Objective lens and optical pickup device
To provide an objective lens and an optical pickup device which can thin the objective lens and a device on which the objective lens is mounted, and which can prevent that the pitch of the diffraction grating at the outer periphery of the objective lens becomes too small in the manufacturing procedure and so it becomes difficult to manufacture the Fresnel lens or which does not require a high-grade fine processing technique in order to minimize the pitch of the diffraction grating, in an objective lens which condenses a laser light emitted from a light source to irradiate on an optical disk, the outer periphery on the side surface of the objective lens in which the laser light is incident is formed by a refractive lens portion 7 a and the inner periphery thereof is formed by a Fresnel lens portion 7 b.
1. An objective lens which condenses a laser light emitted from a light source to irradiate on an optical disk,
wherein the objective lens has a side on which the laser light is incident, the side forming (a) a generally planar first surface portion which is approximately perpendicular to a direction of travel of the laser light and which is formed by a Fresnel lens and (b) a second surface portion which forms a refractive lens, the first surface being surrounded by the second surface portion.
2. The objective lens according to claim 1 , wherein a boundary between the first surface portion and the second surface portion is a position where a pitch of the Fresnel lens is almost three times as large as a wavelength of the laser light.
3. The objective lens according to claim 1 , wherein a boundary between the first surface portion and the second surface portion is a position where a pitch of the Fresnel lens is almost 1.215 nm when a numerical aperture of the objective lens is 0.85.
4. The objective lens according to claim 3 , wherein the pitch of the Fresnel lens is almost 1.215 nm corresponds to a pitch of the Fresnel lens in a range between 1.200 nm and 1.230 am.
5. An optical pickup device comprising:
a light source which emits a laser light; and
the objective lens according to claim 2 which condenses the laser light to irradiate on an optical disk.
6. An optical pickup device comprising:
a light source which emits a laser light; and
the objective lens according to claim 3 which condenses the laser light to irradiate on an optical disk.
7. An optical pickup device comprising:
a light source which emits a laser light; and
the objective lens according to claim 4 which condenses the laser light to irradiate on an optical disk.
8. The optical pickup device according to claim 6 , wherein in a case where the laser light passing through the objective lens is focused on the optical disk, with respect to an angle θ formed between a first phantom line coupling between a center potion of a region of the objective lens where the laser light passes and the focal point and a second phantom line coupling between an end portion of the region of the objective lens where the laser light passes and the focal point, a numerical aperture of the objective lens of 0.85 corresponds to sin θ equal to 0.85.
9. An optical disk drive apparatus comprising the optical pickup device according to claim 5 .
10. An optical disk drive apparatus comprising the optical pickup device according to claim 6 .
11. An optical disk drive apparatus comprising the optical pickup device according to claim 7 .
12. An optical disk drive apparatus comprising the optical pickup device according to claim 8 .
13. The objective lens according to claim 1 , wherein the second surface portion is a generally hemispherical portion and the first surface portion includes a grating portion, tip portions of the grating portion and the hemispherical portion being positioned substantially within a common phantom plane.