| 摘要 |
There is provided an optical device which comprises a light-emitting portion for emitting a laser light, a light-receiving portion for receiving the light emitted from the light-emitting portion, and a converging portion for converging the light emitted from the light-emitting portion to thereby irradiate a portion to be irradiated and for converging a light reflected on and returned from the irradiated portion, wherein the light-receiving portion is located in the vicinity of a confocal point of the converging portion with respect to the light returned from the irradiated portion, the light emitted from the light-emitting portion is received by the light-receiving portion along a path which is coaxial before and after being reflected by the irradiated portion, a push-pull signal is detected by the light-receiving portion, and the push-pull signal is subjected to partial differentiation with the amount of defocus to obtain a coefficient which is used to detect a tracking error signal.
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