System for enhanced astigmatic focus signal detection

1. An auto-focus system of an optical access unit for reading and writing data from and to a first information layer and a second information layer of an optical storage medium, the system comprising:

an astigmatic lens which creates a first set of line images and a second set of line images, wherein the first set of line images comprises at least one line image for refracting light rays from the first information layer, and wherein the second set of line images comprises at least one line image for refracting light rays from the second information layer, and

a confocal aperture placed at a first focal line image from the first set of line images created by the astigmatic lens, wherein the confocal aperture blocks the light rays reflected from the second information layer but not the light rays reflected from the first information layer when accessing the first information layer, and wherein the confocal aperture blocks the light rays reflected from the first information layer but not the light rays reflected from the second information layer when accessing the second information layer.

2. The auto-focus system of claim 1 , wherein the confocal aperture is bow-tie shaped.

3. The auto-focus system of claim 1 , further comprising a quadrant photodiode array placed generally in the circle of least confusion for the light rays refracted through the astigmatic lens.

4. The auto-focus system of claim 3 , further comprising:

a servo assembly connected to an access head of the optical access unit, for moving the access head to a proper position;

wherein the servo assembly is electrically connected to the quadrant photodiode array.

5. The auto-focus system of claim 1 , wherein the optical access unit comprises an objective lens,

wherein the astigmatic lens is placed in a return beam from the objective lens, and

wherein the objective lens is focused on the first information layer or the second information layer of the optical storage medium.

6. The auto-focus system of claim 1 , wherein the optical access unit is a finite conjugate system.

7. An auto-focus system of an optical access unit for reading and writing data from and to a plurality of information layers of an optical storage medium having data stored on at least a first information layer, a second information layer, and a third information layer, the system comprising:

an astigmatic lens which creates a first focal line image and a second focal line image for refracting light rays reflected from an addressed layer, wherein one of the information layers is the addressed layer and the remaining information layers are the non-addressed layers; and

a confocal aperture placed at the first focal line image created by the astigmatic lens, wherein the confocal aperture passes the light rays reflected from the addressed layer, and blocks generally the light rays reflected from the non-addressed layers.

8. The auto-focus system of claim 7 , wherein the confocal aperture is bow-tie shaped.

9. The auto-focus system of claim 7 , further comprising a quadrant photodiode array placed generally in the circle of least confusion for the light rays refracted through the astigmatic lens.

10. The auto-focus system of claim 9 , further comprising:

a servo assembly connected to an access head of the optical access unit, for moving the access head to a proper position;

wherein the servo assembly is electrically connected to the quadrant photodiode array.

11. The auto-focus system of claim 7 , wherein the optical access unit comprises an objective lens,

wherein the astigmatic lens is placed in a return beam from the objective lens, and

wherein the objective lens is focused on the first information layer of the optical storage medium.

12. The auto-focus system of claim 7 , wherein the optical access unit is a finite conjugate system.

13. An auto-focus system of an optical access unit for reading or writing data on a plurality of information layers of an optical storage medium, comprising:

an astigmatic lens which creates a plurality of focal line images for refracting light rays reflected from an addressed layer from one of the plurality of information layers of the optical storage medium; and

a confocal aperture placed at the one of the plurality of focal line images created by the astigmatic lens, wherein the confocal aperture passes the light rays reflected from the addressed information layer, and wherein the confocal aperture blocks generally the light rays reflected from the non-addressed information layers.

14. The auto-focus system of claim 13 , wherein the confocal aperture is bow-tie shaped.

15. The auto-focus system of claim 13 , further comprising a quadrant photodiode array placed generally in the circle of least confusion for the light rays refracted through the astigmatic lens.

16. The auto-focus system of claim 15 , further comprising:

a servo assembly connected to an access head of the optical access unit, for moving the access head to a proper position;

wherein the servo assembly is electrically connected to the quadrant photodiode array.

17. The auto-focus system of claim 13 , wherein the optical access unit comprises an objective lens,

wherein the astigmatic lens is placed in a return beam from the objective lens, and

wherein the objective lens is focused on the corresponding information layer of the optical storage medium.

18. The auto-focus system of claim 13 , wherein the optical access unit is a finite conjugate system.