Patent ID: 7102980

Claim:
An optical pickup apparatus, comprising: a light source; and a light converging optical system including an objective lens and for converging a light flux emitted from the light source onto an information recording surface of an optical information recording medium; wherein the optical pickup apparatus records and/or reproduces information for a first recording medium including a first transparent base board having a thickness t 1 and a second recording medium including a second transparent base board having a thickness t 2 (t 1 <t 2 ); wherein the objective lens is a plastic lens, wherein when the information is recorded for or reproduced from the first or second optical information recording medium, the objective lens converges a divergent light flux emitted from the light source onto an information recording surface of the first or second optical information recording medium; and wherein at least one surface of the objective lens is provided with a diffractive structure on at least a peripheral region within an effective diameter; and wherein the diffractive structure on the peripheral region of the objective lens is ring-shaped diffractive zones, and when n th order light ray represents a diffractive ray with a maximum amount of light generated by the diffractive structure from a light flux passing through the diffractive structure on the peripheral region among light fluxes emitted from the light source, an average pitch Pout of the ring-shaped diffractive zones and a focal length of the objective lens f satisfy the following conditional formula: 2.00×10 −4 <P out/(| n|·f )<3.00×10 −2 .