Subdiffraction and spatial filtering due to periodic spatial modulation   of the gain/loss profile
  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. 
K. Staliunas, R. Herrero, and R.Vilaseca