| 摘要 |
PURPOSE:To detect the track signal or information and thereby decrease the noise due to the dark current by receiving <=80% reflecting luminous flux from the recording medium by a photodetecting element as omitting both end-parts in the direction of track among the reflecting luminous flux from a recording medium. CONSTITUTION:The laser beam from a semiconductor laser 1 is made parallel by a coupling lens 2. The beam passes through a polarizing beam splitter 3 and a 1/4-wavelength plate 4, and further is made the specific spot by an objective lens 5, and focuses on the optical information recording medium 6. The reflected light from the recording medium 6 is changed of its plane of polarization by the wavelength plate 4, is separated from the incidence light by a prism 3, is focussed by a condenser lens 7, and is supplied to a photodetecting element 18 in place of the conventional photodetecting elements 8 and 9. This photodetecting element 18 for detecting the track signal or information signal is halved by the line parallel with the direction of track T. The <=80% of the reflected luminous flux 10 omitting the parts of both ends along the line parallel with the direction T, is received by photodetecting parts 18C and 18D. Accordingly, only the part of strong intensity of light is received to decrease the noise from the dark current. |
