| 摘要 |
PURPOSE:To obtain an optical disk device having a high CN ratio by detecting a reproducing signal by a differential detecting method for offsetting a noise caused by a relative fluctuation of an optical system or an electric system. CONSTITUTION:Only a 1/4 circular light part 14a of a circular luminous flux 14 is allowed to pass through a phase difference plate 3 and a phase is delayed by theta and the luminous flux of this circular light part 14a and the luminous flux of the remaining 3/4 circular light part 14b are projected to a light recording surface 7, and a reflection and a diffraction are generated therein. When the optical amplitude of a 0-th order diffracted light 15b of the 3/4 circular light part is denoted as Ao, the optical amplitude of a 0-th order diffracted light 15a of the 1/4 circular light part becomes AoEXP(jtheta), and also, as for the primary diffracted light, the primary diffracted light 16b of the 3/4 circular light part and the primary diffracted light 16c of the 1/4 circular light part having a phase delay are superposed, and as for the -primary diffracted light, it becomes only the -primary diffracted light 16a of the 3/4 circular light part. In such a way, the luminous flux to which the 0-th order diffracted light and the + or -primary diffracted light have been superposed is led to an optical system split mirror 9, made incident on a differential amplifier through a photosensor 10, and a desired reproducing signal is obtained. |
