Phase-locked sustainment of photorefractive holograms using phase conjugation

When multiple holograms are recorded in a photorefractive crystal, the recording of recent holograms erases early ones. We can equalize the strengths of all recorded holograms by following an appropriate exposure schedule. However, this leads to a composite hologram whose strength decreases as the number of exposures increases. In this paper, we describe a system in which the composite photorefractive hologram reaches a steady state with overall efficiency independent of the number of holograms (N). Furthermore, the phases of the recorded holograms remain locked during this process.