CHECKING DEVICE FOR OPTICAL RECORDING MEDIUM

摘要

PURPOSE:To detect with preference the defect due to a foreign matter mixed into a base material compared with other defects due to other factors, by obtaining difference signals between two pairs of diagonal areas of a 4-split optical detector which receives the reflected light and is divided into four areas by two boundary lines crossing to each other. CONSTITUTION:A 4-split detector 11 is divided into four areas by two boundary lines orthogonal to a reflecting optical axis. The laser light is cut off by a foreign matter on a going route between an aperture lens for laser light and a recording surface. Then the distribution of intensity of the laser light is inverted symmetrically by the reflection caused on the recording surface. The laser light is cut off again by a foreign matter on a coming-back route. Thus a light shielding influence part 12 of the going route and a light shielding influence part 13 of the coming-back route emerge symmetrically centering on the optical axis. Both parts 12 and 13 are shifted symmetrically centering on the optical axis by the rotation of an optical recording medium. Thus it is possible to detect the foreign matters mixed into a base material with high sensitivity by obtaining the difference between paired diagonal areas of the detector 11.