Surface domain engineering in congruent lithium niobate single crystals:   A route to submicron periodic poling
  We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as 1 \mu m. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures. 
Alessandro C. Busacca, Collin L. Sones, Vasilis Apostolopoulos, Robert   W. Eason and Sakellaris Mailis
physics.optics