| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical head device capable of recording/reproducing an optical disk medium having a different thickness of substrate in an optical disk device such as CD. SOLUTION: In an optical head device having an optical lens for making a light beam from a laser source 1 transmit through a parallel plane plate and converging it on a recording surface formed on the rear side surface as a minute spot, a hologram element having a grating pattern formed by the interference of two spherical waves in an optical lens is provided, a lens system is constituted forming the minimum spot when the zero-order transmitted light is transmitted through a parallel plane plate of a first thickness and forming the minimum spot when the first-order transmitted light is transmitted through a parallel plane plate of a second thickness. Since the shape of grating of the hologram element is simple, it is easily prepared. |
