BPM simulation of SNOM measurements of waveguide arrays induced by periodically poled BNN crystals

The simulation of light propagation using standard beam propagation techniques, in periodically inverted domains in Ba₂NaNb₅O₁₂ crystals is presented. The poled domains pattern gives rise to periodic modulation of the refractive index in the crystal, which can be observed with diffraction experiments and simulated by one-dimensional beam propagation methods. The micro-domains are characterized by Scanning Near Field Microscopy, using both transmission and collection modes. In particular, under the collection mode, micro- pictures have been obtained with unexpected high optical contrast between positive and negative domains of up to 80%. Using a beam simulation method, the results are explained considering that the ferroelectric domains operate as a periodic array of planar waveguides.