| 摘要 |
PURPOSE:To obtain an optical pickup which is easy in setting its focusing error detecting extent and alignment in optical axis with an optical system and excellent in mass productivity, by arranging a planoconvex cylindrical lens as a half mirror, with its flat surface side being faced to a light source. CONSTITUTION:A planoconvex cylindrical lens 8 is arranged as a half mirror, with its flat surface part 1 being coated with a semitransparent film and faced to a light source, in such a way that its departure line is inclined by a specific angle against the main optical axis. The cylindrical lens 8 sets the rays of light passed through the lens 8 to a state in which no coma aberration exists by correcting the coma aberration of the astigmatism and coma aberration produced in the rays of light while passing through the optical path until the lens 8 and, at the same time, emits rays of light in which astigmatism composed of the astigmatism originally existing in the rays of light made incident to the lens 8 and the astigmatism newly produced when the rays of light pass through the planoconvex cylindrical lens 8. Thus a focusing error detecting optical system is formed. |
