| 摘要 |
An apparatus automatically controls the laser power of the light source by the feedback output of the APC detector and prevents the increase of laser power due to an abnormality of the APC detector. The automatic power control unit controls the drive amount of the light source by the detection output of the APC detector, which monitors the emission power of the light source, measures the relationship between the APC drive instruction amount and the detection output of the APC detector, and compares this inclination with the inclination at normal time. Also the automatic power control unit compares the error values before and after APC, and detects the change of the quantity of returned light during a predetermined period. As a result, data destruction due to separation, deviation, contamination or deterioration of the APC detector can be prevented effectively.
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