Patent ID: 8593928

Claim:
An optical head comprising: a light source for emitting light beams; an objective lens for converging the light beams onto an optical disc; an optical-signal generation element for dividing the light beams into at least four regions by using a division line extending in radial direction of the optical disc, and a division line extending in track direction of the optical disc, the light beams being reflected by the optical disc; and an optical detector for receiving the light beams divided by the optical-signal generation element, wherein up and down or right and left areas of the at least four regions are made different from each other by using the division line extending in radial direction of optical disc, the at least four regions being created by using the division line extending in radial direction of optical disc, and the division line extending in track direction of optical disc, wherein the at least four regions are deployed in a manner of being line-symmetric to each other with reference to central line of the at least four regions, the central line extending in track direction, wherein an addition signal generated by adding signals generated from two regions out of the four regions is defined as a first addition signal, the division line extending in the track direction being sandwiched between the two regions, the two regions being further positioned on a first diagonal line, an addition signal generated by adding signals generated from two regions being defined as a second addition signal, the two regions being positioned on a second diagonal line which is different from the first diagonal line, a tracking control signal being generated using at least the first addition signal and the second addition signal, and wherein the first addition signal is the addition signal generated by adding one of the signals multiplied by a first correction coefficient, and the other signal of the signals, the signals being generated from the two regions out of the four regions, the division line extending in the track direction being sandwiched between the two regions, the two regions being further positioned on the diagonal line, the second addition signal is the addition signal generated by adding one of the signals multiplied by a second correction coefficient, and the other signal of the signals, the signals being generated from the two regions, the two regions being positioned on the diagonal line which is different from the diagonal line.