| 摘要 |
PURPOSE:To sufficiently shorten the access time by providing a feedback control section changing a wavelength of a laser beam so that a focus of the laser beam made incident on an optical recording medium is placed onto the recording face of an optical recording medium. CONSTITUTION:A laser beam from a semiconductor laser 11 is reflected in a horogram converging element 12 and focused therein and focused further by an objective lens 13 and made incident on an optical recording medium 1. The laser beam reflected in the optical recording medium 1 is reflected and focused in the horogram focus element 12 so as to generate astigmatism and the result is made incident on a focus error detection section 14. A focus detection section 14 inputs a detection output of a quadripartite photodiode 15 to an arithmetic circuit, where a focus error signal FE is calculated. A feedback control circuit 17 applies a focus error signal FE to the semiconductor device 11 as an electric input and the wavelength of the laser beam from the semiconductor laser 11 is varied so that the focus of the laser beam made incident on the optical recording medium 1 is placed onto the recording face of the optical recording medium 1. |
