OBJECTIVE LENS, OPTICAL HEAD DEVICE, OPTICAL INFORMATION DEVICE AND INFORMATION PROCESSING DEVICE

摘要

Provided are an objective lens capable of improving detection accuracy of a focal position, an optical head device, an optical information device and an information processing device. The objective lens (25), in order to reproduce information from an optical disk (28), collects a diffracted light ray (15X) of a longer focal distance among two diffracted light rays (15X and 15Y) upon an information recording surface (28L) through a substrate (28S) of the optical disk (28), wherein the distance (DF3) between focal positions of the two diffracted light rays (15X and 15Y), when collecting the diffracted light ray (15X) of the longer focal distance upon the information recording surface (28L), is longer than twice the distance (WD2) along the optical axis from the surface (25A) of the objective lens (25) to the surface (28A) of the substrate (28S).