Patent ID: 8121012
Filing Date: 2012-02-21
Classification: G11B

Abstract:
1. An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by using a light beam having a wavelength of λ (unit: nm), the optical information recording/reproducing apparatus comprising: an objective lens that converges the light beam onto a recording surface of the optical disc and satisfies a condition: where f represents a focal length (unit: mm) of the objective lens with respect to the wavelength λ, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ; a photoreceptor that receives the light beam reflected from the recording surface of the optical disc; a detector that detects quality of a signal outputted by the photoreceptor based on the light beam reflected from the recording surface of the optical disc; and an objective lens driving unit configured to tilt the objective lens in a direction to improve the quality of the signal based on a result of detection by the detector, wherein: at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon; when (Σφ