Optical pickup device and diffractive optical element

Details Optical pickup device and diffractive optical element Optical pickup device and diffractive optical element

2007-11-27

2007-11-27

Korzuch, William R. (Department: 2627)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

Reexamination Certificate

active

11034986

ABSTRACT:
When a wavelength having the same value as a reference wavelength λ1of a first laser light is set to a designed wavelength λ, a diffractive optical element has: an inner circular side irregular diffraction pattern portion, in which a plurality of irregular portions in which a height of a convex portion is set to approximately 1λ-fold of the designed wavelength λ with respect to a concave portion are repeated, being formed in an annular shape in an inner circular area having a predetermined diameter for the correction of a spherical aberration generated due to a difference in substrate thickness between first and second optical recording mediums centering on a central point through which an optical axis runs while gradually changing a pitch of the irregular portions in a radial direction toward the outer circular side; and an outer circular side tiered diffraction pattern portion which is intended to improve a chromatic aberration with respect to the first laser light by forming in an annular shape in an outer circular area outside the inner circular side irregular diffraction pattern portion a plurality of tiers by setting a height of each tier to approximately mλ-fold (where m is a natural number which does not include0) of the designed wavelength λ or by setting the same while changing a value of m for each tier.

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Katsuhiro Koike et al., “Phase shift element for Blu-ray Disc/ DVD compatibility”,Technical digest for ODS 2003, WA6, pp. 271-273.

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