| 摘要 |
PURPOSE:To detect a reflected converged light and to obtain an excellent error signal and a magneto-optic signal by arranging a concaved lens between two parallel plates so as to vary the converging angle and making the two parallel plates asymmetrical in response to its change. CONSTITUTION:A laser luminous flux radiated from a laser light source 2 is reflected on the parallel plate 7 and collected by a magneto-optic recording medium 5 via a base 4 by an objective lens 3. A magnetic field opposite to a direction of the medium already magnetized is given by a bias magnetic field coil 6 to apply recording. The reflected light is a converged light via the lens 3, passes through the parallel plate 7, a concaved lens 8 and the parallel plate 9, and a luminous flux having an astigmatism is made incident in a 4-split photodetector 10 detect a focus error. Moreover, the luminous flux reflected in the parallel plate 9 is made incident in the photodetector 11, which detect a magneto-optic signal. The converged angle of the converged light is varied by the concaved lens 8 and the two parallel plates 7, 9 are made optically asymmetrical to cancel the coma aberration and to obtain a sufficient astigmatism quantity. |
