| 摘要 |
PURPOSE:To obtain a low-cost and compact optical head, and improve the frequency characteristics of a detection signal and speed up reproduced signal processing by constituting a projecting means so that light from an information recording medium is split into at least >=2 and converged to different positions. CONSTITUTION:The laser beam emitted by a semiconductor laser device 21 passes through a collimator lens 22 and a prism 23, and is reflected by a polarization beam splitter (PBS)24 to be converged to the surface of a recording layer 28 through a lambda/4 plate 25 and an objective lens 26. Its reflected light travels backward through the PBNS24, and is split into two through the projection lens 25 formed by adhering a spherical lens 26 and a spherical lens 27 which is cut partially along a surface parallel to the optical axis together to be converged to photodetectors 30 and 31 at different positions, so that an off-track state, and a read and an out-of-focus state are detected. Thus, the low-cost and compact device is obtained. Reading operation is performed by the small detector 30, so information is read out at a high speed. |
