Tolerance for translation disturbances of template-matching two-dimensional modulation code for holographic memories

Abstract

The decoding performance of the 4 / 9 code, which depends on the accuracies of similarity comparisons for the code and the positional marker, was computationally evaluated in response to translation disturbances. The reproduction bright spot size ͑͒ was constrained to be smaller than the image-sensor pixel pitch ͑p͒ for the code, and Ͼ p was necessary for the marker. These contradictory requirements were solved by a reproduction method in which a large numerical aperture ͑NA͒ was set for the code and a small NA was set for the marker. A bit error rate of 10 −4 and a position detection resolution of ϳp / 10 were confirmed in the read-only-type holographic memory where the above method using two different NAs was applied.