| 摘要 |
Light (111) emitted from a light source (110) is transmitted through an objective lens (140), reflected from an optical disc (10), transmitted again through the objective lens (140), and thereafter divided into central light (111A) transmitted through a central part of the objective lens (140) and peripheral light (111P) transmitted through a peripheral part of the objective lens (140) by a hologram (150). A central light FE signal (S212A) is generated from the central light (111A) and a peripheral light FE signal (S212P) is generated from the peripheral light (111P). In a focus search operation, an S-letter detector (221A) detects a time point at a zero level of the central light FE signal (S212A), and an S-letter detector (221P) detects a time point at a zero level of the peripheral light FE signal (S212P). A time difference is measured by a timer counter (222) in terms of elapsed time. Disc identification means (300) identifies a type of the optical disc (10) based on the time difference.
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