US 7,680,014 B2Granted

Objective optical system and optical pickup device using it

AssigneeFujinon Corporation

InventorsTetsuya Ori, Yu Kitahara, Masao Mori, Toshiaki Katsuma

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Abstract

An objective optical system is formed of a diffractive optical element with a diffractive surface formed on a virtual plane and an objective lens for focusing three collimated light beams of three different wavelengths at three different numerical apertures onto desired positions of three different recording media with substrates that include different thicknesses, such as an AOD, a DVD, and a CD, that introduce different amounts of spherical aberration in the focused beams. The objective optical system provides compensating spherical aberration to the three light beams by varying the distance between the diffractive optical element and the objective lens with the recording medium being used. The objective optical system focuses second-order diffracted light of one wavelength and first-order diffracted light of the other two wavelengths. An optical pickup device includes the objective optical system, the recording media, and a light source that provides the three light beams.

Claims33

Dependent claims

An objective optical system for focusing light from a light source onto optical recording media, the objective optical system comprising, in order from the light source side along an optical axis:

a diffractive optical element having negative refractive power and a diffractive surface on one side;
and
an objective lens having positive refractive power and a rotationally symmetric aspheric surface on each side;
wherein
the distance along the optical axis between the diffractive optical element and the objective lens is variable;
the objective optical system is configured to receive a collimated light beam of a first wavelength λ1 on its light source side and focus second-order diffracted light diffracted by the diffractive surface of the diffractive optical element at a first numerical aperture NA1 onto a desired portion of a first optical recording medium having a substrate thickness T1 when the distance along the optical axis between the diffractive optical element and the objective lens is d1, to receive a collimated light beam of a second wavelength λ2 on its light source side and focus first-order diffracted light diffracted by the diffractive surface of the diffractive optical element at a second numerical aperture NA2 onto a desired portion of a second optical recording medium having a substrate thickness T2 when the distance along the optical axis between the diffractive optical element and the objective lens is d2, and to receive a collimated light beam of a third wavelength λ3 on its light source side and focus first-order diffracted light diffracted by the diffractive surface of the diffractive optical element at a third numerical aperture NA3 onto a desired portion of a third optical recording medium having a substrate thickness T3 when the distance along the optical axis between the diffractive optical element and the objective lens is d3;
and
the following conditions are satisfied:
λ1<λ2<λ3
NA1≧NA2≧NA3
T1≦T2<T3
d1<d3
d2<d3.

10 more elements

An objective optical system for focusing light from a light source onto optical recording media, the objective optical system comprising, in order from the light source side along an optical axis:

a diffractive optical element having a diffractive surface on one side;
and
an objective lens having positive refractive power;
wherein
the distance along the optical axis between the diffractive optical element and the objective lens is variable;
the objective optical system is configured to receive a collimated light beam of a first wavelength λ1 on its light source side and focus diffracted light diffracted by the diffractive surface of the diffractive optical element at a first numerical aperture NA1 onto a desired portion of a first optical recording medium having a substrate thickness T1 when the distance along the optical axis between the diffractive optical element and the objective lens is d1, to receive a collimated light beam of a second wavelength λ2 on its light source side and focus diffracted light diffracted by the diffractive surface of the diffractive optical element at a second numerical aperture NA2 onto a desired portion of a second optical recording medium having a substrate thickness T2 when the distance along the optical axis between the diffractive optical element and the objective lens is d2, and to receive a collimated light beam of a third wavelength λ3 on its light source side and focus diffracted light diffracted by the diffractive surface of the diffractive optical element at a third numerical aperture NA3 onto a desired portion of a third optical recording medium having a substrate thickness T3 when the distance along the optical axis between the diffractive optical element and the objective lens is d3;
the distances d1, d2, and d3 are not all equal;
and
the following conditions are satisfied:
λ1<λ2<λ3
NA1≧NA2>NA3
T1≦T2<T3.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application: 10/972,670Filed 26 Oct 2004
Priority: JP 2003-36548227 Oct 2003
Published: US 2005/0117496 A12 Jun 2005
Granted: 16 Mar 2010
Term ends: Not estimatedThe source records don’t support an estimate.

Classification8 codes

G11B 7/1378
Lenses: separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
G11B 7/1275
Lasers; Multiple laser arrays: two or more lasers having different wavelengths
G11B 7/1353
Means for guiding the beam from the source to the record carrier or from the record carrier to the detector: diffractive elements, e.g. holograms…
G11B 7/1374
Lenses: objective lenses