OBJECTIVE LENS FOR OPTICAL PICKUP DEVICE AND OPTICAL PICKUP DEVICE

摘要

Provided are an optical pickup device and a coupling lens with which it is possible to carry out recording and playing of information on an optical disc having multi-layered information recording faces while being both compact and inexpensive. Given an objective lens such as satisfies formula (1), satisfying formula (2) allows alleviating an occurrence of high-order spherical aberration in all information recording faces when concentrating light. Furthermore, satisfying formula (3) reduces a risk that a beam will be limited at a lateral face of an optical disc, allowing maintaining a spot diameter even when a divergent beam enters the objective lens. F = 1.8mm (1); TMIN*1.2 = T = TMAX*0.86 and TMIN*1.2 < TMAX*0.86 (2); 1.1 = A2/B2 = 1.6 (3); where f is the focal length of the objective lens with respect to the beam; T is the transparent substrate thickness of the optical disc such that third-order spherical aberration |SA3| = 0.05?rms upon parallel beam entry; TMIN is the minimum transparent substrate thickness among the transparent substrate thicknesses of the optical disc; TMAX is the maximum transparent substrate thickness among the transparent substrate thicknesses of the optical disc; A2 is the optical surface diameter of the optical disc-side of the objective lens; and B2 is the effective diameter of the optical disc-side of the objective lens.