Spatial-spectral discrete vortex solitons in quadratic lattices

Manipulation of light beams and pulses in nonlinear photonic lattices or waveguide arrays is attracting increasing attention, due to the potential to control spatial beam shaping combined with manipulation of temporal and spectral characteristics. In particular, photonic lattices created in a medium with quadratic nonlinearity can facilitate ultra-fast all-optical switching through parametric wave mixing between fundamental and second-harmonic waves. Various approaches to beam manipulation rely on the special features of localized modes in the form of discrete or lattice solitons. In this work, we predict the appearance of a novel type of discrete quadratic solitons in one-dimensional lattices, whose power flow forms a closed loop in spatial-spectral domain due to the parametric conversion between the fundamental and second-harmonic waves.