PICKUP APPARATUS FOR MULTI-LAYER OPTICAL DISC

Abstract

An optical pickup apparatus comprises an orbicular zone forming lens group 14 for forming the section of the laser beam, which is irradiated to an optical disc DK having plural recording layers, into an annular shape, a condenser lens 35 that converges the reflected beam from the optical disc DK, and a pinhole plate 36 having formed thereto a pinhole 36a with a size corresponding to a flux diameter of the reflected beam converged by the condenser lens 35. The orbicular zone forming lens group 14 refracts the laser beam irradiated to the optical disc DK so as to form the section of the laser beam into an annular shape in order that the internal diameter of the annular converged flux formed on the pinhole plate 36a by the reflected beam from the recording layers other than the recording layer having an optical spot formed thereon becomes greater than the diameter of the pinhole 36a.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiment when considered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing an overall of an optical pickup apparatus according to one embodiment of the present invention;

FIG. 2 is a perspective view of an orbicular zone forming lens group used in the optical pickup apparatus shown in FIG. 1;

FIGS. 3A and 3B are explanatory views showing the converged state of the reflected beam from the recording layer other than the recording layer having an optical spot formed thereon, in view of the relation with a pinhole plate;

FIG. 4 is an explanatory view for explaining the shape of the laser beam irradiated on each of the recording layers of the multi-layer optical disc;

FIGS. 5A and 5B are explanatory views showing the state in which the reflected beam from the recording layer having the optical spot formed thereon and the reflected beam from the other recording layer pass through the pinhole plate or is shielded;

FIG. 6A is a sectional view of a Fresnel axicon;

FIG. 6B is a sectional view of a holographic axicon; and

FIG. 7 is an explanatory view in which an internal diameter adjusting prism is arranged in an orbicular zone forming lens group according to a modified example of the present invention.

Claims

1. An optical pickup apparatus comprising: a laser source that emits laser beam to a multi-layer optical disc having plural recording layers;a photodetector that receives the laser beam reflected by the multi-layer optical disc and outputs an electrical signal according to the received amount of beam;a collimator lens that converts the laser beam incident thereto from the laser source into parallel beam;a beam splitter that transmits or reflects the laser beam, which is converted into parallel beam by the collimator lens, to be led to the multi-layer optical disc, and transmits or reflects the laser beam reflected by the multi-layer optical disc to be led to the photodetector;an objective lens that converges the laser beam, which is led to the multi-layer optical disc by the beam splitter, so as to form an optical spot on one of the plural recording layers;a condenser lens that converges the laser beam from the multi-layer optical disc led by the beam splitter in the vicinity of the photodetector;orbicular zone forming optical means that is arranged between the collimator lens and the beam splitter, or between the beam splitter and the condenser lens, for forming the section of the laser beam into an annular shape by refracting the laser beam converted into the parallel beam by the collimator lens; anda pinhole plate having formed thereto a pinhole that transmits the laser beam reflected from the one recording layer and converged by the condenser lens,wherein the laser beam, that is reflected from a recording layer other than the one recording layer, forms an annular converged flux at the periphery of the pinhole of the pinhole plate.

2. An optical pickup apparatus according to claim 1, wherein the internal diameter of the annular converged flux formed at the periphery of the pinhole of the pinhole plate is greater than the diameter of the pinhole.

3. An optical pickup apparatus according to claim 1, wherein the orbicular zone forming optical means includes:

4. An optical pickup apparatus according to claim 3, further comprising: internal-diameter adjusting means for changing the internal diameter of the annular laser beam formed by the orbicular zone forming optical means.

5. An optical pickup apparatus according to claim 4, wherein the internal-diameter adjusting means changes the internal diameter of the annular laser beam formed by the orbicular zone forming optical means by changing the relative distance between the first optical device and the second optical device.

6. An optical pickup apparatus according to claim 4, wherein the internal-diameter adjusting means changes the internal diameter of the annular laser beam formed by the orbicular zone forming optical means by refracting the annular divergent beam converted by the first optical device to be led to the second optical device.

7. An optical pickup apparatus according to claim 1, wherein the internal diameter φS of the laser beam that is annularly formed by the orbicular zone forming optical means is defined by the equation of φS≧fC×φP/L, wherein the focal distance of the condenser lens is fC, the diameter of the pinhole is φP, and the distance from the convergent point, where the laser beam reflected by the other recording layers is converged by the condenser lens, to the pinhole is L.

8. An optical pickup apparatus according to claim 7, wherein the diameter φP of the pinhole is defined by the equation of φP≧K×λ/(φC/(2×fC)), wherein the coefficient set by the distribution of light intensity of the laser beam emitted from the laser source is K, the wavelength of the laser beam emitted from the laser source is λ, and the diameter of the flux of the laser beam incident on the condenser lens from the multi-layer optical disc is φC.

9. An optical pickup apparatus according to claim 1, wherein the internal diameter φS of the laser beam that is annularly formed by the orbicular zone forming optical means is defined by the equation of φS≧fC×φP/L+φP, wherein the focal distance of the condenser lens is fC, the diameter of the pinhole is φP, and the distance from the convergent point, where the laser beam reflected by the other recording layers is converged by the condenser lens, to the pinhole is L.

10. An optical pickup apparatus according to claim 9, wherein the diameter φP of the pinhole is defined by the equation of φP≧K×λ/(φC/(2×fC)), wherein the coefficient set by the distribution of light intensity of the laser beam emitted from the laser source is K, the wavelength of the laser beam emitted from the laser source is λ, and the diameter of the flux of the laser beam incident on the condenser lens from the multi-layer optical disc is φC.

11. An optical pickup apparatus according to claim 1, wherein the internal diameter φS of the laser beam that is annularly formed by the orbicular zone forming optical means is defined by the equation of φS≧fC×φP×2/L, wherein the focal distance of the condenser lens is fC, the diameter of the pinhole is φP, and the distance from the convergent point, where the laser beam reflected by the other recording layers is converged by the condenser lens, to the pinhole is L.

12. An optical pickup apparatus according to claim 11, wherein the diameter φP of the pinhole is defined by the equation of φP≧K×λ/(φC/(2×fC)), wherein the coefficient set by the distribution of light intensity of the laser beam emitted from the laser source is K, the wavelength of the laser beam emitted from the laser source is λ, and the diameter of the flux of the laser beam incident on the condenser lens from the multi-layer optical disc is φC.

13. An optical pickup apparatus according to claim 1, wherein the internal diameter φS of the laser beam that is annularly formed by the orbicular zone forming optical means is defined by the equation of φS≧fC×φP×2/L+φP, wherein the focal distance of the condenser lens is fC, the diameter of the pinhole is φP, and the distance from the convergent point, where the laser beam reflected by the other recording layers is converged by the condenser lens, to the pinhole is L.

14. An optical pickup apparatus according to claim 13, wherein the diameter φP of the pinhole is defined by the equation of φP≧K×λ/(φC/(2×fC)), wherein the coefficient set by the distribution of light intensity of the laser beam emitted from the laser source is K, the wavelength of the laser beam emitted from the laser source is λ, and the diameter of the flux of the laser beam incident on the condenser lens from the multi-layer optical disc is φC.

15. An optical pickup apparatus according to claim 1, wherein the objective lens is tracking-servo-controlled in the diameter direction of the multi-layer optical disc by tracking servo control means that causes the optical spot to follow the track of the multi-layer optical disc, and focus-servo-controlled in the optical axial direction of the laser beam by focus servo control means that makes the optical spot to follow each recording layer of the multi-layer optical disc, and