According to speckle modulation on the object beam of a volume holographic correlators, we show that the sidelobes of the correlation patterns along the vertical direction as well as those along the horizontal direction are well suppressed, so that the multiplexing space is markedly reduced and the channel density is largely increased. The experiment of 2030-page human faces correlated storage and recognition are presented, a very clear correlation spots array is achieved, and the recognition accuracy is better than 95%.
The holographic properties of doubly doped lithium niobate crystals with Indium have been investigated. It is found that doping slight Indium concentration (0.5mol%) in LiNbO3:In, Fe crystal can efficiently increase the sensitivity with small dynamic range changing. To improve the whole holographic properties of LiNbO3 crystal, LiNbO3:In, Fe with ideal doping concentrations and a new photorefractive material LiNbO3:In, Mn have been proposed and achieved larger dynamic range, higher sensitivity and better signal-to-noise ratio than LiNbO3:Fe crystal (Fe:0.03wt.%) that is generally considered as a preferable storage medium in holographic memories. In a common volume of LiNbO3:In, Fe crystal proposed, 2030 holograms have been successfully multiplexed and exactly identified in a compact volume holographic data storage and correlation recognition system.