Surface periodic poling in lithium niobate and lithium tantalate

Periodic poling of lithium niobate crystals (PPLN) by means of electric field has revealed the best technique for finely tailoring PPLN structures and parameters, which play a central role in many current researches in the field of nonlinear integrated optics. Besides the most studied technique of bulk poling, recently a novel technique where domain inversion occurs just in a surface layer using photoresist or silica masks has been devised and studied. This surface periodic poling (SPP) approach is best suited when light is confined in a thin surface guiding layer or stripe, as in the case of optical waveguide devices. Also, we found that SPP respect to bulk poling offers two orders of magnitude reduction on the scale of periodicity, so that even nanostructures can be obtained provided a high resolution holographic mask writing technique is adopted. We were able to demonstrate 200 nm domain size, and also good compatibility with alpha-phase proton exchange channel waveguide fabrication. Our first experiments on lithium tantalate have also shown that the SPP technology appears to be applicable to this crystal (SPPLT), whose properties can allow to overcome limitations such as optical damage or UV absorption still present in PPLN devices. Finally, the issue of SPP compatibility with proton exchange waveguide fabrication will be addressed.