Sandwich Holography for Displaying Information

An entirely new method of storing confidential information based on sandwich holography, is presented theoretically and experimentally. The information stored in the holograms can not be read out from one hologram alone; only when two holograms are put together will the information be available. There are two ways to code the information in the sandwich holograms: one is to present it according to sandwich reappeared image dark and bright; the other is to do it according to sandwich reappeared image with or without interference frings. The latter has practical significance.