Objective lens for an optical pickup apparatus

Abstract

An objective lens for use in an optical pickup apparatus, comprises an objective lens satisfying the following expression: 0.01≦|δSA3obj/δλ|<0.1 (λrms/nm), where δSA3obj/δλ represents the wavelength dependency of the 3rd order spherical aberration of the objective lens when the oscillation wavelength is fluctuated between ±2 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing the structure of the optical pickup apparatus of the present embodiment by which the recording/reproducing of the information can be adequately conducted on HD, DVD and CD which are different optical information recording media (called also optical disk).

FIG. 2 is a perspective view of the molded objective lens OBJ.

FIG. 3 is a flowchart showing the manufacturing method of the optical pickup apparatus according to the present embodiment.

FIGS. 4( a)-4(d) are sectional views typically showing several examples of the optical path difference providing structure provided in objective optical element OBJ according to the present invention.

Claims

1. An objective lens for use in an optical pickup apparatus, comprising: an objective lens satisfying the following expression: 0.01≦|δSA3obj/δλ|<0.1(λrms/nm)where δSA3obj/δλ, represents the wavelength dependency of the 3rd order spherical aberration of the objective lens when an oscillation wavelength is fluctuated between ±2 nm from a reference wavelength of 500 nm or less.

2. The objective lens described in claim 1, wherein the objective lens satisfies the following expression. 0.02≦|δSA3obj/δλ|0.1(λrms/nm)

3. The objective lens described in claim 1, wherein the objective lens satisfies the following expression for a specific oscillation wavelength of 500 nm or less: |SA3obj|≦0.030(λrms)where SA3obj represents the 3rd order spherical aberration of the objective lens for the specific oscillation wavelength.

4. The objective lens described in claim 1, wherein the objective lens satisfies the following expression: |δSA3obj/δT|≦0.002(λrms/° C.)where |δSA3obj/δT| represents the temperature dependency of the 3rd order spherical aberration of the objective lens when an wavelength fluctuation for a temperature change in an oscillation wavelength of 500 nm or less is made +0.05 nm/° C.

5. The objective lens described in claim 1, wherein the objective lens is made of a plastic and includes an optical path difference providing structure on at least one surface thereof.

6. The objective lens described in claim 1, wherein the objective lens is used in an optical pickup apparatus using a light source having an oscillation wavelength of 500 nm or less.

7. The objective lens described in claim 6, wherein the optical pickup apparatus comprises a first light source having an oscillation wavelength λ1 of 500 nm or less and a second light source having an oscillation wavelength λ2 (λ1<λ2), and the objective lens converges a light flux from the first light source through a protective substrate having a thickness t1 onto an information recording surface of a first information recording medium so as to conduct recording and/or reproducing information and converges a light flux from the second light source through a protective substrate having a thickness t2 (t1≦t2) onto an information recording surface of a second information recording medium so as to conduct recording and/or reproducing information, and wherein the objective lens is made of a plastic and includes a diffractive structure on at least one surface thereof in which a diffraction order having a maximum diffraction efficiency is different between a case that a light flux from the first light source passes through and a case that a light flux from the second light source passes through.

8. The objective lens described in claim 6, wherein the objective lens is used such that only a light flux from a light source having an oscillation wavelength of 500 nm or less enters into the objective lens.

9. The objective lens described in claim 1, wherein an image side maximum numerical aperture is 0.8 or more.

10. The objective lens described in claim 1, wherein the objective lens is structured with a single lens.

11. An optical pickup apparatus, comprising: a light source having an oscillation wavelength of 500 nm or less; andthe objective lens described in claim 1.