In this paper, the dependences of both multiplexing selectivity and diffraction efficiency in the holographic data storage on the speckle size are derived respectively. Based on these dependences, a new characteristic parameter of speckle holographic storage is defined as the optimization criterion. Then the speckle size is optimized to compromise its influence on the multiplexing selectivity and the diffraction efficiency. The simulated calculation results show that the speckle size should be neither too big nor too small in order to get the best performance of the high-density volume holographic storage with speckle reference beam. In addition, the intensity ratio between the signal beam and the illumination beam that is used to produce speckle reference beam also influences the optimization.
The volume holographic memory in the photorefractive crystal is considered to be an efficient approach for high throughput data storage and retrieval. Among different techniques for data multiplexing, the hologram with speckle reference beam is a potential approach for high-density holographic information storage. However the existing research are mainly focused on the selective properties of volume holograms with speckle reference beam rather than on the capacity of data storage. So it is necessary to analyze the diffraction efficiency of speckle holograms that can be measured by dynamic range metric of storage medium. In this paper, an analytical expression of the effective dynamic range metric of storage medium for speckle volume holographic memory is derived. The effective grating modulation ratio is considered in the dynamic range metric owing to the appearance of speckle. The variation relationship of grating modulation ratio with speckle characteristics is described theoretically. The influences of speckle characteristics on the dynamic range performance are discussed by use of the numerical simulation.
In this paper, the geometric configuration of recording beams and the orientation of crystal axis is optimized for optical holographic storage in order to achieve the preferable effective dynamic range and angle selectivity simultaneity. The influences of the defocusing amount of record crystal on data retrieval in the Fourier transform configuration are studied theoretically. The field lens is used in the optical path for Fourier transform to reduce the length of optical path and the distortion. T he optimization results are used to design the optical architecture for miniaturizing the optical holographic storage system.
The volume holographic optical data storage has been an important and exciting area of research. Recently the more interested study for a high-density holographic memory is focused on the speckle wave used as a coded reference wave in various multiplexing techniques. In this paper, a novel speckle holographic storage scheme is proposed, which a random phase diffuser is added in the front of storage medium along the reference optical path of the original 90 degree storage geometry. In this scheme the incident angle of the reference beam and the place of the random phase diffuser illuminated by the reference beam can be changed simultaneously. The joint action of these changes generated a dynamic speckle wave for the reference beam in holographic storage. A theoretical model has been derived to describe the storage properties of this scheme based on the cross- correlation of dynamic speckle and the diffractive theory. The storage density influenced by the properties of the speckle patterns has been analyzed and experimentally confirmed. The results indicate that this scheme allows an increase in the data storage density with simple storage- retrieval architecture.
In this paper, the dynamical behaviors of the class D lasers with modulated term are investigated numerically. The result shows that there exists the so-called generalized bistability in the period-doubling bifurcations, and the two stable states possess space reflected symmetry.
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