OBJECTIVE LENS FOR OPTICAL PICKUP DEVICE, OPTICAL PICKUP DEVICE, AND OPTICAL INFORMATION READ AND WRITE DEVICE

摘要

Disclosed is an objective lens which is suitable for slim optical pickup devices that ensure compatibility between two types of optical discs. The objective lens has a reduced diameter, an effective diameter f1(mm) that satisfies Equation (1) below when a first optical disc is used, and a focal length of f(mm). The objective lens can be adapted to extend a working distance WD2(mm) for use with a second optical disc to satisfy Equation (2) below by imparting negative paraxial diffraction power using diffracted beams of light of the same order produced in a first optical-path difference imparting structure. Furthermore, both the first and a second optical-path difference imparting structures have no diffraction structure superimposed thereon, thus being simplified in the shape of optical planes to facilitate manufacturing. Furthermore, using diffracted beams of light of the same order produced in the first optical-path difference imparting structure allows for maintaining in a preferred condition spherical aberration which may be caused by variations in wavelength of a light source or variations in environmental temperature. 1.7=f1=2.9 (1) 0.10=WD2/f=0.42 (2)