| 摘要 |
PURPOSE:To obtain specified recording characteristics regardless of places by changing the Curie temp. of an information recording layer continuously in a radial direction in such a manner that the Curie temp. is lower in the outside circumferential part than in the inside circumferential part of a disk. CONSTITUTION:A linear speed is higher nearer the outside circumferential part when the number of revolutions is kept constant. The area where laser light is projected (recording bit) is larger in the specified time as the linear speed is higher. The temp. rising rate (recording sensitivity) with respect to a specified quantity of laser light is smaller as the area is larger. The recording sensitivity is, therefore, poorer as the linear speed is higher. A difference in recording and reproducing characteristics appears between the outside circumferential part and the inside circumferential part. The Curie temp. is consequently made lower nearer the outside circumferential part by forming the disk in such a manner that the recording can be made at the lower temp. nearer the outside circumferential part in the case of executing the recording and reproduction at the constant number of revolutions. The variance in the recording and reproducing characteristics according to the radius of the disk in the place where the recording and reproduction are executed is thereby eliminated in the case of executing the recording and reproduction at the constant number of revolutions.
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