| 摘要 |
PURPOSE:To perform data regeneration and focus tracking servo equally and with high accuracy by distributing a single luminous flux to a regenerating luminous flux and a luminous flux for servo intersecting orthogonally with each other. CONSTITUTION:The data encoded corresponding to the interval of plural marks each other is formed for the tracking of a recording medium 14. A lambda/2 plate 8 irradiated by a laser beam 10 outgoing from a laser 2 has a 4/10 diameter of a luminous flux diameter and is a concentric circular shape to a section intersecting orthogonally with an optical axis, and whose neutral axis forms at an angle of 45 deg. to the polarization direction of an incident beam. Thus, the luminous flux of the central part of the beam 10 is converted into a polarization component intersecting orthogonally with the paper surface by the lambda/2 plate 8 and the peripheral remaining beam 10 not transmitting through the lambda/2 plate 8 maintains a polarizing component parallel to the paper surface. The beam transmitting through the lambda/2 plate 8 in the state of being converged on the medium 14 is not converged sufficiently and has a beam diameter covering a pair of marks constituting a mark set and used for regeneration, and the beam not transmitting through the plate 8 is converged sufficiently and used for a servo. |
