Copying speed is an important characteristic for optical read-only memory (ROM) replication systems. The copying
speed of holographic ROM replication is, however, limited by small energy efficiency of the optical system due to the
small diffraction efficiency of multiplexed holograms. In this paper we propose new holographic ROM replication
systems with a photorefractive amplifier, and analyze the speed gain performance. We improve energy efficiency
significantly and speed up replication by amplifying weak diffraction signal beams using photorefractive wave mixing.
Our new theory and numerical calculations revealed that achievable speed gain can be evaluated from only a single
dimensionless parameter that is the product of the three as follows: (i) the pump beam intensity ratio in the amplifier, (ii)
the ratio of the photopolymer and photorefractive sensitivities, and (iii) the dynamic range per hologram of the copy
medium. In current holographic recording systems, a practical copying speed gain of more than 10 is achievable with
currently available photorefractive materials.
In this paper, we propose a selective erasure method for multiplexed holograms in a photorefractive crystal using a phase conjugate mirror (PCM). In this method, for the accurate selective erasure, we use pai phase shift between the relative phase of the diffracted beam to the transmitted beam by the hologram in photorefractive crystal and the relative phase of the object beam to reference beam in recording process by setting the direction of c-axis to the appropriate direction. In the selective erasure process, the diffracted beam and the transmitted beam by the original hologram in main memory are returned to main memory by PCM. These returned beams automatically propagate through the strictly same pass as the diffracted beam and the transmitted beam. Furthermore, by these returned beams, the pi-phase shifted hologram is overwritten on the original hologram by setting c-axis of main memory to the appropriate direction. Therefore, the pi-phase shifted hologram is automatically overwritten on the strictly same position as the original hologram without the high precise alignment and the original hologram is selectively erased. We perform the analysis and the experiment on selective erasure and demonstrate that one of the multiplexed holograms is selectively erased with our method.