| 摘要 |
PURPOSE:To suppress the increase in noise and fluctuation of an optical output due to a feedback light by adding a means for applying a pulse current to a semiconductor laser of a light source and setting properly the width and period of the pulse current taking the distance between the semiconductor laser and the optical disc into account. CONSTITUTION:Time taur from the time an irradiated pulse is reflected on the optical disc until it is fed back to the irradiated end face is expressed as taur= 2l/c, where l is the distance between the semiconductor laser 12 and the optical disc 7 and (c) is the velocity of light. In superimposing a pulse current to the semiconductor laser 12 so that the irradiated pulse light (in solid lines) and a feedback pulse light (in broken lines) show a time delay as shown in the figure, when the feedback light pulse is fed back to the irradiating end 13 of the semiconductor laser 12, the current value fed to the semiconductor laser 12 is a threshold value or below and even if the feedback light pulse is made incident on the semiconductor laser, it is not be affected at all. Conversely, since no feedback light comes during laser oscillation, neither increase in noise nor light output change is caused. |
