Aberration detection device and optical information recording and reproducing apparatus

摘要

A returning light beam emitted by a light source (101) and reflected by an optical disk (106) is separated by a half mirror (102), and partitioned and deflected at a hologram (109) into a light beam passing a first region and a light beam passing a second region. The light beam passing the first region is received by a plurality of photo-detectors (107), and the aberration is detected by comparing the resulting signals. Based on the aberration detection, the aberration of an optical system can be reduced by driving an aberration correction element (104) in real-time.