Hologram multiplexing using orthogonal phase codes and incremental recording

Abstract

Photorefractive volume holography may prove useful for optical interconnection and data storage applications. However, the process of recording a set of uniform, high quality superimposed holograms normally involves a complicated recording procedure using a schedule calculated from the detailed material characteristics1,2. A small error in material characterization (or change in the material characteristics) can result in highly nonuniform diffraction efficiencies. In this paper, we present a new incremental recording approach that relies only on an approximate knowledge of the materials characteristics. By avoiding long exposures, we avoid the high gain and fanning which tend to disrupt photorefractive performance. To achieve the highly repeatable recording necessary for this approach we use a set of orthogonal phase images for the reference beams. This choice minimizes readout of any unwanted images. The phase only reference images will be more reproducible when generated by a stationary phase spatial light modulator, compared to angular multiplexing. Compared to the simple sequential schedule of recording, the use of phase-coded reference beams and incremental recording of the holograms should produce brighter images with an improved signal-to-noise ratio.