| 摘要 |
<p>A holographic optical correlator includes a matched optical filter and control means therefor including a memory. In use, searching for occurrences of an item to be found is carried out by the control means controlling the input and Fourier transform planes of the filter and a coherent light source for parallel optical processing of the memory content and the output plane of the filter provides information to the control means as to the location in the memory of occurrences of said item. The item and the memory as input to the input plane are coded by means of an M out of N code, where M is a constant in order to solve threshold tolerance problems. Specifically a sparse code (3 out of 13) is used for octet data. Preferably the item recognition is a two stage process. In a first stage, individual characters of a string are matched and in a second stage there is recognition of the correct relative juxtaposition of characters in the string.</p> |
