| 摘要 |
PURPOSE:To obtain a reproduced information signal with excellent S/N, by performing photoelectric conversion with a sole photodetector, without use of a reflected luminous flux for information signal reproduction for the purpose of generation of a focus error signal and without provision of an interference filter in a light path. CONSTITUTION:A light from a semiconductor laser 1 is split into three luminous fluxes at a trapezoidal prism 3. The light reflected reflected on an optical disc 7 passes through a lambda/4 plate 6 and a polarizing prism 4, and is changed into a parallel luminous flux at a convex lens 30. The luminous flux passing through a parallel part at the center of the prism 3 is directly made incident to photodetectors 31-33 and the luminous flux through the wedge part passes through interference filters 8a and 8b and made incident to the photodetectors 31 33 for photoelectric conversion. When the disc 7 is moved up and down to a focusing position, the luminous flux from the lens 30 is changed from parallel into diverged or converged luminous flux, thereby changing the incident angle to the filters 8a and 8b and changing the luminous intensity incident to the photodetectors 32 and 33. A focus error signal is obtained at a terminal 20, a tracking error signal is at a terminal 23 and an information signal is obtained at a terminal 21, respectively. |
