High-directional wave propagation in periodic loss modulated materials

Amplification/attenuation of light waves in artificial materials can become sensitive to the propagation direction by spatially modulating the gain/loss response of the medium on the wavelength scale. We give a numerical proof of the high anisotropy of the gain/loss in two dimensional periodic structures with square and rhombic lattice symmetry by solving the full set of Maxwell's equations using the finite difference time domain method. Anisotropy of amplification/attenuation leads to the narrowing of the angular spectrum of propagating radiation with wavevectors close to the edges of the first Brillouin Zone. The effect provides a novel and useful method to filter out high spatial harmonics from noisy beams.

► Novel beam propagation phenomena are studied in periodically modulated gain/loss materials. ► The anisotropic gain profile of 2D square and rhombic lattices is obtained and discussed. ► The narrowing of the spatial spectrum of a beam is demonstrated. ► The spatial (angular) filtering of noisy beams is demonstrated.