| 摘要 |
PURPOSE:To omit a coma aberration correcting optical element, to reduce the number of parts and to easily assemble the parts by forming a wave front phase correcting layer for correcting a coma aberration on the surface of an optical element for generating astigmatism. CONSTITUTION:The wave front phase correcting layer 1b for correcting the coma aberration of the plate-like optical element (half mirror) 1 for generating astigmatism by passing a focus error detecting reflected beam from a recording medium is formed on the surface of the optical element 1. Since harmful coma aberration secondarily generated by the optical element 1 itself can be completely removed by its own optical element 1 through the correcting layer 1b, ordinary coma aberration correcting optical parts can be omitted. Thereby, the number of parts can be reduced and assembling can be made easy because the optical element difficult in fitting adjustment can be omitted. |
