Objective lens, optical pickup apparatus and recording and/or reproducing apparatus

An objective lens for recording and/or reproducing information of an optical information recording medium for use in an optical pickup apparatus comprising a light source having a wavelength of 500 nm or less, the objective lens comprising:

• a first lens group having a positive refractive power;
• and
• a second lens group having a positive refractive power, wherein the first and second lens groups are arranged in this order from a light source side of the objective lens;
• and
• wherein the following formula is satisfied:
• NA>0.85
• where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium, and wherein the following formula is satisfied:
• DIN<4.5 mm
• where DIN is an effective diameter of a light flux incident surface of the first lens group, and
• wherein the following formula are satisfied:
• in the case that 0.85<NA<0.90,
• 0.020<WD/DIN<0.150,
• and
• in the case that NA≧0.90,
• 0.015<WD/DIN<0.120,
• where WD is a working distance (mm) of the objective lens.

An objective lens for recording and/or reproducing information of an optical information recording medium, comprising:

• a first lens group having a positive refractive power;
• a second lens group having a positive refractive power, wherein the first and second lens groups are arranged in this order from a light source side of the objective lens;
• and
• a ring-shaped diffractive structure on at least one surface of the objective lens;
• wherein the following formula is satisfied:
• NA>0.85
• where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium, and wherein the following formula is satisfied:
• DIN<4.5 mm
• where DIN is an effective diameter of a light flux incident surface of the first lens group, and
• wherein the following formula are satisfied:
• in the case that 0.85<NA<0.90,
• 0.020<WD/DIN<0.150,
• and
• in the case that NA≧0.90,
• 0.015<WD/DIN<0.120,
• where WD is a working distance (mm) of the objective lens.

An objective lens for recording and/or reproducing information of an optical information recording medium, comprising:

• a first lens group having a positive refractive power;
• and
• a second lens group having a positive refractive power, wherein the first and second lens groups are arranged in this order from a light source side of the objective lens and at least one of the first and second lens groups is a hybrid lens including a glass lens having a refractive action and an optical element in which one surface of the optical element is cemented to the glass lens and the other surface of the optical element is an optical surface made of a plastic material;
• and
• wherein the following formula is satisfied:
• NA>0.85
• where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium.

An objective lens for recording and/or reproducing information of an optical information recording medium, comprising:

• a first lens group having a positive refractive power;
• and
• a second lens group having a positive refractive power, wherein the first and second lens groups are arranged in this order from a light source side of the objective lens, one of the first and second lens groups is a glass lens and the other one of the first and second lens groups is a plastic lens;
• and
• wherein the following formula is satisfied:
• NA>0.85
• where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium, and wherein the following formula is satisfied:
• ρG>ρP,
• where ρG is a specific a gravity of the glass lens and ρG is a specific gravity of the plastic lens,
• wherein a lens group having a larger volume among the first and second lens groups is the plastic lens and the following formula is satisfied:
• nG>nP,
• where nG is a refractive index of d-line of the glass lens and nP is a refractive index of d-line of the plastic lens, and
• wherein a lens group having a larger angle in angle formed between an optical axis and a normal to a surface at a position where a marginal ray passes on a surface positioned most closely to the light source is the glass lens among the first and second lens groups.

An objective lens for recording and/or reproducing information of an optical information recording medium, comprising:

• a first lens group having a positive refractive power;
• and
• a second lens group having a positive refractive power, wherein the first and second lens groups are arranged in this order from a light source side of the objective lens;
• and
• wherein at least one the first and second lens groups is a high refractive index lens made of a material having a refractive index of d-line of 1.8 or more and the following formula is satisfied:
• NA>0.85
• where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium.