| 摘要 |
PROBLEM TO BE SOLVED: To actually measure the bottom power level and to correct the fluctuation in recording power conditions by holding automatic power control and turning off high frequency superposition only in a prescribed period of a reproduction mode. SOLUTION: The light emitted from a semiconductor laser 200 is cast on a recording medium 203 through a collimating lens 201, a beam splitter 202 and an objective lens 205. The exit light is partly transduced into a voltage signal by a photodetector 204 through the beam splitter 202. The voltage signal is fed back to a laser power control block(MPU) 207. The laser 200 is subjected to the high frequency superposition(HFM) and the automatic power control(APC) in a data reproduction mode. The MPU 207 turns off the HFM while successively changing the modulation degree of the HFM at a prescribed time fraction in sector unit at the prescribed period, such as start of the disk. The MPU actually measures the calibration straight line of the modulation degree and the bottom power level and updates the setting of the modulation degree corresponding to the regulated value of the bottom power level in accordance therewith. |
