OBJECTIVE LENS AND OPTICAL PICKUP DEVICE

摘要

Provided are an objective lens and an optical pickup device that are used for recording on/playback from an optical disk having at least three information recording surfaces, said objective lens and optical pickup device being capable of effectively inhibiting crosstalk between layers even if said objective lens and optical pickup device are provided with a diffraction structure having a temperature characteristic correction function. The objective lens (OBJ) is a plastic single-element lens with an image-side numerical aperture (NA) of at least 0.8 and less than 0.90, and is designed such that spherical aberration is corrected at design substrate thickness (t) [mm] (where t1 <= t <= t2) and magnification = 0. For the objective lens (OBJ), the change in third-order spherical aberration per unit wavelength (DeltaSA3W) [lambdarms/nm] in response to a change in light source wavelength, multiplied by the change in third-order spherical aberration per unit temperature (DeltaSA3T) [lambdarms/°C] in response to a change in environmental temperature, is negative (< 0). The objective lens (OBJ) has a diffraction structure. A main diffraction beam is generated when a beam of light from a semiconductor laser (LD) is input to the diffraction structure. By condensing said main diffraction beam on one of the information recording surfaces (RL1 to RL3), the objective lens (OBJ) starts recording and/or playback of information, with the steps of the diffraction structure oriented in the light axis direction.