| 摘要 |
There is provided an optical head including (a) a laser source for emitting a light, (b) an objective lens for focusing the light onto a plane of an optical recording medium, (c) a photodetector including a first light-receiving region for receiving a light reflected from the optical recording medium and passing through a central portion of the objective lens and a second light-receiving region for receiving a light reflected from the optical recording medium and passing through a non-central portion of the objective lens, and a device for selecting one of an output signal transmitted from the first light-receiving region and a sum of output signals transmitted from the first and second light-receiving regions. The optical head may further include a holographic optical element disposed in an optical path between the laser source and the objective lens for separating a first reflected light reflected from the optical recording medium and passing through a central portion of the objective lens and a second reflected light reflected from the optical recording medium and passing through a non-central portion of the objective lens from each other, in which case the photodetector includes a first light-receiving region for receiving the first reflected light and a second light-receiving region for receiving the second reflected light. The above mentioned optical head makes it possible to reproduce data recorded in an optical disk having different substrate width with smaller decrease in a light quantity.
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