| 摘要 |
An optical scanning device 1 detects an information signal from an optical record carrier 2 using differential interference contrast. Two radiation beams 13 a , 13 b are generated and focused to two distinct spots 15 a , 15 b respectively displaced along a data track on the information layer of an optical record carrier. The relative positions of the spots in lands and pits can generate a path length difference between the reflected beams 17 a , 17 b. This path length difference causes the beams to interfere either constructively or destructively, depending on the relative land/pit position in the data track of the spots. This interference causes a detectable signal to be generated, the signal being representative of a transition from a pit to a land on the information layer 4 or vice versa.
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