METHOD FOR MEASURING PHASE DIFFERENCE OF RESPECTIVE DETECTION SIGNALS BASED ON REFLECTED LIGHT FORM ONE PAIR OF SUB-SPOTS OF OPTICAL PICKUP

摘要

PURPOSE:To eliminate the influence of the phase change of sub-beams by utilizing the fact that the sub-beam E, F signals are reverse in polarity and deviate at a specified angle from each other and finding the average value of the DC output based on the phase difference between the respective E, F signals and the main beam M signal. CONSTITUTION:The output signal of an integrator 17 based on the phase difference between the electric signal M obtd. from the reflected light from the main spot and the electric signal E obtd. from the reflected light from one of a pair of the sub-spots and the output signal from an integrator 21 based on the phase difference between the signal M and the signal F obtd. from the reflected light from the other of the sub-spot are added 22 and the average output value (i) is obtd. in an average circuit 23. The sub-beam E and F signals are reverse in polarities and deviate by 180 deg. from each other and, therefore, the average output value i can eliminate the influence of the phase change of the sub-beams. The phase difference between the E signal and the F signal is, therefore, measured in the form of having no errors even if the position of the main spot deviates to the inner side of the sub-spot.