| 摘要 |
PROBLEM TO BE SOLVED: To obtain an out-of-focus error signal in an astigmatic system by allowing a quadripartite photodetector to receive zero-order light at the center part and ±1st-order diffracted light at a peripheral part. SOLUTION: The light from a semiconductor laser 1 becomes parallel rays of light by a collimate lens 2, is transmitted through a polarizing beam splitter 3, reflects by a rise mirror 4 and enters on a polarizing grating 5. At this time, incident polarization becomes P polarization to the polarizing beam splitter to become parallel to the central division line of the polarizing grating 5. Then, the light passes through a λ/4 plate 6, and becomes orthogonal circular polarization, and is made incident on an objective lens 7 and converged on an optical disk 9. Further, the reflection light becomes linear polarization by the objective lens 7 and the λ/4 plate 6, and is diffracted in the direction that both side areas make 45 deg. when it is transmitted through the polarizing grating 5. The photodetector 12 receives the zero-order light at the quadripartite photodetector whose central parts are adjacent, and receives the ±1st-order light at the peripheral part. Thus, the out-of-focus error signal in the astigmatic system is obtained. |
