Direct observation of domain inversion in heat-treated LiNbO₃ using surface laser intensity modulation method (SLIMM)

Abstract

Optical waveguides are often fabricated from ferroelectrics such as LiNbO₃, LiTaO₃ and KTP because their domains can be inverted in polarity by various chemical and thermal treatments. Optical microscopy can be used to determine the thickness of the inverted layer, but this is a destructive technique. The nondestructive Surface Laser Intensity Modulation Method (SLIMM) can be used to determine the spatial polarization distribution and thus map the domain structure. In these experiments, a high-temperature thermal treatment was used to invert the domains in about half the thickness of a LiNbO₃ crystal. This produced a “head to head” domain structure which was clearly shown, both by the symmetry of the SLIMM raw data and by optical microscopy. The quantitative polarization distribution was found by a nonlinear fit of the SLIMM data to a theoretical expression based on the “head to head” domain structure.