| 摘要 |
PURPOSE:To obtain an accurate position through linear adjustment by splitting the radiant light of a semiconductor laser into three pieces of luminous flux and guiding them to a disk surface, reading information recorded on tracks, and utilizing the radiant light component of the semiconductor laser which is not utilized for the reading as the 4th luminous flux by an optical path converting means. CONSTITUTION:When a disk 8 is at a proper focusing point position A on an optical axis, the reflected luminous flux of the 4th luminous flux 33 strikes a photodetector 36 while split into two about a splitting line, and if the disk 8 shifts in position as shown by B-C in the optical axis direction owing to surface undulation during the adjustment mentioned above, the reflected luminous flux moves on the two-splitting photodetector 36 at right angles to the splitting line. The signal level of a differential output 38 varies from the zero level in focusing positively or negatively according to the shifting direction as the reflected luminous flux 40 shifts from the focusing point position namely, the shifting direction is known from whether the output signal increases or decreases, and the amount of the shift is detected from the increase or decrease extent. |
