Patent ID: 7379399

Claim:
A reading system for reading a writable optical disc having an information writing track, a guiding track for introducing a laser beam to the information writing track, and prepit information including address information recorded on the guiding track, the system comprising: a first photodetector having photodetecting elements divided at least by a first dividing line optically parallel with a tangential direction of the information writing track of the disc for detecting reflected light of a first laser beam irradiated to the information writing track; a plurality of adders for adding outputs of the photodetecting elements on each side of the first dividing line of the first photodetector; a second photodetector having photodetecting elements divided at least by a second dividing line optically parallel with the tangential direction for detecting reflected light of a second laser beam irradiated to the guiding track; a plurality of adders for adding outputs of photodetecting elements on each side of the second dividing line of the second photodetector; first difference signal producing means for producing a first difference signal based on a difference between the added outputs of the photodetecting elements of each side of the first photodetector being divided by the first dividing line; second difference signal producing means for producing a second difference signal based on a difference between the added outputs of the photodetecting elements of each side of the second photodetector being divided by the second dividing line; level adjust means for adjusting a level of at least the second difference signal, and tracking error signal producing means for producing a tracking error signal based on subtracting an output signal of the level adjust means from the first difference signal.