the subsequent photo-assisted chemical etching (PACE) is investigated. The proton distributions and the morphologies of the proton-exchanged surfaces are studied by using Micro-FT-IR, Micro-Raman, optical and scanning electron microscopy. Through the PAPE process the proton-exchange can be confined in a specific region by an incident laser beam with fixed intensity profile. It is found that the y-surface is much more fragile than the +c-surface and that micro-cracks are easily generated on the y-surface during the PAPE process. Moreover, the range and number of these micro-cracks can be controlled by the experimental parameters of the PAPE process. The etching morphology of the y-surface shows apparent directional features along the c-axis of LiNbO3 crystal and the proton spatial distribution is found elongated along the c-axis. Both effects are attributed to the accumulation of photovoltaic charges at the two sides of the illumination area along the c-axis.

Highlights

Lithium niobate (LN) is a potential material for fabricating integrated optical components due to its outstanding electro-optic and nonlinear optical properties[1]
We report a photo-assisted Proton exchange (PE) (PAPE) effect on Fe-doped LN (LN:Fe) crystals
The results shown in this work may be useful for the refractive index engineering or micro-structure fabrication on the LN surface

Summary

Experimental procedures

The samples used in this work are 1mm-thick, Z-cut or Y-cut LN:Fe crystals, and the Fe2O3 doping concentration is 0.03 wt%. The light absorbed by the sample during the PAPE process is considered to be proportional with the laser intensity, and any nonlinear absorption effect can be neglected. The samples with different absorptions and orientations are used, and the irradiation intensity and the treatment duration are varied from one case to the other. Of the sample properties we label the samples in the following way: use A/a for 42/4 (cm−1) absorption, C/T to differentiate between Circular and Triangular profiles and H/L to indicate the 400/200 (W/cm2) intensity. We measure the Raman spectra within and without the treated region for studying the effect of PAPE on the crystal lattice. An optical microscope (Olympus STM6) and a scanning electron microscope (ZEISS MERLIN Compact) are employed to acquire the morphology of the treated surface

Result and Discussion

Conclusion