Patent ID: 8154978

Claim:
An optical pickup apparatus comprising: an objective lens having a numeric aperture, and including an incident face; and an antireflection coating formed on the incident face of the objective lens, the antireflection coating being a single layer antireflection coating comprised of magnesium fluoride, or a multi-layer antireflection coating comprising a first layer comprised of titanium dioxide (TiO 2 ) formed on a second layer comprised of silicon-oxide (SiO 2 ), wherein, as a result of the thickness of the antireflection coating: a transmittance of laser light that enters the objective lens through the incident face is set at a first predetermined transmittance value, when the numeric aperture of the objective lens is between zero and a first predetermined numeric aperture value; a transmittance of laser light that enters the objective lens through the incident face is set to correlate linearly with the numeric aperture when the numeric aperture of the objective lens is between the first predetermined numeric aperture value and a second predetermined numeric aperture value; and a transmittance of laser light that enters the objective lens through the incident face is set at a second predetermined transmittance value, when the numeric aperture of the objective lens is between the second predetermined numeric aperture value and a third predetermined numeric aperture value, or is equal to the third predetermined numeric aperture value; and wherein the first predetermined transmittance value is set to 55 percent; the first predetermined numerical aperture value is equal to 0.30; the second predetermined numerical aperture value is equal to 0.6; the second predetermined transmittance value is set to 100 percent; and the third predetermined numerical aperture value is equal to 0.85.