This work concerns the fabrication, optical characterization and potential applications of two types of microstructures manufactured in congruent lithium niobate. The first type consists of a simple 2D hexagonal lattice of inverted ferroelectric domains fabricated by standard electric field poling at room temperature. The second structure is the chemically etched version of the first one. Long etching in hot HF acid results in differential etching of opposite ferroelectric domain faces. In this way obtain a 3D structure is obtained in which the hexagonal domain array becomes an array of truncated pyramids. Both these structures are characterized through a digital interferometric analysis. The samples are inserted in the arm of a Mach-Zenhder interferometer and the digital holograms acquired are used to numerically reconstruct both the amplitude and the phase of the wavefront transmitted by the sample. Finally, we report on …