Tilt angle adjustment method for objective lens and optical information recording/reproducing apparatus

An optical information recording/reproducing apparatus that emits a laser beam having a wavelength λ for a multilayer optical disc, the optical information recording reproducing apparatus comprising:

• a light source which emits the light beam having the wavelength λ;
• and
• an objective lens having a numerical aperture NA positioned at a tilt angle, the objective lens being configured to converge the light beam having the wavelength λ onto each recording surface of the multilayer optical disc having a plurality of recording layers the wavelength λ and the numerical aperture NA satisfy the following conditions:
• 390<λ<420 and
• 0.75<NA<0.90,
• a tilt adjuster that is configured to select a predetermined transparent parallel plate to satisfy a condition −0.015<t1−t2<0.005, where t1 represents a thickness of the predetermined transparent parallel flat plate and t2 represents a design protective layer thickness at which a coma caused when off-axis light is incident on the objective lens becomes smallest, t1 and t2having units of mm, to determine the tilt angle of the objective lens by examining if a spot quality of the laser beam defined through the predetermined parallel plate matches a predetermined spot quality standard, and to tilt the objective lens to the determined tilt angle based upon the examination of the spot quality of the laser beam.

An optical information recording/reproducing apparatus that utilizes a multilayer optical disc having a plurality of recording layers, the apparatus comprising:

• a light source which emits a light beam having a wavelength λ;
• an objective lens configured to converge the light beam having the wavelength λ onto each recording surface of the multilayer optical disc having a plurality of recording layers;
• and
• a tilt adjuster is configured to adjust a tilt angle of the objective lens, and the following condition is satisfied:
• −0.015<t3−t2<0.005, where t2 represents a design protective layer thickness at which a coma caused when off-axis light emitted by the light source and incident on the objective lens becomes smallest and t3 represents a protective layer thickness of the multilayer optical disc at which a coma caused when information recording or information reproducing is executed for the multilayer optical disc becomes smallest, and t2 and t3 have units of mm.