Localized holographic recording in doubly doped lithium niobate

In holographic data storage, pages of information are overlapped in the volume of the recording medium. Due to destructive read-out of holograms in photorefractive crystals such as LiNbO_3:Fe, holograms are recorded with an exposure schedule in order to equalize diffraction efficiency. This leads to a final diffraction efficiency proportional to 1/M^2, where M is the number of exposures. Coherent erasure of a particular page also erases all the other pages stored in the same volume. We believe to have found a technique that does not require an exposure schedule and that can record M holograms with diffraction efficiency following a 1/M dependence. Our technique is based on non-destructive read-out in doubly-doped LiNbO_3. The technique is based on the recording of localized holograms in thin layers across the volume of the crystal.