| 摘要 |
An information recording and reproducing apparatus for optically recording/reproducing information to/from a two-layer optical disk comprises a cylindrical lens, which gives astigmatism to a reflected light from a target information recording layer, two caustic curve positions are arranged in the front and in the rear of the optical detector, and an unnecessary reflected light from an another information recording layer has two caustic curve positions arranged in the rear of the optical detector. In this condition, assuming an astigmatism direction of the cylindrical lens is inclined at 45 degree angle to a track direction, a projected image of the target information recording layer is inclined at 90 degree angle to an another projected image of the another information recording layer in a light receiving surface of the optical detector.
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