Selective erasure for dynamic photorefractive memories

Dynamic photorefractive memories (DPMs) have been shown to provide nondestructive readout and write/erase capabilities for multiple storage of 2-D images.1,2 Each image is stored by recording a phase hologram of a small refractive-index modulation Δn0 ≪ Δnmax where Δnmax is the allowable maximum refractive index modulation. In this paper we are concerned with DPMs where a fast erasure process must be used to replace one of the stored images by another. The recording and incoherent erasure processes may be characterized by exponential curves. For the small refractive-index modulation typical of superimposed photo re frac live holograms, the writing process is much faster than the incoherent erasure process. Such asymmetry is appropriate for long term storage but inappropriate for fast updating of the stored information.