Patent ID: 7385904
Filing Date: 2008-06-10
Classification: G11B

Abstract:
1. An optical pickup device which selectively records or reproduces a first optical recording medium, and a second optical recording medium having a recording density lower than that of the first optical recording medium and a substrate thickness larger than that of the first optical recording medium, comprising: a first laser light source which emits a first laser light whose wavelength is not more than 450 nm in accordance with the first optical recording medium; a second laser light source which emits a second laser light whose wavelength is longer than that of the first laser light in accordance with the second optical recording medium; an objective lens which has a numerical aperture (NA) set to 0.75 or above for the first optical recording medium, in which at least one of respective surfaces thereof backing onto each other is formed into an aspherical surface, and which converges the first and second laser lights on the respective signal surfaces of the first and second optical recording mediums; and a phase shift element which is provided between the first and second laser light source side and the objective lens and corrects a spherical aberration generated due to a difference in substrate thickness between the first and second optical recording mediums, wherein the phase shift element has a tiered phase difference pattern portion formed in circular shapes on one surface thereof, the tiered phase difference pattern portion being obtained by continuously connecting an inner circular side tiered phase difference pattern portion with an outer circular side tiered phase difference pattern portion based on a phase function curve acquired by a single phase-function with a wavelength having the same value as a reference wavelength λ