| 摘要 |
PURPOSE: To provide an object lens for optical pickup device and an optical pickup device capable of performing recording and/or reproducing of information with respect to an optical information recording medium having different information recording density. CONSTITUTION: When a luminous flux passing through a peripheral region having a diffraction structure D in the object lens 20 reaches the inside of a spot formed by the luminous flux passing through the central region, the diameter of the spot becomes small because the luminous flux passing through the peripheral region has a large numerical aperture NA. By the object lens 20, the diameter of the spot becomes small when the luminous flux of wavelength λ1 is made incident on the object lens 20 by reducing a light quantity of +1st order diffracted light reaching the inside of the first spot more than a light quantity of +1st order diffracted luminous flux reaching the inside of the first spot, whereby recording or reproducing is performed to an optical information recording medium (DVD or the like) having high recording density, while the diameter of the spot becomes large when the luminous flux of wavelength λ2 (λ2>λ1) is made incident on the object lens 20, thereby, recording or reproducing is performed with respect to the optical information recording medium (CD or the like) having lower recording density.
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