Object lens device with high numerical aperture and optical pickup device adopting the same

An optical pickup device to record and/or reproduce information to and/or from a recording medium, the optical pickup device comprising:

• a light source to emit light;
• an optical path changing member arranged between the light source and the recording medium which changes a proceeding path of the light;
• an object lens arranged between the optical path changing member and the recording medium to focus the emitted light onto the recording medium, the object lens comprising:
• a first surface that is an incident surface on which the light is incident,
• a second surface from which the light exits to be focused on the recording medium, and
• a diffractive optical element disposed on at least one of the first and second surfaces and having a refractivity satisfying fD/f<5 and a numerical aperture of 0.75 or greater, fD being a focal distance of the diffractive optical element and f being a focal distance of the object lens;
• and
• a photodetector to receive the light after the light is reflected by the recording medium and passes through the object lens and the optical path changing member, and to detect an information signal and an error signal from the received light.