Spatial gap solitons due to photonic lattices in photorefractive SBN crystals: An ab initio investigation

This manuscript presents the results of the first-principles calculations revealing the suitable candidature of strontium barium niobate (SBN) photorefractive crystals using globally accepted WIEN2k codes. These computations confirm the good candidature of SBN crystals for photorefractive nonlinear optics and the ensuing applications. Using the DOS, band structure, and optical investigations, these first principle computations address bandgap creation and estimate, directional-dependent refractive index calculation, and absorption coefficient estimation. Optical spatial gap solitons in SBN photorefractive media with Pockel's nonlinearity and an embedded photonic lattice have been the subject of further inquiry. We have setup and solved the paraxial Helmholtz equation along with the imprinted photonic lattice in SBN crystals. We have, for the first time uncovered the existence of many different types of single hump, double hump, and multi hump gap solitons across both the finite band gaps. Multi hump solitons found to exist are of both anti-symmetric and symmetric type with two distinct profiles being seen for the anti-symmetric multihump solitons across both band gaps. Stability of the solitons with respect to small perturbations has been studied in case of each type of soliton solution. Linear stability analysis reveals that all types of gap solitons, including the single hump, double hump and multi hump solitons are stable across both the first and second finite band gap which is quite a significant and novel finding. The linear stability analysis is duly confirmed by direct propagation simulations undertaken using the finite difference beam propagation method.