Composite Vortex Beams Created Using a Sandwich Crystalline System. Three Consequently Set Crystals

In the present work, we have both experimentally and theoretically analyzed the conoscopic patterns produced by a sandwich crystalline system comprising two uniaxial LiNbO3 crystals aligned along their optical axes (Z-cuts), with the third LiNbO3 crystal of X-cut, placed between them.Our results show that the conoscopic patterns, calculated for linearly and circularly polarized incident light, are in good agreement with experimental observations.From the simulation data, maps of the effective phase difference and the effective angle of rotation of the optical indicatrix were derived.The map of the effective angle of rotation contains pairs of topological defects (TDs), each pair consisting of TDs with opposite signs but the same modulus of half-integer defect strengths.These TD pairs lead to the formation of singly charged optical vortices (OVs) pairs under incident circular polarization and to vector beams (VBs) with unit polarization order and opposite signs under incident linear polarization.The system produces two chains of defect pairs oriented along the x-and y-axes.Importantly, we demonstrate that the TDs, OVs, and VBs within these pairs are not entangled.