The use of orbital angular momentum of light beams for optical data storage

We present a method to optically store multiple information in one location by having angular momentum imparted to the scanning beam by optical phase objects that make up the information areas on a surface. We show that the light beam thus perturbed carries an optical vortex, the rotation of which can be detected in the near-field focal region as a function of the longitudinal distance either side of the beam waist at z(0). The spatial variation of the rotation of the E-field and hence the intensity is dependent upon the phase depth (typically in the range pi/2 to 2pi) introduced by quadrant staircase-type structures which approximate well to helical phase defects. We propose that using suitable detection schemes, this spatial variation (rotation) of intensity profiles can be used to extract multiple bits of information from the different quadrant staircase structures of varying phase depths.