| 摘要 |
PROBLEM TO BE SOLVED: To use a nearly common optical path for concentrated partial beams from generation to detection by setting a partial beam-generating means for coupling partial beams to a pencil of light and decoupling therefrom, and a beam acting means for independently acting to the coupled partial beams. SOLUTION: A first partial beam 31 and a second partial beam 32 are coupled in a first unpolarized beam splitter 41. Different partial beams 33 and 34 are coupled in unpolarized beam splitters 42 and 43. When passing the beam splitters 41, 42,..., each partial beam 31, 32,... is coupled again from a feedback pencil of light comprised of information carrier layers 71, 72,... of a recording medium 7. Detecting elements of optical units 91, 92,... are arranged in an optically conjugate system with respect to focuses on the information carrier layers. A second beam acting means 22 correspondingly adjusts the second partial beam 32, and corresponding different beam acting means 23, 24,... readjust the different partial beams 33, 34,....
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