| 摘要 |
PURPOSE:To effectively detect the read signal of an optical disk by providing a polarizing beams splitter using a grating setting a parallel flat plate as a substrate in an optical system for light receiving system, and obtaining the differential output of diffracted light and non-diffracted light. CONSTITUTION:Reflected light from a disk plane 8 is returned on a reverse path, and reflected on a beam splitter 5. The reflected light, after whose polarizing plane being rotated by around 45 deg. by a 1/2-wave plate 22, is changed to convergence light by a lens 9, and S-polarization is diffracted by a parallel and flat type grating element 23, and made incident on a photodetector 24. P-polarization that is the transmission light of the element 23 is made incident on a quadruple photodetector 29. The transmission light of the element 23 becomes astigmatic light by transmitting the substrate of parallel and flat plate of the element 23, and when convergence light is focused on the optical disk plane 8, a light beam on the photodetector 29 becomes the minimum blur circle and is made incident, however, when the focus of the convergence light on the plane is shifted, it becomes an elliptical beam. Therefore, assuming the output of photodetectors 25-28 comprising the detector 29 as V(25) - V(28), a focusing error can be obtained by V(25)+V(28)-V(26)-V(27). |
