| 摘要 |
PURPOSE:To improve the read-out accuracy and also to prevent the deterioration of recording information by controlling laser beam to be radiated, so as to intermitted in a period higher than at least the sample rate of information, so that the non-irradiation time becomes longer than the irradiation time. CONSTITUTION:For instance, when a clock period is t0 (100ns), the pulse width of a pulse LP is set to about 20ns-5ns by setting it to its 1/5-1/20. Accordingly, the average power Pav of a laser beam modulated by such a pulse LP becomes extremely small, and for instance, when the duty of the pulse LP is 10%, even if its peak value power is 10mw, the mean value power can be suppressed to 1mw. In this state, this intermittent modulation laser power is reflected from the disk surface, and when a detecting signal corresponding to a data is detected by a photodetector form a reflected light by which the plane of polarization rotates by a Kerr effect, a signal waveform Sa and Sb are outputted, and by subtracting Sa-Sb, a detecting signal SD is obtained. |
