Patent ID: 7813233

Claim:
An information recording and reproduction apparatus, comprising: an optical pickup unit, the optical pickup unit comprising: a light source emitting a light beam; an objective lens focusing the light beam onto an information recording medium; a light detection part receiving the light beam reflected from the information recording medium; and a light blocking part selectively blocking a part of the light beam with respect to a radial direction, the light blocking part provided in an optical path of the light beam to be centered on an optical axis; and wherein said optical pickup unit further comprises a control part generating an aberration signal by comparing a first signal generated based on a first part of the light beam passing through a first region of said light blocking part and a second signal generated based on a second part of the light beam passing through a second region of said light blocking part, the first region of said light blocking part being arranged to selectively block the first part of the light beam, and wherein the first part of the light beam is internal to the second part of the light beam, and wherein said first region of said light blocking part is provided internal to the second region of said light blocking part.