OPTICAL PICK-UP APPARATUS, AND OBJECTIVE LENS

摘要

An optical pickup device and an object lens are provided to reproduce and to record the information on two kinds of optical discs having a transparent base plate of which the thickness is different according to light sources of two mutually different wavelengths. In an object lens, the information is reproduced from a first optical information recording medium(22) by using a first light source emitting a first light flux having a first wavelength of lambda1. The first optical information recording medium has a first transparent base plate(21) having t1 thickness. The object lens reproduces information from a second optical information recording medium having a second transparent base plate while recording the information to the first optical information recording medium synchronously. The object lens is used for an optical pickup device and being shared when reproducing or recoding the information for the first and the second optical information recording mediums. The object lens has a plurality of steps on an optical surface. The difference between the maximum value and the minimum value of the steps for an optical axis direction are bigger than 1.5 and smaller than 6 times. The maximum step is located more further from a periphery of the optical surface than the minimum step.