  We study the interference and diffraction of light when it propagates through
a metamaterial medium mimicking the spacetime of a cosmic string, -- a
topological defect with curvature singularity. The phenomenon may look like a
gravitational analogue of the Aharonov-Bohm effect, since the light propagates
in a region where the Riemann tensor vanishes being nonetheless affected by the
non-zero curvature confined to the string core. We carry out the full-wave
numerical simulation of the metamaterial medium and give the analytical
interpretation of the results by use of the asymptotic theory of diffraction,
which turns out to be in excellent agreement. In particular we show that the
main features of wave propagation in a medium with conical singularity can be
explained by four-wave interference involving two geometrical-optics and two
diffracted waves.

Optics;Cosmology and Nongalactic Astrophysics;General Relativity and Quantum Cosmology