Optical element, optical pickup, and information recording/reproduction apparatus

An optical element having an incident plane and an exit plane of first laser light and a plurality of laser lights, which has a different wavelength from that of the first laser light, on an optical path of the first laser light and the plurality of laser lights, in order to share an objective lens for focusing light on a first recording medium comprising a recording layer, which receives the first laser light through a transmission protection layer with a thickness of D1, in the plurality of laser lights and in a plurality of recording media corresponding to the respective plurality of laser lights,

• the plurality of laser lights including second laser light, corresponding to a second recording medium having a transmission protection layer with a thickness of D2 (D2>D1), and third laser light, corresponding to a third recording medium having a transmission protection layer with a thickness of D3 (D3>D2) and used in a finite system,
• an effective diameter of a luminous flux required when the first laser light, the second laser light, and the third laser light enter the objective lens being R1, R2 (R1>R2), and R3 (R2>R3), respectively,
• said optical element comprising:
• a first aberration correcting device for correcting aberration caused by a difference between the thickness D1 of the transmission protection layer and the thickness D2 of the transmission protection layer and aberration caused by a difference in wavelength between the first laser light and the second laser light and for selectively reducing the effective diameter of the luminous flux which enters the objective lens to a value corresponding to the effective diameter R2, with respect to the second laser light and the third laser light;
• a second aberration correcting device for correcting aberration of the objective lens caused by an amount of change if a wavelength is changed in the first laser light, the second laser light, or the third laser light;
• and
• a third aberration correcting device, which is disposed in association with the effective diameter R2 and the effective diameter R3, for correcting aberration of the objective lens caused by an amount of change if a wavelength is changed in the first laser light and the second laser light and for selectively diffusing the incident third laser light if the third laser light enters said third aberration correcting device.