Patent ID: 7750276
Filing Date: 2010-07-06
Classification: G11B

Abstract:
1. An optical information detecting method comprising the steps of: dividing a light beam emitted by a light source into a first light beam and a second light beam; focusing the first light beam and irradiating an optical information recording medium therewith; guiding signal light reflected by the optical information recording medium to four detectors; guiding the second light beam to the four detectors as reference light without focusing it onto the optical information recording medium; causing the signal light and the reference light to optically interfere with each other on the four detectors, the signal light and the reference light having different phases from each other; selectively subjecting all or some of the outputs from the four detectors to an operation to obtain a reproduction signal; wherein a phase relationship between the reference light and the signal light (1) at a first detector differs by 180° from that at a second detector, (2) at a third detector differs by 180° from that at a fourth detector, and (3) at the first detector differs by 90° from that at the third detector; and wherein the operation comprises the addition of the square of a differential signal between the first detector and the second detector to the square of a differential signal between the third detector and the fourth detector.