The exposure schedule model for uniform diffraction efficiency is extended to be suitable for the partially overlapping multiplexing method. The proposed model is based on solving an optimization problem. Fifty holograms were multiplexed using the exposure schedule calculated with the extended model. The material used in the experiment is based on the photopolymerization of a free radical. By comparing the intensity of the reconstructed images during recording with that readout after recording, the calculated exposure schedule is verified to be effective to realize the uniform diffraction efficiency for the multiplexing holographic storage.
In this paper, we suggest a simple method of making specified random-phase shifters which are used for speckle-shift
multiplexing in photopolymers. Compared with other kinds of diffusers, they are easier to be made and designed to
control the average speckle size so as to accommodate the requirement for high storage density. The experimental
scheme and the theoretical calculation of the desired speckle size are given. Then the difference between the
experimentally measured and theoretically calculated speckle size is discussed. Finally the unfavorable factors which
influence the performances of shift-multiplexing using this scheme are discussed, and the feasible solutions to those
problems are given.
In the paraelectric phase photorefractive crystal, the quadratic electro-optic effect can result in Bragg gratings in the
volume of the crystal. The reconstruction process and the diffractive properties of the grating can be governed by the
externally applied electric field. The measurement of the diffraction efficiency as a function of the applied electric
field during recording is described. Dependence of electrically controlled Bragg grating in paraelectric phase KLTN:
Cu crystals on readout illumination beam polarization were experimentally investigated. The results of experiments
show that the diffraction efficiency of electric-controlled volume grating can also be controlled by the polarization of
readout light. All these results would offer an possibility for a photorefractive optical switch by adjusting the
polarization of the readout beam to control the diffraction efficiency.
In this paper, the position selectivity of holograms recorded with orthogonal-phase coded reference beams is investigated
by numerical simulation and preliminary experiments. The results of numerical simulation show that with a phase-coded
reference beam, the brightness of the reconstructed image is sensitive to the relative shift between the hologram and the
phase-coding pattern of the reference beam. The position selectivity is not worse than 40μm in both lateral directions.
The results of preliminary experiments also show that the position selectivity is even better. According to both the
numerical simulation and the experiments, it is clear that with orthogonal phase-coded reference beams, the position
selectivity can be satisfying for holographic storage. This suggests that a new hybrid multiplexing method, which
incorporates orthogonal phase-coding multiplexing into shift-multiplexing, could be suitable for high-density and
high-fidelity holographic storage.
In this paper we study the dynamics of refractive index modulation in a dual-monomer photopolymer through grating
growth under different experiment stages. By using different sets of parameters for vinyl monomers (NVC) and acrylate
monomers (POEA) respectively, a composite dual-monomer model, extended from the uniform post-exposure (UPE)
model for single monomer photopolymer, is proposed and fitted with the experiment data very well. Further discussions
indicate that the dominant contribution to the total index modulation is made by NVC monomers, and a brief explanation
of the function of POEA monomers is given.
In recent years, doped KLTN (K1-xLixTa1-yNbyO3) crystal in paraelectric state was reported to be a new type of
holographic storage medium owning to its great promotion for diffraction efficiency, through quadratic electro-optical
effect generated by external electrical field. In this paper, we describe the preparation method of the KLTN crystal in our
laboratory and report our preliminary experimental research on electrically controllable holography in a KLTN: Cu
crystal. It was found that the writing intensity and polarization of the readout beam affect the diffraction efficiency
remarkably, and the voltage selectivity of holograms stored in the crystal was observed, which is potential to increase the
storage capacity.
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