We study the optical fields produced by non-integral binary forked gratings. We analyze experimentally the phase structure of the light beams by interference. We were able to identify individual optical vortices directly by observing the dislocations in the fringe pattern. Our experimental results agree well with of all the generic features predicted by the theoretical model [M.V. Berry, "Optical vortices evolving from helicoidal and fractional phase steps," J. Opt. A 6 , pp. 259-268, 2004.]. Our results underscore the conservation of orbital angular momentum of the light/optical-apparatus system.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.