| 摘要 |
PURPOSE:To obtain a high-performance optical head in spite of miniaturization by minimizing the influence of a spherical aberration and preventing generation of a fresh aberration regardless of the constitution of a detecting system even if there is the generation of the spherical aberration. CONSTITUTION:An effective hologram is formed only in the circular region 21a at the center within the effective diameter 21 of a phase modulation type hologram element 2 of a hologram optical head of a forward and backward optical path co-possession type. A circumferential annular region 21b is formed at a depth at which an intermediate phase of a phase advance part and a phase delay part is given. |
