| 摘要 |
PURPOSE:To increase a focus draw-in range by unifying a beam splitter, a beam section form converting optical system and a split prism into a body. CONSTITUTION:A collimator lens 2 which turns the light radiated from a light source 1 into parallel beams is provided together with a converting optical system 15 which changes the section forms of said parallel beams, a beam splitter having faces (h) and (i) through which the light radiated from the system 15 travels straight, a 1/4 wavelength plate 5, an objective lens 7 which stops down the incident light onto a recording medium 9, and a split prism 15 which splits in terms of space the reflected light obtained by giving the change of optical path to the reflected light given from the medium 9 by the beam splitter having faces (i) and (j) into two beams and leads one both split beams to a photodetector 14 for focus and the other beam to a photodetector 13 for tracking respectively. Then the beam splitter having faces (h), (i) and (j), a beam section form converting optical system 3 and the prism 15 are unified into a body. |
