Pickup apparatus for multi-layer optical disc

An optical pickup apparatus comprising:

• a laser source that emits laser beam to a multi-layer optical disc having plural recording layers;
• a photodetector that receives the laser beam reflected by the multi-layer optical disc and outputs an electrical signal according to the received amount of beam;
• a collimator lens that converts the laser beam incident thereto from the laser source into parallel beam;
• a beam splitter that transmits or reflects the laser beam, which is converted into parallel beam by the collimator lens, to be led to the multi-layer optical disc, and transmits or reflects the laser beam reflected by the multi-layer optical disc to be led to the photodetector;
• an objective lens that converges the laser beam, which is led to the multi-layer optical disc by the beam splitter, so as to form an optical spot on one of the plural recording layers;
• a condenser lens that converges the laser beam from the multi-layer optical disc led by the beam splitter in the vicinity of the photodetector;
• orbicular zone forming optical means that is arranged between the collimator lens and the beam splitter, or between the beam splitter and the condenser lens, for forming the section of the laser beam into an annular shape by refracting the laser beam converted into the parallel beam by the collimator lens;
• and
• a pinhole plate having formed thereto a pinhole that transmits the laser beam reflected from the one recording layer and converged by the condenser lens,
• wherein the laser beam, that is reflected from a recording layer other than the one recording layer, forms an annular converged flux at the periphery of the pinhole of the pinhole plate.