APPARATUS FOR OPTICALLY RECORDING AND REPRODUCING INFORMATION

Abstract

An apparatus for optically reproducing and recording information includes a light source, an objective lens, a light detecting element, and a processor. The objective lens focuses light beams emitted from the light source on an optical recording medium having tracks disposed at a track pitch. The wavelength of the light beams is greater than the track pitch of the medium. The light detecting element receives light beams reflected from the medium. The light detecting element includes a first region that receives substantially only light beams generated by interference between zeroth-order diffracted beams and first-order diffracted beams among the light beams reflected from the tracks of the medium and a second region that receives substantially only the zeroth-order diffracted beams. The processor generates focusing error signals using astigmatic focusing error detection on the basis of an output from the second region of the light detecting element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic top and side views of an optical system according to a first exemplary embodiment of the present invention.

FIG. 2 is a schematic view illustrating diffraction by pregrooves according to the first exemplary embodiment of the present invention.

FIG. 3 is a schematic view of an intensity distribution on a surface of a pupil of an objective lens according to the first exemplary embodiment of the present invention.

FIG. 4 is a schematic view of a photodiode for generating RF signals and servo control signals according to the first exemplary embodiment of the present invention and a spot of light on the photodiode.

FIG. 5 illustrates relationships between disk shifts in a light axis direction and focusing errors at the moment according to the present invention and a known technology.

FIGS. 6A and 6B illustrate the relationships between the disk shifts in the light axis direction and the focusing errors at the moment according to the present invention and the known technology.

FIGS. 7A and 7B are schematic top and side views of an optical system according to a second exemplary embodiment of the present invention.

FIG. 8 is a schematic view of a diffractive element according to the second exemplary embodiment of the present invention.

FIGS. 9A and 9B are schematic views of light detecting portions according to the second exemplary embodiment of the present invention.

FIG. 10 is a schematic view of a light detecting element according to the known technology and a spot on the light detecting element.

Claims

1. An apparatus for optically reproducing and recording information comprising: a light source;an objective lens that focuses light beams emitted from the light source on an optical recording medium having tracks disposed at a track pitch, wherein the wavelength of the light beams emitted from the light source is greater than the track pitch of the optical recording medium;a light detecting element that receives light beams reflected from the optical recording medium, wherein the light detecting element includes a first region that receives substantially only light beams generated by interference between zeroth-order diffracted beams and first-order diffracted beams among the light beams reflected from the tracks of the optical recording medium and a second region that receives substantially only the zeroth-order diffracted beams; anda processor that generates focusing error signals using astigmatic focusing error detection on the basis of an output from the second region of the light detecting element.

2. An apparatus according to claim 1, wherein the light detecting element includes six sections, with the first region including two sections and the second region including four sections.

3. An apparatus according to claim 1, wherein the area of the first region is less than the area of the second region of the light detecting element.

4. An apparatus according to claim 1, wherein at least a portion of the first region is disposed closer than the second region to a center of the light detecting element.

5. An apparatus for optically reproducing and recording information comprising: a light source;an objective lens that focuses light beams emitted from the light source on an optical recording medium having tracks disposed at a track pitch, wherein the wavelength of the light beams emitted from the light source is greater than the track pitch of the optical recording medium;a wavefront splitting element that splits light beams reflected from the optical recording medium, wherein the wavefront splitting element includes a first region that receives mainly light beams generated by interference between zeroth-order diffracted beams and first-order diffracted beams among the light beams reflected from the tracks of the optical recording medium and a second region that receives substantially only the zeroth-order diffracted beams;a light detecting element that receives light beams passing through the wavefront splitting element; anda processor that generates focusing error signals using astigmatic focusing error detection on the basis of an output from the light detecting element that receives the light beams passing through the second region of the wavefront splitting element.

6. An apparatus according to claim 5, wherein the first region of the wavefront splitting element includes a diffraction grating.

7. An apparatus according to claim 5, wherein the first region of the wavefront splitting element includes two sections.

8. An apparatus according to claim 5, wherein at least a portion of the first region is disposed closer than the second region to a center of the wavefront splitting element.

9. An apparatus for optically reproducing and recording information comprising: a light source;focusing means for focusing light beams emitted from the light source on an optical recording medium having tracks disposed at a track pitch, wherein the wavelength of the light beams emitted from the light source is greater than the track pitch of the optical recording medium;receiving means for receiving light beams reflected from the optical recording medium, wherein the receiving means includes a first region for receiving substantially only light beams generated by interference between zeroth-order diffracted beams and first-order diffracted beams among the light beams reflected from the tracks of the optical recording medium and a second region for receiving substantially only the zeroth-order diffracted beams; andgenerating means for generating focusing error signals using astigmatic focusing error detection on the basis of an output from the second region of said receiving means.

10. An apparatus according to claim 9, wherein the receiving means comprises a light detecting element.

11. An apparatus according to claim 9, wherein the receiving means comprises a light detecting element and a wavefront splitting element.