No abstract

We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.

We investigate the origin of the directivity of a dipole antenna embedded in a dielectric slab Fabry-Pérot cavity. It is shown that the focusing effect is due to the angular selection rules in the Bragg-type mirror and is directly correlated to the frequency selectivity of the cavity. For a 6 GHz resonant device, having a quality factor of 100, the aperture of the beam pattern ( -plane) is close to 12 in agreement with the arguments based on frequency and angular selectivities. Hence, this kind of cavity could be used in free-space based communication links.