Optical disc apparatus, optical pickup apparatus, and method for reducing astigmatism

An optical disc apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.94≦β≦1.06;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism;
• and
• means for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

An optical pickup apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.97≦β≦1.03;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism, the optical disc having a protective layer with a thickness error range of 12.5 μm, the objective lens having a numerical aperture NA of 0.85;
• and
• means for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

An optical pickup apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.94≦β≦1.06;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism;
• and means for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

A method for reducing astigmatism, comprising the steps of:

• emitting a laser beam from a light source;
• causing the emitted light beam to pass through a collimator lens and be incident on a upward directing prism having a beam-shaping magnification β in the range of 0.97<β<1.03;
• and
• changing an angle of divergence or convergence of the laser beam and condensing the laser beam on an optical disc via the upward directing prism and an objective lens, the optical disc having a protective layer with a thickness error range of 12.5 μm, the objective lens having a numerical aperture NA of 0.85.

A method for reducing astigmatism, comprising the steps of:

• emitting a laser beam from a light source;
• causing the emitted light beam to pass through a collimator lens and be incident on a upward directing prism having a beam-shaping magnification β in the range of 0.94≦β≦1.06;
• and
• changing an angle of divergence or convergence of the laser beam and condensing the laser beam on an optical disc via the upward directing prism and an objective lens.

An optical disc apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.97<β<1.03;
• an objective lens that condenses the laser beam on an optical disc having a protective layer with a thickness error range of 12.5 μm after the direction of the optical axis is changed by the upward directing prism, the objective lens having a numerical aperture NA of 0.85;
• and
• a unit for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

An optical disc apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.94≦β≦1.06;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism;
• and
• a unit for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

An optical pickup apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.97<β<1.03;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism, the optical disc having a protective layer with a thickness error range of 12.5 μm, the objective lens having a numerical aperture NA of 0.85;
• and
• a unit for changing an angle of divergence or convergence of the laser beam incident on the objective lens.

An optical pickup apparatus comprising:

• a light source that emits a laser beam;
• a collimator lens arranged on an optical axis of the emitted laser beam;
• a upward directing prism that changes the direction of the optical axis of the laser beam output from the collimator lens by approximately 90°, the upward directing prism having a beam-shaping magnification β in the range of 0.94≦β≦1.06;
• an objective lens that condenses the laser beam on an optical disc after the direction of the optical axis is changed by the upward directing prism;
• and
• a unit for changing an angle of divergence or convergence of the laser beam incident on the objective lens.