Chemical Etching Technique for Investigations of a Structure of Annealed and Unannealed Proton Exchange Channel LiNbO₃ Waveguides

Use of method for chemical etching for identification of structure of proton exchange channel waveguides fabricated on Z-cut of lithium niobate crystal

“…It significantly exceeds the etching rate of the annealed channel waveguides on the X cut of LN crystal [7]. Another distinct characteristic of etching of annealed channel waveguides on Z cut is that after etching reaches the depth of ~300 um, the slope of the curve of etching decreases and then the curve passes through the maximum.…”

“…It is worth noting that similar to X cut [7], proton exchange causes immediate fabrication of a comb (protrusion) of ~ 5 nm (Fig. 1) on the channel waveguide, which is probably explained by the strain appeared in the PE layer.…”

Microindentation of proton exchange layers on X cut of lithium niobate crystals

“…The specimen surface roughness r a was 0.3e0.4 nm. PE producing planar waveguides was performed in the molten benzoic acid (BA) at the temperatures of 175 C, 190 C and 210 C during 2 h. The fabricated waveguides consisted of sequential b 1 and b 2 phase layers [3]. Some specimens were annealed under different conditions in an oven in air atmosphere with temperature stability AE1 C. After annealing the specimens slowly cooled to room temperature in the oven.…”

“…This manifests itself, for example, in the chemical resistance decrease as in contrast to LN, proton exchange layers are etched in the HF þ HNO 3 solution [3]. PE should certainly change mechanical properties too.…”

“…PE in a LiNbO 3 [2]. The refractive index of the obtained PE layer is larger than that in the volume of the LN crystal, which makes possible light propagation in the layer due to the total internal reflection.…”