| 摘要 |
PURPOSE:To obtain a focusing error signal with a stable offset by symmetrically bi-secting plural recording and reproducing luminous fluxes perpendicular to the track direction, respectively as focusing error detecting fluxes. CONSTITUTION:A triangular prism 35 with a width (d) is placed in the optical path, in which a distance between optical axes (d) of adjacent luminous fluxes is larger than the flux radius of each flux, as a luminous flux separation means of a focusing error detecting luminous flux. And, a recording beam 23a, which transmits the side space of the triangular prism 35, and a recording beam 23b, which is refracted by the triangular prism 35 and outputted, are symmetrically divided by a side face 35a. Similarly, a reproducing luminous flux is symmetrically divided into reproducing beams 24a and 24b by a side face 35b, received by an octa-dividing photodetector 25 and a focusing error detecting signal is obtained. |
