Recording optical vortices in azo polymer films by applying holographic method

Abstract

In this paper the optical vortices with topological charge <i>q</i> = –1, 1, 2, 4 are recorded in azo polymer films by using holographic technology. The forked holographic gratings formed by the Gaussian beam and optical vortex beam are recorded in the sample films, the original forked holographic grating and the recording rate are analyzed. The vortex beam is reconstructed by illuminating the sample film with a reference beam, and the recording quality is analyzed. Also the erasability and durability of the sample are tested. The experimental results show that the recording rates of vortex beams with different topological charges are relatively uniform, which means that the optical vortices with different topological charges can be recorded at the same speed. The forked holographic grating of the high-order optical vortex splits in the recording process due to the disturbances, such as anisotropic nonlinear light, atmospheric turbulence, and background light field. However, the split vortex beam still maintains a stable ring structure. The reconstructed optical vortex and the original optical vortex are highly consistent in morphology, and the interference fringes of the reconstructed optical vortices are highly consistent with the original vortex holographic gratings, indicating that the topological charge information in the optical vortices can be effectively recorded and read out. The recorded information can be erased by heating the sample to about 97 ℃, and new information can be re-recorded after cooling. There appears no fatigue in the sample after the information has been erased 100 times and good durability is still retained. Optical vortices theoretically have infinite states of topological charges, based on which great success is achieved in optical communication and information encoding. Therefore, storing and reading information of topological charges in optical vortices may have potential applications in optical information storage.