| 摘要 |
PURPOSE:To detect the tracking of each beam, to monitor a recording beam and to detect a reproducing beam with a simple optical system by irradiating a recording medium having a guiding groove with plural beams and receiving the reflected light by means of a multidivision type photodetector through a cylindrical lens disposed in a specified manner. CONSTITUTION:The information recording medium 9 provided with the guiding groove 10 is irradiated with the recording beam and the reproducing beam. The reflected light therefrom passes through a convex lens 31 and a beam splitter 32. The reflected beams 2 and 3 respectively corresponding to the recording and reproducing beams are spatially separated from each other and become linear by the cylindrical lens 33 disposed so that a light focusing point and a far-field area are obtained in directions parallel with an perpendicular to the groove 10 respectively, and respectively made incident on the divided surfaces 34a, 34b, 34d and 34c of the four-division type photodetector 34 arranged at the light focusing point. Then, the respective tracking errors of the recording beam and the reproducing beam are detected by differential amplifiers 35 and 36, the tracking beams are monitored by adders 37 and 38 respectively and a reproducing signal is detected with the simple optical system. |
