| 摘要 |
PURPOSE:To reduce the number of components in an optical device and to realize the low price and high performance of the device, by detecting a servo error signal and a MO reproducing signal by the dispersed light of the return light of an incident laser beam on an optical system on a backward path by using a dispersive optical device. CONSTITUTION:The laser beam, after being converged and projecting on a disk D passing a forward path, is reflected on the plane, and is returned on a path possible to the forward path. The return light is polarized by 90 deg. at a half mirror 13, and is introduced to the backward path, and is dispersed to three beams passing a beam dispersive optical device such as a modified Wollaston prism 23, etc. The servo error signal for focusing and tracking is detected by the beam in the center of the three beams, and the MO reproducing signal is detected by a right and a left beams. In such a way, a servo error signal detecting system and a reproducing signal detecting system can be constituted on the backward path introduced by one half mirror 13, and a signal detecting optical system can be unified in one system, then, it is possible to make an on-going servo error detecting optical system unnecessary. Also, the MO reproducing signal with a large distinction ratio and a high C/N can be obtained. |
