| 摘要 |
PURPOSE:To make parts constituting an astigmatism system unnecessary by emitting a laser beam on the returning path obliquely to the side face of a beam splitter to generate astigmatism. CONSTITUTION:The exit light from a semiconductor laser 11 is focused on an optical disc D, and its return light is converged by a collimator lens 13 and is reflected on a beam splitter 12. A reflecting face 121 of the splitter 12 is inclined at an angle theta0 smaller than 45 deg. to the optical axis of the exit light from the laser 11, and the angle of the return light reflected on the reflecting face 121 is set to an acute angle theta1 (90 deg.>theta1>48.2 deg.) to said optical axis. The return light reflected on the reflecting face 121 is converged in only the direction parallel with the optical path of the going path by the side face of the splitter 12, and astigmatism occurs in the return light thereby,,and it reaches a photodetector 15 and is received and detected. Thus, optical parts constituting the astigmatism system are made unnecessary and the optical path length is shortened. |
