| 摘要 |
PURPOSE:To make accurate tracking possible even in case of a large spot by multiplexing a tracking signal with a bit signal or changing the frequency of a carrier wave for every tracking to multiplex a signal which discriminates an adjacent track and detecting the signal of the adjacent track. CONSTITUTION:The tracking signal is multiplexed with a signal having a certain spectrum width and is recorded in the state where the latter signal is recorded, and the tracking signal is detected to perform tracking. The tracking signal has the frequency changed for every track, and the signal having three frequencies at least is required for the purpose of making signals of adjacent tracks different from each other. If five frequencies are prepared, signals of adjacent tracks are always different in frequency to make accurate control possible; and further, detectors 41-45 of frequencies f1-f5 are provided after addition of auxiliary beams, and individual combinations are compared by comparators 51-55 to make accurate control possible. |
