Patent EP-1416480-A2 (EP)
Inventor: MIMORI MITSURU
IPC: G11B7/135
Filed: 2003-10-24
Abstract: An objective optical element, comprises first light source of wavelength lambda 1, second light source of wavelength lambda 2 (lambda 1 less than lambda 2) and light converging optical system including magnification changing element and objective optical element. The light converging optical system converges light flux from first light source onto information recording plane of first optical information recording medium through protective substrate. An objective optical element for use in an optical pickup apparatus, comprises a first light source of a wavelength lambda 1, a second light source of wavelength lambda 2 (lambda 1 less than lambda 2) and a light converging optical system including a magnification changing element and an objective optical element. The light converging optical system converges a light flux from the first light source onto an information recording plane of a first optical information recording medium through a protective substrate having a thickness t1 so that recording and/or reproducing information is conducted for the first optical information recording medium and the light converging optical system converges a light flux from the second light source onto an information recording plane of a second optical information recording medium through a protective substrate having a thickness t2 (t1=t2) so that recording and/or reproducing information is conducted for the second optical information recording medium. The objective optical element has an optical system magnification m1 for a light flux of the wavelength lambda 1. The optical system magnification m1 satisfies m1 = 1/7 - 1/25 (m1 is less than M1), where M1 is an optical system magnification from the first light source to the first optical information recording medium for a light flux of the wavelength lambda 1 in the optical pickup apparatus. The objective optical element comprises on at least one surface: a common region through which a light flux from the first light source and a light flux from the second light source pass in common so as to form a converged light spot on an information recording plane of the first optical information recording plane and an information recoding plane of the second optical information recording plane respectively; and an exclusive region through which a light flux from the first light source passes so as to form a converged light spot on an information recording plane of the first optical information recording plane and a light flux from the second light source passes so as not to form a converged light spot on an information recording plane of the second optical information recording plane. The exclusive region includes an exclusive diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature in accordance with wavelength fluctuation of a light flux of the wavelength lambda 1 when the light flux of the wavelength lambda 1 having passed through the exclusive diffractive structure is converged on an information recording plane of the first information recording medium. A light flux of a wavelength lambda 2 having passed through the exclusive diffractive structure intersects with the optical axis at a position different from the position of the converged light spot formed on the information recording plane of the second optical information recording medium. Independent claims are also included for: (a) an optical pickup apparatus comprising a first light source of a wavelength lambda 1; a second light source of wavelength lambda 2; a light converging optical system that converges a light flux from the first light source into an information recording plane of a first optical information recording medium through a protective substrate having a thickness t1 so that recording and/or reproducing information is conducted for the first optical information recording medium and the light converging optical system converges a light flux from the second light source into an information recording plane of a second optical information recording medium through a protective substrate having a thickness t2 so that recording and/or reproducing information is conducted from the second optical information recording medium and the light converging optical system being the light converging optical system including the magnification changing element and the objective optical element; and (b) a light converging optical system for converging a light flux having a first wavelength lambda 1 (lambda 1 = 630-680 nm) on an information recording plane of a first optical information recording medium equipped with a protective substrate having a thickness t1 and for converging a light flux having a second wavelength lambda 2 (lambda 2 = 680-760 nm) on an information recording plane of a second optical information recording medium equipped with a protective substrate having a thickness t2 (t1 is less than t2), comprising an optical element section including at least an objective optical element and having one optical element, the objective optical element having an optical magnification m1 (m1 is not 0) for a light flux having the first wavelength lambda 2, the optical element section having a common region on at least one optical surface, where a light flux of the wavelength lambda 1 passes through the common region and the light flux of the wavelength lambda 1 having passed through the common region is converged to the information recording plane and a light flux of wavelength lambda 2 passes through the common region and the light flux of the wavelength lambda 2 having passed through the common region is converged on the information recording plane of the second optical information recording medium; and a ring-shaped structure formed in the common region in which the ring-shaped structure includes ring-shaped optical functional surface having a center on the optical axis and neighboring ring-shaped optical functional surface ar joined through a stepped surface, where the length x of the stepped surfaces parallel to the optical axis satisfies x = 5.57 mu m.