Optical pickup apparatus

Abstract

The present invention provides an optical pickup apparatus including: a first light source; a second light source; and a light-converging optical system including a coupling lens and an objective lens. The coupling lens includes a first diffractive structure. The optical pickup apparatus satisfies a predetermined condition according to the chromatic aberration, focal length, and dispersion of the material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements numbered alike in several Figures, in which:

FIG. 1 illustrates a schematic diagram of an optical pickup apparatus PU1 of an embodiment of the present invention, which is capable of appropriately recording/reproducing information for different optical information recording media (they will be called optical discs), which are HD, DVD and CD;

FIGS. 2( a) and 2(b) illustrate cross sectional views of diffractive structures;

FIGS. 3( a) and 3(b) illustrate cross sectional views of diffractive structures;

FIGS. 4( a) and 4(b) illustrate cross sectional views of diffractive structures; and

FIGS. 5( a) and 4(b) illustrate cross sectional views of diffractive structures.

Claims

1. An optical pickup apparatus comprising: a first light source for emitting a first light flux with a wavelength λ1 (nm);a second light source for emitting a second light flux with a wavelength λ2 (nm) satisfying λ1<λ2; anda light-converging optical system comprising a coupling lens and an objective lens,the light-converging optical system being adopted to converge the first light flux onto an information recording surface of a first optical information recording medium through a protective layer with a thickness t1 so that information can be recorded and/or reproduced for the first optical information recording medium, and adopted to converge the second light flux onto an information recording surface of a second optical information recording medium through a protective layer with a thickness t2 (t1≦t2) so that information can be recorded and/or reproduced for the second optical information recording medium,wherein the coupling lens comprises a first diffractive structure arranged on an area on the coupling lens where the first light flux and the second light flux respectively used for recording or reproducing information on the first information recording medium and the second optical information recording medium, pass through, andthe first diffractive structure includes a plurality of ring-shaped zones which are concentrically arranged around the optical axis and which have steps extending along the optical axis, andwherein the optical pickup apparatus satisfies following expressions: −4.0×10−8 (nm−1·μm−1)≦(ΔfBOBL/fOBL2)+(ΔfBCPL/fCPL2)≦−1.5×10−8 (nm−1·μm−1),5.2×10−8 (nm−1·μm−1)≦ΔfBOBL/fOBL2≦1.0×10−7 (nm−1·μm−1),50≦νdOBL≦65, and50≦νdCPL≦65,where ΔfBOBL is a chromatic aberration (μm/nm) of the objective lens for a light flux with the wavelength λ1,fOBL is a focal length (μm) of the objective lens for a light flux with the wavelength λ1,ΔfBCPL is a chromatic aberration (μm/nm) of the coupling lens for a light flux with the wavelength λ1,fCPL is a focal length (μm) of the coupling lens for the first light flux,νdOBL is a dispersion of the material of the coupling lens for line d, andνdCPL is a dispersion of the material of the coupling lens for line d.

2. The optical pickup apparatus of claim 1, wherein the plurality of ring-shaped zones of the first diffractive structure have the steps with an average step-amount dCPL (μm) satisfying a following expression: λ1×2/(n1−1)×0.95≦dCPL≦λ1×2/(n1−1)×1.3,where n1 is a refractive index of a material forming the first diffractive structure for a light flux with the wavelength λ1.

3. The optical pickup apparatus of claim 1, further comprising: a third light source for emitting a third light flux with a wavelength λ3 (nm) satisfying λ2<λ3,wherein the light-converging optical system is further adopted to converge the third light flux onto an information recording surface of a third optical information recording medium through a protective layer with a thickness t3 (t2<t3) so that information can be recorded and/or reproduced for the third optical information recording medium, andwherein the objective lens comprises a second diffractive structure arranged on an area on the objective lens where the first light flux, the second light flux, and the third light flux respectively used for recording or reproducing information on the first information recording medium, the second optical information recording medium, and the third optical information recording medium, pass through, andthe second diffractive structure includes a plurality of ring-shaped zones which are concentrically arranged around the optical axis and have steps extending along the optical axis, andthe plurality of ring-shaped zones of the second diffractive structure have the steps with an average step-amount dOBL (μm) satisfying a following expression: λ1×2/(n2−1)×0.95≦dOBL≦λ1×2/(n2−1)×1.3where n2 is a refractive index of a material forming the second diffractive structure for a light flux with the wavelength λ1.

4. The optical pickup apparatus of claim 1, wherein the optical pickup apparatus satisfies a following expression andthe coupling lens comprises at least one optical element whose position on the optical axis differs between when information is recorded and/or reproduced for the first optical information recording medium and when information is recorded and/or reproduced for the second information recording medium: 0 (mm)≦|L1−L2|≦0.5 (mm),where L1 (mm) is an optical path length from the first light source to a surface of the first optical information recording medium, which faces the first light source, andL2 (mm) is an optical path length from the second light source to a surface of the second optical information recording medium, which faces the second light source.

5. The optical pickup apparatus of claim 1, wherein the objective lens is a single lens satisfying a following expression: 1.8 (mm)≦fOBL≦3.5 (mm).

6. The optical pickup apparatus of claim 1, wherein the coupling lens comprises two optical elements.