| 摘要 |
PURPOSE:To correct easily and accurately a beam shift component which is superposed on a tracking error signal by specifying the ratio between a differential signal of a non-bit part of a track among two output signals obtained from a photodetecting surface and a differential signal of both output signals and producing a difference signal of both differential signals. CONSTITUTION:Output signals S1 and S2 obtained from photodetecting surfaces 6a and 6b of a photodetector 6 are transmitted through envelope curve wave detection circuit 10 respectively, and a signal corresponding to a signal at a non-pit part of a track of an information recording carrier. This differential signal SA is multiplied by a compensation factor B=1/2 by a compensation factor control circuit 11. A differential signal SB of both signals S1 and S2 is produced, and a difference signal S'B of both signals SA and SB is used as a tracking error signal. In this case, the shift amount of a light beam is set smaller than the light beam diameter on the photodetecting surface. Then betaB=1/2(1+S0L) is satisfied to eliminate the shift component contained in the signal SB with the signal SA. Thus the stable tracking servo is possible despite a fixed factor betaB since no relation is defined with a shift amount alpha of the light beam. As a result, it is possible to obtain tracking error signal having the corrected superposition of the beam shift component. |
