Patent ID: 7787332

Claim:
An optical information recording-reproducing apparatus comprising: a light source; an objective lens for condensing a light beam from the light source on a recording layer of an optical recording medium; a divergence angle-converting element provided in an optical path from the light source to the optical recoding medium for converting a divergence angle of the light beam to be introduced to the objective lens; a focus error detecting optical system including a photodetector for detecting a focus error of the light beam; an optical element for introducing a part of the light beam emitted from the divergence angle-converting element to the focus error detecting optical system; a circuit for detecting the divergence angle of the light beam emitted from the divergence angle-converting element from output from the photodetector; and a circuit for compensating spherical aberration in the recording layer of the optical recording medium by driving the divergence angle-converting element in accordance with the detection result of the divergence angle-detecting circuit.