Patent ID: 7463571

Claim:
An optical element disposed on an optical path of first laser light and a plurality of laser lights, in order to share an objective lens for focusing light on a first recording medium, which comprises a recording layer which receives the first laser light through a transmission protection layer with a thickness of D 1 , in the plurality of laser lights whose wavelengths are different from that of the first laser light and in a plurality of recording media corresponding to the respective plurality of laser lights, the plurality of laser lights including second laser light which corresponds to a second recording medium having a transmission protection layer with a thickness of D 2 (D 2 >D 1 ), and third laser light which corresponds to a third recording medium having a transmission protection layer with a thickness of D 3 (D 3 >D 2 ) and is used in a finite system, an effective diameter of a luminous flux required when the first laser light enters the objective lens being R 1 , an effective diameter of a luminous flux required when the second laser light enters the objective lens being R 2 (R 1 >R 2 ), an effective diameter of a luminous flux required when the third laser light enters the objective lens being R 3 (R 2 >R 3 ), said optical element comprising: a first aberration correcting device for correcting aberration caused by a difference between the thickness D 1 of the transmission protection layer and the thickness D 2 of the transmission protection layer and a difference in wavelength between the first laser light and the second laser light, said first aberration correcting device being disposed in an area corresponding to the effective diameter R 2 of an incidence plane or an emit plane of said optical element; and a second aberration correcting device for correcting aberration caused by the difference between the thickness D 1 of the transmission protection layer and the thickness D 2 of the transmission protection layer, a difference between the thickness D 1 of the transmission protection layer and the thickness D 3 of the transmission protection layer, the difference in wavelength between the first laser light and the second laser light and a difference in wavelength between the first laser light and the third laser light, said second aberration correcting device being disposed in an area corresponding to the effective diameter R 3 of the incidence plane or the emit plane.