| 摘要 |
PURPOSE:To enable erasure to be performed by a simplified optical system, by constituting a condensing optical system assumed as a group having a conjugate point on a light source and an optical recording medium. CONSTITUTION:A laser beam 101 is reflected on a half mirror 102 and is condensed on a recording medium 104, and its transmitted light is made incident on a photodiode 106 via a polarizing plate 105. Reflected light on the medium 104, passing the half mirror, on which astigmatism is attached, is made incident on a photodiode 108 for servo. In such a way, a focus servo signal by the astigmatism and a tracking error signal by a sampling servo method in which a wobbling pit is utilized can be obtained. Thus, by using the condensing optical system assumed as the group having the conjugate point on the point light source and the optical recording medium, it is possible to obtain an erasable recording and reproducing device with the simplified optical system. |
