Optical disc apparatus

Abstract

An optical disc apparatus includes a spherical aberration correction element for correcting spherical aberration and a preadjustment unit for obtaining setting of a spherical aberration correction element for correcting spherical aberration appropriately in a case where a focus position of a light beam emitted from a light source is adjusted on each of recording layers of an optical recording medium every time when the optical recording medium is loaded to the apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram to show a structure of an optical disc apparatus according to the present invention.

FIG. 2 is a schematic diagram of an optical system of an optical pickup that is provided to the optical disc apparatus shown in FIG. 1.

FIG. 3 is a schematic cross sectional view of an optical recording medium having two recording layers.

FIGS. 4A and 4B are explanatory diagrams of a structure of a liquid crystal element that is provided to the optical disc apparatus shown in FIG. 1.

FIG. 5 is a diagram to show schematically a focus error signal that is obtained when an objective lens is driven by the actuator to move in the direction of approaching toward a two-layer disc.

FIG. 6 is a block diagram to show a structure of a preadjustment unit of a first embodiment that is provided to the optical disc apparatus according to the present invention.

FIG. 7 is a flowchart to show preadjustment performed by the preadjustment unit of the first embodiment.

FIG. 8 is a flowchart to show a procedure of detection of an S shaped curve performed by an S shaped curve detection unit.

FIGS. 9A and 9B are schematic diagrams to show a relationship between a displacement of the objective lens and a focus error signal that is generated along with the displacement as to the two-layer disc.

FIG. 10 is a flowchart to show preadjustment performed by a preadjustment unit of a second embodiment that is provided to the optical disc apparatus according to the present invention.

FIG. 11 is a flowchart to show a process flow in a case where focus jump is performed from a second layer to a first layer.

Claims

1. An optical disc apparatus comprising: an objective lens for condensing a light beam emitted from a light source onto a recording layer of an optical recording medium;a light detection unit for receiving reflection light reflected by the recording layer and for converting light information of the reflection light into an electric signal;a spherical aberration correction element disposed between the light source and the objective lens for performing correction of spherical aberration; andan actuator for moving the objective lens in the focus direction that is a direction substantially perpendicular to the recording layer, whereina focus position of the objective lens is moved by using the actuator from one recording layer to another recording layer of the optical recording medium after the spherical aberration correction element is set to a predetermined setting, anda preadjustment unit is provided for obtaining setting of the spherical aberration correction element for correcting spherical aberration appropriately in a case where the focus position is adjusted on the recording layer for each of the recording layers of the optical recording medium and for making the obtained setting be the predetermined setting every time when the optical recording medium is loaded to the apparatus.

2. The optical disc apparatus according to claim 1, wherein the preadjustment unit includes an S shaped curve detection unit that collects signal information of a focus error signal obtained by processing the electric signal while moving the objective lens in the focus direction by the actuator and detects the S shaped curve of the focus error signal based on the collected signal information, anda spherical aberration correction information obtaining unit that changes setting of the spherical aberration correction element to a plurality of settings having different aberration correction quantities after the S shaped curve is detected, measures amplitude of the S shaped curve in each case of the settings, and obtains setting of the spherical aberration correction element for correcting spherical aberration appropriately in a case where the focus position is adjusted on the recording layer for each of the recording layers of the optical recording medium from the obtained amplitude information of the S shaped curve.

3. The optical disc apparatus according to claim 2, wherein the spherical aberration correction information obtaining unit calculates an amplitude ratio of a plurality of S shaped curves in each case of the settings if the S shaped curve detection unit detects the plurality of S shaped curves, and obtains also information concerning the amplitude ratio of the S shaped curves and the setting of the spherical aberration correction element as the spherical aberration correction information, andif movement of the focus position is failed, the predetermined setting of the spherical aberration correction element is readjusted based on the amplitude ratio of the S shaped curve and the spherical aberration correction information when the failure happened.

4. The optical disc apparatus according to claim 2, wherein the preadjustment unit includes a signal gain adjustment block for adjusting a signal gain based on the amplitude value of the S shaped curve obtained by the S shaped curve detection unit.

5. The optical disc apparatus according to claim 3, wherein the preadjustment unit includes a signal gain adjustment block for adjusting a signal gain based on the amplitude value of the S shaped curve obtained by the S shaped curve detection unit.

6. The optical disc apparatus according to claim 2, wherein the S shaped curve detection unit starts time measurement at the same time as starting to collect the focus error signal, and if the collected focus error signal has a maximum value among the signals that have been collected before, time when the maximum value is collected and the maximum value are stored, and information concerning the maximum value is checked when the objective lens is moved by a predetermined distance in the focus direction and in one of the direction approaching toward the optical recording medium and the direction moving away from the optical recording medium, and if there is not the maximum value stored for longer than a predetermined time period, the information concerning the maximum value is reset, and further the objective lens is moved by a predetermined distance in the direction opposite to said one of the directions.

7. The optical disc apparatus according to claim 3, wherein the S shaped curve detection unit starts time measurement at the same time as starting to collect the focus error signal, and if the collected focus error signal has a maximum value among the signals that have been collected before, time when the maximum value is collected and the maximum value are stored, and information concerning the maximum value is checked when the objective lens is moved by a predetermined distance in the focus direction and in one of the direction approaching toward the optical recording medium and the direction moving away from the optical recording medium, and if there is not the maximum value stored for longer than a predetermined time period, the information concerning the maximum value is reset, and further the objective lens is moved by a predetermined distance in the direction opposite to said one of the directions.

8. The optical disc apparatus according to claim 4, wherein the S shaped curve detection unit starts time measurement at the same time as starting to collect the focus error signal, and if the collected focus error signal has a maximum value among the signals that have been collected before, time when the maximum value is collected and the maximum value are stored, and information concerning the maximum value is checked when the objective lens is moved by a predetermined distance in the focus direction and in one of the direction approaching toward the optical recording medium and the direction moving away from the optical recording medium, and if there is not the maximum value stored for longer than a predetermined time period, the information concerning the maximum value is reset, and further the objective lens is moved by a predetermined distance in the direction opposite to said one of the directions.