Patent ID: 6914730

Claim:
An optical recording/reproduction apparatus, which records/reproduces information on/from a recording medium having at least one recording layer, by converging light rays from a light source thereon, comprising when the number of recording layers is represented by N, where N≧2: an objective lens for converging light rays from the light source onto the recording medium; and a spherical-aberration correcting mechanism for correcting spherical aberration of converged light spots formed on the recording layers, wherein, the objective lens is set so that a converged light spot, derived from light rays transmitted through a light-transmitting body having an optical thickness of p 4 and converged, has a minimum spherical aberration, the N recording layers comprise a first recording layer, . . . , an Nth recording layer in succession from the objective lens side, and an optical thickness at a mid-point between the first recording layer and the Nth recording layer is represented by p 3 , p 4 and p 3 are coincident with each other, and a converged light spot formed at the mid-point between the first recording layer and the Nth recording layer by the objective lens has a minimum spherical aberration when light rays emitted from the spherical-aberration correcting mechanism have a minimum spherical aberration.