Bragg-induced oscillations in non-PT photonic lattices

When a monochromatic beam of light propagates through a periodic structure with the incident angle satisfying the Bragg condition, its Fourier spatial spectra oscillates between the resonant modes situated on the edges of the Brillouin zones of the lattice with a nontrivial dynamics. We wish to study here these Bragg-induced oscillations in a specific non-PT periodic structure, that is, a periodic medium not invariant under the combined action of parity and time reversal symmetries. We compare our analytic results based on the expansion of the optical field in Bragg-resonant plane waves with direct numerical integration of the paraxial wave equation using a wide Gaussian beam as initial condition without assuming the shallow potential approximation. In particular, we wish to investigate under what conditions a mode trapping phenomenon can still be observed and to verify closely how the energy exchange between the spectral modes takes place during propagation in this more general class of potentials with arbitrary gain and loss profiles.