An array of equi-spaced photodetectors can be used to detect the reconstructed image of a binary-coded Fraunhofer hologram read out at a different wavelength from that employed in recording the hologram, without the chance of spurious data bits due to reinforcement of intermodulation components, by aperiodically spacing an array of points, corresponding to the bit positions of the binary code, during the recording of the hologram in an appropriate manner.
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