  We investigate light propagation through materials with periodically
modulated gain/loss profile in both transverse and longitudinal directions,
i.e. in material with two-dimensional modulation in space. We predict effects
of self-collimation (diffraction-free propagation) of the beams, as well as
superdiffusion (spatial frequency filtering) of the beams in depending on the
geometry of the gain/loss lattice, and justify the predictions by numerical
simulations of the paraxial wave propagation equations.
