Compatible optical pickup device using a single light source

A compatible optical pickup device to receive first and second optical disks having different thicknesses, comprising:

• a light source to emit a light having a wavelength longer than 650 nm;
• an objective lens having a near axis area, a ring type annular lens area, and a far axis area with respect to an apex, said objective lens being arranged:
• to focus the light emitted from said light source to form a first light spot when the first optical disk, which is relatively thin, is received, and a second light spot when the second optical disk, which is relatively thick, is received, and
• the first light spot having an FWHM (full width at half maximum) less than or equal to 0.72 μm with respect to the first optical disk, and the second light spot having an FWHM greater than or equal to 0.8 μm with respect to the second optical disk;
• an optical path changer arranged on an optical path between said light source and said objective lens, to selectively change a proceeding path of incident light;
• and
• a photo-detector arranged to receive light reflected by the received one of the first and second optical disks and having passed through said objective lens and said optical path changer, and to detect an information signal and/or an error signal.