DYNAMIC-RANGE METRIC FOR A PHOTOREFRACTIVE CRYSTAL IN A VOLUME HOLOGRAPHIC MEMORY SYSTEM

An analytical expression for the dynamic range metric of a photorefrac tive crystal in a volume holographic memory is found on the basis of t he coupled mode theory for polarized waves inside crystals and the lin earized band transport model of photorefractive effect. Taking LiNbO3: Fe and BaTiO3 as examples, we discuss the influences of the impurity d oping level, oxidation-reduction state and geometric configuration of coupling beams on the dynamic range performance. For both crystals we find that if the donor concentration becomes larger and the crystals a re oxidized to greater extent accordingly, the maximum possible dynami c range could be improved. For BaTiO3 crystals the optimum angle betwe en the grating wave vector and the optical axis should be varied with the angle between the signal and reference beams.