| 摘要 |
PURPOSE:To prevent a reflected light from being returned to a semiconductor laser by making a ray reflected on a recording face incident to a reflected face of a prism in an angle approximate to a critical angle or larger and further making a ray from a light source incident to the reflecting face of the prism at the critical angle or below. CONSTITUTION:The ray from the semiconductor laser 10 is made incident to the reflecting face 12 of the prism 11 at an angle causing less reflection. The ray transmitted through the prism 11 and an objective lens 13 and reflected on the recording face 14 passes again through the objective lens 13 and is made incident to the prism 11. This ray is set so as to be made incident to the reflecting face 12 in the vicinity of the critical angle. The light reflected from the replecting face 12 of the prism 11 is made incident to a photodetector 15. The emitted light from a semiconductor laser 10 is made incident to the reflecting face 12 of the prism 11 at a critical angle or little smaller, and the reflected light from the recording face 14 is prevented from being returned to the semiconductor laser 10 and a focus error signal is obtained at the same time by means of the critical angle method by making the irradiated light of the semiconductor laser 10 incident to the reflecting face 12 of the prism 11 at an angle slightly smaller than the critical angle and making the reflected light from the recording face 14 to the reflecting face 12 of the prism 11 at the critical angle. |
