Optical disc device and control method using preceding sub-beam to detect a disc defect

An optical disc device comprising:

• a light source for emitting a laser beam;
• a diffraction grating configured to generate a main optical beam and at least first and second optical beams from the laser beam emitted from said light source, and configured to form a main beam spot and sub-beam spots on an information recording surface of an optical disc;
• a photo detector configured to receive return light;
• corresponding to said sub-beam spots and said main beam spot, said sub-beam spots include a sub-beam spot being formed at a preceding side with respect to scan of said main beam spot, and configured to subtract information from said return light portion corresponding to said preceding sub-beam spot, said information being a portion of said return light corresponding to said main beam spot, outputting a light detection result;
• and
• a determination circuit configured to determine the light detection result of said photo detector, and configured to detect defects on said optical disc.

A control method for an optical disc device in which a main beam spot and sub-beam spots are formed on an information recording surface of an optical disc with irradiation of a laser beam, and laser power of said laser beam is intermittently boosted to record desired data on said optical disc by said main beam spot, said method comprising:

• suppressing changes in signal level according to a light detection result due to boosting of the laser power of said laser beam, the light detection result being obtained by receiving a return light corresponding to said sub-beam spots and said main beam spot, said sub-beam spots including a sub-beam spot being formed at a preceding side with respect to scan of said main beam spot;
• subtracting information from said return light portion corresponding to said preceding sub-beam spot, said information being a portion of said return light corresponding to said main beam spot;
• and
• determining the light detection result and detecting defects on said optical disc.