| 摘要 |
PURPOSE:To realize an optical pick-up device using the astigmatism method at a low cost and in a small-sized and to improve the accuracy of detecting focussing error and tracking error. CONSTITUTION:A luminous flux passed through a detection line 7 is divided into two luminous fluxes La, Lb by a beam splitter 8, the luminous flux La, one of them, is extracted only at a center part by an aperture members 20. The center part luminous flux Laa passed through the aperture members 20 is made incident on a quadripartite photo-detector 10 in a state where the astigmatism is given to the Laa via a cylindrical lens 9. And, another luminous flux Lb is made incident on a bisected photodetector 11. Consequently, the patterns of the 1st-order diffracted light of focussing components are not made incident on the quadripartite photodetector 10 since the luminous flux Laa passed through the aperture members 20 includes only the patterns of the center part. Thus, a focussing servo control is excutede stably since track traversing noise is not superimposed on a focussing error signal. |
