OFFSET TRACKING CORRECTION FOR OPTICAL RECORDING.

In an optical memory, an object-lens servo is used to access information on either side of a central track. As a result of the radial direction offset of the lens, the tracking servo will not center the focused spot on a track. This is due to the fact that the returning beam has an offset which produces unequal intensities on the two halves of the photodetector used in the servo sensor circuit. However, some of the actuator driving signal can be fed back into the sensor circuit with the correct phase to eliminate the offset in the sensor circuit. This can be done with a fixed resistor. For more accurate adjustment, it can be done as outlined in this paper.