Converging optical element and optical pickup apparatus

An optical pickup apparatus for information recording and/or reproducing comprising:

• a first light source for emitting a first light flux with a wavelength λ1 (nm) for recording and/or reproducing information on a first optical disc having a protective substrate with a thickness t1 (mm);
• a second light source for emitting a second light flux with a wavelength λ2 (nm) for recording and/or reproducing information on a second optical disc having a protective substrate with a thickness t2 (mm);
• a third light source for emitting a third light flux with a wavelength λ3 (nm) for recording and/or reproducing information on a third optical disc having a protective substrate with a thickness t3 (mm);
• and
• a converging optical element having a phase structure arranged on at least one surface of the converging optical element, for converging the first light flux, the second light flux and the third light flux on the first disc, the second disc and the third disc, respectively, wherein
• the thicknesses t1, t2 and t3 satisfy t1≦t2<t3,
• when m3 is an optical system magnification of the converging optical element for an effective light flux which is necessary for recording or reproducing information on the third disc and f3 is a focal length of the converging optical element for the third light flux, the focal length f3 satisfies
• 0.01<|m3|×(t3−t1)/f3<0.03, and
• the optical pickup apparatus satisfies
• 0.03<|SC max|/f<0.05
• where SCmax is an amount of an offence against sine condition on an edge of an effective diameter of the converging optical element when the pickup apparatus reproduces or records information on the third disc using a finite coniugated system, and f is a focal length of the converging optical system for a light flux emitted by one of the first to third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis.