Because of the high density and high parallelism of the volume holographic storage, volume holographic correlator can
be used as parallel multiple pattern filters. It has a natural feature for the parallel optical computing. However, the
applications of this kind of correlator are limited due to low accuracy of the computing results and small number of
parallel channels. To improve the data processing accuracy, some methods are proposed and employed to reduce the
noise and computing error of the volume holographic correlator. The sidelobes of the correlation pattern can be totally
suppressed. The shapes of the correlation patterns are made uniform. And the detected intensity can approach the inner
products of the input images and the stored images. The computing speed of the correlator based on the current
optoelectronic elements could be nearly two or three magnitude orders over the computing speed of traditional electronic
processors. The applications of volume holographic correlator in the star field identification are demonstrated.
A coherent optical data-processing method based on volume holographic correlator is described, which has the potential
for performing Walsh transform at a high processing rate. The input image and stored images of volume holographic
correlator are encoded to represent the data vector and Walsh functions in Walsh transform. And the output of volume
holographic correlator can represent the result of Walsh transform. An experiment is carried out, and the correspondency
of experimental result and theoretical one proves the effectiveness of the method.
Effects of phase masks, used in content-addressable volume holographic data storage system, on the spectrum
modulation, image reconstruction, and content search capability are analyzed. We have investigated the influence of
varying the pixel structure of phase masks on Fourier-transform holographic recording and reconstruction errors. The
effect on reconstruction errors of using a (0, π) two-level phase mask is studied. The case that a single pixel in the phase
mask extended to cover four or more pixels in the spatial light modulator (SLM) is discussed. The reconstruction errors
of a recorded binary data page and the field amplitude in the Fourier plane are evaluated when the phase mask is
misaligned to the SLM. We have also investigated the performance of phase masks in terms of suppressing the
diffraction sidelobes which lead to correlation cross talk and sharpening the correlation peaks. The results provide a
useful support for the mask design, fabrication and applications in the practical content-addressable volume holographic
data storage.
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