| 摘要 |
PURPOSE:To obtain a high quality reproducing signal by inserting a filter to the optical system of a signal detection section, cutting off an elliptic polarized light generated at the outside of luminous flux and extracting a circularly polarized light at the center as an optical signal detection system. CONSTITUTION:A reflected light from an optical disk 6 is split by a half mirror 7, the luminous flux as the optical signal detection system to the extracted is inputted to a detector 8 and its output is used as a reproducing signal. A filter 10 made of an opaque material such as metal, paper or plastic or the like cutting partly the outside of the luminous flux is inserted between the half-mirror 7 and the detector 8 to cut off the part subjected to elliptical polarization. The shape of the filter 10 is constituted in a way that a circular through- hole 11 having a smaller diameter than the outer diameter A of the luminous flux shown in dotted lines at the center is formed and the outside of the luminous flux having smaller elliptic rate is cut off. In cutting off the elliptically polarized light, the returned light quantity to the laser diode 1 is reduced and the signal light quantity is reduced, but its absolute value is in the order of several muW and S/N is not deteriorated. |
