| 摘要 |
PURPOSE:To prevent the position shift of a focal point due to the change of the wavelength of a laser beam from being generated and to surely perform the tracking of a servo mechanism, by confronting refracting hologram lenses with specific intervals against those of condensing holograms. CONSTITUTION:In an optical head constituted of a laser diode 10, the hologram lenses 2-9, and an optical detection circuit 11, when the wavelength changes by the mode hop of the diode 10, the focal point comes off a targeted track on an optical disk 1. To prevent the shift, the specific interval is provided between the objective and the condensing holograms 4 and 2. In other words, assuming the interval between the lenses 2 and 4 as X, and that a position passing on the lens 2 is shifted by D when the wavelength lambda of a beam of light being made incident on the lens 4 at a refraction angle theta1' is changed by DELTAeta, the lenses 2 and 4 are arranged so as to satisfy an equation D=X (DELTAetasintheta1')/(eta+DELTAeta). In such a way, it is possible to prevent the position shift of the focal point from being generated, and to perform track servo and focus servo. |
