Sub-Rayleigh optical vortex coronagraphy

We introduce a new optical vortex coronagraph(OVC) method to determine the angular distance between two sources when the separation is sub-Rayleigh.We have found a direct relationship between the position of the minima and the source angular separation. A priori knowledge about the location of the two sources is not required. The superresolution capabilities of an OVC, equipped with an ℓ = 2 N-step spiral phase plate in its optical path, were investigated numerically. The results of these investigations show that a fraction of the light, increasing with N, from the secondary source can be detected with a sub-Rayleigh resolution of at least 0.1 l/D.