US 7,613,096 B2
Converging optical element and optical pickup apparatus
Mika Wachi, Hino (Japan)
Assigned to Konica Minolta Opto, Inc., Tokyo (Japan)
Filed on Jun. 16, 2005, as Appl. No. 11/153,391.
Claims priority of application No. 2004-183986 (JP), filed on Jun. 22, 2004.
Prior Publication US 2005/0281172 A1, Dec. 22, 2005
Int. Cl. G11B 7/00 (2006.01)
U.S. Cl. 369—112.08  [369/112.06; 369/112.07] 22 Claims
OG exemplary drawing
 
1. A converging optical element for use in an optical pickup apparatus reproducing and/or recording information on a first optical disc having a protective substrate with a thickness t1 (mm) using a first light flux with a wavelength λI (nm) emitted by a first light source, reproducing and/or recording information on a second optical disc having a protective substrate with a thickness t2 (mm) using a second light flux with a wavelength λ2 (nm) emitted by a second light source, and reproducing and/or recording information on a third optical disc having a protective substrate with a thickness t3 (mm) using a third light flux with a wavelength λ3 (nm) emitted by a third light source, the converting optical element comprising:
a phase structure arranged on at least one surface of the converging optical element, 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 converging optical element 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.