Patent ID: 6920102

Claim:
A converging element which converges a first light beam from a first light source onto a first optical information recording medium having a transparent plate, and converges a second light beam from a second light source onto a second optical information medium having a second transparent plate thicker than the first optical information recording medium, said converging element having an inner region near a center axis of the first and second light beams and an outer region far from the center axis, said outer region having a plane optimized to converge the first light beam transmitting said outer region onto the first optical information recording medium, said inner region having a plane optimized to converge the second light beam transmitting said inner region onto the second information recording medium having a larger thickness than the first information recording medium, wherein a phase of the light beam transmitting an innermost portion in the plane of said outer region is shifted relative to that of the light beam transmitting an outermost portion in the plane of said inner region, said converging element comprising: a lens which converges the first light beam onto the first optical information recording medium and the second light beam onto the second optical information recording medium; and an optical plate element to be cooperated with said lens; wherein said lens comprises a first inner subregion near a center axis of the first and second light beams and a first outer subregion far from the center axis, said first outer subregion having a plane optimized to converge the first light beam transmitting said first outer subregion onto the first optical information recording medium, said first inner subregion having a plane optimized to converge the second light beam transmitting said first inner subregion onto the second optical information recording medium having a larger thickness than the first optical information recording medium; wherein said optical plate element comprises a second inner subregion and a second outer subregion divided from the second inner subregion with an optical step; wherein said second inner subregion and said second outer subregion are arranged such that the first light beam transmitting said first outer subregion transmits said second outer subregion while the second light beam transmitting said first inner subregion transmits said second inner subregion; wherein said inner region comprises said first inner subregion and said second inner subregion, and said outer region comprises said first outer subregion and said second outer subregion.