The possibility of optical creation of polymer structures with a periodic distribution of the refractive index in a layer of a photopolymerizing composition, the thickness of which significantly exceeds the depth of field of the used projection system, is considered. Nonlinear wave processes in such an irreversible photorefractive medium for grating‐forming radiation are considered. Using computer simulation, modes of stable self‐channeling of closely propagating light beams have been found, as a result of which regular extended waveguide tracks can be obtained. The results of experiments on the creation of thick polymer gratings using a conventional incoherent projection system are demonstrated. In a composition based on industrial monomer OCM‐2, gratings with a period of 10 μm and a thickness of more than 1 mm were obtained.