Axicon-shape photonic crystals and limited-diffraction light propagation

Abstract

Electromagnetic beams are subject to spatial spreading as they propagate. We have investigated the light propagation passing through a finite-aperture which is obtained by the two-dimensional square-lattice photonic crystals. It is observed that the beam that is coupled to the free-space by exiting the axicon-shape photonic crystal resists considerably against the diffraction. The inspection of the beam profile in the transverse to the propagation direction reveals the appearance of the side-lobes and we attributed the limited-diffraction beam propagation to these artificially created lobes. We show that an order of magnitude improvement for beating the diffraction length is achievable with axicon-shape photonic crystal. The advantages of the presented photonic crystal based axicon over the bulk refractive axicons are the compactness and the integrated nature of the former one in addition to the flexibility of engineering individual unit cells of photonic crystal structure.