Figure 1
From: Orthogonal quasi-phase-matched superlattice for generation of hyperentangled photons
(a) Schematic of the superlattice structure showing the two interleaved sets of nonlinear layers with orthogonal optic axes and orthogonal directions of poling, as indicated by the g H (z) and g V (z) functions. The arrows show the periodically flipped directions of nonlinearity for each set along the crystal domains, which implement the orthogonal QPM processes. When illuminated by a linearly polarized pump beam with components along the horizontal and vertical directions, parametric downconversion creates in photon pairs with alternating orthogonal polarizations. (b) Space-time diagrams illustrating the propagation of biphotons born in cascaded-crystals (top), double-nonlinearity (middle), and superlattice (bottom) structures (dotted line: o ray; solid line: e ray). The orthogonal poling in the superlattice performs continuous group-velocity matching per two-layer set for the pump (green line) and downconverted (red line) photons.
