  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.
