| 摘要 |
<P>PROBLEM TO BE SOLVED: To make linear reading possible and to improve an SNR even when the amplitude of a coherent light beam to be added is not uniform. Ž<P>SOLUTION: A first image signal and a second image signal are obtained by sequentially adding two kinds of coherent light beams having intensity larger than the absolute maximum of the amplitude of a reproduced image and having phase differences of "0" and "π" from (reference phase of) the reproduced image to the reproduced image respectively and receiving the addition results through an image sensor. Square roots of the first image signal and the second image signal are calculated, and the difference between the calculated square roots is calculated. Thus, a linear read signal representing phase information recorded in the medium can be obtained. This also improves the SNR because differential detection is carried out by calculating a difference in the results of adding two kinds of coherent light beams having reversed phases from each other. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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