| 摘要 |
PURPOSE:To detect a tracking error with high accuracy by using an objective lens, a light convergent lens, a beam splitter and a two-split photodetector. CONSTITUTION:The light delivered from a semiconductor laser 1 and reflected by a disk 6 is divided in the direction orthogonal to an incident luminous flux by a 1/4-wavelength plate 3 and a polarized beam splitter 2 via an objective lens 5, the plate 3 and a collimator lens 4. Here the reflected luminous flux passed through the half face defining the plane formed by the optical axis and the track direction as a boundary and the reflected luminous flux passed through the other half face are divided opposite to each other in the direction vertical to the optical axis and in the directions A and B symmetrical to the boundary line formed by an apex of a beam splitter 7 and the optical axis by the function of the splitter 7. The two-split photodetecting elements 11 and 11' are set in both directions A and B. Then the half luminous fluxes are made incident on both elements 11 and 11' respectively. Then both elements 11 and 11' are controlled so that the outputs of these elements are equal to each other in a focused state. Thus it is possible to detect a tracking error with high accuracy. |
