Peculiarities of chemical etching of the annealed proton exchange channel waveguides fabricated on Z cut of lithium niobate crystal

The chemical etching of annealed proton-exchanged channel waveguides fabricated on a Z-cut lithium niobate crystal, revealed two layers different in structure. The first layer is etched rapidly (~ 600 nm / h) and uniformly, and the second layer is etched slow and extremely uneven. This etching behavior may be related to the presence of two proton-exchange waveguide phases (k₁- and α-phases) or a possible local inversion of domain structures in a waveguide due to proton exchange and temperature effects in the manufacture of the waveguide.